Feeder Sizes??

[mstrlucky74]

What am I missing here? This board is 277/480. There are two750 kva transformers stepping down and feeding the two 3000a bus ducts. The 1200abus duct is 277/480. All bus ducts and transformers are within 50’ of eachother. First the feeders don’t’ make sense. Why would the 1200A be the samefeeder size as the 300A up to the transformers. Then I think on the secondaryside you would have larger feeders although I think they are oversized to beginwith and they don’t specify whether they are AL or CU conductors.

BTW the footage from the gear to xfrmrs/bus duct is ~250'.

Thanks!!

 

[petersonra]

typo maybe?

future needs that they do not want you to know about?

might be somewhere else they spec'd Al or Cu wire.

I would suggest an RFI to the engineer.

 

[don_resqcapt19]

Your description and the cable schedule does not make a lot of sense to me. I don't understand what the 750 kVA transformers feed. I would be nice to see the one line for this installation.

As far as the conductor sizes, the circuit conductors could be aluminum based on the specified conductor size, but the EGCs would have to be copper based on Table 250.122. If the circuit conductors are copper, then 250.122(B) would require a larger EGC than what is shown on the schedule.

 

[mstrlucky74]

Your description and the cable schedule does not make a lot of sense to me. I don't understand what the 750 kVA transformers feed. I would be nice to see the one line for this installation.

As far as the conductor sizes, the circuit conductors could be aluminum based on the specified conductor size, but the EGCs would have to be copper based on Table 250.122. If the circuit conductors are copper, then 250.122(B) would require a larger EGC than what is shown on the schedule.

thanks.. will get more info tomorrow or Sunday when I do some work on it. the thanks

 

[Smart $]

... I would be nice to see the one line for this installation.
...

Agreed. Need more info'. :happyyes:

 

[mstrlucky74]

Here you go. Some feeder intercepts as you can see.

 

[don_resqcapt19]

I don't think that the conduit schedule in the first post shows primary to the 750 kva transformers. The conductors are all a bit oversized if they are copper, but that is a design issue not a code issue. I don't see any OCPD on the secondary side of the transformers and I see that as a code violation.

 

[Smart $]

Here you go. Some feeder intercepts as you can see.

That's a riser diagram, not a one-line diagram... and the engineer is using some semi-standard one-line symbology on the riser diagram.

Anyway, FWIW, you only have four feeders shown on your schedule. The one with 5 sets of 600MCM is powered by a 1600AF/1600AT breaker.

The three with 4 sets of 600MCM are powered with 1200AF/1200AT breakers.

Conductors are copper. (ETA: could be aluminum...???]


Are there any other questions?

 

[Smart $]

...
Conductors are copper. (ETA: could be aluminum...???]
...

If copper, could be upsized for voltage drop. If aluminum, I'd say they were not upsized for voltage drop. And we're talking 250'. I'd be leaning towards copper.... especially when they are using 3000A bus duct on a 2,083A 208Y/120V secondary.

 

[don_resqcapt19]

I also say copper because the size of the EGC is the copper size that is required for the upstream OCPD. Not very likely for the circuit conductors to be aluminum and the EGC to be copper.

 

[Smart $]

.... Not very likely for the circuit conductors to be aluminum and the EGC to be copper.

Not very likely, I agree, but I had occasion to run into several existing on a large project. Had to make two distinct piles of scrap wire. :happyyes:

 

[hmspe]

I also say copper because the size of the EGC is the copper size that is required for the upstream OCPD. Not very likely for the circuit conductors to be aluminum and the EGC to be copper.

Not sure I agree. I spec aluminum for phase conductors frequently, but the EGC is always copper.

 

[don_resqcapt19]

Not sure I agree. I spec aluminum for phase conductors frequently, but the EGC is always copper.

I have never seen that in the specs...in fact at least 90% of the specs I see prohibit aluminum.

 

[mstrlucky74]

That's a riser diagram, not a one-line diagram... and the engineer is using some semi-standard one-line symbology on the riser diagram.

Anyway, FWIW, you only have four feeders shown on your schedule. The one with 5 sets of 600MCM is powered by a 1600AF/1600AT breaker.

The three with 4 sets of 600MCM are powered with 1200AF/1200AT breakers.

Conductors are copper. (ETA: could be aluminum...???]


Are there any other questions?

I know it's a riser....all that was issued.
OK. I was questioning feeder sizes.

 

[hmspe]

I have never seen that in the specs...in fact at least 90% of the specs I see prohibit aluminum.

My standard spec is all copper, but contractors frequently ask for approval for aluminum due to the cost difference. I generally approve the change for all but the EGC. I've also seen plans from other EEs in the area that are AL except for a CU EGC. This could be a regional thing. Soil conditions here turn AL to powder rather quickly. I want to do what I can to be sure the EGC maintains integrity.

 

[don_resqcapt19]

My standard spec is all copper, but contractors frequently ask for approval for aluminum due to the cost difference. I generally approve the change for all but the EGC. I've also seen plans from other EEs in the area that are AL except for a CU EGC. This could be a regional thing. Soil conditions here turn AL to powder rather quickly. I want to do what I can to be sure the EGC maintains integrity.

If the connection to the grounding electrode is with 18" of the earth, you don't have a choice, per the code rules.

 

[Ingenieur]

Cu always in bldg
if owner is responsible for service conductors and a long run large conductors will allow Al with a credit