another genset ?

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ceb58

ceb58

Senior Member
Location
Raeford, NC
Moving a 30kw genset from one location to another. Today I was removing all the old wireing getting ready to rewire when I noticed something I am not sure of. Here is my set up I am feeding the utility connection on transfer switch from a 100amp breaker in the MDP, 100amp breaker in genset is connected to a disconnect and then to the emergy. connection, line side feeds a new panel that will have the selected branch circ. needed for operation of the building. The neutrals are all tied together in the transfer switch ( no switching of the neutrals) On the gen. the neutral and EGC were tied together along with the GEC. I am thinking the neutral and ground should be separate on the genset. But looking at it no mater where you would land the EGC it would still be bonded with the neutral. Neutral buss solid to armature frame, frame bolted to housing, etc....
DOI inspector also wanted a G rod at genset. Am I over thinking this? I have the neutral and ground separate in the disconnect. the neutral and ground are separate in trans. switch And I have the neutral and ground separate in new panel
 
If someone from the DOI is doing the inspection this means you are doing this job for some state building, yes?

Have the inspector to show you where in the NEC that you are allowed to bond the grounded and grounding conductors at two different locatiions.

Have him/her explain 250.30(A)(1) Exception 2
 
jwelectric said:
If someone from the DOI is doing the inspection this means you are doing this job for some state building, yes?

Have the inspector to show you where in the NEC that you are allowed to bond the grounded and grounding conductors at two different locatiions.

Have him/her explain 250.30(A)(1) Exception 2
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Yes it is a state building.
This is what has me scratching my head. I can see no way to just ground the frame of the genset with out it bonding the neutral also
 
ceb58 said:
I can see no way to just ground the frame of the genset with out it bonding the neutral also
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How about this Curtis?


SDS.jpg
 
Thanks Bob, missed that. I'm surprised you didn't mention removing the leads from the buss and floating them. I'm sure you have done that before.
 
Going to have DOI inspector come look at it this morning and give "divine" guidance. The only way I see Is to just hook the EGC to the g rod and use it as a suplement.
 
ceb58 said:
The only way I see Is to just hook the EGC to the g rod and use it as a suplement.
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I don't see that as code compliant either. You would be using the neutral as the bonding means for the generator.

You really need a transfer switch that switches the neutral.
 
ceb58 said:
Going to have DOI inspector come look at it this morning and give "divine" guidance. The only way I see Is to just hook the EGC to the g rod and use it as a suplement.
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If the generator is bonded and is a SDS then it would require the grounding electrode to be installed at the generator.

Is this inspector male or female?
 
jwelectric said:
Don't mean any harm, it is that I know both that might be in that area of NC. It will be either a male or female and this information will give me the persons name.
The line runs somewhere in that area that splits their areas from each other
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I am working in the Raleigh area. The regular insp. is Mr.Bullock that I have been dealing with but he was unavailable today so Mr. Chilton and I had a good conversation.

Here is the way this problem was solved. After talking with the mfg. I learned how to remove the neutrals from the buss. I also received a letter from the mfg. stating it was ok to remove the wires from the buss and "float" the neutral, as Chris's diagram showed. Thanks Chris. In the mfg. letter it also refers you to 250.20 which you can find 250.20 (D) fpn 1.
Mr. Chilton, who is the head inspector for DOI, told me that I could do this as long as I had mfg. permission. Which I now have.
So I am going to float the neutral and bond the genset with the EGC and g rod. This is too much thinking for one day
 
Yes, regardless of the switching of the neutral or not in the transfer switch, with the switch thrown towards the genset, there would be two bonds between neutral and the egc - one at the genset, and one in the panel. When the genset is powering the panel, the neutral/egc bond in the panel would cause current to flow from the panel to the genset on the egc, since it is in parallel with the neutral from the panel to the genset. The only real solution to eliminate the current is to remove the egc/neutral bonding at one place or the other - the most reasonable would seem to be at the genset.

If the transfer switch was powering a sub that didn't have the neutral/egc bond, it would be another story...
 
SAC said:
Yes, regardless of the switching of the neutral or not in the transfer switch, with the switch thrown towards the genset, there would be two bonds between neutral and the egc - one at the genset, and one in the panel.
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Bonding at the service and at the generator is entirely code compliant and fairly common if the transfer switch also switches the neutral.

This is up to the designer to decide which way to go, if the service has GFP then switching the neutral and bonding at both the service and the genset is the recommended practice.
 
iwire said:
Bonding at the service and at the generator is entirely code compliant and fairly common if the transfer switch also switches the neutral.

This is up to the designer to decide which way to go, if the service has GFP then switching the neutral and bonding at both the service and the genset is the recommended practice.
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Interesting. What is the point of a 4-wire connection to the genset - there isn't an egc and neutral, just two parallel neutrals with one masquerading as an egc. This seems, at a minimum, very misleading...
 
When the transfer switches the neutral and you have a bond at both the service and the genset there is only one bond connected to the system at any given moment.

It is a lot easier to see if you draw it out.
 
iwire said:
When the transfer switches the neutral and you have a bond at both the service and the genset there is only one bond connected to the system at any given moment.

It is a lot easier to see if you draw it out.
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Yes - I think we are talking about the same thing. The diagram given was my comment about the "sub" which is driven by the transfer switch, and in which the egc and the neutral are not bonded. I had misunderstood the OP in that the transfer switch was ahead of the main panel where the ecg and the neutral were bonded - so they were bonded in the building even when selecting the genset. That was what I thought didn't seem right. Thanks helping me get back on track.
 
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