Max ampere rating of multi mc cables

[Chris6245]

OK, I am confused. Table 310.15 (B) talks about more than 3 CCC's in a raceway or cable. I don't see where multiple raceways or cable assemblies have to be derated when you only have 3 CCC's in each raceway or cable assembly? What am I missing? Did I miss the OP's actuall question?

 

[infinity]

OK, I am confused. Table 310.15 (B) talks about more than 3 CCC's in a raceway or cable. I don't see where multiple raceways or cable assemblies have to be derated when you only have 3 CCC's in each raceway or cable assembly? What am I missing? Did I miss the OP's actuall question?

Cables bundled for more than 24" require derating also.

310.15(B)(2) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

 

[Chris6245]

Cables bundled for more than 24" require derating also.

I see what you are saying. I guess I always considered MC as a raceway and I always read that section as bundling NM type cables and such. So you can't bundle MC without derating but you could bundle FMC without derating right? Just goes to show how you can get something in your head and swear it's right no matter how much you read over something.

 

[M. D.]

The thing I find interesting is that whether it is 21 or 121 C.C.C. the adjustment is 60%

 

[ivsenroute]

So we all agree that it is 18A and they need to be on a 15A breaker??????????

 

[infinity]

So we all agree that it is 18A and they need to be on a 15A breaker??????????

Depends on the loads. If there are no multi-receptacle loads involved they can be on a 20 amp OCPD.

 

[M. D.]

.....each 208/120v single phase multiwire circuit in the cable serves office space receptacle outlets.........

Infinity,it seems to me there are some,.. if not all,.. that serve multiple receptacle loads.. So for those he is talking about here it is a 15 amp ocpd with a conductor ampacity of 18

 

[LarryFine]

I guess I always considered MC as a raceway and I always read that section as bundling NM type cables and such. So you can't bundle MC without derating but you could bundle FMC without derating right?

Right. MC is a cable assembly, while FMC is a raceway in which we install conductors.

MC cable comes with conductors packed in, while FMC must follow conductor fill limitations.

Note that we may bury angle connectors on MC, but angle connectors on FMC must be accessible.

 

[infinity]

Infinity,it seems to me there are some,.. if not all,.. that serve multiple receptacle loads.. So for those he is talking about here it is a 15 amp ocpd with a conductor ampacity of 18

A lighting circuit would be one example of a non-multi-receptacle circuit. So an adjusted ampacity of 18 amps on multiple lighting circuits could go up to the next standard sized OCPD which would be 20 amps. Other 18 amp adjusted circuits serving single loads or single receptacles would also be permitted to go up to 20 amps too. As you can see it's not really all.