Generator bonding question

Reply

  #1  
Old 08-26-05, 05:14 PM
MAMAN
Visiting Guest
Posts: n/a
Generator bonding question

I recently bought a house and one of the things that attracted me to it was it had a large backup generator (20KW says in produces 90AMPS). I have reviewed the wiring and have a question about whether or not it is correctly bonded. I live in Massachusetts and want to ensure it meets the local codes and is safe to operate. Any input would be much appreciated.

Here is the current configuration:

Generator is in a shed about 150 from main house. There is conduit running between the house and the shed. It carries (3) 2 AWG copper (Neutral and 2 hot lines) and a 8AWG copper ground these cables feed into a 200 amp Double Pull Double Throw transfer switch. The neutral is not bonded at the generator and the ground is connected to the frame of the generator. There is also a ground wire running from the frame of the generator to a grounding rod at the shed. The neutral is not bonded at the transfer switch but all three neutrals are attached within the transfer switch (Commercial power feed, Generator feed and feed going to the panel. On the commercial feed side the lines come from my meter (mounted on the outside of the house) into a 200 amp breaker/disconnect (in my basement) and then into the transfer switch. Again the neutral lines are not bounded in the 200 amp disconnect but the box itself has a ground running to the transfer switch and then back to the main breaker panel. The main breaker panel has the neutral bonded to the panel and has a ground running to the incoming city water pipe. This ground is attached before and after the meter.

My questions are:

Should the neutral be bonded anywhere besides the main house breaker box. In the commercial power disconnect or the transfer switch?
Also there is a breaker/disconnect at the generator but no disconnect for the generator before the transfer switch in the basement, should there be?
The commercial power neutral from the street is still attached when the generator is running is this a problem. The transfer switch only switches the two hot lines.
 
Sponsored Links
  #2  
Old 08-26-05, 09:17 PM
Member
Join Date: Aug 2004
Location: NA
Posts: 1,065
There is also a ground wire running from the frame of the generator to a grounding rod at the shed
.
This IMO this would be incorrect as you are not switching the neutral and your generator does not have the neutral bonded to the frame. This would not be a seperately derived system and you would not connect the generator to a ground rod. You are connected to the supply (commercial you call it) neutral and it is grounded at the service, therefore the generator should not be grounded.
You want the transfer box bonded to the main panel with the wire you speak of in your description.



Should the neutral be bonded anywhere besides the main house breaker box. In the commercial power disconnect or the transfer switch?
No you dont want it bonded to the egc or transfer box. You only want it bonded at the service panel in your case.

Also there is a breaker/disconnect at the generator but no disconnect for the generator before the transfer switch in the basement, should there be?
NO

The commercial power neutral from the street is still attached when the generator is running is this a problem. The transfer switch only switches the two hot lines
.
NO...this is what is keeping the generator from being a seperately derived system....it would then require a ground rod.
 

Last edited by Roger; 08-26-05 at 09:29 PM.
  #3  
Old 08-27-05, 07:14 PM
Member
Join Date: Jun 2002
Location: Brethren, Mi
Posts: 1,648
That will depend on the type of generator that is to be installed. If the generator is to be permanently installed then the answer is governed by the bonding of the neutral at the generator.

If the neutral is bonded at the generator then you transfer the neutral in the transfer switch. This is done to avoid having two connections to ground on the neutral at both the service equipment and the frame of the generator.

If the neutral is not bonded to the frame of the generator then you do not transfer the neutral so that the generator's neutral will be grounded by the main bonding jumper in the home's service disconnecting means.

A power inlet for a portable generator is done the same way in that a four wire with ground inlet, such as the L14-XX 120/240, is wired to a two pole transfer mechanism. A three wire without ground inlet, such as a L11-XX is wired to a three pole transfer device. In general three pole transfer devices are only available as switches.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'