Parallel equipment grounding conductor

[don_resqcapt19]

"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.

First I don't use MC, but I was refering to standard MC that does not have an oversized EGC. That is the EGC is sized based on the ampacity of the circuit conductors.

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

It is my opinion that as long as the EGC or part of the EGC is a wire, then 250.122(F) applies and you have to find a way to increase the size of that wire type EGC.

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.

A quick look at the spec sheets did not show me anything that would change my mind about needing an oversized EGC when these cables are used in paralle

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.

So you are talking about the rounding rule in 240.4(B)?

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

I still don't understand this one.

 

[iceworm]

... It is my opinion that as long as the EGC or part of the EGC is a wire, then 250.122(F) applies and you have to find a way to increase the size of that wire type EGC. ...

I'm missing your point. Of course NEC 2011 250.122.F applies. Paraphrased (specifically for parallel cables): The grounding conductor in each cable is sized for the feeder CB.

So what constitutes a grounding conductor in the particular cable I am using? For that one goes to NEC 2011 250.118.10.c

(10) Type MC cable that provides an efective ground-fault current path in accordance with one of the following"

c. The metalic sheath or the combined metalic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable That is listed ...​

Again, I'm thinking you already know all of this.

... A quick look at the spec sheets did not show me anything that would change my mind about needing an oversized EGC when these cables are used in paralle...

I wouldn't want to change your mind. Of course paralleled cables protected by a fat CB require an EGC in each cable suitable for the CB rating. However, perhaps I may convince you that the grounding conductor (in this particular cable) is the parallel combination of the grounding conductors (there is often three little ones in the interstices) and the metalic sheath. The copper equivalent of the Al sheath is huge compared to the three little CU grounding conductors.

ice

 

[iceworm]

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

... I still don't understand this one.

I did the research about eight years ago. So I am a little hazy on the exact numbers - but the principles should be correct.

Example 1:
The sheath and grounding conductors in 500kcmil are equivalent to 3/0 CU. 3-500 are good for 1140A. Table 250.122 says a 1200A CB takes a 3/0 EGC. So this is okay as long as the trip is set down to 1140a or less (95% on a 1200A trip unit)

4-500 are good for 1520A. EGC for a 1600A is 4/0. So 4 parallel 500s won't work.

Example 2:
The sheath and grounding conductors in 750kcmil are equivalent to 250kcmil CU. 4-750 are good for 1900A. Table 250.122 says a 2000A CB takes a 250kcmill EGC. Hummm ... Looks like 4-750 will work. My research paper table did not go over 3-750. After 8 years I don't know why not. Maybe 4-750 will work.

In any case, looking at 5-750, 2375A, 2500A CB requires 350kcmil. This won't work.

ice

 

[don_resqcapt19]

I'm missing your point. Of course NEC 2011 250.122.F applies. Paraphrased (specifically for parallel cables): The grounding conductor in each cable is sized for the feeder CB.

So what constitutes a grounding conductor in the particular cable I am using? For that one goes to NEC 2011 250.118.10.c

(10) Type MC cable that provides an efective ground-fault current path in accordance with one of the following"

c. The metalic sheath or the combined metalic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable That is listed ...​

Again, I'm thinking you already know all of this.

If it is only the metal sheath used as the EGC, I would treat it like conduit and not require anything special for the EGC of a parallel circuit. If it uses wires as part of the EGC, then I want to see the total cross sectional area of the wires in the cable meet the requirements of 250.122(F) if the cable is used as part of a parallel installation.

I wouldn't want to change your mind. Of course paralleled cables protected by a fat CB require an EGC in each cable suitable for the CB rating. However, perhaps I may convince you that the grounding conductor (in this particular cable) is the parallel combination of the grounding conductors (there is often three little ones in the interstices) and the metalic sheath. The copper equivalent of the Al sheath is huge compared to the three little CU grounding conductors.
ice

Yes, I am aware that these cables use "sectional" EGCs, but they are not sized to meet the rules for use in parallel circuits. Without something in writing that says that the combined sheath and internal EGCs are suitable for use in parallel installations, I would not accept that product for parallel installations.

 

[iceworm]

If it is only the metal sheath used as the EGC, I would treat it like conduit and not require anything special for the EGC of a parallel circuit. If it uses wires as part of the EGC, then I want to see the total cross sectional area of the wires in the cable meet the requirements of 250.122(F) if the cable is used as part of a parallel installation. ...

... Without something in writing that says that the combined sheath and internal EGCs are suitable for use in parallel installations, I would not accept that product for parallel installations.

... A quick look at the spec sheets did not show me anything that would change my mind about needing an oversized EGC when these cables are used in paralle...

I'm completely baffledwhy you are stuck on this one. The code is clear, the cable spec is clear, industry standard design practice is clear.

Hummm ... I guess you will just have to do more than just skim the CLX specs to see in writing that it meets 250.118.10.c. I can't help you there.

As for you not accetping the product for parallel installations - Well, all of us in industry are thankful you aren't the one translating the NEC for the AHJs. Cause we would all be screwed. MC cable cable is a great method. A bit expensive, but well worth it for installation and reliability.

"And that is all I have to say about that."

ice

 

[don_resqcapt19]

I'm completely baffledwhy you are stuck on this one. The code is clear, the cable spec is clear, industry standard design practice is clear.

Hummm ... I guess you will just have to do more than just skim the CLX specs to see in writing that it meets 250.118.10.c. I can't help you there.

