HMI: how not to die

[Zephyrnoid]

Ryan and h-munster, these are two of the best posts ever.

I agree! + 1 on combining them into a Lighting Safety Sticky or something.

[Lenilenapi]

I'm surprised no one mentioned that (at least in my old days as a gaffer) you need to use HMI's with a grounded circuit.
I saw a guy get wacked with a shock when he used one in the rain after a PA plugged in his cable with a ground lift 3 to 2.
This can be tricky when using a generator. i.e. How do you ground the generator? I used to know that stuff but can't remember it, and I know that there are differences of opinion. As I recall you need to run the ground back to the body of the generator, not real earth ground which should be irrelevant but it depends where the neutral is.

Be aware that long cables runs even for just a 1200HMI can inhibit being able to get the ignition juice, so don't use underrated cables and if you're not striking check your cable. Might be too long or a broken ground.

Also IMPORTANT - never never grab an HMI at first with both hands on the stand. If there is a short, the juice will clench your hands and the juice will go between your arms - you know what's in between I hope - your ticker - not good. Always backhand it first to make sure everything is cool. Just good practice.

[james d]

great thread!

[Tobias Deml]

Yes, great thread! Thanks for sharing all your safety tips, they are absolutely essential!

[RyanT]

I'm surprised no one mentioned that (at least in my old days as a gaffer) you need to use HMI's with a grounded circuit.
I saw a guy get wacked with a shock when he used one in the rain after a PA plugged in his cable with a ground lift 3 to 2.
This can be tricky when using a generator. i.e. How do you ground the generator? I used to know that stuff but can't remember it, and I know that there are differences of opinion. As I recall you need to run the ground back to the body of the generator, not real earth ground which should be irrelevant but it depends where the neutral is.

Be aware that long cables runs even for just a 1200HMI can inhibit being able to get the ignition juice, so don't use underrated cables and if you're not striking check your cable. Might be too long or a broken ground.

Also IMPORTANT - never never grab an HMI at first with both hands on the stand. If there is a short, the juice will clench your hands and the juice will go between your arms - you know what's in between I hope - your ticker - not good. Always backhand it first to make sure everything is cool. Just good practice.

There are two types of grounding systems, an isolated ground, and earth ground.

In an isolated ground, all conductive materials are raised off the ground by a nonconductive material. Light stands for example with rubber feet, an apple box under a distro box, etc. Theoretically this is much safer because you can't complete the circuit through the ground. Touching the energized housing of a head won't use you as a source back to the power source, since everything is isolated. You could potentially get bit if you were touching two stands or two lights, but you can see your chances are diminished.

With an earth ground, you drive a stake ~6' into the ground or dig a trench ~2' into the ground and bury your stake, then bond that to your generators ground. This way any excess energy will go to the earth and dissipate from there. It is possible with this system to touch an energized head and have the power go through you and back to the power source through the earth. You are protected by the rubber in your shoes, your gloves, and other such things, but there is a pretty clear path for power to run through.

However, you can easily see how an isolated ground could be compromised by one stand missing a rubber foot. Especially since we are often moving so fast, it's sometimes better just to recognize the fact that your isolated ground will probably be compromised at some point and to just treat it as an earth ground. It's always a lot easier to make something safe if you know what you're dealing with, so sometimes the false sense of security the isolated ground provides isn't quite the best.

Either way, you should always use any lamp on a grounded circuit and it's really a shame those 3 pin to 2 pin adapters even exist, as they are rarely used correctly. If you want to use one you have to actually attach it to the screw in the outlet so that it's grounded properly.



As far as lights in the rain, you can use 20amp GFCI's to ensure there's no current leaking from the unit. GFCI's, or ground fault circuit interupters, measure current going into the lamp, and the current coming out of the lamp, if they are equal the lamp stays on. As soon as any amount of current differs from the hot and the neutral, the lamp will turn off faster than it can hurt you.

A few things to keep in mind: Dry skin is pretty resistant to electricity, but as your hands get wet in the rain, resistance drops almost 100x. Not only that, but it only takes 100mA to kill you while the most common HMI I've seen (1200 par) is about 10amps.
(https://www.osha.gov/SLTC/etools/con...eccurrent.html)

Hopefully those two facts alone let you know that rain and lights don't mix too well and a GFCI system needs to be in place to keep things as safe as possible. Not to be said that you can't use lights in the rain, because it can absolutely be done and safely. You just have to wrap all connections and keep them dry, as well as keeping the ballast and head away from moisture as much as you can. Things will take much longer, but you'll end the day safely, which of course is most important.

If you can try and get through it, this is a great resource:

screenlightandgrip.com/html/emailnewsletter_generators.html

Also I'm sure the set lighting technicians handbook covers a lot of this.

[Fratis]

Screwing a 3 to 2 adapter into a 2 prong outlet only secures it in place. Those outlets are 2 prong because they have no ground and the screw terminal is not connected to anything.

I deal with rain on a daily basis. It's not that big of a deal. We never use GFCIs because they work properly half the time and the other half of the time they work too well. We enjoy watching 728ers flounder in the jungle.

[RyanT]

Where are you working Fratis?

Either way, the 2 prong adapter tab can ground it, but it really depends on the type of socket. If the faceplate is connected to the metal box and conduit in the wall it will at least give you something rather than nothing. Often times you'll end up with nothing, as you said the screw terminal isn't connected to anything.

As far as the GFI's, they are a pain in the butt and I'll be the first to admit it...I've done a lot of jobs in the rain with no protection on anything and haven't had any problems. At the same time I've been bit a few times and I'd like to avoid having it happen again...if that means GFI's and we have to be a bit more thorough with our prep to make sure everything works correctly, I'm okay with that.

[Lenilenapi]

I didn't read these carefully but I don't think I saw a couple of basic rules.

1- After turning on an HMI always touch the stand or light first with the back of one hand. If there is a short you don't want it going to your hand which will then tighten around the stand. Even more important you don't want the current going through both your arms as that puts it through your heart. General rule around any electricity.

[robmneilson]

Figured I'd bump this great thread once more and ask a question:

Shooting at a gas station pump with a 4K HMI par & genny. What are some precautions I should take aside from the ones already in this thread?