NEC tap rule feeding multiple OCPD's

J

JBRT

Member
Location
Belgium
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Electrical Engineer
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.
 
JBRT said:
However, this requirement is not present in 240.21(B)(1) for taps 10 ft or less.
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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
 
wwhitney said:
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
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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.
 
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.
 
jaggedben said:
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.
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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.
 
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.
 
jim dungar said:
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.
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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.
 
wwhitney said:
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?
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There was some I-Line panels that specifically allowed in the instructions to feed the main lugs with service conductors and have six breakers as service disconnects installed. 2020 NEC however doesn't allow to set up services that way anymore but I would sort of think those particular panelboards would been allowed that way for 10 foot feeder tap as the supply as well. Not all I-Line panels were like this only certain ones. I don't think you could find any with less than 600 amp bus that allowed this.
 
Up until the 2020 change to 230.71, the following appeared in 408.36.
Exception No. 1:
Individual protection shall not be required for a panelboard used as service equipment with multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panelboard assembly.
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don_resqcapt19 said:
Up until the 2020 change to 230.71, the following appeared in 408.36.
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Correct.

You still could supply a separate building via a feeder to a main lug panel and have up to six main disconnecting means in that panel as long as the overcurrent protection of the feeder does not exceed the rating of the panelboard.

Could you use the panelboard like I mentioned before as the possible multiple overcurrent devices with the 10 foot tap rule since it doesn't specifically limit you to landing the tap into a single overcurrent device?

How about a if the overcurrent device ahead of the tap conductor is still equal or less than the rating of the panelboard regardless what the ampacity of the tap conductor may be? Combination of the overcurrent devices supplied likely still not allowed to exceed ampacity of the tap conductor though.
 
kwired said:
Correct.

You still could supply a separate building via a feeder to a main lug panel and have up to six main disconnecting means in that panel as long as the overcurrent protection of the feeder does not exceed the rating of the panelboard.

Could you use the panelboard like I mentioned before as the possible multiple overcurrent devices with the 10 foot tap rule since it doesn't specifically limit you to landing the tap into a single overcurrent device?

How about a if the overcurrent device ahead of the tap conductor is still equal or less than the rating of the panelboard regardless what the ampacity of the tap conductor may be? Combination of the overcurrent devices supplied likely still not allowed to exceed ampacity of the tap conductor though.
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Assuming there is a line side service disconnect you can do that.
 
The original topic was about tap conductors on the line side of the feeder protection (main breaker) in an Industrial Control Panel feeding multiple overcurrent devices in the same panel, not feeding a different panelboard.

In my case, the tap conductors feed two overcurrent devices of control circuits that may not be switched off by the main breaker and therefore are tapped on the line side of the main breaker.

As pointed out by Jim Dunglar, UL508A does apply on the Control Panel. I was just looking in the NEC because I didn't find an answer in UL508A.

So, if anyone knows the answer on my question based on the rules of UL508A, please let me know. Thanks.
 
jim dungar said:
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.
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This is what I do regularly in a control / MCC panel. Come from the main disconnect (fused) to a PDB. Then split to the individual branch circuit OCPD's. But this all stays within the confines of the same cabinet.
 
jim dungar said:
If you are going to use a power distribution block, be sure to check its SCCR.
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In power distribution block situation you generally can't "tap a tap". So the incoming conductor to the block needs to have ampacity that correlates with the overcurrent protection on the supply side. The outgoing smaller conductors are the "tap conductors".
 
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