Actually, both systems are 3-phase 4-wire. Both the poco and the SDS has the neutral grounded at the source. The only difference is the genset feeder does not require the grounded conductor down stream on the equipment it is backing up.
Generator Neutral Required?
- Thread starter sparkyguy545
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Actually, both systems are 3-phase 4-wire. Both the poco and the SDS has the neutral grounded at the source. The only difference is the genset feeder does not require the grounded conductor down stream on the equipment it is backing up.
Mvillines
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- Western KY on the Ohio River
IMO....Assuming we are talking about a wye system, I believe one would bond the center of the wye in the generator to the frame. This connection is done on the source side of the Generator OCPD. See (250.30(A)(2), 250.102(C), and (Table 250.66).
Size the EGC by the amperage rating of the OCPD on the generator (Table 250.122). Keeping in mind the EGC is considered to be on the load side of the OCPD. No Grounded conductor installed results in a SDS. Now a GEC should be installed according to 250.30(A)(3), 250.30(A)(7), and (Table 250.66)
Size the EGC by the amperage rating of the OCPD on the generator (Table 250.122). Keeping in mind the EGC is considered to be on the load side of the OCPD. No Grounded conductor installed results in a SDS. Now a GEC should be installed according to 250.30(A)(3), 250.30(A)(7), and (Table 250.66)
Why run 5 wires total (3 hots, 1 EGC, and 1 GEC) when you can run 4 (3 hots and 1 GEC)?
And even if you want to run 5, why not run 3 Hots, 1 Neutral and 1 EGC? Since the neutral is not being used, it can be the minimum size (i.e. sized per 250.66) So you would have the same number and sizes of the wires that you want to run, but this way you have a solidly grounded neutral conductor and no SDS. This would also permit future line-to-neutral loads to be added (with max unbalanced neutral current up to the ampacity of the neutral that is already in place).
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Mvillines
Senior Member
- Location
- Western KY on the Ohio River
The way my post is described you could run only three phase conductors if metallic conduit or approved raceway for grounding were used to encase the phase conductors. If the system bonding jumper is not installed at the generator you would then need the EGC and a grounded conductor. Both would be required. Draw a schematic,worth a thousand words.
The OP asked for the minimum code requirement. I suggested 3 hots and an equipment ground. Bond the genset neutral. No GEC required in the raceway, no grounded conductor required. Installing any more is better design but not required.
Rick
Yeah but a GEC is still required and has to be run going this route. And it would cost even more if you didn't run it with the feeder.
Why is a "grounding electrode conductor" required to be run with the feeder? The OCP is at the gen set.
If the ocp was remote as i stated before, an "equipment bonding jumper" would be required to run with the conductors. A GEC is only used to connect to a grounding electrode.
Rick
Mvillines
Senior Member
- Location
- Western KY on the Ohio River
Ditto....Rick
I'm not saying it has to be run with the feeder... I'm saying it has to be run (i.e. going with the SDS version here).
250.30(A)(3) specifies a Grounding Electrode Conductor.
250.30(A)(7) refers to the required grounding electrode.
250.30(A)(7) Exception 2 provides an alternative.
I understand that it may be more convenient to run the GEC in another direction from the feeder, but it still has to be run... and if you do run it in another direction, an EGC is required between genset and xfer switch. Right?
Chances are the xfer switch is relatively close to the service disconnect where the service GES to main bonding jumper is located. Why not just run the GEC with the feeder and eliminate the EGC. 4 wires total, one run.
...or we could go with the non-SDS version which one would run a Neutral conductor sized to 250.66 and an EGC sized to 250.122, no fuss, no muss, call it a good design and a good day at that.
Mvillines
Senior Member
- Location
- Western KY on the Ohio River
...or we could go with the non-SDS version which one would run a Neutral conductor sized to 250.66
Agree except look at 215.2(A)(1) if you go with the non-SDS. Grounded (Neutral) conductor would be sized by 259.122. This secton is new in the 05 edition where as before the grounded conductor had no minimun as long as it was 14 awg or larger.
Agree except look at 215.2(A)(1) if you go with the non-SDS. Grounded (Neutral) conductor would be sized by 259.122. This secton is new in the 05 edition where as before the grounded conductor had no minimun as long as it was 14 awg or larger.
Non seperately derived systems are required to follow 250.122 as well. Only service supplied systems follow 250.24(C)1.
Rick
Yes that is right and that would be the code minimum requirement.
I believe the GEC would be required to land uninterrupted to the grounding electrode, thereby leaving the system ungrounded.Smart $ said:
Smart $ said:
There are different ways of wiring this setup, but the OP was looking for code minimum. Thats all i was offering.
If we go with a non-SDS system, i.e. solidly-connected grounded conductor, 250.24(C) applies, because it is a grounded conductor brought to service equipment.
If we go with an SDS system, 250.30(A)(8) applies.
Both say the minimum size is as per 250.66.
That don't make any sense, i.e. the leaving the system ungrounded part.
As for the GEC going uninterrupted to the electrode, that is as required per 250.30(A)(7) prior to Exception 2, which allows us a little latitude because it permits using the same electrode(s) as the service or feeder equipment being supplied, provided the genset is listed as equipment suitable for use as service equipment... which it should be if it is backing up a service. There is no restriction from extending the service GEC to the genset.
Actually the OP'er is looking for the most cost effective and compliant way.
All the same however. You want to run 3 hots, 1 GEC, and 1 EGC. I say run 3 hots, 1 neutral, and 1 EGC. The latter by far is the better design. Wire sizes are the same and, other than some cost differences due to length of the GEC and its routing, either method appears on the surface to be equal in cost.
Originally Posted by Smart $
Why not just run the GEC with the feeder and eliminate the EGC. 4 wires total, one run.
My point to your statement about not running the EGC was, the GEC per 250.64(C) needs to be continuous to the electrode.
IMO you can't use the GEC inplace of the EGC if it is supposed to ran continuous.Would you run a jumper to the equipment bar in the enclosure?
Smart$ said:
Depending on the size of the feeder it could be a wash, Although a ground rod and a # 6 awg GEC next to the genset isn't that much to deal with verses set up and pull time and routing the GEC through the equipment enclosure of the feeder to the existing GES.
I will agree if the gen set is located inside the GEC could be a large increase in size if all the electrodes present need to be hit.
Rick
250.24(C) only applies to service conductors. The feeders from the gen set are not service conductors. 215.2(A)1 applies to feeders and to be honest i haven't figured out the minimum size for outdoor feeder neutral conductors.
Rick
That depends on whether the ATS is service equipment or not (I don't mean simply listed for use as). Some ATS's incorporate both a utility and a generator disconnect and in effect is the service disconnect. In the case of the ATS being service equipment, 250.24(C) applies when the grounded conductor is not switched, i.e. solidly connected to the service grounded conductor. It applies because it is a "grounded conductor brought to service equipment" and part of the "grounded-service system", i.e. not an SDS system.
Otherwise, I concur 215.2 would be the applicable requirement.
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
Mvillines
Senior Member
- Location
- Western KY on the Ohio River
Maybe the OCPD at the generator is the problem with Table 250.66 and Table 250.122. Remove the Generator OCPD then run the phase conductors a grounded conductor and an equipment grounding conductor and size this grounding conductor from Table 250.66 because it is now on the source side of the OCPD.
This post is to address the two tables not other issues such service rated equipment and sizes of the grounded and phase conductors.
This post is to address the two tables not other issues such service rated equipment and sizes of the grounded and phase conductors.
If the OCPD is remote from a SDS article 250.30(A)2 addresses the equipment bonding jumper. That will take you to 250.66.
Rick
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