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Question RE: Rule 26 -746 subrule 3 two or more cooking appliances being considered one . Hi I read your input in how to install cooking appliances,ranges etc... iam confused though. Say you have a 12000watt range and a smaller 8000watt range what one of these numbers do you use for calculating your demand factor if you want two or more units to be considered one.(26-746 (3)) Or do you have to add both of them together and base your demand factor on that? Thanks. B.D. Answer Yes, you are confused...If you have 2 ranges, then the primary range is considered at 6000 watts for the first 12 000 watts and 40% of anything over 12000 watts. The second range is then considered as 25% of its actual load. So in your example, you would have 12000 at 6000 watts, and 8000 at 25% for 2000 watts for a total demand of 8000 watts. this comes from demand factors in section 8 rules 8-200 (1) (a) (iv) and also 8-300 (1) 26-746 (3) is saying that if it is a cooking appliance (Which a range is) then it needs to be on its own circuit all by itself and nothing else on it, and if it is under 30 amps, it can have a plug on it, if it is over 30 amps it needs an indicator to say it is on, except if it has more than 1 heating element, then it must have an indicator light for every element on it that says it is turned on. 26-746 (3) has nothing to do with the demand of the range. It is saying that if it is a setup with 2 or more separate units such as a counter cooktop and a built in oven, then they can be considered as a single range. (That way you can put them both on a single circuit) As For the demand... 8-300 (2) says that if you have the cooktop / oven setup, then they can be considered as one unit to calculate the demand as i stated in the first paragraph. So if you have a 12000 watt oven and a 8000 watt cooktop, then they are added together as 1 unit for a total of 20000 watts. Then you take the first 12000 watts at 6000 watts and the remaining 8000 watts at 40% = 3200 for a grand total demand of 9200 watts. Les ========================================================================== Question: Hi 911: I recently took a test for the public utility. One of the questions ask: Your discover that the neutral for a customers single phase 3 wire service is disconnected at the customers lateral. You check the and find 6 ohm load on L1 and 15 ohm on L2. What will be the voltage at the customers lateral on L1 and L2. I am lost, what they were looking for. There doesn't seem to be enough info to determine voltage drop. What do you think? Thanks...."L" Answer: Hi "L": They have worded it very poorly, but I would say they are looking for the voltages caused from the broken neutral. You now have 6 ohms and 15 ohms in series across 240 volts since the neutral is no longer in the circuit. Therefore, you will have a total load of 6 + 15 = 21 ohms. 21 ohms at 240 volts = 11.43 amps. If you have 11.43 amps flowing through L1 at 6 ohms (E = I x R ) , 6 ohms x 11.43 amps = 68.57 volts. Same for L2 at 15 ohms so 15 x 11.43 = 171.43 volts..... It is a typical situation for this to happen if the utility loses a neutral. In this case, everything on L2 will be fried at 172 volts, and everything on L1 will be undervoltage at 69 volts.(Which could also destroy sensitive electronics and motors). Then....as things burn out, the resistance changes again, and so does the voltages across everything. So it would be: 68.57 volts on L1 and 171.43 volts on L2.... P.S. This is the major reason that all neutrals can not be Broken in switching etc... and that devices have to be removable without interrupting the neutral in the circuit. Hope this helps....Cody. ========================================================================== Question Hello If you go from your meter right to your panel, using conduit. My question is where is the grounding bushing put is it put on the end of the pipe at the meter base or at the end of the pipe in the panel I have only done one of these in the past 3 years so my memory of it is shot. I was looking in the code book in i believe sec. 10 it says you can use the grounded conductor on the supply side of the dissconnect to bond to ground your meter base, Now you wouldnt bring your "bonding" wire from the grounding bushing to where your netrual is grounded right, Shouldnt you bring the "bonding" wire from the grounding bushing to the main system ground lug in the supply side of the panel or connect it using a split bolt to the main system grounding conductor? Thanks. B.D. Answer Hi B.D...... First, lets not mix up Grounding and Bonding. Grounding is 1 wire as a system ground to the service disconnect. Almost everything else is bonding. Grounding bushings are almost always actually "Bonding" Bushings, although everyone in the trade calls them ground bushings. (When you tell your apprentice to make sure he hooks up the ground in a plug, you actually mean the bond wire) Anyways, You need a bond here because the code says unless 2 locknuts are used as in the case of a rigid nipple, you need to Bond the service conduit. Rule 10-614 (b) (i)(B). (Remember it is only metal conduit we are dealing with, and if you use PVC, it is not required). So, if you run EMT, you bond the conduit at either end to the metal box it goes in, either the panel end or the meter end. NOTE! Although its OK at either end, inspectors like it done at the panel end as they cant see it in the meter after it is all closed up and sealed!! The bond wire from the ground bushing simply goes from the bushing to the metal can. (Not to the neutral connections) Just use the manufacturers Bond lug, or you can install your own ground lug. (cant be in a screw that supports the box) Usually if there is not a lug, we teck screw a new lug to the box (clean off the paint where the lug will sit). Also note that in an EMT run, the couplings are considered an effective bond for the run as per rule 10-606 (1)(b). it is only at