Ranger86
Member
- Location
- Las Vegas, NV
This section talks about using the metallic sheath in combination with the ground conductor. Is this section allowing the ground conductor to be undersized and not meet table 250.122 requirements ???
Exactly what do you have?We have a MC type cable, and the ground conductor is smaller than Table 250.122. At this point, I do not know if it is listed as stated in 250.118 (10) c. But, if it is listed, does this mean that the ground conductor can be smaller than what it should be per T250.122 ?
We have a MC type cable, and the ground conductor is smaller than Table 250.122. At this point, I do not know if it is listed as stated in 250.118 (10) c. But, if it is listed, does this mean that the ground conductor can be smaller than what it should be per T250.122 ?
Thats exactly what that provision is for....Things like MC-SG and MC-AP type products.If you read it again it says "The combined metallic sheath and uninsulated equipment grounding/bonding conductor". Sounds like the reference is actually for a cable like MC-ap where the sheath and the bare bonding conductor act in concert to form the EGC.
Thats exactly what that provision is for....Things like MC-SG and MC-AP type products.
Exactly what do you have?
Size and number of conductors.
Exact labeling (on packaging or reel; may be on binder wrap between armor and conductors).
Insulated EGC's in MC cable are sized for typical OCPD ratings. Other EGC sizes are available by special order.
There are several "flavors" of Type MC cable, and we don't know what you have until you tell us.
We don't read minds... at least not very well at times.
You cannot use standard MC for that application. You will have to special order MC with the appropriate EGC size (note a few manufacturers offer non-standard-size EGC in there product listing, but your local supply house usually does not stock them).I have a couple of scenarios, here is one of them ....
A parallel 400A feeder, 400A OCPD, the conductor size also had to be increased for voltage drop. So, I ended up with parallel 4/0 phase & neutral with #2 ground. The 4/0 MC cable comes with #4 ground conductor.
You cannot use standard MC for that application. You will have to special order MC with the appropriate EGC size (note a few manufacturers offer non-standard-size EGC in there product listing, but your local supply house usually does not stock them).
It does not. The general statement to (10) says effective ground-fault current path... and that effectiveness is determined by an EGC sized per 250.122. Where the combined sheath and conductor is listed as an EGC, the listing would have to indicate an effective size in order for 250.122 to be applied correctly. AFAIK, such are usually redundant EGC's, and compliance is met by the 'primary' EGC.This is the part that gets confusing to me..... So, 250.118 (10), does it or does it not allow the ground conductor to be smaller than what the T250.122 requires ?
It does not. The general statement to (10) says effective ground-fault current path... and that effectiveness is determined by an EGC sized per 250.122. Where the combined sheath and conductor is listed as an EGC, the listing would have to indicate an effective size in order for 250.122 to be applied correctly. AFAIK, such are usually redundant EGC's, and compliance is met by the 'primary' EGC.
Ranger-- when we talk about T. 250.122 you should say equipment grounding conductor not ground conductor. A neutral can be looked at as a ground conductor because it is grounded. One normally says grounded conductor or neutral for the neutral-- although there is a technical difference and the grounding conductor is the equipment grounding conductor
This helps us understand what you are asking. At first I thought you wanted to know if the grounded conductor could be smaller than the equipment grounding conductor. Thanks
Sorry about that, thanks for letting me know. I am trying to get the manufacturer data to verify the listings of the MC cable... the manufacturer was bought by another one around 10 years ago so I am hoping they have that data.
Just curious, exactly what data are you looking for?
@Rander86-This is the part that gets confusing to me..... So, 250.118 (10), does it or does it not allow the ground conductor to be smaller than what the T250.122 requires ?
@Rander86-
I am a bit confused at your question. Where in Section 250.118(10) does it say anything regarding size of the EGC? It basically says that if you meet one of the following in (a) through (c) then the metal sheathing qualifies no different than it would for RMC, IMC, EMT and so on. Nothing in Section 250.118 has to do with sizing....but when you get to Section 250.122(A) you will read in the first sentence that it has to do with EGC's of the "Wire Type" when using T 250.122.
Hope that clears your confusion.
Suppose the cable shorts out in the middle of the run. If the mc cable is not capable of carrying the short back to the panel then the cable will just glow rather than short the breaker. This is why there is a steel or aluminum wire that runs the entire length of the cable. This wire insures that the impedance on the cable is not too great so that the breaker will trip. The equipment grounding conductor will tie all parts together