Max Size for Paralleled EGCs?

[petersonra]

That is correct. There is one alternative, however, and that is to use the raceway as the EGC. What I would do is to separate the distribution system into smaller sub-groups, so that no single feeder is that large.

6000 amps is a monster. I can't imagine that it is real practical in most cases. Better to spread it out like Charlie suggests if you can.

 

[infinity]

6000 amps is a monster. I can't imagine that it is real practical in most cases. Better to spread it out like Charlie suggests if you can.

Do they even make an OCPD for more than 6000 amps? I've seen some 600V/5000 amp fuses. Seems like anything larger than that you would get into a paralleling arrangement.

 

[AQC]

The 1st sentence of 250.122 does clearly state that "EGC's of the wire type shall not be smaller than shown in Table 250.122". Thank you everybody for your answers. All these answers to all these questions helps me a lot!

When taking proportional EGC size increase for voltage drop, is it possible to utilize these larger conductor sizes such as #900, #1000, #1250, #1500, #1750, #2000??

 

[infinity]

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When taking proportional EGC size increase for voltage drop, is it possible to utilize these larger conductor sizes such as #900, #1000, #1250, #1500, #1750, #2000??

I agree, but when trying to install those conductors and with the difficulties that may arise, it might be better to design a system that didn't require them.

 

[petersonra]

I agree, but when trying to install those conductors and with the difficulties that may arise, it might be better to design a system that didn't require them.

I am not convinced that some of these systems are ever designed. They just sort of happen.

I ran across a system that was supplied by 4160V by the utility. The plant transformed it to 480V and then had another transformer to go from 480 up to 15kv because they had one motor that was 15kV. I can't even imagine what they were thinking when they put that in.

 

[LarryFine]

IMO the sizes in the table are singular and make no provisions for paralleling.

Can't the same be said about T.310.16?

 

[iwire]

My point exactly-- there are no provisions against it. If we meet the definition of parallel conductors in 310.4 then I don't see this as a violation. I could be, and usually am, wrong......

Check out 310.4, it does not apply to EGCs.

 

[LarryFine]

I ran across a system that was supplied by 4160V by the utility. The plant transformed it to 480V and then had another transformer to go from 480 up to 15kv because they had one motor that was 15kV. I can't even imagine what they were thinking when they put that in.

I can't either. It seems the right transformer would have cost less than the ampacity at 480v did.

Never mind specifying a different motor voltage from the onset.

 

[charlie b]

Can't the same be said about T.310.16?

I try not to mention that one very often. :roll: But although it is true that 310.4 allows us to parallel ungrounded conductors, I don't know of anything that tells us what happens when we do. That is, if we were to parallel a pair of 1/0 copper THWN conductors (ampacity 150), we will quickly conclude that we now have a total ampacity of 300. But where exactly does the NEC tell us that? :-?:grin:

 

[Dennis Alwon]

I don't understand that the EGC is not mentioned in 310.4. Section 310.4(E) is all about EGC.

310.4(E) Equipment Grounding Conductors. Where parallel equipment grounding conductors are used, they shall be sized in accordance with 250.122. Sectioned equipment grounding conductors smaller than 1/0 AWG shall be permitted in multiconductor cables in accordance with 310.13, provided the combined circular mil area in each cable complies with 250.122.

 

[iwire]

I don't understand that the EGC is not mentioned in 310.4. Section 310.4(E) is all about EGC.

I was talking about 310.4(A)

(E) is brand new to the 2008 and applies only to cables.

Some large MC cables use sectioned EGCs, the factory can do that, we cannot.

 

[Dennis Alwon]

I was talking about 310.4(A)

(E) is brand new to the 2008 and applies only to cables.

Some large MC cables use sectioned EGCs, the factory can do that, we cannot.

I don't see where 310.4(E) only applies to cables. The first sentence stands alone and says to me that parallel egc may be used. The second sentence applies to cables saying they can be smaller than 1/0.

I am not trying to be a pain but I am trying to understand.

 

[eprice]

The first sentence stands alone and says to me that parallel egc may be used. The second sentence applies to cables saying they can be smaller than 1/0.

Right, but the first sentence sends us to 250.122 which includes 250.122(F), so that sentence isn't really telling us anything new. It is the second sentence that gives us some new latitude and that sentence only applies to cables.

 

[petersonra]

I can't either. It seems the right transformer would have cost less than the ampacity at 480v did.

Never mind specifying a different motor voltage from the onset.

I am guessing that it was either cheaper or quicker to do it that way, depending on what was more important at the time. It might have been that they had a 480V feed already run to the vicinity of the motor and they got a big surprise when it came in as a 15kV motor.

Could have been a used piece of equipment someone bought without looking real close at it.

Who knows how some of these things happen.

At a previous place of employment a customer ran a 1 inch water line to supply some equipment we provided. I think we needed something like 200 gpm for the equipment.

Another place we supplied a steam heat exchanger as part of the equipment. The plant had no steam in the area so they bought a large electric hot water heater and installed it next to the equipment and piped in the hot water heater where the heat exchanger was. It did not work real well, but was adequate.

Another place specified a 125VDC annunciator. When it got there, it turned out the plant did not have 125VDC. They ended up buying 10 car batteries and a 125VDC battery charger to keep it topped off.