one end and because of rule 10-614 that we need the ground bushing. ========================================================================== Question Hello there, My boss and I are butting heads on this one. A customer wants to upgrade his electric hot water heater 40gal to a 60gal. At present there is 12/2 wire and a 20amp breaker. Manufacturer's recommendation says that the 60gal heater requires a 25amp breaker, which in turn we will then have to run new 10/2 wire, correct? As a hot water heater is taken at 100%, doing the math means upgrading. My boss says he isn't going to upgrade the wire or the breaker... what is the right answer? H, Castlegar Answer Hi "H" Rule 8-302(2) says it has to be considered a continuous load. Then rule 8-104 (5) (a) says the breaker has to be considered at 80% for continuous loads. You need to know the draw of the HWT to know exactly what sizes you need. Manufacturers recommendation could be misleading, as it may have been written for a different jurersdiction where their minimun doesnt meet our minimum. But...lets consider it at 4800 watts per element. Most HWT's have a thermostat that only allows 1 element on at a time ( Called Flip Flop arrangement ). That means the HWT draws 20 amps, so you can use #12. Then you need to have 80% of the breaker size, so you need a 20 / .8 = 25 Since most Manufacturers make 25 amp breakers, you have to use a 25 amp breaker. Then table 13 says you have to consider table 13 LAST, (This table allows a smaller wire size up to the next available size breaker or fuse as per rule 14-104 (a)) which means you have to use a #10 wire if it is protected by a 25 amp breaker. Since you used #10, you can also use a 30 amp breaker. Now lets consider an average sized tank. 3000 watts per element connected flip flop. That will draw 12.5 amps. Derate a 15 amp Breaker to 80% and you only get 12 amps. You are at 12.5, therefore you need a 20 amp breaker. Wire size good for 20 amps is #12, so you need a #12 wire. Remember that overcurrent protection is there to protect the wiring, not the device. We dont care if Grandma's hot water tank or hair dryer burns up as long as the wiring to it is safe. (OK., we care, but it is CSA or ULC that needs to make sure that end is all safe...) ========================================================================== Question Subject: Heat pump problem Hi Les: I have had a heat pump installed. The outdoor unit ( LENNOX ) has a name plate rating of 16.1 amps, 197 to 253 volts. MCA 20.8. Newer house, voltage at unit is 244 Being an electrician, I ran 1/2" emt through our finished garage, then changed to 10/2 heatex which was fished through a ceiling cavity, then switched to 1/2" pvc along the outside of the house. Total length of the conductors is 98'. (one way). When the outdoor unit starts, there is a "dead short rattle" in the metal conduit inside the garage. Heat pump installer maintains it is faulty wiring. He thought #10 was too small, then asked if I'd used aluminum, then suggested the cable had some extreme kinks.I had the electrical safety officer, Ivan Pye, physically come out to inspect my work. He saw no problems. I have checked my wiring and the unit for any kind of ground faults. I " lifted" the bond wire in the unit. Still made the noise. I put a gfci breaker in the panel; it did not trip. I removed the compressor from the circuit and the noise stops. put the compressor back in the circuit and the noise is back. My digital amprobe reads 83 amps for a split on start up. Compressor name plate reads 85 LRA. I even went so far as to put a 4800 w. construction heater on " my " wire that enters and feeds the outdoor unit, disconnected the compressor, but left the condenser fan in the circuit, so as to give the wiring a heavier load: 20 amps. And no dead short rattle. I should also mention that it has gone through 2 condenser fan motors. This is why the installer is questioning my wiring method. First one "burnt out". 2nd one, the bearings seized, I was able to take motor # 2 to "my" motor shop. They took it apart and said the windings had signs of over heating. They said whether the windings overheated and caused the bearing to go or whether the bearing failed and caused the windings to over heat, they could not say. Any ideas? Regards, Chris Answer Hi Chris: Well, it sounds like you have gone thru most of the testing already. I know exactly what you are talking about with the very good description of the “Dead Short Rattle” First, the Math: 2/10 at 98 feet is 0.22 ohms. With 83 amps that is an 18.26 volt drop during startup. With 244 volts at source, that gives you 221 volts during start-up at the unit. Ok…That should be fine…. After starting, When its Running, you should have about a 5 volt drop drawing 20.8 amps. Going to the Code, at that current, #10 will be fine for up to 120 feet at 21 amps to be within the 3% voltage drop rule, so that should be fine …. Heatex cable is just NMD90 with Red instead of white and Black which should be fine…. You are an electrician, so the splices from cable to conduit should be fine…. Kinks in the wire? …Not likely, especially with #10 wire…. BUT…It Rattles. Drawing 83+ amps at startup seems excessive, but is certainly possible. It should decline VERY quickly as soon as the motor starts turning. (In this case both motors. The fan as well) If the unit has been completely checked out and the motors are starting with as light a load as they can, (ie: compressor not starting with a pre load, or with bad bearings) I would unhook the fan motor and try it with the compressor only and see if the problem stops. Having 2 fan motor failures peaks my curiosity, but being different failures, it still could be coincidental, although both failures point to excessive load…1 mechanical (Bearings) and 1 electrical (Burnt). Failing anything else, you already know the stresses are causing the rattle, and even though in a perfect world, it all should be O.K., …..it is not. The short burst