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277v with 120v fixtures

Posted by robjamell (My Page) on
Fri, Apr 29, 11 at 17:58

Hello - I have (3) 12v Progress lighting fixtures for a conference room. We will be using very low wattage in the fixtures. I tied them into the fluorescent ceiling tile type light fixtures that were existing. I then realized the existing fixtures have 277v single phase wiring.

What are my options and why does the fixture say 120v max as it would seem to me if I used a 277v bulb, the current draw would be less.

thanks in advane.


Follow-Up Postings:

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RE: 277v with 120v fixtures

You can only use fixtures at their rated voltage.

It is more than just the bulb voltage.


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RE: 277v with 120v fixtures

12v Progress lighting fixtures for a conference room

If you wire a 120v transformer to a 277v line, you're just going to blow the transformer. Take the fixtures back and get ones with a transformer rated for 277v.

If that's a typo and you meant 120v, first off you aren't going to find many 277v lamps. Second, and more importantly, the fixture needs to be rated for the line voltage. It's a simple code issue.


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RE: 277v with 120v fixtures

It is much more than a code issue. Codes can be promulgated at the whims of people. The voltage issues involve the laws of physics which are not controlled by politics.


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RE: 277v with 120v fixtures

Am I the only one who is concerned that a DIYer is doing work in a commercial building?


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RE: 277v with 120v fixtures

NO YOU ARE NOT btharmy!

The person who wrote that original post should not only NOT be doing electrical work in a commercial setting, they should NOT be doing electrical work for pay!!!
They are profoundly unqualified.


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RE: 277v with 120v fixtures

I had typed a paragraph about unqualified persons doing work in a commerical building but then decided to delete it.


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RE: 277v with 120v fixtures

Guys - Thanks for all the replys and discussions.

Let me clarify a few things.

1)I am not doing this for pay. It is my own office that I rent.
2)The Progress fixtures take a standard med screw base bulb.
3)The already existing fixtures in the room that are controlled by a swith are 277v 4-bulb flourescent that are dropped into the drop ceiling grid.
4)I have already thought of some options but wanted some additional opinions as I prefer to not have to install a seperate wall switch for multiple cosmetic reasons
OPTION 1 - 277v relay
OPTION 2 - 277v to 120v transformer
5)I do not want to change the Progress fixtures for cosmetic reasons.

The main reason I posted this is to understand the theory behind. Here are my thoughts on that. It is my understanding that it is the flow of current that creates heat. For the same wattage of bulb it would seem that with 277v, the current draw would be lower and the fixture would experience LESS heat. In turn I am trying to learn why the fixture would have a voltage limit. I thought maybe because with the standard 120v, a wattage limit is normally given. It would seem to me that you could put, 120v 60w max or 277v 120w max and print a label accordingly. Just trying to understand why I am wrong.

Please help me to understand.


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RE: 277v with 120v fixtures

The resistance of the filament determines how much power the bulb will draw.

A 100 watt bulb designed for a 120 V system will be about 144 ohms once it is hot.
If you try and use the bulb on a 277 V system, it will draw (briefly before failing) 532 Watts, overheat the filament and burning out.

It may even produce a nice arc inside the bulb and then explode since the bulb is designed with internal spacing between conductors operating at 120 V, not at 277 V.

If you try to use a transformer above its rated/design voltage it is likely to draw excessive power in the input (primary) side and fail in a very short time with a lot of smoke, burning, and worse.
Transformers in metal covers (cans) can explode.

It is very unlikely your lease does not stipulate that any changes/alterations/etc. be done by a licensed electrician.
You are not the owner.


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RE: 277v with 120v fixtures

Rob, other than the legal issues of whether you as the tenant are permitted to work on the building's wiring (you're not, and you wouldn't be even if you owned it), there are the liability issues. If someone using your rewired conference room is somehow injured or killed by your wiring errors, you can be held legally liable. If you really want that on your shoulders, I suggest you buy the largest liability policy you can find.


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RE: 277v with 120v fixtures

I'm pretty sure that most liability policies don't cover illegal acts, which is what's happening here. I would imagine there may be criminal penalties as well should property be damaged or persons being injured or worse.

It doesn't matter if you understand the theory or not, you can not simply install whatever kind of fixture you'd like and stick some kind of label on it. This is why this kind of work should be performed by licensed professionals. Hire one!


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RE: 277v with 120v fixtures

Guys- Thanks for your concern about myself and others. Due to all of your suggestions, I will not be doing the work. I will hire a professional.

That being said, I thought this would be a good place to learn, but it seems I may have been wrong. I will try again in hopes someone can explain. BTW- I would NEVER consider putting a label on it.

With all due respect as it is obviously ME doing something wrong, I feel as though you guys do not fully read the post before replying.

Not from a LEGAL or LIABILITY standpoint, but simply from an understanding stand point, could someone explain what will happen if 277v 30w bulb is used in a fixture rated for 120v 60w max?
Why a 277v coil side relay cannot be used?
Why a 277v to 120v drop down transformer would not work?

Thanks again and please be assured that I am taking your recommendations to get a professional. I have already called.


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RE: 277v with 120v fixtures

The socket for a 120 V bulb is NOT going to be adequate or fit a 277 V bulb.

They are normally made different to prevent mistakes.

A 277 V to 120 V transformer will work just fine.
The problem is that it must be mounted in an enclosure or dedicated room, it cannot just be shoved above a ceiling (especially if the ceiling space is used as part of the HVAC return).


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RE: 277v with 120v fixtures

brickeyee - thank you for the concise and direct answer.

