Generator Neutral Required?

[Smart $]

I'd like to work with you on this but generator feeders can only be service conductors if the utility would own the generator and i don't see any reference to allowing 250.24(C) for minimum size in article 225 or 220 if the neutral does not have a load. Maybe somebody can address this.

Rick

The problem here is, with a solidly-connected grounded conductor, the generator is not an SDS. Therefore the grounded conductor is considered part of the service system. It does not matter where the generator OCPD is located. The grounded conductor is not switched or otherwise isolated from the service grounded conductor. Code designates only two types of sources in this regard, a service system and an SDS system. Again, we've already established that with a solidly-connected grounded conductor, the generator is not an SDS.

This is similar to one trying to size a service or feeder neutral conductor based solely on the calculation of 220.61. Taking that section in the context of its requirements, one could install the smallest neutral conductor for the calculated value. That section does not indicate there is a minimum-size stipulation elsewhere in the code. The same goes for your wanting th size the grounded conductor to the generator, based on the stipulations solely in the feeders section.

If you continue to not see this point on the issue, the best I can do is agree to disagree

 

[sparkyguy545]

Holy Crap Batman !!
I checked my original post for a couple of hours without a nibble, so rather than the much frowned-upon "bumping" . . . I logged out. I checked back today and found more opinions than what we should do to AIG. Thanks for all the insight. It's going to take a day to sort through all the comments.

Couple of clarifications: Yes, POCO supply is 4-wire solidly grounded. The N-G bond will be installed only within the SE gear. ALL facility loads are 3-wire only; we currently have NO L-N loads whatsoever. Genset will be specified with internal load CB. We were NOT intending on bonding N-G at the genset, and raceway is non-metallic. Therefore no SDS. So far, everyone seems to pretty-much agree.

Then the question came up . . . since we don't have any L-N loads, do we even HAVE to even pull the neutral to the generator. Without it, the system would be a 4-wire solidly-grounded utility supply and a 3-wire ungrounded generator supply (although the generator windings would be an ungrounded wye). The generator FRAME will still be grounded with an EGC. At the utility end, the Service Neutral was installed for L-G fault clearing per 250.24C.

After we went through many similar loops and jumps (but not quite as deep as the thread went into); the FAR simpler answer is to add the neutral to the generator conduit (3 Hots, 1 GEC, and 1 EGC) and go have a beer. It also just makes logical sense to have both systems full 4-wire. Heck, it's only one additional conductor; and as noted by several folks, if they EVER want to add a 277 V load, they are already set up and are good-to-go.

 

[Mvillines]

I agree with everything said. This is where it gets fuzzy.... no neutral to generator bonding at the generator, removing the OCPD at the generator and run all conductors as you stated. These conductors are still feeders aren't they? The code is clear for sizing the EGC per 250.66 but what about sizing the grounded conductor? Smart $ has a very good point, code section 215.2 references Table 250.122 but these are feeder taps and the grounded conductor warrants the same safety as the EGC should a short occur between a phase conductor and the grounded conductor. I would rather error on the safe side and use 250.66 in this case.

 

[Smart $]

...the FAR simpler answer is to add the neutral to the generator conduit (3 Hots, 1 GEC, and 1 EGC)...

I believe you meant to write 3 Hots, 1 Neutral, and 1 EGC :grin:

 

[RUWired]

Couple of clarifications: Yes, POCO supply is 4-wire solidly grounded.
The N-G bond will be installed only within the SE gear.
ALL facility loads are 3-wire only; we currently have NO L-N loads whatsoever.
Genset will be specified with internal load CB.
We were NOT intending on bonding N-G at the genset, and raceway is non-metallic.
Therefore no SDS. So far, everyone seems to pretty-much agree.

I can't agree with your assement that it's a non SDS.With all your statements above the gen will not have any fault clearing paths while the generator is running. In this example, you would need to make the bond in the generator and consider it a SDS.

 

[Smart $]

I can't agree with your assement that it's a non SDS.With all your statements above the gen will not have any fault clearing paths while the generator is running. In this example, you would need to make the bond in the generator and consider it a SDS.

Fault-to-ground current path is the neutral from the SE gear, where the system bonding jumper is located, to the generator neutral terminal.

 

[ceb58]

The one question I have not seen ask is what is the transfer switch going to do? Is it going to be 3 pole for the ungrounded cond. or is it 4 pole so it could switch the neutral?

 

[RUWired]

Fault-to-ground current path is the neutral from the SE gear, where the system bonding jumper is located, to the generator neutral terminal.

The OP just stated that the bond was not made in the gen set and he didn't run a grounded conductor . If the generator is running and faults to ground, and he didn't run the grounded conductor, the fault current will follow the EGC and go through the main bonding jumper like you said but will stop at the switch gear main because it is open or at the ats because it is in the em run position because the generator is running. Either the grounded conductor needs to be ran from the generator (non SDS)to the ats and back to the main gear or the bonding jumper needs to be installed in the gen set.

Rick

 

[RUWired]

The one question I have not seen ask is what is the transfer switch going to do? Is it going to be 3 pole for the ungrounded cond. or is it 4 pole so it could switch the neutral?

The OP stated it is a 3-pole solid neutral ats.

 

[ceb58]

The OP just stated that the bond was not made in the gen set and he didn't run a grounded conductor . If the generator is running and faults to ground, and he didn't run the grounded conductor, the fault current will follow the EGC and go through the main bonding jumper like you said but will stop at the switch gear main because it is open or at the ats because it is in the em run position because the generator is running. Either the grounded conductor needs to be ran from the generator (non SDS)to the ats and back to the main gear or the bonding jumper needs to be installed in the gen set.

