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Old 11-05-2012, 07:40 PM   #1
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Question about backfeeding and electrical supply.


I have a properly wired generator, but this whole incident has sparked my interest in our distribution system. From my understanding, when I turn off the main on my breaker I am only disconnecting the two hot leads. The neutral return is still connected to my utility company. If I were to connect a generator to my panel (Using a 240V cable, connecting the two 120V cables to the power rails and the neutral and grounding wires to their respective bus bars) and have the main breaker open, am I still sending power down the neutral? Thank you anybody for any clarification.
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Old 11-05-2012, 09:24 PM   #2
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Question about backfeeding and electrical supply.


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Originally Posted by Wnt2bsleepin View Post
I have a properly wired generator, but this whole incident has sparked my interest in our distribution system. From my understanding, when I turn off the main on my breaker I am only disconnecting the two hot leads. The neutral return is still connected to my utility company. If I were to connect a generator to my panel (Using a 240V cable, connecting the two 120V cables to the power rails and the neutral and grounding wires to their respective bus bars) and have the main breaker open, am I still sending power down the neutral? Thank you anybody for any clarification.
When the generator is operating (and the main breaker for utility power switched off) the current wants to return to the generator, not the earth or the utility pole. So no current should be sent out the neutral of the service drop from the pole.
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Old 11-05-2012, 09:41 PM   #3
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Question about backfeeding and electrical supply.


The key point is that in the US, it should be IMPOSSIBLE for the generator to to put power to the grid. It must be a an an approved Interlock or transfer switch. Relying on the homeowner to turn off the main is not acceptable. I have read some things (but don't trust) that it is OK to rely on on a responsible person to ensure that the man breaker is in fact opened.

I would like to hear from some pro's on this question... as well as the neutral question.
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Old 11-05-2012, 09:42 PM   #4
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Question about backfeeding and electrical supply.


Nope, can't do that. There has to be some mechanical protection from having the main on with the generator running.
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Old 11-05-2012, 09:55 PM   #5
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Question about backfeeding and electrical supply.


Thanks KB -

Is there some different rule about the neutral being separated in the US vs Canada ? (just curious).
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Old 11-05-2012, 09:56 PM   #6
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Question about backfeeding and electrical supply.


Don't know
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Old 11-05-2012, 10:08 PM   #7
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Question about backfeeding and electrical supply.


YES !
Under most circumstances you can back feed.
Under what circumstances ?
If both hots had identical loads
then no backfeed.
But if the two hots have different loads
then the difference could bleed back thru the neutral.

In Australia,
Change over switchs MUST isolate completely,
that means all actives and neutrals are switched out.
we do not use mechanical interlocks,
we use large multi-pole switchs.
So the supply is completely isolated.

Last edited by dmxtothemax; 11-05-2012 at 10:31 PM.
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Old 11-06-2012, 06:26 AM   #8
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Question about backfeeding and electrical supply.


You can get 3 pole transfer switches so you can isolate the neutral but 2 pole transfer switches that isolate just the two hot lines are very common and are legal in some places.

Interlocks, where permitted, must be of the proper kind for the panel so both the main breaker for the utility power feed (service cable) and the side breaker for the generator backfeed cannot be forced to their on positions at the same time. Interlocks are not allowed in some jurisdictions for reasons including the loss of the interlock protection if the panel cover plate, to which the interlock slider is attached, was removed.
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Last edited by AllanJ; 11-06-2012 at 06:28 AM.
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Old 11-06-2012, 07:57 AM   #9
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Question about backfeeding and electrical supply.


No, A single wire sent to your main panel cannot send power,
It would need a path back to the Genny and that is not possible from your description.
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Old 11-06-2012, 09:56 AM   #10
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Question about backfeeding and electrical supply.


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You can get 3 pole transfer switches so you can isolate the neutral but 2 pole transfer switches that isolate just the two hot lines are very common and are legal in some places.
Do they actually sell transfer switches that switch the neutral? I've never seen one for residential purposes.
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Old 11-06-2012, 11:44 AM   #11
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Question about backfeeding and electrical supply.


Quote:
Originally Posted by Wnt2bsleepin View Post
I have a properly wired generator, but this whole incident has sparked my interest in our distribution system. From my understanding, when I turn off the main on my breaker I am only disconnecting the two hot leads. The neutral return is still connected to my utility company. If I were to connect a generator to my panel (Using a 240V cable, connecting the two 120V cables to the power rails and the neutral and grounding wires to their respective bus bars) and have the main breaker open, am I still sending power down the neutral? Thank you anybody for any clarification.
That is correct,you may have 100A or 200A 120V/240V,4-wire residential service with appropriate 2-pole braker.Switching neutral (white) is forbidden by CEC since this is an "identyfing conductor.
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Old 11-06-2012, 01:20 PM   #12
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Question about backfeeding and electrical supply.


Yes they sell 3 pole residential switches for switching the neutral. There is one mfg. that sells a separate neutral switching kit to go with their 2 pole switches.

"Switching neutral (white) is forbidden by CEC since this is an "identyfing conductor. "

We are not talking about switching the neutral as in installing a light switch in the neutral conductor.

If you have a generator with a neutral ground bond and you connect it to the house wiring, you would end up with 2 bonds in the system, which can be dangerous under some conditions. A transfer switch that "switches the neutral" is breaking the connection to the house neutral ground bond, and connecting to the generator neutral ground bond.

Here is what Schneider Electric Canada says on the subject. (See page 2)
http://members.rennlist.org/warren/G...pl_Note_EN.pdf
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Old 11-06-2012, 05:09 PM   #13
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Question about backfeeding and electrical supply.


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Do they actually sell transfer switches that switch the neutral? I've never seen one for residential purposes.
They do in Australia !
surely you have something simulair ?
Name:  genny 2.bmp
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Old 11-06-2012, 05:20 PM   #14
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Question about backfeeding and electrical supply.


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They do in Australia !
surely you have something simulair ?
Attachment 60150
What would you put that into?
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Old 11-06-2012, 10:13 PM   #15
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Question about backfeeding and electrical supply.


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What would you put that into?
Name:  change over 2.bmp
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How about this type of mounting ?
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