of 83+ amps are stressing the wire enough to rattle in the conduit during startup. From your description, you probably have about 40 to 50 feet of heatex tied on to #10 in the conduit. I would change the wire size from #10 to #8 in the conduit (2 #8’s are allowed in ½” ). Most wholesalers will cut #8 so you don’t need to buy a whole roll. If I had to guess at what the problem is, I would probably say the compressor is too tight and taking too long to start turning. Also, i am not sure if your ammeter has a "Peak" setting, but if it is a standard clip on just reading the current, and it still has time to read 83 amps while you are watching it, the motors are probably taking too long to get moving. Again, probably very little you can do about it, except compensate by up-ing the wire size. Please keep me informed as to the outcome...... Thanks.... Follow-up Hi Les: I called up a well known refrigeration guy that I have a lot of respect for. He came out, checked the total installation. He too was familiar with the dead short rattle and thought that there was a problem. After looking it over and doing some testing of his own, he could not find a problem, other than it was low on refigerant. I told him about the # 8 wire and he thought give it a try. I changed the "emt" wire to # 8 (thru the garage) and the PVC wire to # 8 ( on the house exterior), about 68 ft. in total, leaving approx. 30 ft. of heatex. It still rattles. Maybe not as bad. The refrigeration guy has since come back and put more refrigerant in and now it is heating just fine. I may change the inside wire to teck in the near future, but for now case closed. Thank you very much for your time and info...Chris ========================================================================== Question Hi Les Do you have this one? : http://www.esainspection.net/main_index/Recalls.php Wade Answer Hi Wade...No, i didnt have that link, and it is a good one! I will add it to the web pages. Thank you for the help......... ========================================================================== Question Hi: Would you know the rule number for having to provide a barrier for low voltage and high voltage wiring in the same box. i.e. 208v/24v Thanks... Kevin Answer 16-116, 16-212, 60-318 ========================================================================== Question Hey guys.What is the rule on kitchen counter receptacles on islands. Are they needed,do they have to be split receptacles. I was told if the island has a backsplash then you need them,but alot of islands that have backsplashes are just the back of the island and no where to mount the receptacle. Help,Rudy Hi Rudy: I am going to give you 2 answers to this. The existing 2002 Code and the new 2006 Code The 2006 Code is not in effect yet until it is passed this fall (Sept 2006), and you MUST still conform to the 2002 code until it is. 2002 answer....There are no requirements to install plugs on an island unless it has a back splash. (They consider the backsplash as a wall) The rule says that if the counter space is wider than 11.8 inches (300 mm) it needs a plug. There are also no specific rules on the plug itself, and technically, it can just be a general purpose receptacle, and does not have to be split..But...... In the real world.... In New houses, we always put plugs on the islands. We wire them as split receptacles the same as any other kitchen plug. They are installed on the side of the island, not on the top, and are usually put as close to the top as we can and still get a plate on it. In Reno's, we usually install a 20 amp T-slot receptacle wired with 2 / 12 wire because it is legal, and only needs a single breaker when the panel is almost full. The rules are CEC # 26-712, 26-710, and 26-726 2006 Code says you MUST put a plug in an island. it can be split with any other kitchen plug, or can be a 20 amp T-slot.(Rule 712 (D) (iv)) Also note that in the new code, it no longer requires that "Adjacent" plugs in a kitchen be in differrent circuits. (The finally got rid of that really dumb rule!) ========================================================================== Question I am supplying a garage with a 40ft run from my panel. My welder has a max amp load of 54Amps. Can I supply this load with a #8 Copper 3 wire using a 60AMP breaker? Thanks, Maple Ridge Answer No... As per Table 2 and section 42 of the Code, #8 Copper is only good for 40 amps if it is TW or R75 or good for 45 amps if it is RW90. If you know the "Duty cycle" of the welder you may derate it, and use overcurrent protection (Breakers and /or Fuses) up to 200%. (Welder only....not welder and other garage loads) If you dont, everything must be 100% ========================================================================== Question I did peruse your webpage and although I'm assuming this question has already been asked, I was unable to find my answer. In your resistance calculations could you give me all your numbers because I'm not coming out the same amount...close though. Here is how I calculated it...let me know where I've gone off track. Use the formula R= K x L/ CMA so for a #10 copper 10.4 x 1(foot)/10,380 = 0.001001927 I again apologize if you've already covered this, I realize it's only a difference of 178.073 microOhms.....is that the definition of a negligible difference?? lol lol Kind regards, Harland Answer Hi Harland: I think the 10.4 may be a rounded number as well. I got this chart from Pirelli Cables who say they measure the resistance of 10 Km of actual wire and made their chart. I also had a chart from Phillips and Canada wire and they both had minute differences as well. I think that unless it is extremely critical, i would call it negligable.. ========================================================================== Question What is meant by this, better yet what is the purpose of it? how can you consider two or more cooking devices to be one range if say there is 3 separate units but they are each at 8000 