400 parallel question

[Al Pike]

I have a 320a meter feeding one 400a panel with a connected load of 181 amps. The meter also feeds a 400a outside panel with a connected load of 216a. Both panels have a 4in conduit installed to them.

My question is can I size my wire useing the 90deg table and parallel 4/0 at 80%=328a as long as Im under the 75deg ampacity of 288a with my load?

I think I have to parallel 300mcm al at 80%=368 and round up.

 

[Dennis Alwon]

I have a 320a meter feeding one 400a panel with a connected load of 181 amps. The meter also feeds a 400a outside panel with a connected load of 216a. Both panels have a 4in conduit installed to them.

My question is can I size my wire useing the 90deg table and parallel 4/0 at 80%=328a as long as Im under the 75deg ampacity of 288a with my load?

I think I have to parallel 300mcm al at 80%=368 and round up.

I did not do the math but you can derate from the 90C column but the end product cannot carry a load higher than the 75C column. Now if the ampacity is 368 you can protect it at 400 amps as long as the load is less than 368. Look at 240.4(B) and 240.6

 

[infinity]

Why 80%?

 

[ggunn]

I did not do the math but you can derate from the 90C column but the end product cannot carry a load higher than the 75C column. Now if the ampacity is 368 you can protect it at 400 amps as long as the load is less than 368. Look at 240.4(B) and 240.6

From 240.6, why is there an additional standard fuse rating of 601A? Is there a real difference between a 600A fuse and a 601A fuse?

 

[infinity]

From 240.6, why is there an additional standard fuse rating of 601A? Is there a real difference between a 600A fuse and a 601A fuse?

No, but if I remember correctly there is a difference in gap size when you go from 600 amps to 800 amps. So an 800 amp fuse gap will accept a 601 amp fuse without needing any fuse adapters.

 

[Ragin Cajun]

You have 397A of connected load. Have you calculated the demand amps? You could be OK.

Be careful of the meter rating.

RC

 

[kwired]

I am a little lost with where some of the OP numbers are coming from.

Here is what I see based on loads of 181 and 216 you have a total of 397.

You have single raceway and want to install parallel conductors in the single raceway. This will require deration of installed conductors because of number of conductors in the raceway, the deration amount will be 80% for 4-6 current carrying conductors in the raceway.

If you parallel 2 #3/0 Cu you will have 400 amps of conductor at 75?C. The conductors will have to be this size minimum no matter what deration process ends up allowing.

If your conductor is 90?C insulation you can use 90? ampacity for deration.


@90?C

2 #3/0 is 450 amps x .8 = 360 - less than needed 397.
2 #4/0 is 520 amps x .80 = 416 - enough to carry 397 amps.

As mentioned be careful of ratings. If this 397 amps is all continuous everything here needs to be multiplied by 125%. That will put you over 400 amps and over the 320 continuous rating of the meter socket also.

If your 397 is 125% of continuous plus 100% of non continuous load then you are fine, but will have basically no room for added load down the road.

 

[Smart $]

I did not do the math but you can derate from the 90C column but the end product cannot carry a load higher than the 75C column. Now if the ampacity is 368 you can protect it at 400 amps as long as the load is less than 368. Look at 240.4(B) and 240.6

OP states conductor are between meter and each of two panels. That would make each panel's MCB the service disconnecting means (not grouped if one inside another outside?), and the conductors are service [entrance] conductors. Though Article 240 doesn't specifically say it does not apply to service conductors, I believe it does not. If it did, then what about the first sentence of 230.90(A) which states, "[overcurrent] protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor."

 

[kwired]

I have a 320a meter feeding one 400a panel with a connected load of 181 amps. The meter also feeds a 400a outside panel with a connected load of 216a. Both panels have a 4in conduit installed to them.

My question is can I size my wire useing the 90deg table and parallel 4/0 at 80%=328a as long as Im under the 75deg ampacity of 288a with my load?

I think I have to parallel 300mcm al at 80%=368 and round up.

Could you give us some more detail of what you are installing, and which conductors are you asking about? Information I had in my previous post would be for sizing conductors that supply the entire load that was mentioned.

Concuctors to each individual panel are loaded to 181 and 216. You said they are each 400 amp panels. Do they have 400 amp main breakers, or are they using up to six mains within a 400 amp main lug panel? Is the inside and outside panels separate buildings or structures? If not Smart$ brought up a problem with having them both on same building if they are both the service disconnecting means - the mains would need to be grouped in same location.

 

[Al Pike]

Could you give us some more detail of what you are installing, and which conductors are you asking about? Information I had in my previous post would be for sizing conductors that supply the entire load that was mentioned.

Concuctors to each individual panel are loaded to 181 and 216. You said they are each 400 amp panels. Do they have 400 amp main breakers, or are they using up to six mains within a 400 amp main lug panel? Is the inside and outside panels separate buildings or structures? If not Smart$ brought up a problem with having them both on same building if they are both the service disconnecting means - the mains would need to be grouped in same location.

The meter is in the middle of a field with one 4in conduit going into a bath house 400a main panel for lights and outlets and the another 4in conduit from the meter going to a 400a main panel outside for RV hook ups. The POCO cost for additional meter locations was costly so the engineer designed it with one meter.