NEC tap rule feeding multiple OCPD's

[JBRT]

Question in short:
Does the NEC tap rule allow a feeder tap to supply more than one OCPD?

Question in more detail:
240.21(B)(2) requires that taps under 25 ft terminate in a single circuit breaker or a single set of fuses.

However, this requirement is not present in 240.21(B)(1) for taps 10 ft or less.

So, I assume that taps under 10 ft can feed multiple overcurrent protective devices, given that the conductors are sized based on the combined loads?

For example, a tap from a feeder to a circuit breaker which is connected on the line side with another breaker using the same wire size as the tap conductors and using double wire ferrules, thus creating "one" whole tap conductor.

 

[wwhitney]

However, this requirement is not present in 240.21(B)(1) for taps 10 ft or less.

My comment is that the corresponding rule in 240.21(B)(1) says that the tap ampacity shall be "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors." (Along with an exception for certain equipment with specified minimum conductor size.)

So if you are using the first part of that "or" phrase, the tap conductors would have to land in a single piece of equipment with multiple overcurrent devices, and the ampacity would have to be not less than the rating of that piece of equipment.

Not sure what a practical example of using this allowance would be. If the equipment having multiple overcurrent devices is a panelboard, 408.36 is going to require a single OCPD to protect the panelboard. Although maybe Exception 2 would let you use an MLO panelboard with only 2 OCPD in it? E.g. 10' feeder taps protected on their supply side at 600A, then 60A tap conductors going to a 60A MLO panelboard containing just (2) 30A OCPD?

Cheers, Wayne

 

[JBRT]

My comment is that the corresponding rule in 240.21(B)(1) says that the tap ampacity shall be "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors." (Along with an exception for certain equipment with specified minimum conductor size.)

So if you are using the first part of that "or" phrase, the tap conductors would have to land in a single piece of equipment with multiple overcurrent devices, and the ampacity would have to be not less than the rating of that piece of equipment.

Not sure what a practical example of using this allowance would be. If the equipment having multiple overcurrent devices is a panelboard, 408.36 is going to require a single OCPD to protect the panelboard. Although maybe Exception 2 would let you use an MLO panelboard with only 2 OCPD in it? E.g. 10' feeder taps protected on their supply side at 600A, then 60A tap conductors going to a 60A MLO panelboard containing just (2) 30A OCPD?

Cheers, Wayne

Thanks for your comment.

I understand your reasoning, but I am still wondering, if the tap conductors should always land on a single overcurrent protection device, then why 240.21B(1) part (a) talks about combined loads?

240.21(B)(1)​

​

(1) The ampacity of the tap conductors is:​

​

a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and​

​

b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.​

The practical example in my case is a tap on the line side of the main breaker in an Industrial Control Panel (UL508A). This tap goes to two small circuit breakers for control circuits: one 1A breaker for voltage presence indicator lights and one 6A breaker for an emergency stop circuit via shunt trip coil. So, the tap doesn't land on a single circuit breaker.

 

[jaggedben]

I think the answer is that while the 10ft tap rule technically allows terminating in equipment with multiple OCPDs, practically speaking this is overridden by 408.36 because that equipment is almost always going to be a panelboard.

 

[JBRT]

I think the answer is that while the 10ft tap rule technically allows terminating in equipment with multiple OCPDs, practically speaking this is overridden by 408.36 because that equipment is almost always going to be a panelboard.

But in my case, the tap conductors do not land on external equipment or another panelboard but they land on circuit breakers in the panel itself. The tap conductors do not leave the panel enclosure.

 

[jim dungar]

Are you building a "control panel"?
The NEC doesn't apply internal to a Listed control panel. You would need to follow the Listing standard such as UL508A.

 

[JBRT]

Are you building a "control panel"?
The NEC doesn't apply internal to a Listed control panel. You would need to follow the Listing standard such as UL508A.

Ok I see...
Yes, I'm designing a listed control panel and in fact I am following UL508A, but since this standard doesn't say anything about taps before the main breaker, I went looking in the NEC. A lot of UL508A is based on the NEC I think, since there are lots of similar phrases.

 

[jim dungar]

A lot of UL508A is based on the NEC I think, since there are lots of similar phrases.

Yes it is.
The NEC does allow a tap to feed multiple OCPDs as does UL508E.
Article 408.36 was added only for panelboards.

If you are going to use a power distribution block, be sure to check its SCCR.