watts this would be way bigger than one range? Brandon Answer Hi Brandon.... You have to consider rule 8-300 (1) as well as subrule (2) says "For the purpose of subrule 1" That means that if you have 3 units at 8000 watts each, then the demand will be: 8 Kw for the first 12 kw of range, plus 40% of anything over 12 Kw, 3 at 8 Kw = 24 Kw, so the first 12Kw = 8kw demand plus the remaining 12 Kw At 40% = 4.8 Kw so the demand for 3 x 8000 watt separate units would be 12.8Kw The feeder to this array would have to be capable of 53.3333 amps, so #6 copper will work. Remember this is residential only! If it is in a restaurant, it would be considered as the full 100% or 24 Kw. Then it would be 100 amps and need a #3 wire. Follow-up question: Sorry to be a hassle, on your site where it tells you how to install ranges it shows pictures. If you look at rule 26-746 1a i believe it says for appliances over 1500 watts if you have say 2 of them you need a manual switch of sort to make sure only one unit is energized at a time, or an automatic device that will keep the overcurrent device from tripping. Is this also true for these ranges? I know it says for cooking appliances over 1500 watts which would seem to make ranges included, but you never know with this damn code, there could be some hidden rule that says otherwise. Follow-up Answer You stopped reading too soon....read 26-746 (3)..which says 2 or more separate built in units shall be considered as 1 appliance...... ==========================================================================. Question Hi. I recently wrote the 'B' test and i know 1 question i messed up on and it cost me six marks ! Hopefully you will understand what i am saying and write up an example for the website asap.It goes something like this. You have a base board heater of a certain wattage running at 240v. The same heater is now to be run on 208v.What is the new amperage and wire size.I simply used the wattage and voltage figures to come up with an answer that of course was listed in the answers. But i think the formula P I/R comes into play here which makes the answer alot different than what i came up with. Thanks..... C.L. Answer Hi C.L.: Thanks for visiting www.bcelectrician.com Here is an Example: 1500 watts 240v volts what is current and watts at 208 Volts? You need these 2 formulas---- P = E x I and E = I x R P = E x I 1500 = 240 x I Therefore I = 6.25 Amps E= I x R 240 = 6.25 x R Therefore R = 38.4 Ohms Now we know that the heater is a 38.4 ohm fixed resistance! Nothing is going to change that …. Now apply the new voltage: E = I x R 208 = I x 38.4 I = 5.417 Amps P = E x I P = 208 x 5.417 P = 1126.7 watts Hope this Helps, and yes, I will post this for everyone elses benefit..........Les ========================================================================== Question Hello I'm wondering where in the code book it will explain about distance of feeders from your meter to the main panel. Some people say it is 20 feet and if it is any longer it has to be surrounded by 2" of concrete? how come I cant seem to find this anywhere. One more panel heights it says you CANT have a circuit protection device more than 1.7 meters from ground. Yet most people mount the MIDDLE of the panel at 5.5 ft above ground, doesnt this go against the 1.7 meter rule since the breakers in the top area would be above 1.7m? Thanks....Brandon. Answer Hi Brandon: The rule you are looking for is 6-206 (1) (e) which says "As close as practicable to the point where the consumers service enters the building"The Inspectors have taken that literally and that means it must be very close. If you run it 20 feet you will get rejected!. There was an unwritten rule a few years ago that they would allow 20 feet, but that is no longer allowed. They will allow you to get to the basement right below the meter, or else mount the panel right behind the meter. Thats about all. The 2" of concrete means that the service conductors are considered outside the building where there is no limitation on the length. Rule 6-208 (1) (a) Yes, a panel must be mounted with the highest breaker at 1.7 meters, and that is the way it is done. Some people get away with a little higher, but the inspectors also will call you if it is not close. If someone is mounting the middle of the panel at 5.5 feet (66 inches) they could get called on it. The highest breaker must be 67 inches (1.7 Meters) 26-402 (2) Hope this helps ========================================================================== Question Hi Les and Cody. I was recently asked by a plumber who was installing a dishwasher if it was common practice for the electrician to put a receptacle in for a "built in dishwaher".I have never heard of this being done have you? Answer Hi AAron: No, you are correct that it is not "Common" practice, but it is done sometimes. There was a period when all the dishwashers came with a cord on them and a receptacle was installed under the sink area and they were just plugged in......but this is not usually done nowdays. ========================================================================== Question I would like to wire my GAS HEAT Furnace with a pigtail so I could connect it to a generator during a long power outage. I assume I would need to wire the furnace blower and the controls each to their own pigtail, then connect to the generator which would have enough power to start the blower. Can you offer any other insight into this, or is it that simple? Answer Hi Richard: I'm Assuming that you are not an electrician, due to the fact that any electrician will probably shudder if he reads what you wrote... No, it is not that simple! The furnace must be completely disconnected from its main power source before it can be connected to a generator. Failing to do so creates a very dangerous situation which could cause an employee that works for the power company to be killed. Your generator will feed back through the panel...meter....transformer...hydro lines...and