Parallel equipment grounding conductor

[cppoly]

If a circuit breaker is feeding multiple sets of feeder cables, does the equipment grounding conductor have to be sized for the breaker and be sized the same in each set of parallel feeders? Or can it be divided among the sets?

For example, an 800 amp circuit breaker feeds two sets of 600 kcmils. Is one #1/0 equipment grounding conductor (the requirement for an 800 amp circuit breaker) required in each set of cables or can the #1/0 equipment grounding conductor be substituted for two #4 equipment grounding conductors since there are two conductors being run in parallel?

 

[Cow]

If a circuit breaker is feeding multiple sets of feeder cables, does the equipment grounding conductor have to be sized for the breaker and be sized the same in each set of parallel feeders?

This.

 

[travish]

pretty sure it is 1/0 in each conduit

 

[jusme123]

250.122(F) '08 code , which sends you to table 250.122, and states its a 1/0 conductor in EACH conduit if fed from 800A breaker.

 

[masterinbama]

250.122(F) '08 code , which sends you to table 250.122, and states its a 1/0 conductor in EACH conduit if fed from 800A breaker.

But never required to be larger than the current carrying conductors, I do believe?

 

[jusme123]

But never required to be larger than the current carrying conductors, I do believe?

....that's correct, read 250.122(A)

 

[resistance]

I believe you guys should re-evaluate your answer—where some are saying 1/0cu. Note: This isn’t to say 1/0cu want work.

 

[jusme123]

...are you saying I'm wrong?

 

[kwired]

I believe you guys should re-evaluate your answer?where some are saying 1/0cu. Note: This isn?t to say 1/0cu want work.

T250.122 says 1/0 for 800 amps. Only time you can be smaller is if the associated ungrounded conductors are smaller than 1/0. That mostly limits that situation to feeder taps.

 

[SIRSPARKSALOT]

I was just in a building that was newly wired and got it's CO. I bid on the building prior to construction and I was unsuccessful in getting the job. After pulling a couple of tiles out to get an idea of deck height, since we are now finishing a tenant space, I saw a paralleled MC feeders (I believe they were for an 800A feeder). I was bent because the EC not only did he not follow the spec and get away with murder, it was non-compliant!

 

[Dennis Alwon]

If a circuit breaker is feeding multiple sets of feeder cables, does the equipment grounding conductor have to be sized for the breaker and be sized the same in each set of parallel feeders? Or can it be divided among the sets?

For example, an 800 amp circuit breaker feeds two sets of 600 kcmils. Is one #1/0 equipment grounding conductor (the requirement for an 800 amp circuit breaker) required in each set of cables or can the #1/0 equipment grounding conductor be substituted for two #4 equipment grounding conductors since there are two conductors being run in parallel?

As others have stated the egc needs to be sized for the overcurrent protection in each conduit. 310.4(E) takes us to 250.122(F)

 

[mlnk]

I was just in a building that was newly wired and got it's CO. I bid on the building prior to construction and I was unsuccessful in getting the job. After pulling a couple of tiles out to get an idea of deck height, since we are now finishing a tenant space, I saw a paralleled MC feeders (I believe they were for an 800A feeder). I was bent because the EC not only did he not follow the spec and get away with murder, it was non-compliant!

What are paralleled MC feeders? Were they in the same conduit? Why is it non compliant?

 

[kwired]

What are paralleled MC feeders? Were they in the same conduit? Why is it non compliant?

Most likely two runs of MC cable with 500 KCMIL conductors but only #3 AWG equipment grounding conductor in the cable. Would be just fine for a 400 amp circuit, but to parallel them and put on 800 amp overcurrent device the EGC's are now too small.

 

[SIRSPARKSALOT]

kwired hit the nail on the head.

 

[Greg1707]

sizing egc

sizing egc

But never required to be larger than the current carrying conductors, I do believe?

Is this correct? 250.122 A refers to "shall not be required to be larger than the circuit conductors supplying the equipment."
I believe the OP is sizing a feeder?

 

[Dennis Alwon]

Is this correct? 250.122 A refers to "shall not be required to be larger than the circuit conductors supplying the equipment."
I believe the OP is sizing a feeder?

