Load Balance


  #1  
Old 01-03-04, 07:01 PM
rubin_l
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Load Balance

I am installing a Generac Guardian 15KV generator. The instructions involving the installation of the transfer switch states:

"Balance must be maintained when moving cicuit locations from main electrical distribution panel to emergency load center. Circuit breaker positions alternate bus bars vertically. Circuits sharing a neutral wire should either be moved together to adjacent positions in emergency load center or not moved."

Is the balancing only to do with having two breakers sharing the same neutral wire? Why is it a problem to move one circuit to the transfer panel (keeping the breaker amperage the same) while leaving the other circuit in the main panel? No neutral wires get moved anyway.

In my main panel I can't locate any instances of a single neutral wire and more than one hot wire coming out of a cable. All neutrals and grounds are connected to the respective panel bar, and all hots are connected to their own breakers. What should I be looking for?

The instructions also state to use 12 AWG stranded copper wire to connect to the copper grounding rod. The 12 AWG wire I purchased looks awfully thin and is encased in green insulation. The last time I did something with a ground rod it involved very thick stranded copper wire, with the bundle being at least 1/4" in diameter, and no insulation. Is the 12 AWG really thick enough?

Thank you in advance for your help; I am determined to correctly and carefully do this myself!
 
  #2  
Old 01-03-04, 07:15 PM
R
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Load balancing has nothing to do with balancing the load between the main panel and the transfer switch panel.

What they are talking about is keeping the load as even as possible on both halves of the 220 volts that the generator provides.

Look at the circuits you want in the panel and split tham as best as possible. For example, if you have a refrigerator and a freezer to plug in, put on on one half of the 220 and the other on the other half.

When the generator is actually running (and even when you are running on utility power) you want the power used on each half of the 220 to be fairly even.

As for the ground wire, I believe that you are reading the instructions incorrectly.

Another word of caution. What you are intending to do will put you very close to electrocution and death. Think twice about doing this yourself, especially if you have never worked in a circuit breaker panel before. If you insist on doing this yourself make sure that you do so with the main power off, with no jewelry on (watches, rings, necklaces, etc.) and double check all your connections before turning the power back on. ONE MISTAKE AND YOU COULD END UP DEAD.
 
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Old 01-03-04, 07:16 PM
J
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The first sentence regarding balance is a different topic than the last sentence regarding shared neutrals.

The warning against moving only one hot wire of a pair of hot wires sharing the neutral is guarding against overloading the neutral by not having the two hots 180 degrees out of phase. Such an overload could start a fire.

It is not always easy to identify a shared neutral. If the wiring is NM-B, you can usually see which neutral goes with which hot (if you follow them closely). If the wiring is in conduit, it may be almost impossible to tell.

12-gauge wire is big enough for some grounding wires but not for others. You really didn't give us any numbers, so we can't tell about your application. But if the directions say 12, I don't see how I can argue.
 
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Old 01-03-04, 08:25 PM
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The definition of a multiwire branch circuit is instructive.

"Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system." Copyright 2002 National Fire Protection Association.

The danger is that if in shifting only one circuit of a multiwire branch circuit you fail to keep the two circuits on opposite legs of the utility supply the neutral will carry more current than is safe when both circuits are being powered by utiliity power and a fire can result. Since the instructions are written for DIYs they tell you to shift both legs of the circuit or shift neither. I have installed these generator transfer assemblies and as long as when you are done the two ungrounded conductors of the circuit still have 240 volts between them the neutral of the circuit will only carry the difference between the current flowing in the two ungrounded conductors. If you fail to maintain this relationship the neutral will carry the sum of the current that is flowing in the two ungrounded conductors.

Do you by any chance have a SquareD panel with a horizontal throw main breaker? If yes there is a better solution to your problem that will involve less work and provide much greater flexibility. SquareD offers an interlock assembly for their late model panels that will allow you to select any load in the panel that your generator is large enough to carry. If this applies to you let me know and I can direct you further.
--
Tom Horne
 
  #5  
Old 01-06-04, 08:35 AM
rubin_l
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The wires for each circuit are in their own jacket; none are conduits with multiple sets of wires.