more transformers........Each transformer it backfeeds through creates higher voltages on the lines feeding it. There are VERY strict rules on this. You need to install a transfer switch, or a "Generator Panel". You must also inform Hydro and supply a drawing, and it must be inspected. Call an Electrician! Thanks.....Cody ========================================================================== Question Hi my name is Darren and recently I was doing a service change in a house and I came across something that I thought was odd. What I saw was the conductors coming in from the meter were passed through a couple of small CTs and then into the main breaker. From these current transformers there was a 14/3 NMD that went somewhere in the house, I could not see where the wire was going. The service was only a 100 amp residential service. Do you have any idea what this could have been for and where the wire might have gone? If you have any idea let me know Answer Hi Darren: You got me on this one. Unless it was some home owner that wanted an ammeter to see what his draw was, or unless it might have been something like a recording ammeter using this as a test house for demands or something. Some places in B.C. used to have separate metering for Hot Water tanks, (Mostly in the Kootenys) and had special rates with a separate meter for the HWT, but it wasnt done with CT's on the mains. I willl post this in 911, and see if anybody comes up with any other explanation Answer from Joe in Maple Ridge...Thanks Joe...You bring up a VERY good point!! The question regarding ct's in the meter base has the makings of a grow-op monitoring situation, with a 100A service it's usually important to balance the phases as most fires are caused by an overloaded neutral. Also Hydro would be extremely upset to see ct's on a residential meter with no multiplying factor. With reference to the above, I also forgot to say that any resident of the house would be put in extreme danger if he/she tried to disconnect the ammeters (open circuit voltage) Thanks, Joe ========================================================================== Question Are there any situations (i.e. sloped ceilings, shallow ceilings, insulated ceilings) where I am not allowed to install a heat lamp? Answer Hi: Not as long as you use an approved fixture....ie: in insulation, it must be an "IC rated fixture. in damp areas such as showers it must be a sealed type. The manufacturers instructions will tell you how close to things like walls it has to be, so make sure you read them and decide what fixture you are going to use before you do any layouts.. ========================================================================== Question When dealing with a gen set that will be used to supply power to a site in the event of major power failure, what are the requirements for bonding and grounding. ie is a "service" ground also established at the generator that is located 100 feet away? Is it treated like a service in that grounding bushings are required at raceway where it enters the transfer switch or where transfer switch enters main building service? I think that a ground is established at the generator but is that ground bonded to the neutral as in a service entance? Answer Hi, The generator should be treated as a separate service. Grounding and bonding is required accordingly. The generator neutral must be grounded. See section 10-204(4) which allows a common grounding conductor for circuits supplied from a common enclosure if that is applicable. (transfer switch) Please contact your local safety officer for details on the specific installation. ========================================================================== Question Hi Les & Cody Just going thought the BC bulletins and BC Hydro Specs and cannot remember where I saw the specs for a temporary pole service. Any Help on where to look for it would be appreciated. Thanks-- Kamloops Guy Answer Hi K.G. It is probably easier to do a page on that information, so i have made a web page up with pictures and explanations. Cody.... (Click for the page) ========================================================================== Question Can the rule allowing space heating loads be loaded to 100% capacity as long as the o/c device is increased be applied to hot water tanks? Our particular situation has hot water tanks @ 16.5 amps we want to use #12 with a 30 amp breaker ( residential ) Thanks Larry Answer The heating section refers only to fixed resistance space heating, (yes this is also fixed resistance, but not space heating) but 8-302 (2) talks more about it. Hot water tanks ARE considered continuous loads and therefore need the 80% derating. .....Les ========================================================================== Question Hi, Would you have a list of acceptable sub-type panels for connecting a gasoline powered generator to a house . This is for when we lose hydro due to broken power lines. We just went through 4 days of no power, boy do we appreciate hydro now. Thanks, Dave Answer Hi Dave: Wow...4 days in this weather! Where do you live? All the panel manufacturers make them, (Square D, Federal , Cutler Hammer-Eaton, Seimens) and they are called "Generator Panels". They are readily available at any Electrical wholesaler or Revy (Rona) or Home Depot. In Kelowna, our Electrical Wholesalers are closed today being Sunday, so i called Home Depot and they have: 60 Amp 8 circuit Cutler Hammer $178 30 Amp 8 circuit Square D for $142 60 Amp 8 circuit Square D for $156 Their prices are usually within pennies of the prices at the Wholesalers. About the best article i know of on how to connect a generator panel is listed in my "Interesting Links" page under Generator Panels. Of course you will have to follow all your local codes etc...... Hi Les, Thanks for the help, of course if I had looked at the links page I would not have had to ask you, However thats the way it goes. Silly eh ? I live on Mudge Island (Just