Power Distribution Options - 150 Amps

[califflash]

Tspisak,

I do not have the NEC in front of me at the moment but you DO NOT have to size the wire of the individual taps to carry the full current allowed by the primary over current device. You do, however, have to size the branch protector that the tap feeds to protect the wire. For example you can tap off a 000 feed with 10 awg wire, with the appropriate device (ie: pdp), but that tap must connect to a branch protector rated at no more than 30 amps, or less depending on de-rating factors. This is quite common.

On a side note, if your fusing is located in one location, you may use a bus bar and terminal lugs to feed the individual branch protectors. The sum of the branch protector ratings cannot exceed the rating of the bus bar, lugs, or fusing. This is my preferred method because it cuts down on the number of wires, labels, and assembly time.

 

[DwSoFt]

If you use the distribution blocks then why are you running a ~200 amp wire into a 30 amp fuse?

#1 AWG Is not approx 200 amp wire. #3/0 AWG copper is 200A.

But I am curious why such a large Conductor to a 30a fuse holder. .. I mean voltage drop that must be a pretty long run... lol

 

[jraef]

TWS - Thanks! That is what I needed. I thought that you had to size ALL of the conductors for the fuse above the PDTB in case of a direct short to ground.

All of my power distribution is in the same cabinet so I am good to go.

INSIDE of the same enclosure, the risk of one of those #10 wires going to ground is accepted as being small, as long as the distance is kept short, hence the 10ft. limitation. If any one of those conductors must leave the box, it will have to terminate on a breaker or fuse first.

There are also numerous bus bar distribution systems out there to accomplish this as well, most of the major motor control component mfrs offer them now. So your power would come into the main disconnect, then out of it to feed a set of bus bar rails. Then each sub-circuit would clamp onto those bus bar rails with a SCPD device (fuse holder, circuit breaker or motor protection circuit breaker, combination motor starters) to feed your individual loads. More expensive hardware, less install time.

 

[Bering C Sparky]

Just so the OP knows,
If you do need to run any of the tap conductors outside of the same enclosure as your main disconnect you are tapping from, you can do this BUT...

You cannot make your runs more than 25 ft long (see 25' tap rule), you must terminate into a single circuit breaker or set of fuses, the tap conductor must increase in size to 1/3 the size of the circuit you are tapping from (for 150 amp that would be #6 tap conductor) and your wiring must be suitably protected from phyiscal damage. (I think back in the day the physical damage part stated must be in conduit)

Unless you have something special going on or already have the enclosure you are working out of, why would you not just purchase a 150 amp main breaker panel with sufficent poles to accomidate your installation. (Would probably be a lot cheaper and you could lock out the individual breakers alot easier than 6 double or triple pole fuse blocks)

BCS