DC feeder circuit 1

[buzzp]

We have 125VDC in our plant, which comes through one breaker (50A). The load side of this breaker feeds many other smaller breakers (15A). One wire is ran from the load side of the 50A breaker to one 15A breaker. This in turn is 'daisy chained' to the other 15A breakers in the panel. My question is: does the same conductor rules apply for 'feeders' that are DC? I am trying to size the conductors according to code but I do not believe this is addressed in article 220 (because its DC). My feeling is to size these using the wires that make up the daisy chain (50A).
Any comments or other suggestions? My code experience is almost nil so please keep that in mind as you bash me (hehe). Thanks in advance.

 

[busbar]

Convservatively, my guess is to base the installation on Article 240 and not 220. Keep all jumpers between MCCBs 50-ampere rated. Assure that everything in the daisy chain {except maybe the “last” 15A jumpers} are minimum 50A rated. Plan on using breaker terminals that will unquestionably be intended for two 50A stranded conductors, like a face-to-face pair of tool-compressed seamless-copper-tubing terminals, [not 'setscrew' type] secured with a machine screw and captive nut per pole.

 

[buzzp]

Busbar,
Your suggestions are the way I am planning on wiring this. Someone told me the wires could be smaller given the configuration. I did not find this in the NEC and have not heard of it before. To be safe, I will use the 50A to size all the wires on the load side of this breaker. Thanks for your suggestions.

 

[busbar]

Given that use of all-50-ampere wiring would intuitively be OK, the ‘permission’ to use anything less {in ANSI regions} would be acceptable by (99)NEC240-21—“tap rules”.

 

[buzzp]

"Tap rules", thats what I was looking for. Would these same rules apply to DC even though they do not explicitly say yes or no they don't (traditionally think of a feeder as AC)? Thanks busbar. I am going to give you a star for helping me out. Take care.

 

[busbar]

buzzp, (99)NEC240-21 does not directly mention DC one way or another, but some rules apply to transformer circuits, so clearly not applciable to DC. {That may have changed in the 2002 edition.}

 

[buzzp]

Ooops! Star should be there now.