Mixed use branch circuit

[jackvis]

Does this comply with the NEC? I don't believe so, but I can't find a reference to this kind of arrangement. This is from a new 4oo amp, 480 volt, 4 wire service supplying high school football field lighting. My question concerns a branch circuit supplying security lights behind the bleachers on opposite sides of the field. A 15 amp, 2 pole breaker in the 4oo amp panel passes through a contact of a lighting contactor then to terminal blocks where it is split. One pair of 480 volt single phase conductors leaves the terminal blocks and supplies 4 400w luminaires behind the West bleachers. Another pair of conductors leave the same terminal blocks along with a neutral conductor from the same panel board, and supply 2 277 volt circuits to 12 70w luminaires behind the East bleachers.

 

[petersonra]

Re: Mixed use branch circuit

I don't see how this is a code violation.

 

[iwire]

Re: Mixed use branch circuit

I agree with Bob, it sounds good to me.

You have a 2 pole breaker feeding a multiwire branch circuit.

 

[peter d]

Re: Mixed use branch circuit

I think the issue here is whether or not the breaker is "common trip." I would assume a multipole 480 volt breaker would be "common trip" by "common sense", but then again I never deal with 480 equipment so I don't know for sure.

[ September 28, 2005, 05:29 PM: Message edited by: peter d ]

 

[charlie b]

Re: Mixed use branch circuit

Originally posted by iwire:You have a 2 pole breaker feeding a multiwire branch circuit.

I see it as a multi-wire branch circuit with a tap to another circuit. The "multi-wire" part is the 3-wire (phase, phase, neutral) going to the 277 volt lights (840 VA total). The "other circuit," the circuit that is tapped into the first one, is the 2-wire (phase, phase) going to the 480 volt lights (1600 VA total).

This should still be code-compliant. But you need to get there via 240.21(A) and 210.19. The key requirement is that each conductor must have a sufficient ampacity for the load it will carry. But as the total load is about 5 amps (2,440 VA at 480 volts single phase), that should not be hard to achieve.

 

[iwire]

Re: Mixed use branch circuit

Originally posted by charlie b:
I see it as a multi-wire branch circuit with a tap to another circuit. The "multi-wire" part is the 3-wire (phase, phase, neutral) going to the 277 volt lights (840 VA total). The "other circuit," the circuit that is tapped into the first one, is the 2-wire (phase, phase) going to the 480 volt lights (1600 VA total).

The NEC would not call it a tap as the overcurrent protection and the conductor sizes match.

We could call it a branch circuit fed from a multiwire branch circuit.

 

[charlie b]

Re: Mixed use branch circuit

Originally posted by iwire: The NEC would not call it a tap as the overcurrent protection and the conductor sizes match.

I don't see it that way. The NEC does not define "tap," and I've always found the term perplexing. But from the first sentence of 240.21, I get the notion that a "tap" is a point at which an ungrounded conductor (going to some load) gets its origin from another ungrounded conductor, without there being an overcurrent protective device at that point to serve the new conductors.

It becomes OK or Not OK, depending on the sizes of the conductors, their lengths, and the ratings of overcurrent protective devices at the beginning or end of any given conductor. The "Tap Rules" give us the Ok / Not OK criteria. But the "tap" itself is merely the point of connection of the new conductors.

 

[don_resqcapt19]

Re: Mixed use branch circuit

240.2 ... Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

The key point is that the conductor is not a tap conductor if protected at its ampacity.
Don

 

[iwire]

Re: Mixed use branch circuit

Originally posted by charlie b:
I get the notion that a "tap" is a point at which an ungrounded conductor (going to some load) gets its origin from another ungrounded conductor, without there being an overcurrent protective device at that point to serve the new conductors.

That very inclusive definition would get ugly fast.

Assume 20 amp OCP and 12 AWG copper on the following questions.

If I run a home run from panel to an outlet would any conductors past that outlet be taps?

If I run a home run from the panel to a centrally located JB and go four different directions from there?

Would I have 4 taps or 3 taps and one branch circuit continuing on?


For what it is worth I consider the design described in the opening post to be poor.

The way it is set up one fault takes out the lighting on opposite sides of the field.

The homeruns are already separate so adding another breaker would be quick and could keep half the lighting going when a fault happens.

Bob

 

[charlie b]

Re: Mixed use branch circuit

OK Don and Bob. I surrender. That's what I get for relying on Article 100.

I think I'll go stand in the pillory for a while.