paralleling question....

[emahler]

we have a situation where we need to relocate an existing 400A sub-panel approximately 100' further away from the MDP...

the existing installation location is fed with a 4" EMT and a set of 500 MCM's...we plan on installing a trough in the ceiling above the existing panel location, and extend the feed the 100'....

the question, does anyone know any reason why we would not be allowed to install parallel 3/0's from the trough to the new panel? leave the 500's from the MDP to the trough, and bug in parallel 3/0's from there...

I can't find anything in the code book to prohibit this...just curious if anyone knows something I don't.

 

[iwire]

.just curious if anyone knows something I don't.

I am sure someone does.



But you could do what your suggesting.

 

[emahler]

I am sure someone does.



But you could do what your suggesting.

In general, I'm positive many people do.

 

[iwire]

How are you splicing them?

 

[cadpoint]

Why is a 400 amp panel fed by 500?s and why is only 3/0's OK for another 100 feet? (as I read it)

You said your in the ceiling, is there any temperature changes in the original run to the 500?s, and will there be any temperature change in the last one hundred feet to the new location?

Why aren?t you asking your AHJ?

What?s the size of the trough?

 

[iwire]

Why is a 400 amp panel fed by 500?s

500s are rated 380 amps, 240.4(B) allows using a 400 amp breaker with them. (This assumes the load is under 380 amps)

and why is only 3/0's OK for another 100 feet?

He is running two sets of 3/0, assuming no derating required that is good for 400 amps.

Why aren?t you asking your AHJ?

The answers are in the book, unless the AHJ makes up their own rules on the spot.

 

[infinity]

Your parallel #3/0's are fine for 400 amps if they're in separate raceways. In one raceway your adjusted ampacity drops down to 360 amps. (225 * 2 * 80%). Still OK on a 400 amp OCPD providing the load is 360 amps or less.

 

[kwired]

As long as you are splicing on conductors that are allowed to be protected at 400 amps you can use anything you want. Single or parallel aluminum would also be acceptable, busway, split off to multiple panels if you wish and the load calculation is still below the conductor ampacity would also be acceptable.

Any conductor that is less in ampacity, will need to meet tap rule requirements before it could be used.

 

[iwire]

Any conductor that is less in ampacity, will need to meet tap rule requirements before it could be used.

Unless they are covered by 210.4(B).

 

[emahler]

Clear taps

(2) 2-1/2" emt, each with 4- 3/0 and a ground

24' ceiling, conduit is at 20'. Aff

Calculated load is sub 300

8x8x48 trough

Particular AHJ was requiring EC's to test arc faults to pass inspection. Not gonna just accept his decision. I'll talk to him, but just to inform him, not ask him.

 

[iwire]

Clear taps

So each clear tap will be listed for 3 condutors?

(2) 2-1/2" emt, each with 4- 3/0 and a ground

That is a 2" job around here.

 

[emahler]

100' of 4- 3/0 and a 3 is, while legal in 2", a tough pull...2 1/2" is pretty standard for us, and an easier pull...

and yes,

is good for 3 conductors...

 

[acrwc10]

..................................

 

[iwire]

100' of 4- 3/0 and a 3 is, while legal in 2", a tough pull...2 1/2" is pretty standard for us, and an easier pull...

Sorry, I assumed it was men doing the job.:grin:

We do four 4/0s and grd in 2" all the time.

 

[masterinbama]

Sorry, I assumed it was men doing the job.:grin:

We do four 4/0s and grd in 2" all the time.

With one of these

and one of these

That's a 2 man job in 2".

 

[iwire]

We have all that, we would not normally bother with the feeder for 4/0s.

 

[masterinbama]

We have all that, we would not normally bother with the feeder for 4/0s.

Depends on the conduit run whether I will or not.

 

[iwire]

Depends on the conduit run whether I will or not.

I agree, I said usually.

I mean would we normally have the feeder shipped to the job for a 2" run? No.

If the feeder is there on the job anyway we might take advantage of it, as with everything electrical there are a lot of variables.

One thing that would not be variable would be the dope slap the owner would want to give me for wasting money on 2.5" for this run. :grin:

Of course I am cheap like that, I run 3" EMT for four 500s with grd.

 

[masterinbama]

I agree, I said usually.

I mean would we normally have the feeder shipped to the job for a 2" run? No.

If the feeder is there on the job anyway we might take advantage of it, as with everything electrical there are a lot of variables.

One thing that would not be variable would be the dope slap the owner would want to give me for wasting money on 2.5" for this run. :grin:

Of course I am cheap like that, I run 3" EMT for four 500s with grd.

So do I, unless plans or specs say otherwise.

 

[emahler]

well, we're gonna pull using one of these

but as backup, I got a whole crew of these

but in reality, i need to check the wire, might be XHHW....we are able to reuse it from a deleted run in the same facility...so, the small upcharge to 2.5" is minimal to not purchasing 400'+ of 3/0....

but, now that I know how real men would do it, I'll let my guys know that they've been virtually bitch slapped by a guy from Massachusetts....