A feeder is a circuit just not a branch circuit. Look at the definition in art. 100

 

[iceworm]

Most likely two runs of MC cable with 500 KCMIL conductors but only #3 AWG equipment grounding conductor in the cable. Would be just fine for a 400 amp circuit, but to parallel them and put on 800 amp overcurrent device the EGC's are now too small.

Doesn't that depend on the particular type of MC cable? Some types of MC use the combination of the internal grounding conductor in parallel with the sheath.

2011 250.118.10.b and c

I use a lot of MC. The particular type I use is rated to use both the sheath and internal ground conductor, as a paralleled grounding conductor. Generally speaking, parallel combinations up to 2 - 500 are fine, up to 3 - 750 require adjustable trips and supervised access.

Given the information we have, I could not say, "Good" or "Bad".

ice

 

[kwired]

Doesn't that depend on the particular type of MC cable? Some types of MC use the combination of the internal grounding conductor in parallel with the sheath.

2011 250.118.10.b and c

I use a lot of MC. The particular type I use is rated to use both the sheath and internal ground conductor, as a paralleled grounding conductor. Generally speaking, parallel combinations up to 2 - 500 are fine, up to 3 - 750 require adjustable trips and supervised access.

Given the information we have, I could not say, "Good" or "Bad".

ice

I am not familiar with what is common with larger sizes, as I pretty much have only used 10AWG and smaller MC cables, I would guess there is some similarities though and equipment grounding with MC must comply with 330.108 which sends you to 250.118(10) which says:

Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
a.

It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1)

b.

The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape?type MC cable that is listed and identified as an equipment grounding conductor

c.

The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that is listed and identified as an equipment grounding conductor

Is a cable armor listed for grounding with or without bonding conductor or insulated conductor rated for equipment grounding at any overcurrent device setting, or just for settings equivelant to ampacity of the ungrounded conductors contained in the cable? I would look into exactly what the listing for the cable assembly includes especially if running paralleled cables as the overcurrent device will be higher than it otherwise would be for a run of single cable.

Using raceways for equipment grounding is a different ballgame than using cable assemblies for equipment grounding.

 

[don_resqcapt19]

Doesn't that depend on the particular type of MC cable? Some types of MC use the combination of the internal grounding conductor in parallel with the sheath.

2011 250.118.10.b and c

I use a lot of MC. The particular type I use is rated to use both the sheath and internal ground conductor, as a paralleled grounding conductor. Generally speaking, parallel combinations up to 2 - 500 are fine, up to 3 - 750 require adjustable trips and supervised access.

Given the information we have, I could not say, "Good" or "Bad".

ice

I am not aware of any standard MC cable that has an EGC that is suitable for use with parallel circuits. I don't recall anything saying that the 250.118(10)(b) or (c) cables are suitable for use in parallel circuits.

Do you have a link to the cable you are talking about?

Also what do you mean by "up to 3 - 750 require adjustable trips and supervised access"?

 

[iceworm]

I am not aware of any standard MC cable that has an EGC that is suitable for use with parallel circuits. ...

"Standard" - that probably means the stuff you normally buy. In which case, probably not. But if "standard" means the stuff I normally buy - the yep plenty exists.

... I don't recall anything saying that the 250.118(10)(b) or (c) cables are suitable for use in parallel circuits. ...

Why would there need to be anything in 250.118 about parallel cables. It is discussing what constitutes an equipment grounding conductor.

... Do you have a link to the cable you are talking about? ...

My norm is Okonite CLX. Rockbestos makes similar and as I recall (that's code meaning I woiuld have to check) so does Southwire. I'm sure a search will turn up the link. The spec I use is a corrogated tube type.

... Also what do you mean by "up to 3 - 750 require adjustable trips and supervised access"?

Hummm ... You already know all this - my shorthand is just not clear. Over 800A requires tailoring the trip to be under the cable ampacity and the adjustable trip has to be sealed/bolted covers/supervised access.

Above 3 - 750kcmill, the sheath plus the internal grounding conductor is no longer enough to meet the CB size requirement.

ice