As for you not accetping the product for parallel installations - Well, all of us in industry are thankful you aren't the one translating the NEC for the AHJs. Cause we would all be screwed. MC cable cable is a great method. A bit expensive, but well worth it for installation and reliability.

"And that is all I have to say about that."

ice

I don't have any issues when the product is not used in parallel installations. I only have an issue where part of the EGC is of the wire type and the product is used in a parallel installation.

 

[iceworm]

... I only have an issue where part of the EGC is of the wire type and the product is used in a parallel installation.

Don -
With all due respect:

1. The code is perfectly clear.
2. You are really, really, really going to have to read the the cable spec before you can have an informed opinion.​

ice

 

[iceworm]

... I only have an issue where part of the EGC is of the wire type and the product is used in a parallel installation.

Perhaps I misunderstood.

Thought just occured to me that:

1. You clearly understand the code allows using both the sheath and the internal conductors.

2. You clearly understand the CLX spec clearly shows the cable is listed as required in 250.118.10.c

3. You still don't like it because it does not meet your precetpion of how other receways work.​

If so, we're done. I'm okay with you not liking it.

ice

 

[don_resqcapt19]

....c

3. You still don't like it because it does not meet your precetpion of how other receways work.
If so, we're done. I'm okay with you not liking it.

ice

Its not that I don't like it. I am just not convinced that the code permits it.

 

[iceworm]

Its not that I don't like it. I am just not convinced that the code permits it.

It does. But since you don't work with MC cables, it likely dows not matter.

ice

 

[petersonra]

Its not that I don't like it. I am just not convinced that the code permits it.

IMO, none of the little wires in MC armor would make for a code sized EGC. So does that prohibit the use of MC?

 

[don_resqcapt19]

IMO, none of the little wires in MC armor would make for a code sized EGC. So does that prohibit the use of MC?

The code says that some types of MC have a sheath that is suitable for use as an EGC. If it only has a sheath and no internal EGCs of the wire type, I would treat it like conduit and not see a code issue using it in parallel applications.

The other two types of MC use EGCs of the wire type, either alone or in combination with the sheath to provide the grounding path. It is clear that the type that only uses the interal wire type of EGC cannot be used in parallel circuits as the size of the internal EGC is based on the ampacity of the ungrounded conductors within the cable. That would not comply with the "full size" rule in 250.122(F).
The last type uses a combination of the sheath and internal grounding conductors and I have not been convinced that it is suitable for parallel applications.

 

[don_resqcapt19]

It does. But since you don't work with MC cables, it likely dows not matter.

ice

I have not seen any document that tells me that the type of MC that uses a combination of the sheath and interal wires is suitable for use as the EGC in parallel applications.

 

[don_resqcapt19]

If I install a metal raceway system with conductors that are used in a parallel application and I install an EGC of the wire type in that metal raceway, it has to be "full" sized in each raceway. Why would MC cable where the combination of the sheath and interal grounding wires is used as the EGC be any different?

 

[iceworm]

If I install a metal raceway system with conductors that are used in a parallel application and I install an EGC of the wire type in that metal raceway, it has to be "full" sized in each raceway. Why would MC cable where the combination of the sheath and interal grounding wires is used as the EGC be any different?

Because one is raceway and one is cable. They are not the same animal. And the code teats them differently. There are even different UL specs. And there are even different code sections, RMC is Art 344. MC is Art 330. What applies to one does not necessarily apply to the other.

ice

 

[tkb]

Don -
With all due respect:

1. The code is perfectly clear.
2. You are really, really, really going to have to read the the cable spec before you can have an informed opinion.​

ice

How about a link to this magical cable that you speak of?

 

[iceworm]

I have not seen any document that tells me that the type of MC that uses a combination of the sheath and interal wires is suitable for use as the EGC in parallel applications.

Can't say I have either. Never knew I needed one. The code is permissive. Do you have a document that says "no". Paralleled installation is not listed in 330.12.

250.122.F tells the required size of an equipment grounding conductor. 250.118.10.c tells what constitutes an equipment grounding conductor.

330.108 says When used to provide and EGC, the MC must comply with 250.122 and 250.118.10.

Strictly from a design point of view:
The parallel MC cable installation that I am describing is an industry standard. Considering the weather and soggy ground I work around, MC-HL (Okonite CLX) is far superior to any conduit installation. When we kicked over and started using MC-HL, that did wonders for the jobs. Reliability is far superior to any conduit installation.

In the 15 years I've been using it, I've never had an AHJ tell me paralleled installation was wrong.

But then again - who knows. Maybe tomorrow we will be tearing it all out cause it never met code.

ice

 

[iceworm]

How about a link to this magical cable that you speak of?

Try a search on "Okonite CLX". I'm sure you will find it. But it will help if you spell "magic: as "MC-HL" :happyyes:

ice

 

[iceworm]

How about a link to this magical cable that you speak of?

This is not new. My library goes back to 1996. It is in there.

But if one does not do heavy feeds, outside, cold weather - conduit is likely more cost effective. So, it is probably not something you have been around much. Not majik - just not stoneage.

ice

 

[don_resqcapt19]

Because one is raceway and one is cable. They are not the same animal. And the code teats them differently. There are even different UL specs. And there are even different code sections, RMC is Art 344. MC is Art 330. What applies to one does not necessarily apply to the other.

ice

There is nothing in 250.122(F) that says that. In fact that section says "...Where conductors are installed in parallel in multiple raceways or cables ..."