Conductor ampacity

Therealcrt

Senior Member
Location
Kansas City
Occupation
Electrician
If I have 10 number 12 THHN conductors in a three-quarter inch conduit EMT D-Ray the conductors to 50% of their ampacity. I can use 310.16 tables under the 90° C for my adjustment factor which is number 12 rated for 30a but 50% now they’re only ready for 15 A. Could I still put them on a 20 amp breaker or do I need to remove a conductor from the conduit to only adjust to 70% making the conductor rated for 21 A
 
What unusual equipment are you connecting to your 3P4W MWBCs that causes the neutral to be a current carrying conductor?

Cheers, Wayne
Well it’s a 4 wire 3 phase system aka Wye. I’m connecting new circuits in new conduit to a J-Box that serves existing things within the tenants space. So I don’t know the exact loads that will be connected. But I understand now that from panel to J box in my new conduit I don’t count neutral as CCC unless the neutral is serving only 2 of the 3 phases. Which in some cases it does when I connect them to the existing circuits in the J box. So for example 1 of the existing conduits has black red blue white Black red blue white then a black blue white. So if I wanted to re feed that within my new conduit I don’t count the neutral for the black red blue circuits but I do count it for the black blue circuit
 
So for example 1 of the existing conduits has black red blue white Black red blue white then a black blue white. So if I wanted to re feed that within my new conduit I don’t count the neutral for the black red blue circuits but I do count it for the black blue circuit
So that's 9 CCCs in your example. And in your previous post, it would be 6 CCCs, not 8.

Cheers, Wayne
 
What unusual equipment are you connecting to your 3P4W MWBCs that causes the neutral to be a current carrying conductor?

Cheers, Wayne
But with that being said when I connect them to the existing circuits, I’m not sure which ones are gonna be non-linear loads because I don’t know what they serve such as printers or TVs computer things like that so should I be safe and count the neutral as a current carrying conductor in case they are connected to non-linear loads
 
But with that being said when I connect them to the existing circuits, I’m not sure which ones are gonna be non-linear loads because I don’t know what they serve such as printers or TVs computer things like that so should I be safe and count the neutral as a current carrying conductor in case they are connected to non-linear loads
My understanding is that modern equipment is basically all power factor corrected so that it would not be considered non-linear. So unless the majority of the load is computers from the 1980s, I believe it would reasonable to not count the neutral as the current carrying.

That's just from what I've read here, others may have more definitive commentary.

Cheers, Wayne
 
Well it’s a 4 wire 3 phase system aka Wye. I’m connecting new circuits in new conduit to a J-Box that serves existing things within the tenants space. So I don’t know the exact loads that will be connected. But I understand now that from panel to J box in my new conduit I don’t count neutral as CCC unless the neutral is serving only 2 of the 3 phases. Which in some cases it does when I connect them to the existing circuits in the J box. So for example 1 of the existing conduits has black red blue white Black red blue white then a black blue white. So if I wanted to re feed that within my new conduit I don’t count the neutral for the black red blue circuits but I do count it for the black blue circuit
Bingo! (y)

And that example would be 9 CCCs, not 10.
 
Top