Electrician Talk banner
1 - 10 of 10 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
Guys, is it typical to install a parallel setup with all of your conductors in the same conduit? I have a set of plans here that call for two sets of 2/0 to be installed in a 3" conduit for a 200 amp 3 phase panelboard. The run is only about 80'...
 

·
Registered
Joined
·
1,544 Posts
It's done all the time. The only real issue would be the need to derate due to having more than 3 current carrying conductors in a raceway.

The real issue here is why someone would parallel 2 sets of 2/0 for a 200 amp feeder when all you need is 1 set of 3/0. Seems like a waste of copper.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #4 ·
no, its copper and I agree...why pull two sets when I could pull one? The engineer is in question here...
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #5 ·
and here is another question I have. In calculating the load side or feeder for the transformer I have applied a continuous load calculation. primary calls for 90 amps so I feed the transformer with #2 copper. Do I have to apply continuous load to the secondary conductors?
 

·
Ahead of the class
Joined
·
71 Posts
yes the secondary ocpd must be sized per 125% continuous load and the wire must be sized accordingly. dont forget to derate the wires as well if its three phase.
 

·
Administrator
Retired EC
Joined
·
23,650 Posts
Can you show me a code article that requires the overcurrent protective device to be 125% on the secondary side.
 

·
Administrator
Retired EC
Joined
·
23,650 Posts
sorry i meant 215.3, 240.6 is the ocpd ratings
215.3 is for feeders that supply both continuous and noncontinuous load. This mean that the feeder must be sized at 100% for noncontinuous loads and 125% for the loads that are continuous. That does not mean the overcurrent protective device on the secondary must be 125%. I believe 125% is the max it can be set to-- look at table 450.3(A)

I am no expert on this but this is how I see it. In fact sometimes the secondary conductors don't need an ocpd-- look at 240.21(C)
 
  • Like
Reactions: Pete m.

·
Ahead of the class
Joined
·
71 Posts
ok so if you size the feeders for 125% of the continuous load, why not use the max 125% ocpd and get the most out of your transformer? just my two cents. and yes you dont need secondary protection when the transformer is feedin a dedicated load or no lighting or branch circuits.
 
1 - 10 of 10 Posts
Top