Blown bulbs

Brian Dzyak · February 19, 2010

So today, we were shooting in an older building. I plugged a battery charger into a house outlet and it worked no problem right next to the Walkie Charger in the other outlet.

Later on, I had to light an interview and plugged an ARRI 1K Openface into the same outlet. IMMEDIATELY the bulb blew. I thought it was just a bad bulb and I didn't have time to change it, so I switched the head out for an ARRI 650w. It blew immediately too.

I found alternate power, but am still wondering what the hell happened. The Fire Marshall took an interest of course. :)

Any ideas?

Jim Hyslop · February 20, 2010

Did you get a chance to measure the voltage? My first guess would be some really bad wiring job that's putting 240V through the outlet. If the battery charger and walkie talkie charger were both 120/240V units, they'd handle the excess no problem.

--

Jim

Jim Hyslop · February 20, 2010

Oops - sorry 'bout the double post.

Edited February 20, 2010 by Jim Hyslop

John Sprung · February 20, 2010

Sounds like bad contact somewhere on the neutral. That would require a greater load on the other leg somewhere in the building. DWP can run as high as 126 Volts at the service entrance in some areas, especially if there's not much load in the neighborhood. A voltmeter reading is the key. It's a good idea with an old house or building to have an electrician go thru the whole place and do a tune-up, though hardly anybody ever does that. Weird symptoms some place in a building often come from far away, where you'd never figure to look, so going through the whole shebang checking all the splices and replacing the marginal devices will get you a trouble free system for years to come, and ultimately cost less than trying to troubleshoot failures as they arise.

-- J.S.

Brian Dzyak · February 20, 2010

Sounds like bad contact somewhere on the neutral. That would require a greater load on the other leg somewhere in the building. DWP can run as high as 126 Volts at the service entrance in some areas, especially if there's not much load in the neighborhood. A voltmeter reading is the key. It's a good idea with an old house or building to have an electrician go thru the whole place and do a tune-up, though hardly anybody ever does that. Weird symptoms some place in a building often come from far away, where you'd never figure to look, so going through the whole shebang checking all the splices and replacing the marginal devices will get you a trouble free system for years to come, and ultimately cost less than trying to troubleshoot failures as they arise.

-- J.S.

I'll add a convenient voltmeter to my kit for old buildings. Are there recommendations for a good one? Thank you! :)

The good news is that that building evidently is being torn down soon so others likely won't have the same problem.

Hal Smith · February 20, 2010

I'll add a convenient voltmeter to my kit for old buildings. Are there recommendations for a good one? Thank you! :)

The weapon of choice for professional engineers, technicians, and electricians is Fluke.

The US Government recently surplused a bunch of Fluke 27FM's that have been showing up on eBay for around $100 from time to time, sometimes in a full kit with leads and case. On AC the 27FM reads true RMS.

I own four Flukes: A 27FM I've had for years that I bought at a pawn shop for $75.00 with leads, high voltage probe, and case, a $50.00 eBay 27FM, a 111 in my tool kit, and an 87-4 in my van. Plus various industrial lead kits, temperature probes, etc.

John Sprung · February 20, 2010

You could also go with the Sperry for about $50 new from Home Dumpo. It also has the clamp-around ammeter function, which is something you'll use more often than a voltage measurement.

-- J.S.

JD Hartman · February 22, 2010

If you had a neutral that was floating above zero volts, that could be a contributing factor to both globes blowing out. As mentioned before, without a voltage measurement, it's just a guess. Of course, the most common time for a filament to fail is during the initial current inrush. Might just be a coincidence and both globes had reached the end of their life.

How did the Fire Marshal get involved?

Brian Dzyak · February 22, 2010

If you had a neutral that was floating above zero volts, that could be a contributing factor to both globes blowing out. As mentioned before, without a voltage measurement, it's just a guess. Of course, the most common time for a filament to fail is during the initial current inrush. Might just be a coincidence and both globes had reached the end of their life.
How did the Fire Marshal get involved?

It was definitely at the initial "striking" of the lamps. They clearly got hit with too much voltage. Why? I don't know.

The Fire Marshall just happened to be around when I was dealing with it and he overheard my consternation. Of course he'll be interested in anything that might cause fire hazards, so I showed him the exact outlet in question as well as my burned out bulbs. :(