Rick

This I agree with. The only thing now is the transfer switch. With the 3 pole he has no way to switch the neutral so this would be a non- SDS. The simple way is to float the neutral at the gen set, tie it to the neutral from the MD panel in the TS (isolated in the TS)

 

[RUWired]

This I agree with. The only thing now is the transfer switch. With the 3 pole he has no way to switch the neutral so this would be a non- SDS. The simple way is to float the neutral at the gen set, tie it to the neutral from the MD panel in the TS (isolated in the TS)

This is all true if the OP ran a grounded conductor. A lot of the discussion was because the OP was going to omit it.

 

[ceb58]

This is all true if the OP ran a grounded conductor. A lot of the discussion was because the OP was going to omit it.

This is what I was going on. I know it started out without a grounded cond. but wound up here.

After we went through many similar loops and jumps (but not quite as deep as the thread went into); the FAR simpler answer is to add the neutral to the generator conduit (3 Hots, 1 GEC, and 1 EGC) and go have a beer. It also just makes logical sense to have both systems full 4-wire. Heck, it's only one additional conductor; and as noted by several folks, if they EVER want to add a 277 V load, they are already set up and are good-to-go.

On a side rant I have been installing a 25kw 240/120v gen. this week. I was pulling the wires to it today and making the connections.The installation manual showed a 3 wire terminal block for the 120v utility line for the charger. No term. block. Call mfg. and find out since it was specked to have a GFCI recp. factory installed on unit all I needed to do was bring my line to the GFCI recp. OK. pull recp out of box 3 BLACK wires( for batt. charger feed) landed on load side of GFIC. 1 hot, 1 neutral and EGC. Wire in 3/8" flex tube shoved inside 1/2" KO in box, no connector. The thing that got me was looking through the elect. installation chapter in the service manual every where I looked it was in bold print. ALL ELECTRIACL WIREING AND CONNECTIONS TO BE INSTALLED PER NEC AND LOCAL CODES. Its amazing what a mfg. can get away with.

 

[Smart $]

The OP just stated that the bond was not made in the gen set and he didn't run a grounded conductor . If the generator is running and faults to ground, and he didn't run the grounded conductor, the fault current will follow the EGC and go through the main bonding jumper like you said but will stop at the switch gear main because it is open or at the ats because it is in the em run position because the generator is running. Either the grounded conductor needs to be ran from the generator (non SDS)to the ats and back to the main gear or the bonding jumper needs to be installed in the gen set.

Rick

Please re-read his last paragraph...

...

After we went through many similar loops and jumps (but not quite as deep as the thread went into); the FAR simpler answer is to add the neutral to the generator conduit (3 Hots, 1 GEC, and 1 EGC) and go have a beer. It also just makes logical sense to have both systems full 4-wire. Heck, it's only one additional conductor; and as noted by several folks, if they EVER want to add a 277 V load, they are already set up and are good-to-go.

I also made the following comment, to which there was no response...

I believe you meant to write 3 Hots, 1 Neutral, and 1 EGC :grin:

 

[RUWired]

Please re-read his last paragraph...



I also made the following comment, to which there was no response...

I did read his last paragraph and saw your response and had no problems with either. I was responding about how he thought that everyone agreed with the way he wanted to wire it with out making the bond and that it was not an approved method.
Rick

 

[Pierre C Belarge]

Draw a line diagram for the fault current and you will have your answer to this question.

note:
this is a non-separately derived system - which is based on the transfer switch design, not the over current device placement of the generator.

 

[Smart $]

I did read his last paragraph and saw your response and had no problems with either. I was responding about how he thought that everyone agreed with the way he wanted to wire it with out making the bond and that it was not an approved method.
Rick

Bonding at the generator creates a parallel neutral path, which is a non-compliant wiring method except under certain circumstances... and offhand I do not believe this is one of 'em.

 

[RUWired]

Bonding at the generator creates a parallel neutral path, which is a non-compliant wiring method except under certain circumstances... and offhand I do not believe this is one of 'em.

Not so when the OP said he wasn't running a grounded conductor and not installing the bonding jumper. He can't have a parallel neutral path when he doesn't even have a neutral.

This is what he OP stated that i said wasn't compliant unless he install the bonding jumper in the gen set, thereby making it a SDS.

Couple of clarifications: Yes, POCO supply is 4-wire solidly grounded. The N-G bond will be installed only within the SE gear. ALL facility loads are 3-wire only; we currently have NO L-N loads whatsoever. Genset will be specified with internal load CB. We were NOT intending on bonding N-G at the genset, and raceway is non-metallic. Therefore no SDS. So far, everyone seems to pretty-much agree.

I understand and read the rest of his post and agree with installing the xo all the way through. I said before that was a better design but i also said he was looking for bare minimum and code compliant. He can go bare minimum and still meet code, but it needs to be done correctly.

Rick

 

[RUWired]

Draw a line diagram for the fault current and you will have your answer to this question.

note:
this is a non-separately derived system - which is based on the transfer switch design, not the over current device placement of the generator.

Now i'm only talking about the original OP's thought about not installing the grounded conductor. In this sketch, i put in the bonding jumper so you all won't say that this is non compliant. In the sketch you'll see with the solid neutral switch, and with out a grounded conductor, it is required to install the bonding jumper in the gen set and call it a SDS.

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