I know that you would have to derate conductors if there are more than 30 current carrying conductors in wireway but suppose you put multiple MC cable in a wireway and they are bundled, do you have to derate the conductors based on NEC 376.22(B)? does it negate the requirement of having to derate them if you have more than 3 current carrying conductors.
MC cable in a wireway and derating
- Thread starter Tainted
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yesterlectric
Senior Member
- Location
- PA
- Occupation
- Electrician
I’ve never heard of putting MC cable with its casing in a wireway. I’m assuming that you took the casing off the cable in the wireway. If so, you treat them like the conductors they are when in the wireway, not as MC cable. You would have to follow the rules in 310.15 and also article 376.
Outside of the wire way, you have rules 310.15 for MC cable bundling.
Outside of the wire way, you have rules 310.15 for MC cable bundling.
So if you don’t strip off the MC cable you would have to treat derating as if it’s outside the wireway?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If the MC cables are considered bundled within the wireway then you need to derate after you exceed 3 CCC's.So if you don’t strip off the MC cable you would have to treat derating as if it’s outside the wireway?
How can you maintain spacing inside the wireway so that we don’t have to derate?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I would say they have spacing unless they are tightly zip tied together
But what if making that judgment call is false?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Tightly strapping the conductors together at frequent intervals is the only way I can see the conductors not " Maintaining spacing for a continuous length longer than 24" If they aren't touching then they have spacing. Doesn't seem ambiguous to me.
Yea but how do I make sure they do not ever touch in a wireway? I’m planning on using MC cables to feed apartments but I don’t want to strip like 100’ of MC cable per apartment, wireway will be used as support from meter bank to the shaft where all the MC cables will be going to. Cable tray is another option for support but I need to figure out how to maintain spacing
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Read 310.15(B)(2). They can touch, just not for more than 24 inches. I don't see how they are going to touch continuously for 24" without some serious human intervention making sure that happens.
- Location
- Illinois
- Occupation
- retired electrician
That section is often read to say what you have stated, but it is also read to say that if you don't install some active measure to separate the cables, spacing has not been maintained. This is a judgement call and only YOUR AHJ knows the answer that applies to your installation.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
Roll some tape up in a ball every 23” and tape in the middle of your bundle, now you now there not touching every 24”
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