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soma 11-07-2011 06:55 AM

generator transfer switch neutral
 
The information I have seen on the web on how to hook up transfer switches has seemed pretty unclear.

It would seem simplest to disconnect (float) the generator neutral from the ground - ground the generator chassis - and connect the generator neutral through the transfer switch to the breaker box neutral. I assume the breaker box neutral is always connected to the ground?

If the generator ground and neutral are left bonded, I assume you would need to somehow wire the breaker box so that the breaker box ground can be disconnected from the breaker box neutral?

AllanJ 11-07-2011 07:13 AM

I am not say8ing you should do it this way but:

Sometimes the main panel neutrals and grounds need to be separated, say, for compatibility with an upstream (whole house) transfer switch or an upstream main disconnect switch.

But I would not separate the neutrals and grounds of what has been my main panel for the sole purpose of accommodating a particular generator.

It would be better to separate ground and neutral at the generator. But if this cannot be done easily then I would be tempted to not connect the green wire running between the generator and the rest of the system,and set the generator on a wood or other insulating platform. This prevents the "neutral" current from splitting itself between the white and green lines back to the generator and tripping a ground fault interrupter built into the generator.

Or if the generator did not have built in GFCI's that kept tripping, leave neutral-ground bonding in place in both the main panel and the generator.

soma 11-08-2011 04:46 PM

Quote:

Originally Posted by AllanJ (Post 765628)
[....] Or if the generator did not have built in ground fault interrupters that kept tripping, leave neutral-ground bonding in place in both the main panel and the generator.

I was wondering why it's not good to have more than 1 ground for a house. I guess, depending on how close the grounds are, current could run between them, especially if the soil is wet. But, considering that your neighbor's house has a ground, then it would seem that a ground should be a certain distance from another ground in order to be safe?

soma 11-08-2011 04:52 PM

Quote:

Originally Posted by AllanJ (Post 765628)
I am not say8ing you should do it this way but:

Sometimes the main panel neutrals and grounds need to be separated, say, for compatibility with an upstream (whole house) transfer switch or an upstream main disconnect switch.

But I would not separate the neutrals and grounds of what has been my main panel for the sole purpose of accommodating a particular generator.

Or, maybe the generator neutral/ground could be permanently connected to the house and become the new ground.

Quote:

It would be better to separate ground and neutral at the generator
Was wondering how this is usually done? This is a black max 7000W (honda) generator.

Thanks.

brric 11-08-2011 05:14 PM

There is no reason to tamper with the generator at all. It is not a separately derived system.

brric 11-08-2011 05:49 PM

Quote:

Originally Posted by soma (Post 766782)
I was wondering why it's not good to have more than 1 ground for a house. I guess, depending on how close the grounds are, current could run between them, especially if the soil is wet. But, considering that your neighbor's house has a ground, then it would seem that a ground should be a certain distance from another ground in order to be safe?

Most electrical services have multiple grounds. For instance, ground rods, metallic water service, concrete encased electrodes and building steel.

joed 11-08-2011 06:27 PM

Quote:

Originally Posted by brric (Post 766816)
Most electrical services have multiple grounds. For instance, ground rods, metallic water service, concrete encased electrodes and building steel.

Isn't only one of them a ground? The rest is all bonding of the metal objects to the ground.

brric 11-08-2011 06:58 PM

Quote:

Originally Posted by joed (Post 766849)
Isn't only one of them a ground? The rest is all bonding of the metal objects to the ground.

Nope..........

All part of the grounding electrode system.

Billy_Bob 11-08-2011 07:48 PM

OSHA requires generators used at construction sites and so forth to have GFCI protection...

However these GFCI's trip when connected to a regular transfer switch! (Considered a "non-separately derived system" because the neutral from the generator is connected to the service panel neutral.)

But you can use a different type of transfer switch called a "neutral switching transfer switch", then this solves the GFCI tripping problem. (Then considered a "separately derived system" as the neutral from the generator is switched and then isolated from the service panel neutral.)

soma 11-08-2011 07:58 PM

Quote:

Originally Posted by brric (Post 766816)
Most electrical services have multiple grounds. For instance, ground rods, metallic water service, concrete encased electrodes and building steel.

This is from http://members.rennlist.org/warren/G...pl_Note_EN.pdf and is from Schneider Electric:
"Why does the neutral bonding in the generator
determine the type of generator panel used?
For an answer we refer to the CEC. Rule 10-
400 requires that equipment (generator frames)
be bonded to ground. Rule 10-106 requires AC
systems to be grounded. Rule 10-204 requires
the ground to be located at the service
entrance switch or panel. And finally, Rule 10-
204(1)(d) does not allow a connection between
the neutral conductor and the grounding elec-
trode on the load side of the service entrance
panel, effectively this does not allow bonding of
the neutral to the ground electrode in more than
one location."

soma 11-08-2011 08:06 PM

Quote:

Originally Posted by Billy_Bob (Post 766911)
OSHA requires generators used at construction sites and so forth to have GFCI protection...

However these GFCI's trip when connected to a regular transfer switch! (Considered a "non-separately derived system" because the neutral from the generator is connected to the service panel neutral.)

I think that's because the 2 neutral/grounds divide the neutral current so that it's different than the hot wire current. So if you disconnect the generator neutral from the ground that should solve the problem.

Billy_Bob 11-08-2011 08:57 PM

Quote:

Originally Posted by soma (Post 766929)
I think that's because the 2 neutral/grounds divide the neutral current so that it's different than the hot wire current. So if you disconnect the generator neutral from the ground that should solve the problem.

Exactly right!

Some of the electricity flows back to the generator via the neutral. And some electricity via the bonding connection in the main electrical panel, then through the ground wire from that panel to the generator ground, then through the bonded ground to neutral at the generator. Thus causing the GFCI to trip.

So another solution is to remove the neutral/ground bond at the generator, however the generator is no longer useable for construction sites, etc. and I believe it must be labeled so. For example...

http://www.gen-tran.com/assets/pdfs/...Bulletin20.pdf

soma 11-09-2011 01:21 AM

I'm still wondering why there's a code against connecting the neutral to the ground in more than one place. Is there some danger, or is it because it could throw off gfci?

frenchelectrican 11-09-2011 01:51 AM

Quote:

Originally Posted by soma (Post 767119)
I'm still wondering why there's a code against connecting the neutral to the ground in more than one place. Is there some danger, or is it because it could throw off gfci?

Couple reason why .,

One it will trip the GFCI no question asked { this is true with Honda generators but other brands may do the simauir sistuation as well so check that manufacter instruction on the details }

Second thing that the main house system the netual and earth { ground } is allready bonded at the main breaker box but once it go out after that it will be seperated the main reason so it can able get the OCPD tripped if any fault show up.

Hope this will help ya and I know other guys if they have more info they can chime in as well.

Merci,
Marc

KE2KB 11-11-2011 03:21 PM

Are all portable generators now being supplied with GFCI breakers, or just those that are certified for use in construction sites?

FW


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