EMT Design Question

[Doug Miller]

That's all he's *planning* to put in there -- what made you think otherwise?

[Scott Lurndal]

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Section 410-31 of the NEC (1999 Edition) states:

Fixtures shall not be used as a raceway for circuit conductors.

Exception #1: Fixtures listed for use as a raceway Exception #2: Fixtures designed for end-to-end assembly to form a continuous raceway or fixtures connected together by recognized wiring methods shall be permitted to carry through conductors of a 2-wire or multiwire branch circuit supplying the fixtures. Exception #3: One additional 2-wire branch circuit separately supplying one or more of the connected fixtures described in exception #2 shall be permitted to be carried through the fixtures.

Branch-circuit conductors within 3 inches of a ballast within the ballast compartment shall have an insulation temperature rating not lower than 90 degrees C such as Types RHH, THW, THHN, THHW, FEP, FEPB, SA and XHHW.

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Most consumer grade flourescents aren't listed as raceways. That pretty much leaves exception #2 as the guidance for this application. It also limits you to 2 two-wire or 1 three-wire and 1 two-wire branch circuits for the string of fixtures.

Do note the "recognized wiring methods".

Please also be aware that the temperature rating of the conductors being passed through must be at least 90c (THHN should suffice, but never use NM or NM-B)

scott

[Bill]

Scott.

There is only 1 15A branch circuit. However, I had planned for it to "split" through 3 switches in the switchbox and pass the resultant 5 wires--3 hot, 1 neutral, 1 ground, through the fixtures as necessary to power them. If I understand correctly, this would qualify as a single

2-wire branch circuit, wouldn't it?

TYVM! Bill

[Doug Miller]

Absolutely. It's still one circuit, and it's still a "two-wire branch circuit" despite there being four wires (the ground is not counted) because your three hots are derived from the same point.

In any event, since the exception permits a multi-wire branch circuit, that particular point is moot anyway. It's clearly a single circuit: there's only one single-pole breaker.

Which would include, presumably, being connected by a properly-installed section of EMT.

[Bill]

Thank you for your confirmation Doug!

[Scott Lurndal]

Yes. The extra wires in this case do not matter[*], since they'll sum to the maximum branch circuit current (15a, in this case). This is would not be considered a multiwire branch circuit, however, per article 100 and 210-4, which requires a potential difference between the ungrounded conductors.

In other words, you have multiple paths for the same branch circuit.

scott

[*] subject to raceway fill guidlines.