The panel I have is a GE PowerMark Gold load center. It does have a horizontal throw main breaker that is 4 poles wide, with two poles each going to the two vertical hot bus bars.

The breaker that powers the transfer switch is a 70A double pole that gets installed in the main breaker panel.

Then up to 10 120V circuits and 2 220V circuits come off the main panel and flow through the transfer switch powered by that 70A breaker.

Is the goal to leave the main breaker panel with roughly equal breaker distributions (suming up the amp ratings on each breaker) between the two bus bars?

Since I want to put the vital circuits on the transfer switch, wouldn't then one main panel bus bar be carrying much more load than the other since it is the vital curcuits that gets used the most?

Would it have been better to purchase two single pole 70 amp breakers and put one on each bus bar?

Even though in the end I may resign myself to get an electrician to do this, at least I want to understand it.

Larry
 
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Old 01-06-04, 09:05 AM
R
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As long as you maintain equal distribution within the main panel and within the transfer panel you will maintain equal distribution between both legs of the incoming 220, as both legs of the incoming 220 go through the 70 amp breaker to the transfer panel.

However, do not simply add up the breaker ratings. You must analyze what is on the circuits to maintain a balance. For example, a 15 or 20 amp circuit that powers an unused bedroom or two draws very little or even no current, while a 15 or 20 amp circuit that powers the refirgerator draws much current. Keep in mind that you don't have to exact here (that's not really possible anyway), just try to evenly split the load.

What you put in the transfer panel and what you leave ikn themain panel is entirely up to you. Just keep in mind what you want to have power during an outage and don;t go overboard either.
 
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Old 01-06-04, 03:08 PM
rubin_l
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I appreciate all of the words of wisdom. I just need one bit of clarification with the 70 amp breaker.

The double pole breaker only connects to one leg of the power bus. So up to 70 amps will be drawn out of that one leg, not counting any other circuits I would leave on the main panel. My main service is 200 amps, if that info helps.

So if my critical circuits, like the furnace, fridge, and certain room lights, are on that 70 amp breaker (and those are the circuits we use most often anyway), approximate balance does not seem possible.

Am I creating a potential problem? I was not aware power was so finicky.
 
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Old 01-06-04, 03:51 PM
R
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You are incorrect. A Double pole breaker connects to both legs. That is how you get 220, by using both 110 legs together. If you did not have both sides of the buss you would only have 110.
 
  #9  
Old 01-06-04, 04:10 PM
hotarc
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Re: Load Balance

Originally posted by rubin_l

In my main panel I can't locate any instances of a single neutral wire and more than one hot wire coming out of a cable. All neutrals and grounds are connected to the respective panel bar, and all hots are connected to their own breakers. What should I be looking for?
Do you see any red wires entering your panel?
 
  #10  
Old 01-07-04, 08:38 AM
rubin_l
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Yes, there are some red wires in that panel. But I did not see black wires coming out the same cable (except for the oven).

My intention was to move either all hot wires out of a given power cable to the transfer switch, or to not move any of them.

I presume this is correct?
 
  #11  
Old 01-07-04, 08:49 AM
rubin_l
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What you say below makes pefect sense to me, but the breaker I bought does not look like it connects to both legs of the buss.

Both breaker contacts are on one side. The breaker itself does say it is double pole. Is there some other type of breaker I should be looking for?

It seems that if you need to connect to each leg of the buss, you need to separate single pole breakers, one for each side. What am I missing here??



Originally posted by racraft
You are incorrect. A Double pole breaker connects to both legs. That is how you get 220, by using both 110 legs together. If you did not have both sides of the buss you would only have 110.
 
  #12  
Old 01-07-04, 08:56 AM
J
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The power buses are not divided left and right, even though it looks that way with the panel cover on. As you go down the panel, the spaces alternate between the two buses.

If the breaker is 2 inches wide, it is the right one.
 
 

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