310.15.B.3(a) Adjustment Factor for MultiConductor

[hill900505]

Could anybody explain if multiconductor cables are installed in a conduit, do we need to apply adjustment factors twice? Once for conductors in multiconductor cable and the second time for the number of multiconductors installed in a raceway? For example, a total number of four multiconductors each of which contains four current carrying insulated conductors are installed in a PVC conduit. Thanks a lot!

 

[Dennis Alwon]

IMO, only need to de-rate once.

 

[Smart $]

I'll second that... only once.

But you do have a valid premise for your query. IF Code were physics-driven without deviation, I'd say apply twice or Code would have explicit provisions for additional derating. :happyyes:

 

[Carultch]

Could anybody explain if multiconductor cables are installed in a conduit, do we need to apply adjustment factors twice? Once for conductors in multiconductor cable and the second time for the number of multiconductors installed in a raceway? For example, a total number of four multiconductors each of which contains four current carrying insulated conductors are installed in a PVC conduit. Thanks a lot!

I would calculate it based on the grand total number of current-carrying conductors in the conduit, forgetting about the fact that they are grouped in multiconductor cables. So four cables with four active conductors each, would be 16 total current-carrying conductors.

 

[Ingenieur]

Where the number of current-carrying conductors in a raceway or cable exceeds three,
or
where single conductors or multi-conductor cables are stacked or bundled longer than 24 inches without maintaining spacing and are not installed in raceways,the allowable ampacity of each conductor shall be reduced as shown in the following table xxxxx
each current carrying conductor of a paralled set of conductors shall be counted as a current carrying conductor

does it need derated at all? the way I read it
cond or cable >3 in raceway derate
if a cable has 4 derate the cable
but if only 3 cond in a cable no derate and mutliple cables can be used with no derating
or is EACH cond counted?

if run >24" and no raceway
EACH conductor is derated (and counted)
so 3 cables with 3 cond would count as 9


???

 

[Smart $]

Multiconductor cables in a raceway = conductors in raceway (i.e. total number of current-carrying conductors in cables in raceway)

 

[Ingenieur]

In the op's query
derate for 4 or for 16?

 

[Smart $]

In the op's query
derate for 4 or for 16?

16