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Old 12-03-2011, 08:53 PM   #1
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generator neutral and ground connections


We've got our 7000W generator now hooked up to a transfer switch with the middle of the switch going to the 150A main breaker, and the top and bottom of the switch to the PO and generator. We've got the bonded neutral and ground from the generator going to the neutral bank and ground screw on the switch and a neutral from the breaker box going to the neutral bank on the switch.

The generator manual recommends grounding the generator chassis to a ground pole. I assume this isn't necessary since the ground from the generator is grounded through the breaker box?

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Old 12-04-2011, 08:22 PM   #2
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generator neutral and ground connections


It's not necessary per NEC 205.34:
Quote:
250.34 Generators-Portable and Vehicle-Mounted
(A) Portable Generators. The frame of a portable generator is not be required to be grounded to the earth if:
(1) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.
Though it's not a bad idea to ground the chassis in any case, if not to its own 8ft ground rod then a small stake in the ground. I chain my generator when in use to the two rods at the service entrance.

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Old 12-06-2011, 06:11 AM   #3
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generator neutral and ground connections


On the same topic. Can anyone tell me why when wiring a generator transfer switch, you are required to move the neutrals (of the circuits being transfered) from the main panel to the transfer switch. I have read in another forum that the NEC requires that the neutrals be in the same enclosure as the breaker. In the case of my installation (Generac RTS12EZA1 transfer switch) The manufacturer says to wire nut the neutral wire (of the circuit being moved in the main panel) and connect it to the neutral bar in the transfer switch. It also requires a #6 wire to be run from the main panel neutral to the transfer switch neutral. I can understand why you need to run the #6 wire between the two neutrals (the neutral wire from the generator gets landed on the neutral bar in the transfer switch). But isn't it redundant to have to move the individual neutrals from each circuit being transfered since the switch is connected to the main neutral bar already. I'm sure there is a legitimate electrical reason for it, but it my mind it seems to be unnecessary
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Old 12-06-2011, 06:50 AM   #4
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generator neutral and ground connections


The neutral for a branch circuit must be terminated (attached to the neutral bus in) the same panel (or subpanel) where the breaker for that branch circuit is.

I am not sure how this works with transfer switch boxes with a half dozen to a dozen individual transfer switches each perhaps with overcurrent protection (built in breakers), one for each branch circuit eligible for generator power. For each individual switch two wires go through a fat flexible conduit to the main panel, one to the branch circuit hot conductor, the other to the main panel breaker for that circuit. Here each individual switch in the transfer switch box is like on a switch loop with respect to the main panel.

When the transfer switch box comes with neutral pigtails terminated in the switch box and coming through the fat flexible conduit for for each respective branch circuit, then this gets around the problem with a generator whose ground and neutral are bonded and not easily unbonded. In the latter case, had the branch circuit neutrals remained unmodified in the main panel neutral bus, there would be double bonding of neutral to ground, once in the generator and again in the main panel.
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Old 12-06-2011, 09:33 AM   #5
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generator neutral and ground connections


The simplest way to look at this is consider what is happening to become a separately derived system per NEC... excluding those mounted on vehicles.

1.) Is the generator solidly connected to the homes grounded conductor (Service Neutral) or does the whole house transfer switch by mechanical or automatic means switch the incoming service neutral to that of the generator ?

2.) If the service neutral is switched and the generator has bonded neutral and ground then the generator is a separately derived power source and you would install a grounding electrode or two at the generator.

Here is a graphic from the IAEI that shows pretty much what you have at your home. Notice that no current carrying wires from the utility are solidly connected to the homes distribution panel load side of the transfer switch once the transfer switch is in the generator position.



This example may be closer to yours
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Old 12-06-2011, 12:37 PM   #6
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Thanks for the replies, (I KIND OF GET IT). Again on the same topic. I wonder why your not required to move the ground wires from each circuit being transfered from the main panel to the transfer switch?
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Old 12-06-2011, 03:14 PM   #7
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generator neutral and ground connections


Ground wires remain connected together wherever they come together.

When several ground wires are wire nutted together short of the panel with just a single wire continuing on to the panel the latter is sized equal to the larger(est) of the various ground wires coming together.
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Old 12-13-2011, 07:43 PM   #8
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generator neutral and ground connections


my local electrical inspectors have always required it to be done.
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Old 12-13-2011, 07:47 PM   #9
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generator neutral and ground connections


My boo-boo..now I see that you were referring to a portable...disregard my last post.
The whole house units require a grounding electrode.
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Old 12-15-2011, 05:25 AM   #10
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Quote:
Originally Posted by VA master elect View Post
My boo-boo..now I see that you were referring to a portable...disregard my last post.
The whole house units require a grounding electrode.
When you say "grounding electrode" are you referring to a metal pole being driven into the dirt?

Our transfer switch is hooked to the main of the breaker panel so it's powering the whole house. The generator neutral is bonded to ground and hooked to the neutral bank of the switch as is the neutral from the breaker. (This was the original question for this thread).
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Old 12-15-2011, 05:56 PM   #11
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generator neutral and ground connections


If your transfer switch is "service rated" then two grounding electrodes (rods) are required.
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Old 12-15-2011, 06:43 PM   #12
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generator neutral and ground connections


A grounding electrode can be:
1. A ground rod (needs to have 8 feet of it sunk),
2. The cold water line to the building, if metal and having at least 10' of underground run,
3. The reinforcing bars in a concrete foundation, need at least 20' worth.

Rebars are normally tied to one another using steel wire. It is assumed that, if the piece that protrudes to attach the fat ground wire (grounding electrode conductor) to is less than 20 feet long, that it is bonded to other rebars via such steel wire ties.
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Old 12-16-2011, 12:39 AM   #13
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Quote:
Originally Posted by VA master elect View Post
If your transfer switch is "service rated" then two grounding electrodes (rods) are required.
It's a GE TC10324R. (http://www.homedepot.com/webapp/wcs/...cStoreNum=6175)
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Old 12-16-2011, 03:58 AM   #14
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generator neutral and ground connections


That transfer switch is 3 pole ... it switches the utility neutral and transfers to the generator neutral ... yes? No solid connection thru the switch ?

I'm understanding you have this setup .... and your instructions are telling you to drive a ground rod at the generator as shown in the drawing
Attached Thumbnails
generator neutral and ground connections-emergency-transfer.jpg  
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Old 12-19-2011, 01:24 AM   #15
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Originally Posted by Stubbie View Post
That transfer switch is 3 pole ... it switches the utility neutral and transfers to the generator neutral ... yes? No solid connection thru the switch ?
It's a solid connection. The generator neutral and ground are connected to the neutral bar and so is the breaker neutral. It's not switched.

This is a picture of the tc10323r which is supposed to have the same setup as the 10324r except it's rated at 100A. The ge catalog lists it as a 2 pole switch.
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generator neutral and ground connections-geswitch.jpg  


Last edited by soma; 12-19-2011 at 06:26 AM.
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