south of Nanaimo,next to Gabriola Island) I gather you live in Kelowna so our electrical codes would be the same. Again Thanks very much, Cheers Dave ========================================================================== Question Gentlemen I presume; I am involved in a project in northern B.C. and have been told conflicting stories on grounding requirements for portable light towers …help me please. Thnx Ken Answer Hi Ken: The requirements are the same as they are for any service. You need 2 x 10 foot ground rods 10 feet apart, or you can bury a ground plate 2 feet under the ground. You also need to make sure the light tower is bonded to the rest of the frame and metal stuff. I talked to the Manager of the B.C. Safety Authority (The Inspectors department head). I called him to ask what they would accept in the event of the "Frozen North" where it was absolutely impossible to get into the earth. He said the local inspectors have "room" to move and that in one case they even allowed the light plant tire to sit on a ground plate to hold it firmly down because there was absolutely nothing else they could do. Also, if there are any things like fire hydrants or other "grounded" things then you could possibly use them. Always get your local inspectors blessing first. Hope this helps..........Les ========================================================================== Question I think your site is fantastic! Here is my question:What is the current on the neutral on a three wire branch circuit, that is connected to a three phase 4 wire service. The three wire branch circuit has 12 amps load on each leg.What is the formula for calculating the vector sum of these two currents. Thanks Brad Answer I think you are referring to the Neutral Conductor of a wye system. It would be a Common Conductor when connected to two phases since it is no longer a Neutral. It would only be a true “Neutral” if connected to all 3 phases or as single phase since it only carries the unbalanced current. To find the neutral current on a wye system the here is the formula: (I dont have a square root symbol so the V and line are them) ______________________________________ V (AI^2 + BI^2 + CI^2) - (AxB)+(BxC)+(CxA) Written out, that would be: The square root of: (A phase squared + B phase squared + C phase squared) - (A phase x B phase + B phase x C phase + C phase x A phase) Lets give all three phases your value of 12 amps to get the Neutral load from the formula. (12x12 + 12x12 + 12x12) = 432 - (12x12 + 12x12 + 12x12) = 432 432 – 432 = 0. The square root of 0 is 0. Therefore the identified conductor is actually a neutral. With only 2 phases and a common (single phase) used, then: (12x12 + 12x12 + 0x0 = 288) - (12x12 + 0x0 + 0x0 = 144) = 144 The square root of 144 is 12, so you see the Grounded Conductor carries the same current as the two phase conductors, and your answer is 12 amps.... Also if you think about it as vectors, they are 120 degrees apart. If they were 180 degrees apart, they would cancel each other as for every positive move there is a negative in the opposite direction which would make the neutral current "0". Because they are 120 degrees apart, then they dont have the same positive value on one phase as the negative value on the other phase. ....Les ========================================================================== Question Hi B.C.Electrician: The local building authority requires that the furnace blower and a bathroom exhaust fan come on, by timer, twice per day for four hours per cycle. I have power ( 2 wire) to the bathroom exhaust fan switch box and have run a 3 wire from this box down to the timer ( intermatic mechanical timer). I am not sure what connections are required at the bathroom switch box, at the timer, or the furnace. Any suggestions? Answer Hi Len: UPDATE! I Drew a diagram of it here (Click Here) Build an airtight house, then suck in outside air because it's too airtight? Do our Building codes make sense to you? Anyways haha , here is how it's done. Always follow your manufacturers instructions and local codes first!!! 2 wire Power to the Switch box 2 wire to the fan 3 wire to the timer at the furnace. In the Bathroom Fan switch box: All whites marretted together (Neutrals) Black from power to black in 3 wire to timer with a pigtail to one side of the fan switch. Red from the timer 3 wire to black to fan with a pigtail to the other side of the fan switch In the Timer: There are 2 sets of dry contacts Timer has a "Hot" and a "Neutral" terminal. From the 3 wire put the Black to the hot and the white to the neutral terminal. This powers up the timer Jumper from the black in the 3 wire (or the Hot terminal) to one of the N/O contacts Red from the 3 wire to the common of that N/O contact On the other set of normally open contacts, put a wire to the "G" terminal in the furnace Tthe other side of the contact goes to the "R" terminal in the furnace These wires are at the same place the thermostat hook up and are: "G" is the fan only terminal, and "R" is the common to the "G" terminal Mount the timer on the outside of furnace Wire it through the back of the timer through a knockout. Set the times with the dip switches and you're done!!! I will post a wiring diagram on the website for this as soon as i get a chance to draw one up. Hope this helps.......... Cody@bcelectrician.com ========================================================================== Question Hello bcelectrician, A manufacturing plant has an ungrounded (Delta) supply feeding several large motors. Equipment ground has been installed correctly and one of the motors develops a phase to ground, the ground fault indicator light registers the fault. In the same electrical room as the delta supply, there is also a lighting transformer wired for 3ph. 4 wire, with the centre tap bonded to the (delta) equipment ground. Will the grounded phase of the delta system complete the circuit through the wye centre tap and blow the fuse ? Thanks....Joe