2500 amp service

[27hillcrest]

When sizing a 2500 amp service am I correct in using the 90 degree column and using the adjustment factor of .8 because I have more than 3 current carrying conductors in a raceway?

TIA

 

[iwire]

When sizing a 2500 amp service am I correct in using the 90 degree column and using the adjustment factor of .8 because I have more than 3 current carrying conductors in a raceway?

TIA

Is there any reason your counting the neutral as a current carrying conductor?

 

[27hillcrest]

I was always taught that the neutral was a current carrying conductor. It is not??

 

[ron]

Why will you have more than 3 CCC?
Use the 75 degree column or a derated 90 deg conductor, whichever is lower.

 

[27hillcrest]

So the neutral is not considered to be CCC?

 

[dbuckley]

Unlerss there is some reason for the neutral to be counted as a CCC, then it wont be.

Good reasons include mainly non-linear loads. If that service is in a mall, then you'll be fine, no neutral CCC. If the service is in a data centre, then neutral is definitely a CCC.

Judgement call required as to percentage of non-linear loads...

 

[radiopet]

so what are you running.....how many sets and how many conductors per raceway? Is the service Single Phase or Three Phase? and if Three Phase what type...check out 310.15(B)(4) in regard to if you count the grounded conductor or not.

 

[27hillcrest]

The service is for a machine shop. (CNC equipment) 120/208Y 3phase. I came up with 8 4"conduits with 4 500mcm and 2/0 gnd. Does that make sense to everyone?

 

[Pierre C Belarge]

For consideration of whether the grounded/neutral conductor is to be treated as a CCC, reference 310.15(B)(4)-(a), (b) or (c).



8 x 380A = 3040Amps
7 x 380A = 2660Amps
6 x 380A = 2280Amps

If you have one service disconnecting means, you will have to follow 230.42.

If you have multiple service disconnects, you can reference 230.90 ex 3
The perform a load calculation to make sure your load does not exceed 2280Amps

 

[Dennis Alwon]

if you do 8 conduits you would only need 350 Kcm. The 350 Kcm are good for 310 amps

310 amps x 8 = 2480amps

No need to count the neutral

Just make sure your calculated load is less than 2480 and your good to go.

 

[raider1]

if you do 8 conduits you would only need 350 Kcm. The 350 Kcm are good for 310 amps

310 amps x 8 = 2480amps

No need to count the neutral

Just make sure your calculated load is less than 2480 and your good to go.

That depends on if there is a single overcurrent device for the service disconnecting means. 230.90(A) requires that the overcurrent device be rated not higher than the allowable ampacity of the conductor. So if the OPer has a 2500 amp breaker protecting the service conductors the ampacity of the conductors must be equal to or greater than the overcurrent protective device.

Chris

 

[don_resqcapt19]

If these are service cables then there should be no need for a grounding conductor.

 

[Dennis Alwon]

That depends on if there is a single overcurrent device for the service disconnecting means. 230.90(A) requires that the overcurrent device be rated not higher than the allowable ampacity of the conductor. So if the OPer has a 2500 amp breaker protecting the service conductors the ampacity of the conductors must be equal to or greater than the overcurrent protective device.

Chris

I guess I assumed a parallel service with one OCPD since there were 8 conduits. Not necessarily the case but that was my thinking. Thanks for the clarification.

 

[cripple]

That depends on if there is a single overcurrent device for the service disconnecting means. 230.90(A) requires that the overcurrent device be rated not higher than the allowable ampacity of the conductor. So if the OPer has a 2500 amp breaker protecting the service conductors the ampacity of the conductors must be equal to or greater than the overcurrent protective device.

Chris

Where the conductor rating does not correspond to the standard ampere rating of a circuit breaker or fuse, the next-larger-size circuit breaker or fuse may be used, provided its rating does not exceed 800 amperes, as permitted in 240.4(B)(3). See 240.6 for standard ampere ratings of fuses and circuit breakers.
Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6 shall be permitted.

 

[Dennis Alwon]

Where the conductor rating does not correspond to the standard ampere rating of a circuit breaker or fuse, the next-larger-size circuit breaker or fuse may be used, provided its rating does not exceed 800 amperes, as permitted in 240.4(B)(3). See 240.6 for standard ampere ratings of fuses and circuit breakers.
Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6 shall be permitted.

Actually you make a good point. At 2480 amps for the 350 kcm I was talking about then I cannot go to a 2500 amp breaker. I would have to use 400 KCM conductors.

 

[raider1]

Where the conductor rating does not correspond to the standard ampere rating of a circuit breaker or fuse, the next-larger-size circuit breaker or fuse may be used, provided its rating does not exceed 800 amperes, as permitted in 240.4(B)(3). See 240.6 for standard ampere ratings of fuses and circuit breakers.
Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6 shall be permitted.

Yes, but the original post was talking about a 2500 amp service so 240.4(B)(3) would not apply for a single overcurrent protective device for the service.

Chris

 

[raider1]

Actually you make a good point. At 2480 amps for the 350 kcm I was talking about then I cannot go to a 2500 amp breaker. I would have to use 400 KCM conductors.

Correct, but your original design with 350 kcmil would work if you had 2-6 overcurrent devices constituting your service disconnecting means, in accordance with Exception #3 to 230.90(A).

Chris

 

[Dennis Alwon]

Correct, but your original design with 350 kcmil would work if you had 2-6 overcurrent devices constituting your service disconnecting means, in accordance with Exception #3 to 230.90(A).

Chris

Yes, but I was thinking only one--doh...

 

[raider1]

Yes, but I was thinking only one--doh...

I understand, I have those moments all the time.

Chris

 

[petersonra]

When sizing a 2500 amp service am I correct in using the 90 degree column and using the adjustment factor of .8 because I have more than 3 current carrying conductors in a raceway?

TIA

the size of the service is not relevant.