Tap conductors same size as feeder

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AJSmith135

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I have a question regarding 240.21(B)(1)

If a feeder is suitably protected and tapped to supply multiple panelboards. Is it acceptable for the panelboards to be MLO if the taps are the same size as the feeder?

Common sense tells me that the taps are still protected by the OCPD at the feeder from both overload and short circuits. They cannot be overloaded due to the feeder OCPD being at a lower current rating than the ampacity of the cable. For shorts circuits, a breaker at the termination wouldn't provide protection anyways it wouldn't see a fault on the cable.

However, per 240.21(B)(1)(b) they appear they must terminate into a OCPD.

Is there some exception that makes taps not considered taps if they are equal or greater than their feeder?

For what it's worth this is a current installation and I am trying to see if it is code compliant or not.

Thanks!
 
augie47

augie47

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Check the definition of a "Tap" in 240.2.
If you are connecting multiple conductors with the same of greater ampacity as the overcurrent device protecting them we tend to say we are "tapping" but that is not a "tap" by NEC definition therefore the 240.21 rules don;t apply and if your MLO panel buss is adequately rated the feeder OCP device can suffice per 408.36
 
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Carultch

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Massachusetts
AJSmith135 said:
Is there some exception that makes taps not considered taps if they are equal or greater than their feeder?
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This is a solution that I call "promoting a tap to a feeder". Once you "promote" a tap conductor to a size where it is considered protected by the feeder OCPD, it is no longer a tap, and you no longer need to think about the length constraints of 240.21(B).

We instinctively think of the conductor as a tap, because it is the third wire leaving what a manufacturer would call a tap connector. But the NEC only considers it a tap, when it is less than the ampacity than the feeder OCPD, that is protecting it.
 
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winnie

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Location
Springfield, MA, USA
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Electric motor research
If you have a fat wire and you splice on a skinny wire to feed a load, we often call that a tap.

But under the NEC it isn't a tap if the skinny wire is protected at its supply end at its ampacity. As @infinity describes, the wire protected at its ampacity is simply a splice.

If the wire is not protected at its ampacity, then the special tap rule permissions come into play.
 
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