Answer Hi Joe: Short answer, No it shouldn't. Remember the Lighting transformer is a transformer, and as such, it creates a new system. It is only magnetically coupled, and as such, it really doesnt have any electrical reference to the line supplying it. (just Induced to create the new system). The grounded wye point is on the secondary side. When you have a ground on a delta phase, always correct it A.S.A.P. as any other phase to ground short will be a problem in the mill. Also, remember that with any phase shorted to ground, any other phase will show voltage to ground, and can be very dangerous to the unexpecting person.... ========================================================================== Question Hi BC Electrician: Once again I love this site. Can you tell me how Arc Fault Breakers work... its test time again. I know the code rule but need to how they work so I can remember the rule. Any input would be very helpful thanks. David (dawson creek) journeyman Answer Hi David: Basically, what an "AFCI" (Arc Fault Circuit interrupter) does is measure and look for a intermittent high current between the hot and neutral. When a Hot wire makes a solid contact with a ground or a neutral, the current draw will be high enough to trip the breaker. But if the contact is intermittent and not a solid contact due to loose or corroded connections or failing insulation, what develops is an arc. The arc causes heat, which left uncorrected could eventually cause a fire. The AFCI breaker detects an arc by the characteristic wave an arc causes in the electrical flow. (this is usually called a "Signature waveform") When it sees a big enough arc fault, it trips the breaker. There is a good explanation of this here:(Click Here) P.S. Since you are up north, the test button on some some earlier Seimens arc fault breakers dont work in below zero temperarures and were recalled.Also lots of Square D breakers were recalled!! ========================================================================== Question Hi bcelectrician i work for a company that has a employee that does every thing jack of a trades, is he allowed to work on any thing to do with electrical. do you understand what i'm trying to ask............ Vancouver Island. Answer That Company MUST have a FSR to do any electrical work. If it does not have an FSR, it can not do electrical work. There are NO provisions in B.C. For any Handyman. If it is working on electrical without an FSR, It is illegal.. ========================================================================== Question Hi BC Electricians: A customer I work for has a rock conveyor that was about 65 feet long. He added another 25 feet to it, and has used the same motor and starter. The motor wont start anymore if it is full. Will a soft start or autotransformer starter help this? Answer Probably not. Remember that an AC motor delivers about 150% of its nameplate rated torque when started across the line at full voltage. Anything less than the rated voltage will result in much less torque (inverse square). Depending on how the conveyor is filled, you may try a smaller motor sprocket to slow it down, but you will have to keep in mind if it runs slower, it may get more rock on it. What is your HP and wire size and starter size? 10 hp, Size 2 starter, and #6 Teck, and 208 volts 3 phase You should be fine with everything if you change to a 15 hp motor. You will need to change the fuses & overload heaters if they are not the adjustable type. Hi Again...I'm a bit sheepish about telling you this, but i tried a soft start and it wouldnt work even though the guy i got it from guaranteed it would. I took it back and we ended up putting a 15 hp motor in. We could not cut back the rock feed very easily without a lot of work, so slowing it down wasn't a good option. Its working good now. Thanks Youre welcome......Glad it all worked out.....Cody ========================================================================== Question Dear bcelectrician: If I have a 200 amp service, do I actually have a 400 amp service? Can I not put 200 amps on each hot wire giving me 400 amps? (2nd yr) JT, Prince George Answer Hi JT. Always remember with Electricity, you dont get something for nothing. Your service is rated at 200 amps at 240 volts. (P=E x i ) Thats a total of 48000 watts. Each "hot" leg to neutral is capable of 200 amps at 120 volts. That gives you 24000 watts on each hot leg...Times 2 = 48000 watts. Remember the neutral only carries the unbalanced current, so if each leg is loaded to 200 amps, there will be no current in the neutral, so you're back to 200 amps at 240 volts....Cody ========================================================================== Question Hi: i'm not sure if i'm doing this right but here is my question. I was called to check a problem in a welding and mechanics shop. The compressor is the trouble. It has a 240 volt motor on it. I have been an electrician for 17 years and have never seen a motor like this. The nameplate is there but it is worn so only thing i can read is 1 1/2 horsepower and General Electric. I was lucky to find that it was a air pressure switch that was buggered up, and when i replaced it all works fine again. My question is : What kind of motor is this with a commutator and brushes and looks really old. It is also huge for a 1 1/2 hp motor. If it craps out, will a new 1 1/2 hp new motor work? Thanks Tony (Kelowna) Answer Hi Tony: Sounds to me like an old repulsion induction motor. I have seen 3 of these in my travels, 2 on compressors, and both working fine, and one that I was given by a guy who didnt want it. They are a different breed alright. They use a wound rotor and commutator to start it as a series motor (Repulsion Mode) and then it shorts out the windings with a shorting collar device that works kind of like a start switch (induction mode). They have very high starting torque like a DC. motor and after they reach a certain speed, the shorting collar shorts