conduit fill

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Use Tables 4 and 5 in Chapter 9

Chapter 5 gives you the area of the conductors-- so 3/0 THHN is .2679 sq. in. Now multiply by how many conductors you have and then do the same for 1/0.

Now add them together and go to Table 4 -- the first table is for EMT and look under the col. for more than 2 wires and find a conduit size that is at least as large as your calculation
 

steve66

Senior Member
annex C is only if all the conductors are the same size
You can still use annex C in this particular case - just look at how many 3/0’s fit in a certain size.

the 1/0 could be for medical equipment or other equipment that asks for a larger than normal ground. Or maybe it’s 3/0 wire on something like a 20A breaker and everything is upsized for voltage drop.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
You can still use annex C in this particular case - just look at how many 3/0’s fit in a certain size.

the 1/0 could be for medical equipment or other equipment that asks for a larger than normal ground. Or maybe it’s 3/0 wire on something like a 20A breaker and everything is upsized for voltage drop.
Sure you can do that sometimes but in some cases that wont work and you aren't guaranteed the smallest conduit. Imo, it is best to calculate when there are different sizes--
 

kwired

Electron manager
Location
NE Nebraska
You can still use annex C in this particular case - just look at how many 3/0’s fit in a certain size.

the 1/0 could be for medical equipment or other equipment that asks for a larger than normal ground. Or maybe it’s 3/0 wire on something like a 20A breaker and everything is upsized for voltage drop.
If it is a 20 amp circuit upsized for VD, then the EGC would also need to be 3/0.

Where might one need a 1/0 EGC with 3/0 ungrounded conductors? How about with a feeder tap from an 800 amp feeder?
 
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