Paralell conductors to feed a piece of equipment

[RIDGELY]

I have an inspector that has sited a code to me that states I can not run 2 4/0 thhn to the eqipment .
the facts Service 400 amps disconect and fussed at 300 amps and Im feeding off load side with paralell 4/0 thhn cu to feed a piece of eqipment rated at 300amps . He said we are not able to do this , what code artical will support me to do this and show him this is ok ? in lu of say running 350mcm cu to feed the unit .

 

[Dennis Alwon]

What kind of equipment. If the equipment is rated 300 amps you may need to add 25% to it. Also if the service is only 300 amps then the OCPD would have to be rated at 100% if the equipment is a continuous load.

Please clarify
What kind of equipment
Is the 300 amps marked on the machine?
Is it a continuous load?

 

[ray cyr]

Are you feeding 3 phase equipment with 2-4/0 per phase all in the same conduit?
More information will be quite helpful.

 

[infinity]

I have an inspector that has sited a code to me that states I can not run 2 4/0 thhn to the eqipment .
the facts Service 400 amps disconect and fussed at 300 amps and Im feeding off load side with paralell 4/0 thhn cu to feed a piece of eqipment rated at 300amps . He said we are not able to do this , what code artical will support me to do this and show him this is ok ? in lu of say running 350mcm cu to feed the unit .

Why article did he cite? Parallel #4/0 Cu condcutors in separate raceways would have an ampacity of 460 amps, 350 kcmil Cu conductors only 260 amps. Obviously something is wrong here.

 

[augie47]

I will agree, on the surface, something seems remiss.
Please provide us with more details, such as the exact ratings on the machine, the method of install (separate conduits, etc.), grounding and termination data.
Did the inspector specifically tell you the 4/0s were the problem.
Often time things get lost in passed on info.

 

[Dennis Alwon]

I thought the OP said the service had a 400 amp disco with 300 amp fuses. Sounded like a service just for this machine but who knows.

 

[charlie b]

Forget about all the numbers for a moment. Is the inspector saying that the NEC forbids using parallel conductors for a branch circuit? If so, he is wrong. He will not be able to cite an article to back up that claim, for no such article exists. 310.10(H) does not limit us to services or feeders.

 

[DARUSA]

Are you using bx cable or mc cable? Because if you are using one of this probably you can not meet the grounding requirements for parallel conductors!!!

 

[infinity]

Are you using bx cable or mc cable? Because if you are using one of this probably you can not meet the grounding requirements for parallel conductors!!!

Why would BX cable (type AC) have an EGC problem?

 

[DARUSA]

Why would BX cable (type AC) have an EGC problem?

4/0 mc cable is rated for 225 amps at 75 degrees per 310.16, based on the table 250.122 for 225 amps you need a number 6 ground, most of the 4/0 mc cable comes with a #4 ground inside. Now if you paralleling 2 , 4/0 Mc cable for a 400 amps DS you will be ok with the amp rated of the wire but each mc is a raceway and you will need a #3 ground wire in each cable!

 

[LarryFine]

Now if you paralleling 2 , 4/0 Mc cable for a 400 amps DS you will be ok with the amp rated of the wire but each mc is a raceway and you will need a #3 ground wire in each cable!

That's where custom cable ordering comes in, or you could use one more conductor than needed and use that as the EGC.

 

[DARUSA]

That's where custom cable ordering comes in, or you could use one more conductor than needed and use that as the EGC.

You right but Sometimes people are not aware of it.!!!

 

[infinity]

Are you using bx cable or mc cable? Because if you are using one of this probably you can not meet the grounding requirements for parallel conductors!!!

Why would BX cable (type AC) have an EGC problem?

4/0 mc cable is rated for 225 amps at 75 degrees per 310.16, based on the table 250.122 for 225 amps you need a number 6 ground, most of the 4/0 mc cable comes with a #4 ground inside. Now if you paralleling 2 , 4/0 Mc cable for a 400 amps DS you will be ok with the amp rated of the wire but each mc is a raceway and you will need a #3 ground wire in each cable!

You mentioned BX, I was asking about AC cable not MC.

 

[DARUSA]

Assuming the ground path of the AC cable is texted based on the amp rated of the cable , you should have the same problem!!!
If not Can i use 4 set of 3/0-4 wires AC bx cable to supply a 800 amp Panel ?
How ca I show the inspector that I meating the grounding requirement for it?

 

[Dennis Alwon]

So the op asks a question almost 3 days ago and never responds.

 

[infinity]

Assuming the ground path of the AC cable is texted based on the amp rated of the cable , you should have the same problem!!!
If not Can i use 4 set of 3/0-4 wires AC bx cable to supply a 800 amp Panel ?
How ca I show the inspector that I meating the grounding requirement for it?

If I remember correctly type A/C cable only comes in sizes up to #2 so the point is moot.

 

[DARUSA]

If I remember correctly type A/C cable only comes in sizes up to #2 so the point is moot.

 

[infinity]

View attachment 5382

Thanks, I think that I was probably thinking of NM cable. So now back to the question do you have any data that suggests you cannot run AC cable in parallel?

 

[DARUSA]

Thanks, I think that I was probably thinking of NM cable. So now back to the question do you have any data that suggests you cannot run AC cable in parallel?

No I don't,As long you take care the grounding issue your fine.
As other says special order come in to play!!!

 

[iwire]

Are you using bx cable or mc cable? Because if you are using one of this probably you can not meet the grounding requirements for parallel conductors!!!

You mentioned BX, I was asking about AC cable not MC.

Assuming the ground path of the AC cable is texted based on the amp rated of the cable , you should have the same problem!!!
If not Can i use 4 set of 3/0-4 wires AC bx cable to supply a 800 amp Panel ?
How ca I show the inspector that I meating the grounding requirement for it?

Thanks, I think that I was probably thinking of NM cable. So now back to the question do you have any data that suggests you cannot run AC cable in parallel?

No I don't,As long you take care the grounding issue your fine.
As other says special order come in to play!!!

Type AC has no 'wire' grounding conductor to worry about.

There is nothing in 250.122 about increasing the size of the armor.