# t 5 120v -277v ballast running on 347v



## Wingnut (Jan 31, 2010)

sparky105 said:


> Called today for some lighting issues and opened up a 347v fed t 5 fixture with 2 120 - 277 v ballasts
> Asked the warehouse guy how long it had been there and he said 2 years asked him how long it was not working he said 2 or 3 weeks
> WTF 2 years to let the smoke out ?:blink:


 
They don't last that long at 277v..


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## Big John (May 23, 2010)

I'd be really hard pressed to believe that a ballast would run at 125% of rated voltage for two years.

Someone should check me on this, but I believe the maximum voltage a piece of equipment is required to accept is +6% of nominal, which in this case would mean that ballast would top out at 293.6 volts. That's an awful long way from 347. 

I think warehouse guy is either talking out of his backside, or else there's something else going on.

-John


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## Electric_Light (Apr 6, 2010)

They're nominal. Many ballasts are rated +/- 10% with minimal impact on output for continuous operation. Some, like Motorola were rated +/- 20% without failure. 


277 @ +10% is 305v 
If 347 nominal was running -10%, it is 312v 

If +10% was the limit for proper (correct ballast factor) operation, and 347v was on the low end, this isn't surprising.


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## Big John (May 23, 2010)

Electric_Light said:


> They're nominal. Many ballasts are rated +/- 10% with minimal impact on output for continuous operation. Some, like Motorola were rated +/- 20% without failure.
> 
> 
> 277 @ +10% is 305v
> ...


 Are those factory standards, or is that ANSI or NEMA? I thought it might be more than 6% but that's the only NEMA standard I've come across.

-John


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## sparky105 (Sep 29, 2009)

that is what I was thinking however the ballasts were OEM to the fixture and the fixture had the normal layer of dust build up. I called a couple my co workers and they say what you guys say should not last for any period of time . One of the guys wondered if there might be some kind of voltage choke or something in the electronics I'm still baffled.


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## HARRY304E (Sep 15, 2010)

sparky105 said:


> that is what I was thinking however the ballasts were OEM to the fixture and the fixture had the normal layer of dust build up. I called a couple my co workers and they say what you guys say should not last for any period of time . One of the guys wondered if there might be some kind of voltage choke or something in the electronics I'm still baffled.


 It is possible that the ballast's were missmarked and were suposed to be 347 volts and they just died early.


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## sparky105 (Sep 29, 2009)

HARRY304E said:


> It is possible that the ballast's were missmarked and were suposed to be 347 volts and they just died early.


hmm that is something I never thought however I think unlikely


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## Electric_Light (Apr 6, 2010)

Big John said:


> Are those factory standards, or is that ANSI or NEMA? I thought it might be more than 6% but that's the only NEMA standard I've come across.
> 
> -John


I'm not sure if it's part of ANSI specs. 

If you look in ballast specifier sheets, +/- 10% for indefinite use is common these days. (so, 108 to 305v). If you go outside these range it might adversely affect output, ignition process, or fail prematurely. Just how much it will tolerate depends on the design. 

I believe the cheaper ones use components with very close tolerance, i.e. 85C operation and 90C caps, where as better ones use 105C caps. 

Older electronic ballasts that used magnetic front end varied in power consumption and light output roughly proportional with input voltage, so when utility voltage went up a few percent, so did power use. 

Almost all the new electronic ones are auto-compensating. If voltage goes up 10%, current goes down 10% (assuming same PF) and maintains same wattage.


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