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Neutral(s) for step dimming ballast fed by 2 circuits?

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  • jonathankpa
    replied
    Thanks

    Originally posted by david View Post
    From your description I assume 40 ballast are feed from LP-1 and LP-2 and by the way you are switching the ballast the assumption would be two circuits would be needed for the load.
    Is there a reason LP-1 could not supply both ballast leads for 20 fixtures and have LP-2 supply both ballast leads for the remaining 20 fixtures. I’m guessing the answer to that to be you would need one additional step dimmer
    David - I believe this is the answer - to simply feed given fixtures from 1 circuit. I like simple answers; thanks so much for your time & help. I may post a wiring diagram later for any who are interested, once I digest it all.

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  • jonathankpa
    replied
    Response

    Thanks for the thoughts so far - thinking it over.

    Originally posted by iwire View Post
    I agree with GoldDigger, you can't supply these fixtures from two separate panels.
    iwire - FYI this is two different circuits, on the same phase, out of *one* panel.

    Leave a comment:


  • david
    replied
    Originally posted by david View Post
    From your description I assume 40 ballast are feed from LP-1 and LP-2 and by the way you are switching the ballast the assumption would be two circuits would be needed for the load.
    Is there a reason LP-1 could not supply both ballast leads for 20 fixtures and have LP-2 supply both ballast leads for the remaining 20 fixtures. I’m guessing the answer to that to be you would need one additional step dimmer
    i should add step dimming by adding additional switching

    Leave a comment:


  • david
    replied
    Originally posted by GoldDigger View Post
    As far as I can see the only code compliant way to wire that configuration with one neutral and two hots at a fixture would be to use an MWBC. Which you do not have if both hots are derived from the same hot.
    Otherwise using a common neutral wire for both hots at the luminaire would, as you say, require connecting the two branch neutrals together, which is not compliant.
    i also believe a multi wire circuit using LP-1 and say LP-3 instead of LP-2 would work for the neutral current since this is a three phase 277 volt panel except you would be supplying the ballast with 480 volts

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  • david
    replied
    Originally posted by jonathankpa View Post
    We have designed a large room with 40 light fixtures, each with a step dimming ballast. Two 277V circuits feed this area from a 480/277V, 3 phase, 4 wire panel. Say the circuits are LP-1 and LP-2 (both on phase A). For our purposes, each ballast has 3 wires: a neutral, and 2 hots. (Feeding either hot lights the fixture's lamps at 50% brightness; feeding both hots lights the lamps at 100% brightness.) Each circuit (LP-1 & LP-2) has 2 wires, of course, a hot & a neutral. However, note that while the ballast has 2 hot leads, it only has 1 neutral lead. Neutrals for the 2 circuits were originally sized based on load, and are #10 from the panel to a local J-box. From the J-box to each fixture, #12's were run. The neutral lead in the ballast itself is #16. The neutral home runs were originally sized correctly for the load of the fixtures on that circuit. The electrician has asked: what neutrals does he connect? Currently he's connecting 1 neutral per fixture: the neutral for circuit LP-1. The neutral for LP-2 (again, same phase, same panel) isn't connected or run. Will this suffice? Or must he run the neutral for LP-2 also, in essence creating a parallel neutral feed from the panel, and connect both neutrals to the ballast's neutral lead? Please educate me. What's the right way to wire the neutrals here? Thanks for your time helping on this - you guys make the world safer and smarter.
    From your description I assume 40 ballast are feed from LP-1 and LP-2 and by the way you are switching the ballast the assumption would be two circuits would be needed for the load.
    Is there a reason LP-1 could not supply both ballast leads for 20 fixtures and have LP-2 supply both ballast leads for the remaining 20 fixtures. I’m guessing the answer to that to be you would need one additional step dimmer

    Leave a comment:


  • iwire
    replied
    I agree with GoldDigger, you can't supply these fixtures from two separate panels.

    Leave a comment:


  • GoldDigger
    replied
    As far as I can see the only code compliant way to wire that configuration with one neutral and two hots at a fixture would be to use an MWBC. Which you do not have if both hots are derived from the same hot.
    Otherwise using a common neutral wire for both hots at the luminaire would, as you say, require connecting the two branch neutrals together, which is not compliant.

    Leave a comment:


  • Neutral(s) for step dimming ballast fed by 2 circuits?

    We have designed a large room with 40 light fixtures, each with a step dimming ballast. Two 277V circuits feed this area from a 480/277V, 3 phase, 4 wire panel. Say the circuits are LP-1 and LP-2 (both on phase A). For our purposes, each ballast has 3 wires: a neutral, and 2 hots. (Feeding either hot lights the fixture's lamps at 50% brightness; feeding both hots lights the lamps at 100% brightness.) Each circuit (LP-1 & LP-2) has 2 wires, of course, a hot & a neutral. However, note that while the ballast has 2 hot leads, it only has 1 neutral lead. Neutrals for the 2 circuits were originally sized based on load, and are #10 from the panel to a local J-box. From the J-box to each fixture, #12's were run. The neutral lead in the ballast itself is #16. The neutral home runs were originally sized correctly for the load of the fixtures on that circuit. The electrician has asked: what neutrals does he connect? Currently he's connecting 1 neutral per fixture: the neutral for circuit LP-1. The neutral for LP-2 (again, same phase, same panel) isn't connected or run. Will this suffice? Or must he run the neutral for LP-2 also, in essence creating a parallel neutral feed from the panel, and connect both neutrals to the ballast's neutral lead? Please educate me. What's the right way to wire the neutrals here? Thanks for your time helping on this - you guys make the world safer and smarter.
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