Aluminum Phase Conductors & Copper Ground Conductors

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lizzie14

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Is it ok to run aluminum phase conductors and a copper equipment ground? It has come up on a job and I've just never heard of that before.
 
In a word..... yes. The equipment ground just has to be sized in accordance with 250.122.

Pete
 
I believe it is. They have run 8-750kcmil Aluminum for a 3000A service. The equipment ground is a 400 kcmil CU.

It just seems strange...I guess whatever works?
 
I assume that the conductors we are talking about are part of a feeder? If they are the service lateral or service entrance from the point of delivery I would wonder about the purpose of the 400kcmil cu conductor.

Secondly, if this part of a feeder there will need to be a 400kcmil cu in each raceway. 250.122(F)

Pete
 
Not technically a feeder. That had me confused too. We didn't show a ground, on the feeder, but then they put one in, but this part isn't really the feeder.

It goes from the utility transformer, to an exterior switchgear with main circuit breaker(this is the part I consider a feeder). Then it goes from the exterior switchgear to the main distribution panel which is the 3000A panel. From the SES (Service Exterior Switchgear) to the MDP, they have 8 sets of 4-750 kcmil Al and 1-400 kcmil Cu.

Does that make any sense?
 
Bare Ground

Bare Ground

Insulated aluminum phase and/or neutral and bare copper equipment ground. Sometimes the bare copper ground can be less expensive. Cannot go bare with aluminum. Rather common.
 
Cannot go bare with aluminum.
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Why not?

250.120(B) Aluminum and copper-clad aluminum conductors. Equipment grounding conductors of bare or insulated aluminum or copper-clad aluminum shall be permitted. Bare conductors shall not come in direct contact with masonary or the earth or where subject to corrosive conditions. Aluminum or copper-clad aluminum conductors shall not be terminated within 18 in. of the earth.

As long as you install the EGC in accordance with this section you are permitted to use bare aluminum.

Chris
 
Bare Ground

Bare Ground

I agree. Code permits it. IMHO, single conductor bare aluminum will find few applications.

As long as it is kept dry and away from galvanic action (galvanized conduit), it would be suitable. Bare aluminum in a damp/moist galvanized conduit would "be subject to corrosive conditions" and thus not permitted. Most of my work work includes underground conduit which is considered wet so bare CU is OK but not bare AL.
 
IMHO, single conductor bare aluminum will find few applications.
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Agreed, I don't know of anytime that I have seen a single conductor bare aluminum EGC used, but the code does permit it.

Chris
 
lizzie14 said:
Is it ok to run aluminum phase conductors and a copper equipment ground? It has come up on a job and I've just never heard of that before.
Click to expand...

Not that anyone would do it, but are the three phase conductors required to be the same material?
 
wasasparky said:
Not that anyone would do it, but are the three phase conductors required to be the same material?
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No, as long as they are properly sized, there is no requirement for the different phase conductors to be the same material.

Now if you are paralleling conductors each conductor of the same phase must have the same conductor material. (See 310.4)

Chris
 
raider1 said:
No, as long as they are properly sized, there is no requirement for the different phase conductors to be the same material.

Now if you are paralleling conductors each conductor of the same phase must have the same conductor material. (See 310.4)

Chris
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How about copper for half the run, then switch to aluminum? (assuming proper splicing method).
Actually this might have been a VFD issue where the change in material caused reflected waves that could cause problems...something like that...)

Seems to me I saw something about mixing conductor types, a long time ago, can't remember the exact verbage...must have drank too much beer back then.
 
How about copper for half the run, then switch to aluminum? (assuming proper splicing method).
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Again I am not aware of an NEC section that prohibits changing conductors material in a run as long as the proper splices were installed, and the conductors were properly sized.

IMHO, this would not be the best design choice, but code compliant.

Chris
 
lizzie14 said:
It goes from the utility transformer, to an exterior switchgear with main circuit breaker(this is the part I consider a feeder). Then it goes from the exterior switchgear to the main distribution panel which is the 3000A panel. From the SES (Service Exterior Switchgear) to the MDP, they have 8 sets of 4-750 kcmil Al and 1-400 kcmil Cu.
Click to expand...

The conductors from the SES to the MDP, as I see by your description, would be the feeders. The feeder would require the EGC.

Installing this 400kcmil cu conductor from the transformer to the SES would most likely put that conductor in parallel with the grounded conductor thus creating a violation of 310.4 (assuming that this is a grounded system). Further the conductor between the transformer and the SES would probably be, at best, a bonding jumper.

Pete
 
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