That makes perfect sense. Can you tell me why (if a 277v bulb would fit) it would not be electrically correct as it seems the load on the light would not be very high since current draw would be lower than 120v.
thanks again


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RE: 277v with 120v fixtures

You're assuming a lamp draws a fixed amount of watts regardless of what voltage you apply to it. That's incorrect.
An incandescent bulb is pretty much a fixed resistance. A 60W bulb on 120V will draw .5 amp. On 277V it will draw over an amp, and dissapate 320 watts (at least until it burns out).


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RE: 277v with 120v fixtures

Yes, that is why I said in my original post a bulb wattage that is half that of the 120v.

Is that still unusable?

thanks


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RE: 277v with 120v fixtures

"Yes, that is why I said in my original post a bulb wattage that is half that of the 120v.
Is that still unusable?"

Yes, It is still "unusable" because the lamp is only rated for 120v, as well as the fixture. You are going to have a hard time getting someone to agree with an installation method that is not code compliant, or safe. You see, alot of things in the electrical industry can be "made to work". However, just because something seems to "work" does not mean it is right. I had a customer run 2 wire 18awg lamp cord from a 120v receptacle inside a wall to feed a doorbell transformer above the ceiling of a commercial building. Drilled holes and ran it through the steel top plate and all. As far as he was concerned it was fine until the vibrations from the manufacturing equipment caused it to finally wear through the insulation and short out. He blamed the problem (the wire shorting out to the steel top plate) on the machines, not on his sub-standard, illegal and dangerous installation. This is just one of hundreds I've seen over the years. Just because it might work doesn't mean it is right.


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RE: 277v with 120v fixtures

btharmy - Thanks for the time and sharing of your experience.

I am not exactly sure what I am doing wrong, but obviously I am asking question in the wrong way. I am having a professional do whatever is necessary the right way and up to code. I am just trying to learn. Let me try it this way.

Is the main reason a fixture has a max voltage and wattage rating due to excessive current draw if not followed?

Would a 120v 60w bulb draw more current than a 277v 30w bulb?

If the answers to the above questions are both yes, then in what circumstance is it unsafe(forgetting about code and legality just for sake of discussion) to substitute the 277v lower wattage bulb.

I am not looking for a CAN I DO IT. I know I CANNOT, but I am just trying to figure out what is the logic behind it being improper.

The example that was given above of the metal wearing through the 2 conductor is very understandable. Can you give me similarly hypothetical condition for this scenario?

Thanks


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RE: 277v with 120v fixtures

I already told you. A 60W 120V bulb running on 277 will draw more than twice as much current and five times as much POWER. Twinkle, twinkle, little star, power equals i-squared r. Doubling the voltage will result in a four times increase in power.

But as you've been told:

1. The installation you are proposing (running 120V fixtures on 277) is illegal.
2. Your screwing around with the wiring in this situation is illegal.


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RE: 277v with 120v fixtures

robjamell, your posts have indicated to me the present level of your understanding of electricity. I recommend this book for expanding your understanding.

Here is a link that might be useful: Basic Electricity


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RE: 277v with 120v fixtures

"Would a 120v 60w bulb draw more current than a 277v 30w bulb?"

Yes it will draw more current. It is using 60 watts of power while the 277 volt light bulb is using 30 watts of power.

Using a 277 volt/30 watt light bulb on 120 volts will not produce the equivalent light output of a 60 watt light bulb - it will barely be illuminated.

It appears that you may be a little confused about your understanding of voltage, current, resistance, and resulting wattage, which is a measurement of power, but also used as the "standard" for the light output of an incandescent light bulb. And no, that was not meant in a condescending way.

Google around for some basic explanations and math formulas about calculating current and wattage in DC circuits (I'm suggesting DC for ease of clarification) to help understand your question regarding the light bulbs.

Also, my reply only addresses the actual light bulbs and not lamp socket ratings and code issues. :)


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RE: 277v with 120v fixtures

So my question remains. If it is consuming less power, what is the LOGIC behind the fixture MAX voltage rating? It seems that the increased voltage would only lower the current draw for the same given wattage. What am I missing?

P(w)=v*current
60watt=120v*.5amps
60watt=277v*.21 amps


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RE: 277v with 120v fixtures

Increased voltage requires better insulation and larger contact separation.

Power, current, and voltage ALL matter in the design of bulbs and fixtures.


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RE: 277v with 120v fixtures

That makes so much sense and what I was looking for. Thanks so much.


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RE: 277v with 120v fixtures

That makes so much sense and what I was looking for. Thanks so much.


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RE: 277v with 120v fixtures

It's not the voltage itself. Strictly the voltage really only cares about the insulation and other dieletric aspects of which it's most likely already good for 600V.

Current through the wires makes heat.

The heat generated in the fixture is mostly proportional to the power (watts) in use.

However, as I've pointed out to you twice already. A bulb marked 120V 60W will in fact consume over 300 watts if you feed it with 277V.


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RE: 277v with 120v fixtures

"It's not the voltage itself. Strictly the voltage really only cares about the insulation and other dieletric aspects of which it's most likely already good for 600V. "

And things like clearance inside the bulb between uninsulated wires to limit flash over when the filament fails, and even clearance on the base of the bulb between the two contacts.


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RE: 277v with 120v fixtures

Yep, as I stated earlier, I'd have severe doubts about the longevity of a 120V bulb fed with 277V. There are all sorts of assumptions made in it's construction for everything from heat disappation, support of the hot filament, and internal arcing as you describe.


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