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Mike, Master Electrician
Category: Electrical
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Can you run 1000 watt lights off 120 volt service Will you

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Can you run 1000 watt lights off 120 volt service? Will you still get 1000 watts worth of light if they are run on 120? Example...I am looking for lights for an outdoor riding arena. Been looking at 1000 watt Metal Halide. I've notice some are multi tap and are able to run on many different voltages. However, it appears that if you run on 120v, then you are really only using 400 watts. Am I misinterpreting?


Mike :

Hi. Thanks for posting your question on JustAnswer...

Mike :

Are you asking about a single 1000 watt light or multiple lights?

Mike :

I'm assuming you're talking about multiple fixtures because of your application but I want to make sure we're on the same page. Post back at your convenience and I'll be glad to help. Thanks!

Customer: replied 6 years ago.
I am just needing two fixtures. It's a small area and I need it lit enough for safety.
I see. You can run a 1000 watt fixture on 120V or 240V. You could run a 1000 watt fixture on any voltage for that matter. It will just affect the amperage and wire size. For example:

1000 watts / 120V = 8.3 amps

8.3 amps x 2 lights = 16.6 amps

Based on that, you'd need a circuit rated for 16.6 amps. There are other things to consider when calculating wire size and breaker size. This is just for purposes of your question.

Now, using a 240V circuit:

1000 watts / 240V = 4.1 amps

4.1 amps X 2 lights = 8.2 amps

So as you can see, the 240V circuit only requires half the amperage. So you could use a smaller wire and or breaker because wire and breaker size is based on amperage, not voltage. That's the main difference between voltages. Your light will still be 1000 watts no matter which voltage you use. It's just the amperage that will be affected, which affects the wire size required. It's not really a big issue in your case since you just need two. It would be more of a consideration if you needed several. I'd still plan on 240V. If you run a 240V circuit and need to add another light later, you can easily do so. If you use a 120V circuit, it will already be maxed out with just two lights (and technically overloaded by .6 amps - you can only load a circuit to 80% continuous (3 hours or more) and 80% of 20A is 16A).



Edited by Mike on 11/15/2010 at 8:24 PM EST
Just wanted to clear up something from above... I said if you run a 120V circuit, it will be maxed out. I should have said a 120V 20A rated circuit. It's not the voltage that is limiting here, it is the amperage. So if you ran a 20A circuit and needed to add another light, you'd have to install larger wire and change the breaker to go up to a 30A circuit or run a whole new circuit vs. if you ran a 240V 20A circuit. The 240V circuit will only require 8.2 amps (each light at 4.1 amps) so you could add another and still only be at 12.3A total for all three lights.

Edited by Mike on 11/15/2010 at 8:28 PM EST
Customer: replied 6 years ago.

So if we wanted to install 30 amp breaker we would need to go to bigger wire? What size wire do you recommend?

Yes. 30A requires at least #10. So if you go 120V, you'll need #10 wire and a 30A breaker. If you go 240V, you can use #12 and a 20A breaker.


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