Generator grounding

[augie47]

A have a residence that has a 200 amp main distribution panel. There is no POCO service. The 200 amp panel has two interlocked breakers connected to generators. Breaker #1 connects to a 20 kw permanently installed generator with a 4 wire 240/120 + G connection (the neutral is not bonded at the generator).
Generator #2 is a cord and plug connected portable with 240/120 3 wire cable.
My opinion is that the MDP must have a neutral-ground bond.
Any one see a problem with this installation ?

 

[texie]

A have a residence that has a 200 amp main distribution panel. There is no POCO service. The 200 amp panel has two interlocked breakers connected to generators. Breaker #1 connects to a 20 kw permanently installed generator with a 4 wire 240/120 + G connection (the neutral is not bonded at the generator).
Generator #2 is a cord and plug connected portable with 240/120 3 wire cable.
My opinion is that the MDP must have a neutral-ground bond.
Any one see a problem with this installation ?

Augie, are you sure you want to go here? Wait 'til Mike Whitt sees this! This should be fun.
Kidding aside, one problem I see here is that you have one as a 3 wire and one as a 4 wire and since you are using breakers w/ an interlock you can't set it up as an sds (as you can't switch the neutral). Have to think this through a little bit.

Of course many here will say not a problem, 3 wire, 4 wire, parallel neutral and grounds.

 

[texie]

Augie, are you sure you want to go here? Wait 'til Mike Whitt sees this! This should be fun.
Kidding aside, one problem I see here is that you have one as a 3 wire and one as a 4 wire and since you are using breakers w/ an interlock you can't set it up as an sds (as you can't switch the neutral). Have to think this through a little bit.

Of course many here will say not a problem, 3 wire, 4 wire, parallel neutral and grounds.

OK, thought it through a little.

Since you are using interlocked breakers and can't switch the neutral:
1)bond the neutral at the 200 A panel and install a grounding electrode system
2)convert the 3 wire machine to 4 wire to match the 20KW machine

I believe this would make it safe and code compliant.

 

[RUWired]

Generator #2 is a cord and plug connected portable with 240/120 3 wire cable.
My opinion is that the MDP must have a neutral-ground bond.
Any one see a problem with this installation ?

Other than including an equipment bonding jumper with the portable gen set 3-wire cable, i think 250.30(A)1 exception 1 would allow the system bonding jumper in the main panel.

Exception No. 1: For separately derived systems that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each power source shall be permitted.

 

[augie47]

Thanks.
I missed that.
I'm also unable to find a Code reference ('08) requiring the portable generator to have an equipment bonding jumper.

 

[jwelectric]

See 250.20 and 250.26

 

[RUWired]

For 2011, the exception to 250.30(A)1 has been changed to only apply to transformer secondary ties (450.6). This would then only allow the SBJ installed at the 20 kW gen set per 250.30(A)1. The GEC connection would also be required at the SDS.(250.30(A)5.

Rick

 

[augie47]

See 250.20 and 250.26

I guess I'm having a bad day. I don't see where that changes 250.34(A)

For 2011, the exception to 250.30(A)1 has been changed to only apply to transformer secondary ties (450.6). This would then only allow the SBJ installed at the 20 kW gen set per 250.30(A)1. The GEC connection would also be required at the SDS.(250.30(A)5.

Rick

I think it's time for me to retire. I'm getting where I understand the Code less each day.
In the '11 change, could the SBJ not be at either the generator or the panel ?

 

[jwelectric]

250.34(A) is addressing the connection to earth. Your question was addressing the connection of a premises wiring system to the generator.

As long as the generator is supplying equipment plugged into one of the receptacles mounted on the frame of the generator then no earth connection is required but the connection of premises wiring is a big difference.

 

[texie]

250.34(A) is addressing the connection to earth. Your question was addressing the connection of a premises wiring system to the generator.

As long as the generator is supplying equipment plugged into one of the receptacles mounted on the frame of the generator then no earth connection is required but the connection of premises wiring is a big difference.

Mike, I get the impression that, like me, you have reservations about the way many of these generator installs are done. Is that a fair statement?
Do you think my comments in post #3 are valid?

 

[jwelectric]

I have been to several different seminars where the discussion of the cord and plug generators have been the topic and at each and every seminar the answer has always been the same. A cord and plug generator MUST be installed as a SDS.

Mark Ode went to length to explain the dangers of installing one with the bonding done at both the generator and panel as well as the dangers of having the cord and plug generator installed as a non-SDS.

Both Roger and Dennis was present in Raleigh the second and third as Mark explained, maybe one of them will chime in on this.

 

[augie47]

I'd like to hear his explaination. In most portable generator installs I've seen the neutral isn't broken unless you consider the cord and plug a "break", but Mark is a sharp cookie so I must be overlooking something,

 

[jwelectric]

I completely miss his first explanation which was on the second and caught the tail end of the one on the third but it had to do with parallel paths, inductance, capacitance, and a task committee that has been studying these types of generators being connected to a premises wiring system since 2002.

He also on a side bar said something about 110.2 and the note under that section as well as the definitions found in the note concerning the listing of these types of equipment.

I know that there are a lot on this site that beg to differ with what I have to say but I am only repeating what I have heard others say.

Where is Dennis and Roger when we need them? I just don't want to get into this discussion again as it makes me have an Inferior complex and runs my medical bills through the roof having to take Thorazine and such other drugs to keep me from having a nervous breakdown.:lol:


A simple answer is that it just ain't right so don't do it but then again who am I?

 

[RUWired]

In the '11 change, could the SBJ not be at either the generator or the panel ?

If the generator has the OCPD as it should, then the exception doesn't apply because the SBJ has to be located between the source and the first OCPD or disconnect. If this was a transformer, then the location could apply at both locations pending the requirement in the exception.

Rick

 

[kwired]

I have been to several different seminars where the discussion of the cord and plug generators have been the topic and at each and every seminar the answer has always been the same. A cord and plug generator MUST be installed as a SDS.

Mark Ode went to length to explain the dangers of installing one with the bonding done at both the generator and panel as well as the dangers of having the cord and plug generator installed as a non-SDS.

Both Roger and Dennis was present in Raleigh the second and third as Mark explained, maybe one of them will chime in on this.

I can see the dangers of installing one with bonding done at both generator and panel, why is it so dangerous to install a cord and plug connected generator as a non-SDS? If you would lose the neutral you will have voltage problems with 120 volt loads, but there will not be stray currents and shock hazards if the generator frame is not bonded to the neutral. If installed as SDS and the neutral is lost you will have voltage between the premesis grounding system and the generator frame.