Help understanding Outside taps of unlimited length- 240.21(B)(5)??

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greenspark1

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A coworker recently brought this to my attention. Apparently you can tap a feeder and not provide OC protection until you get to the load, as long as you run outside a building and follow the other requirements of 240.21(B)(5). This seems counterintuitive since you could have a long run of tap conductor that could develop faults and would never trip the upstream device (on the feeder). Am I reading this correctly? What is the logic here?

The situation I have is 600A feeders being tapped with #12 wires outside and run up to 50' before a set of fuses are installed.
 
If the outside portion is carrying fault current and gets real hot, what is it going to burn down in comparison to a feeder tap inside a building?

There is probably more to it then that, but start with that reasoning.

Why can we run service conductors all the way around a building on the outside, but need to hit an overcurrent device very soon after entering the building? At least the feeder does have some protection compared to what the service conductor may not have.
 
Well yes you won't burn down a building. But the point where you make the splice could still overheat, melt the insulation, and then have an issue on the feeder.

My coworker's example would involve tapping the feeder in an outdoor switchgear. It's not clear if it can follow this unlimited tap rule.
 
greenspark1 said:
Well yes you won't burn down a building. But the point where you make the splice could still overheat, melt the insulation, and then have an issue on the feeder.
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I think that is exactly what the section allows.

My coworker's example would involve tapping the feeder in an outdoor switchgear. It's not clear if it can follow this unlimited tap rule.
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If it is outside for sure.
 
Here is the section

240.21(B)(5) Outside Taps of Unlimited Length. Where the conductors
are located outdoors of a building or structure, except
at the point of load termination, and comply with all of
the following conditions:

(1) The conductors are protected from physical damage in
an approved manner.

(2) The conductors terminate at a single circuit breaker or
a single set of fuses that limit the load to the ampacity
of the conductors. This single overcurrent device shall
be permitted to supply any number of additional overcurrent
devices on its load side.

(3) The overcurrent device for the conductors is an integral
part of a disconnecting means or shall be located immediately
adjacent thereto.

(4) The disconnecting means for the conductors is installed
at a readily accessible location complying with one of
the following:

a. Outside of a building or structure

b. Inside, nearest the point of entrance of the conductors

c. Where installed in accordance with 230.6, nearest
the point of entrance of the conductors
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It is worth noting that (4)(c) allows the conductors to travel inside a building as far as you want as long as you follow the rules in 230.6.
 
iwire said:
Here is the section



It is worth noting that (4)(c) allows the conductors to travel inside a building as far as you want as long as you follow the rules in 230.6.
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Basically gives them a lot of the same treatment allowed when dealing with service conductors.
 
iwire said:
Consider that the bonding point can be at the disconnecting means making it very much like a service. No EGC.
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How so? You need either a supply side bonding jumper (in the case of a SDS) or an EGC in the case of a tap circuit.
 
Actually I think 240.21(B)(5)(2) is the most notable in that code section.

(2) The conductors terminate at a single circuit breaker or
a single set of fuses that limit the load to the ampacity
of the conductors. This single overcurrent device shall
be permitted to supply any number of additional overcurrent
devices on its load side.
 
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