Are there appreciable efficiency gains from 480 V vs 277 V 1

[wuddog]

I am not an electrical engineer.
Now that I got that out of the way, I have been asked if there is an efficiency advantage between 480V vs. 277V. Intuitively I said yes due to the lower amperage of the 480V, but I was then asked if I could prove it with numbers. At this point I am stumped.
The issue is that we have lights in a parking lot running at 277V. We are going to change them to LEDs that can run at 480V or 277V. The impetus for this change is obviously energy savings, but if we can run at an appreciable more efficient level at 480V we may want to do that. Keep in mind that we will be using the existing wiring which was for 277V so the wires will be oversized I would think. Is there a way to calculate or otherwise show numerically how the efficiency will differ?
I welcome any and all feedback.

Thanks

 

[Mbrooke]

A bit off topic, but where in the code does it require phase to phase connected lighting to have 2 pole switches? Unless the switch was a service disconnect, I see no need to break more than one pole in hot to hot connected lighting or two poles in 3 phase 3 wire circuits.

 

[jraef]

You are technically correct, as far as switching. But the Code requires an OCPD in all ungrounded conductors (240.15). If your OCPD is a circuit breaker, which is also being used as the switch, then it would be 2 pole. If you had 2 fuses or a 2 pole breaker, and you wanted a separate switch, then yes, the switch could be 1 pole.

Side note, and possibly important to this discussion: outdoor parking lot lighting cannot be more than 277V unless the luminaire is on a pole at least 22ft high, or on a wall at least 18ft off the ground (i.e.tunnel). 210.6(D)1


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Mbrooke]

Thanks for that, I completely forgot the height rule existed. It pays to be on forums like this!

As for the breakers you are correct, a disconnect/OCPD must open both all ungrounded conductors both manually and automatically.

 

[iceworm]

... Our main is 480 then it transforms to 277. We would bypass the transformer to achieve 480 throughout the system.

... That's what makes me wonder, what transformer is the OP talking about?

Well, one option is the system is HRG 480Y. Small xfm (75kva), 480D/480 grounded Y were installed to feed the 277V lighting. That's pretty common in most of the industrial facilities I work in.

Why exactly was this used instead of 480V lighting fed from the HRG 480? in addition to the reasons already given, I suspect it had to do with not having to have lighting contactors with 120V rated switches.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[davidbeach]

HRG systems also come with the requirement to have qualified electrical personnel on staff. If such existed, there probably wouldn't be much reason for a mechanical engineer to be asking about lighting voltage. My guess is that someone familiar with 3-wire 480V to motors doesn't realize that the 277V comes from the same service transformer. I could be wrong and if I am the lack of qualified electrical personnel is a far more important problem than the choice of lighting voltage.

 

[iceworm]

davidbeach (Electrical)31 Jan 15 17:58
HRG systems also come with the requirement to have qualified electrical personnel on staff. If such existed, there probably wouldn't be much reason for a mechanical engineer to be asking about lighting voltage. ...

True. But that wouldn't necessarily stop a mechanical project sort from looking into it.

davidbeach (Electrical)31 Jan 15 17:58
... My guess is that someone familiar with 3-wire 480V to motors doesn't realize that the 277V comes from the same service transformer. ....

I missed your point on this one.

davidbeach (Electrical)31 Jan 15 17:58
... I could be wrong ...

Yes, you could. The fact of 277V lighting and the existance of small lighting transformers, points to HRG 480 as a possible - even probable system. It certainly is in my world.

davidbeach (Electrical)31 Jan 15 17:58
... and if I am the lack of qualified electrical personnel is a far more important problem than the choice of lighting voltage.

True. Unless it is just a mechanical looking for what the boss asked for.

I'm not telling you (as in "all y'all plural), "The system is HRG 480." I'm saying HRG 480 fits the OP descriptions

ice



Harmless flakes working together can unleash an avalanche of destruction

 

[davidbeach]

Occam's Razor has never failed me in sorting out real-life problems and a 480/277V service falls on the simple side of the razor. But, if there is an HRG 480V system then it is imperative that the lighting remain on a solidly grounded system and off the HRG system. The risk of a ground fault in the parking lot lighting is just too great. Consider the case of a phase to ground fault somewhere in the critical process (that justifies the existence of the HRG) and while it is being tracked down, the parking lot lights come on and there just happens to be a ground fault on a different phase. Now you have a phase-phase fault through ground and a bunch of stuff that was never intended to carry fault current.

 

[iceworm]

Occam's Razor has never failed me in sorting out real-life problems and a 480/277V service falls on the simple side of the razor. ...

Never? Never? Well Hardly .... Yes, without needing to read Russel's, History of Western Philosophy, I agree one should investigate the simpler solutions first. However, at least half of my clients have HRG 480. One also has resistance grounded 13.8kV. It is not much of a step for me to see the OP posts as reasonably supporting HRG 480V.

... But, if there is an HRG 480V system then it is imperative that the lighting remain on a solidly grounded system and off the HRG system. The risk of a ground fault ...

In practice, at least two of my clients have the outdoor process area lighting operating on 480V HRG circuits. And yes, during the winter, it is normal for a few of the heads to fill with water and freeze solid. Ground detector light comes right on. Since these are very difficult to repair during the winter, often they are left until early spring. The usual practice is to track down the offender (usually the one that is blinking or out)and isolate. And yes, occasionally a second will fail before the first is tracked down. If the coordination is anywhere right it trips a 20A CB. Life (and the process) goes on.

So, no, it is not imperative the process area lighting remain on a solidly grounded system.

You are correct in that I would never recommend parking lot lights on the HRG system. Hard to justify parking lot lights as being process critical. Which, of course, explains the OP's small transformers.

Which has nothing to do with my statement:

... The fact of 277V lighting and the existance of small lighting transformers, points to HRG 480 as a possible - even probable system. It certainly is in my world.

That still looks valid to me - until the OP comes back and verifies NOT. I'll be okay if that happens. It is an alternative - not a sureity

ice


Harmless flakes working together can unleash an avalanche of destruction