Heres a head-scratcher, Ive never seen fluorescent installations wired this way before. I began an old factory/warehouse lighting retrofit earlier this week, the large room I began working in has about a hundred 3-lamp preheat F40T12 fixtures of unknown brand (ive seen these fixtures before, I believe theyre Sylvania-made), heres the odd thing, the fixtures are ran on 240v phase-to-phase! The supply conduit to each fixture contains two phases (each 120v to ground) and a ground wire. The ballasts in the fixtures have no branding or info whatsoever, and most are well-rusted. Has anybody heard of this before?? Its wired just like any ordinary preheat fluorescent circuit, but using two 120v legs instead of a neutral.

For 240V supply the series choke is good enough (it is the basic, most common circuit for 230V part of the globe), so no wonder someone used it.

240 volt preheat ballasts used to be readily available. I have an old Westinghouse catalog that lists them.

I understand the 240v installation allows for less copper as the wire size can be reduced or the circuit can run double the amount lights (compared to 120v). But where would one ever be able to source replacement ballasts here in the US? As far as I know preheat fluorescent ballasts were never available in anything other than 120v here.

Also found out quickly that the LED (line voltage) retrofit tubes that the customer wanted me to use are not going to work.

I understand the 240v installation allows for less copper as the wire size can be reduced or the circuit can run double the amount lights (compared to 120v). But where would one ever be able to source replacement ballasts here in the US?

Nowadays? Not available. At the time they were installed, though, they were readily available in the US.

I understand the 240v installation allows for less copper as the wire size can be reduced or the circuit can run double the amount lights (compared to 120v).

Here it is not just about the copper size, but the series choke ballast has way lower (more than 2x) losses than the "120V standard" autotransformer types, at the same time it is way cheaper to make (more than 3x - just a single coil, instead of the many windings and at least two core sections). I guess that was the main motivation to use the 240V for the lighting (if available at given place).
Later the efficiency was "solved" by using HF electronic ballasts, sufficing with just 120V, so quite big part of the motivation for 240V lighting installations disappeared.

But where would one ever be able to source replacement ballasts here in the US?

You may use European ballasts, the only drawback would be the ballast factor of about 0.8, which is still good enough in my eyes...

the fixtures are ran on 240v phase-to-phase! The supply conduit to each fixture contains two phases (each 120v to ground) and a ground wire. The ballasts in the fixtures have no branding or info whatsoever, and most are well-rusted. Has anybody heard of this before?? Its wired just like any ordinary preheat fluorescent circuit, but using two 120v legs instead of a neutral.

If its truly 240v, then its a split-phase like used in houses. Still a single phase (center-tapped transformer so you get 120v/240v).
Going phase-to-phase on 120v would be 208v. (this common setup/voltage in large commercial buildings)

@xmaslightguy No, this is an old delta 120/208/240 high-leg service which yields 240v between any three phases, phases "A" and "C" are 120v to neutral, and phase "B" (the "high leg") is 208v to neutral. The service youre thinking of is the typical Wye 208Y/120 which is much more common.

Actually I think youre at least partially right now that I think about it, this older delta service makes use of only two phases and two transformers, I almost never work on this type of service so I am not super familiar with it.

this older delta service makes use of only two phases and two transformers, I almost never work on this type of service so I am not super familiar with it.

Are you thinking of open delta?

@nogden, the service is 4-wire (three phases or "legs" and neutral), however the primary side of the transformers only uses two phases from the grid. There are large receptacles in the building (I assume for motors) that use all three phases without a neutral (I didnt think 3-ph electric motors could run on anything other than 120 degree phase angle).

I can't say I have ever heard of anything like this. Did you take any pictures of the ballasts?

I've never heard of this but it's not that surprising to me. What I don't understand is why you couldn't use line voltage LED tubes. All the ones I've seen are 120-277V. As far as replacement ballasts go, 120-277V electronic ballasts should do just fine.

All three LED retrofit tubes failed immediately when I tested them in one fixture, they are in fact rated for 120-277, but for whatever reason must need a neutral 0v connection. Im not sure why.

And yes, ive already begun retrofitted all fixtures to T8 with Advance F32T8 ballasts, which work fine on the phase-to-phase configuration. The customer might not be saving as much power compared to the 22w LED tubes, but F32T8's produce more light in my opinion and the customer is happy with the way it looks.

The old preheat ballasts look just like any other F40T12 preheat ballast, its a single coil ballast exposed (not potted) with spade terminals and that early PVC or rubber insulation that is super brittle and flakes off the wire when you bend it. It was also clear that others had issues finding 240v replacement ballasts for these lights prior to the advent of electronics as ive already come across two fixtures that have 80's rapid start ballasts in them, using only one 120v leg and using the ground as a neutral, leaving the other unused 120v capped off...not good.

Interesting. I have no good explanation for the failure of the LED tubes unless they're just not really rated for that voltage or were duds. The F32T8 solution sounds like a good one, and it allows the use of ballast-compatible LED tubes down the road.