out the rotor windings effectively turning it into an induction motor. If you ever take one apart, mark the location of the brushes. Rotating the brushgear over the "neutral plane" will reverse the motor, and adjusting them slightly will alter the amount of brush arcing. If you replace it, go about 1/2 hp higher to get the starting torque you need. ========================================================================== Question Hi BC electrician: I'm in Trail B.C. My Brother in law has a shop with a belt that takes waste outside. I am a Journeyman electrician, and here is what is happening. Its 208 3 phase feed to the motor. When he first called, I checked it and it was tripped on overload, and 1 fuse was blown. I replaced the fuse and reset the o/l, but it did the same thing again. I checked the motor, and no shorts or grounds. I disconnected the motor and checked the voltage at the motor and have all 3 phases at 208 volts? We put another spare motor in and it did exactly the same thing. Any ideas or suggestions would be appreciated.....Thanks Troy Answer Hi Troy: I used to live in Trail (Rossland). Anyways, here is what i suggest. It looks to me like you have a poor connection somewhere. Often a bad contact in a contactor, breaker or disconnect can cause this. You will read the proper voltages when there is no load on it, but as soon as the current appears with a load, the contacts wont carry it. Also check any disconnects to make sure the knife blades are making good connections. Check for signs of heat like burnt insulation around the connection terminals. You may also have a overload heater that is opened (Almost) or poor connection. If none of these works, we'll look at some other stuff. Please let us know so others may benefit....Thanks....Cody Hi again BC Electrician: It was the contactor. One set of contacts is very badly burnt. I couldnt find replacement contacts, so i put in a new one and it is working fine now. ========================================================================== Question Hi from Nanimo: i was wondering if there is a way to start by blower motor from more than 1 place that will be not too costly. It is a wood working shop and the blower is to remove sawdust to a bag outside. It is actually a vacuum. and is 1 horsepower 240 volts. I need to be able to start it at every machine i have which is 7. thanks ED. (1st year apprentice) Answer Hi Ed: Yes there are a number of ways to do this. The standard way is with a mag (Contactor / starter) using stop start pushbuttons. This could be a bit costly. The cheapest way would probably be to use a remote system. Here is a link to a place that makes them. (Click Here) Another way is to do it with 3 & 4 way switches and use low voltage. Here is a picture of what you would need to do. (Click Here) ....Let us know what you decide.....Thanks....Cody Hey Cody: That 3 way switch way is really cool! . I decided to go with the remote though because it is so easy. I have ordered it but it will take a week to get it. Thanks..Ed ========================================================================== Question Hi: I have an Allan Bradley 1771-SDN DeviceNet card in a remote rack 4 on a plc 5/40b. If I locate it in the main processor chassis will i get better speed responses? Does it make any difference? RD. Answer Hi R.D. Yes it will make a huge difference. The device net scanner will be communicating through a parallel backplane instead of the serial RIO at 500 kbaud. Also, use the minimum words (less than 62 if you dont need them) in your block transfer to speed it up even more.....Cody ========================================================================== Question Hello bcelectrician. I am a second year apprentice and last week I had to install a thermal device. It had a choice so that it could be hooked up either 0-10 volts and 4-20 ma. The specs asked for 4-20 ma. Why would they want to use 4-20 ma instead of 0-10 volts? Wouldnt it be a lot easier to test and troubleshoot if it was 0-10 volts? B.K Cranbrook Answer Hi BK You are right that it is easier to check a 0-10 volt signal than a 4-20 ma current. The main reason for using 4-20 goes back to good old Kirchoff's law. In a series circuit the current is always the same everywhere in the circuit. When you use 4-20 ma, you can install more devices and run a longer distance and all your meters will read the same current. With 0-10 volts, you have to worry about voltage drop and if you have 2 or more meters a long distance apart, they will probably read different.....Cody Thanks Cody. That makes sense. Great website! BK ========================================================================== Question Hi:Bcelectrician--Cody Here is something that I just dont get. Whats the difference between BINARY and BCD? I know binary, but whats BCD? Rob (not an electrician yet) Answer Hi Rob: Well, BCD (Binary Coded Decimal) is Binary, but it's called "coded" because it breaks up the numbers into groups of integers. This was done in older PLC's and digital electronics because a 4 bit binary system could only count up to 0-15 (Binary 1111) They needed a way to count higher, so they grouped 4 of these together each representing an integer and only let them count as high as the decimal #9. For example: 1001 in binary is the decimal #9. With 4 groups of these they can now count to 9999 shown as a bcd # of : 1001 1001 1001 1001. In binary 9999 is represented as 10011100001111 which requires 13 bits, but they only had 4 bit machines! Here are some more examples: # 7 BCD: 0000 0000 0000 0111 Binary: 0111 # 23 BCD: 0000 0000 0010 0011 Binary: 10111 # 458 BCD: 0000 0100 0101 1000 Binary: 111001010 # 3362 BCD: 0011 0011 0110 0010 Binary: 110100100010 Ok. so the # 1947 would be 11110011011 or BCD 0001 1001 0100 0111 ? --Yup! Remember-There are only 10 types of people. Those who know binary and those who dont.. : ) .......Cody BC Electrician Home . |
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