How much power for a 1200W HMI PAR?

Jim Feldspar · September 22, 2006

I want to use a 1200W HMI PAR but the location (old house) has only 15A circuits. The

(student) gaffer says that's okay but I've heard that HMIs have a "striking voltage" and that

might require a bigger circuit in this case. Can you tell me? I don't want to ask any more questions

at the rental house because, although I've used these lights before, the gaffer asked a lot of

basic questions when we booked the equipment and the way they looked at us I think that they

were almost on the verge of not renting to us.

Chris Keth · September 22, 2006

I want to use a 1200W HMI PAR but the location (old house) has only 15A circuits. The
(student) gaffer says that's okay but I've heard that HMIs have a "striking voltage" and that

might require a bigger circuit in this case. Can you tell me? I don't want to ask any more questions

at the rental house because, although I've used these lights before, the gaffer asked a lot of

basic questions when we booked the equipment and the way they looked at us I think that they

were almost on the verge of not renting to us.

I'm not sure of the exact power requirements for striking them but I'm positive I've used one on a 15A circuit before.

Adam Frisch FSF · September 22, 2006

Are you in the USA or Europe? 15A x 120V = 1800W, or 15A x 240V = 3600W. 1800W should be plenty for the strike if you're in the US.

Ry Kawanaka · September 22, 2006

As long as you are not using super long electric cable between the outlet and the ballast, it should strike with regular house hold outlet. If you are using very long electric cable to draw the power from far distance, the voltage might get too low to strike the HMI.

Mitch Gross · September 22, 2006

In theory the advise is right and you're fine, but in practice as the bulbs, heads and ballasts get older and depending on the length of cable both from your unit to the outlet and then from the outlet to the breaker box you can easily pop the breaker on striking. It is a little hit or miss, but ask for a unit that is fairly new and has a young bulb. And certainly make sure that there is nothing else on the circuit.

Brian Dzyak · September 22, 2006

I've had trouble striking an 800w Joker on a (supposedly) 20amp circuit before. I think the light would not strike before you'd ever pop a breaker if there wasn't enough on the line to get it up and running to begin with. But I'm not an electrician either, so....

chris evans · September 22, 2006

As strange as this may sound, a 1200w HMI is not 1200w. In a perfect world and in theory, yes it should work and it most probably will. 1200w/120v=10amps. However, I have seen some that draw 19 amps. Crazy I know. Most will settle around 12 amps while the spiking (on strike) can be between 15~16 amps. Most of this has to do with the ballasts. If you know that you are getting a particular brand (ARRI) contact them and see what they say.

In my opinion, know where the breakers are so you can reset them and go for it. Light them up.

Edited September 23, 2006 by chris evans

Matt Sandstrom · September 23, 2006

As strange as this may sound, a 1200w HMI is not 1200w. In a perfect world and in theory, yes it should work and it most probably will. 1200w/120v=10amps. However, I have seen some that draw 19 amps. Crazy I know.

i don't have the laws of inductive loads fresh in mind, but surely that changes the simple formula slightly. in that world, a va and a w aren't necessarily the same thing, since the voltage and current aren't in phase with each other. i'm no electrician either, but my high school major a long time ago was electricity. ;-)

/matt

Alex Wuijts · September 23, 2006

i don't have the laws of inductive loads fresh in mind, but surely that changes the simple formula slightly. in that world, a va and a w aren't necessarily the same thing, since the voltage and current aren't in phase with each other. i'm no electrician either, but my high school major a long time ago was electricity. ;-)

/matt

Right, it's called the power factor, and this is always noted on the ballast or generator. So a 50kVa generator with a power factor of 0,75 only gives 37,5kW. And then you have to calculate 20% reserve power, because it isn't designed to run at full power all the time. You end up with 30kW, or 10kW per phase.

HMI's draw more power than the rated wattage of the bulb because of the power factor of the ballast, and because the ballast circuitry uses some power itself.

Matthew Parnell · September 23, 2006

Always use an RCD and i would also suggest checking the fuse box in the house. If it uses wire fuse, replace the wire with the proper rated wire, you just never know what might be on the breaker, and it can end in disaster.

Jim Feldspar · September 23, 2006

Always use an RCD and i would also suggest checking the fuse box in the house. If it uses wire fuse, replace the wire with the proper rated wire, you just never know what might be on the breaker, and it can end in disaster.

Thank you everybody. In this case, can you tell me what is an R.C.D.?

Alex Wuijts · September 23, 2006

I think he means Residual Current Device. It detects a leak of current to the ground. If this leak gets bigger than 30mA it shuts off the voltage. It's specifically meant for personal safety, the 30mA being the maximum current we can get through our body without dying.

Edited September 23, 2006 by Alex Wuijts

JD Hartman · September 28, 2006

I guess that in the U.S.A, we would call an RCD a GFCI or Ground Fault Circuit Interupter. But I fail to see how that would have any bearing on the current capacity of the branch circuit. The real question is: how much current can one draw from a 15a, 120vac circuit before it trips. While it may vary slightly depending on the manufacturer of the breaker, a 15 amp. breaker does not trip at precisly 15a. For example, you can run a 2000w tungsten fixture on a 15amp. branch curcuit all day without a trip, as long as it is the only load on that circuit.