Derating Feeders

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jonny1982

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Do (3) phase feeders have to be derated?

For instance, If I had a (3) phase 225 amp panel I was installing in a commercial application, could I use 3/0 copper. Lets say they where in emt conduit.
Wouldn't I have to derate at 80 percent since there will be 4 current carrying conductors in the pipe?

Thanks
 
jonny1982 said:
Do (3) phase feeders have to be derated?

For instance, If I had a (3) phase 225 amp panel I was installing in a commercial application, could I use 3/0 copper. Lets say they where in emt conduit.
Wouldn't I have to derate at 80 percent since there will be 4 current carrying conductors in the pipe?

Thanks
Click to expand...

Even without dearting you would need 4/0 copper for 225 amps.

You most likely will not have to derate unless the majority of the load is 'non-linear' which would be computers, electronic ballasts etc.

Follow Dave's code reference.
 
iwire said:
You most likely will not have to derate unless the majority of the load is 'non-linear' which would be computers, electronic ballasts etc.
Click to expand...

The need to count the neutral as a CCC, is a tough one to enforce. Almost all lighting in new commercial construction is a majority of non-linear lighting (fluorescent or LED) and most receptacles are used for PC's or VFD's.
 
I don't know what actually 310.15 says on that but in IEC the multi conductors cable has three different ampacities based on three different installations for (Free air, ducts, underground), and so you don't need any group derating based on the selected installation.
 
m sleem said:
I don't know what actually 310.15 says on that but in IEC the multi conductors cable has three different ampacities based on three different installations for (Free air, ducts, underground), and so you don't need any group derating based on the selected installation.
Click to expand...
Being he's in the US, I doubt he's installing per IEC. ;)
 
m sleem said:
I don't know what actually 310.15 says on that but in IEC the multi conductors cable has three different ampacities based on three different installations for (Free air, ducts, underground), and so you don't need any group derating based on the selected installation.
Click to expand...

We have different ampacities for those as well that still does not let us escape derating when more than three current carrying conductors are run together.
 
That makes sense particularly for those non-linear loads.
 
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