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#128341 - 01/19/03 04:13 AM unbalanced 3 phase load
bryan Offline
Junior Member

Registered: 01/19/03
Posts: 6
will an unbalanced phase/neutral load in a 3 phase 120/240 system cause flourescent ballasts to go bad?

#128342 - 01/19/03 06:42 AM Re: unbalanced 3 phase load
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Not normally, unless the imbalance is causing a crucial voltage problem (too low or too high), or if the loads are bouncing high Harmonic Distortion all around.

Also, placing 120 VAC loads on the "B Phase" of a 120/240 VAC 3 Phase 4 Wire Delta will cause failures, regardless of load balance!
(Line "B" will have apx. 208 VAC to ground)
I mention this because your post included system specs of 120/240 VAC 3Ø

Please add a little more information (frequency of failures, types of failures, system data, etc.), so we can come up with a more complete answer.

Scott35 s.e.t.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128343 - 01/19/03 07:34 AM Re: unbalanced 3 phase load
bryan Offline
Junior Member

Registered: 01/19/03
Posts: 6
this building is 20+ yrs old. the ballasts are magnetic and many are probably original. typically, either the inboard or outboard ballast fails. the failure is infrequent, but the tenent wants to upgrade the lighting to electronic t8 fixtures. since so many circuits have been added with no apparant thought to keeping the load balanced, I am concerned that electronic ballasts could fail. Lighting shares circuits with wall receps. what a spider web they have above ceiling. Why would the b phase have 208vac to ground?

#128344 - 01/19/03 08:53 AM Re: unbalanced 3 phase load
electric-ed Offline

Registered: 07/08/02
Posts: 184
Loc: Canada
Why would the b phase have 208vac to ground?

The high leg to neutral voltage is the vector sum of one full transformer winding (A) and half of another (C).

#128345 - 01/19/03 09:15 AM Re: unbalanced 3 phase load
bryan Offline
Junior Member

Registered: 01/19/03
Posts: 6
okay, so now i understand the voltage to ground on the b phase. I've been going on what the tenent is telling me so i believe i need to put my meter on it and see exactly what is what. since there are no apparant problems with 120 volt recep circuits I'm starting to think that their service is 120/208. they have no xfrmr of their own, just the poco xfrmr outside of the blding.

#128346 - 01/19/03 10:13 AM Re: unbalanced 3 phase load
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Excellent illustrations, e-ed. Just one side note to add…

The acceptable ANSI Standard voltage range for 120V 60Hz utilization equipment is 110-127, with some non-lighting cases down to 106.

[This message has been edited by Bjarney (edited 01-19-2003).]

#128347 - 01/19/03 05:12 PM Re: unbalanced 3 phase load
lighthouse Offline

Registered: 01/02/03
Posts: 141
Loc: philadelphia pa 19125
bryan....i would have to say it's the age of the ballast(20 plus years)is the reason.go with the electronic ballasts.there more energy efficient.with a savings of 26% to 38%.over standard ballasts. and a reduce amp draw per ballast.

what size fluorescent light fixtures are we talking about.4 foot 2 tube or 4 tube
the old standard 4 tube fixture will have 2 ballast in it.with an electronic ballast in the same fixture you only need one ballast.


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