4W Lighting Panels is connected to 3 wire Distribution Panel

Rez83

Member
Location
California
Occupation
Electrical Engineer
Hello Everyone

Currently dealing with a situation that the lighting panel 480/277 4W is tied to 480V, 3P,3W distribution panel upstream, and there is no available neutral from the source panel to use in the 4W lighting panel and feed lighting at 277V. What would be the best solution to provide neutral to the lighting panel board? Is adding 480/480 V isolation transformer with neutral on the secondary will do the work? Or Should we bring neutral wire from another 4W panel board? please advise the code compliant and cost effective way to resolve the issue?
 
IMO the only real solution is to use a 480-480Y/277 volt transformer to create a neutral. You cannot just grab a neutral from somewhere else. What's the total load?

Welcome to the Forum.
 
Thank you for the response, I have about 90kVA Demand Load. what would be the problem if I run neutral from main switchgear?
 
Options to possibly consider:

- pull a new neutral to go with the feeder circuit feeding the existing panelboard, assuming the system feeding it has a neutral point

- use an isolation transformer

- rewire the lighting to a different panelboard that has a neutral

You cannot bring a neutral from a different panelboard. The neutral must originate from the same source and be wired in the same conduit or cable as the ungrounded conductors.
 
.... what would be the problem if I run neutral from main switchgear?

If you don't run the neutral with the existing ungrounded conductors it's a code violation and possibly an inductive heating hazard. See 300.3 and 300.20.

If you have space in the existing conduit to pull a neutral to the existing panelboard and it's worth shutting it down to do that to avoid using a transformer, then that would probably be best.

Hope the panelboard is sized for the additonal load.
 
If you don't run the neutral with the existing ungrounded conductors it's a code violation and possibly an inductive heating hazard. See 300.3 and 300.20.
Thank you for the response. My initial thought was to use isolation transformer, I will also consider rewiring to 4 wire source if there is any. due to lead time issue of getting new transformer, the second option might be an easy solution. Just need to check the availability of 4 wire panel with adequate size of breaker,
 
An “oops” existing lighting was 480? Retrofitting new LED? Some lighting manufacturers used a multi tap ballast for each fixture as an auto transformer to change the 480 to 277. If it’s not a whole lot of fixtures, that may be a route to go. An isolation transformer would probably be the quickest route.
 
Thank you for the response, I have about 90kVA Demand Load. what would be the problem if I run neutral from main switchgear?
None as long as it is in the same raceway or cable that contains the ungrounded conductors for that feeder.
 
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