why does AL 4/0 SER cable have a 2/0 ground?

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KyleFowler

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is it because its not in conduit? I was just curious where the code referenced this. I see if the grounding wire is in conduit it can be as small as #4 AL for a 200 amp circuit.

Thanks for humoring me :)
 
That is service entrance cable and where used for that purpose there is no EGC, the smaller conductor is the neutral conductor. The neutral conductor is almost always permitted to be smaller than the ungrounded conductors for service entrance. I think there was a "two sizes smaller" rule for the service neutral at one time. The neutral is permitted to be a bare conductor in service entrance cable.
 
don_resqcapt19 said:
That is service entrance cable and where used for that purpose there is no EGC, the smaller conductor is the neutral conductor. The neutral conductor is almost always permitted to be smaller than the ungrounded conductors for service entrance. I think there was a "two sizes smaller" rule for the service neutral at one time. The neutral is permitted to be a bare conductor in service entrance cable.
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He's referring to 4/0, 4/0, 4/0, 2/0 SER with a bare EGC.
 
don_resqcapt19 said:
That is service entrance cable and where used for that purpose there is no EGC, the smaller conductor is the neutral conductor. The neutral conductor is almost always permitted to be smaller than the ungrounded conductors for service entrance. I think there was a "two sizes smaller" rule for the service neutral at one time. The neutral is permitted to be a bare conductor in service entrance cable.
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IDK if there ever was anything in NEC on this or not, but kind of seems to be acceptable to many AHJ's as well that you can go a couple sizes smaller when neutral is only carrying unbalanced current and not need to prove any required ampacity.

There are times when I have seen or myself used 4/0 AL ungrounded conductors and only 2 AWG grounded conductor for service - when there was little or no neutral load and 2 AWG happened to be smallest grounded conductor allowed otherwise it maybe would have been even smaller.

Feeder on 200 amp OCPD could have 4 AWG AL, if you can prove the maximum neutral load is not more than the #4 can handle, or go two sizes smaller and you don't have to prove anything as a general unwritten rule. If there is reason to believe there can be significant neutral load you still may need to prove you have sufficient conductor though.
 
don_resqcapt19 said:
That is service entrance cable and where used for that purpose there is no EGC, the smaller conductor is the neutral conductor. The neutral conductor is almost always permitted to be smaller than the ungrounded conductors for service entrance. I think there was a "two sizes smaller" rule for the service neutral at one time. The neutral is permitted to be a bare conductor in service entrance cable.
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Is it permissible to use the 2/0 bare as a neutral in the SER cable?
If this is three phase you’re talking about then where is the equipment grounding conductor if the 2/0 Is being used as a neutral?


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Peter Furrow said:
Is it permissible to use the 2/0 bare as a neutral in the SER cable?
If this is three phase you’re talking about then where is the equipment grounding conductor if the 2/0 Is being used as a neutral?
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It is permissible used as neutral on service, but not as a feeder.
 
Got it.
I should’ve read all those posts
Thoroughly before commented


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As Don mentioned there was a 2 trade size smaller rule in the code some time ago. the CMP changed that as the size of the neutral is based on the larger of the two - unbalanced load or ground fault (250.66). With individual conductors, its 4/0-4/0-2/0, if you installed say a #1, the inspector will have seen that and you will need to do a neutral calc. But this makes a good test question, "what is the smallest size neutral for a 200 Amp dwelling unit service".
 
Dennis Alwon said:
Another possible reason is that it can be used for 3 phase service conductors with a slightly reduced neutral
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You can order a 5 wire SER with a full size neutral and reduced ground....4/0-4/0-4/0-4/0-2/0.

You can also get three wire with full size conductors on all 3.... 4/0-4/0-4/0.


If using quad or triplex direct burial, you can order full size on all 4 conductors.

Most supply houses will stock something like 4/0-4/0-2/0-2 in the URD type.


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All this 4/0 talk is making me confused. Code needs to make it simple.


“ shoot low boys their riding shetland ponies”
 
McLintock said:
All this 4/0 talk is making me confused. Code needs to make it simple.


“ shoot low boys their riding shetland ponies”
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Simple as in what can you supply with 4/0 aluminum? Even without the dwelling unit allowances 4/0 aluminum still works for 200 overcurrent device as long as actual load is 180 or less.

If you buy 250 triplexed or Quad assemblies they often still have two sizes smaller 3/0 for neutral conductor.
 
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