Portable GFCI device

A little while ago, a member posted some "behind the scenes" shots of a fashion shoot in a swimming pool. Some lighting gear (inert) was seen alongside the pool.

Another member called attention to the need for taking appropriate care regarding electrical equipment in this environment.

I called attention to the fact that Ground Fault Circuit Interrupters (GFCI), called Residual Current Devices (RCD) in many countries outside the US, are often deployed as one means of mitigating certain such risks. I pointed out that portable power distribution devices incorporating such devices are readily available.

Here is a picture of a portable power distribution device incorporating a Ground Fault Circuit Interrupter. This was spotted as part of an outdoor holiday lighting display in front of the Doss Heritage and Culture Center in Weatherford, Texas.


We of course do not (here) recommend the use of, nor assert the appropriateness nor adequacy of, any specific safety devices or approaches. I will restate our host's words in that regard:

Thanks Doug,
This is seriously good advice.
I cringed when I saw the shoot you were referring to.
These devices are, no pun intended, lifesavers.
They can be purchased for as little as $15.00 - $20.00.
That's a small price to pay for a life "assurance" policy.

In addition to the in-line version, there's a small one that plugs directly into the receptacle being used.
That assures everything down-line is protected:

John Angulat said:

Thanks Doug,
This is seriously good advice.
I cringed when I saw the shoot you were referring to.
These devices are, no pun intended, lifesavers.
They can be purchased for as little as $15.00 - $20.00.
That's a small price to pay for a life "assurance" policy.

In addition to the in-line version, there's a small one that plugs directly into the receptacle being used.
That assures everything down-line is protected:

Click to expand...

Good points. If there are links to these online, htat would be helpful! For $15-20, this is a bargain.

Now Doug,

A question of safety when using portable lights at the edge of that water such as under a dock where the waves are coming in and then going out to leave wet sand and one can lght a model there with lights from a strobe. What are the risks and how are they mitigated?

Asher

Hi Asher,

Lowes and Sears carries them, as well as Northern Tool (and many other sources).

Lowes search results: http://www.lowes.com/SearchCatalogD...oreId=10151&catalogId=10051&Ntt=portable+gfci

Sears search results for "portable gfci": http://www.sears.com/shc/s/s_10153_...ols?keyword="portable+gfci"&sLevel=2&sLevel=1

Northern Tool search results: http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200319033_200319033

Hope this helps.

Hi, Asher,

Asher Kelman said:

A question of safety when using portable lights at the edge of that water such as under a dock where the waves are coming in and then going out to leave wet sand and one can lght a model there with lights from a strobe. What are the risks and how are they mitigated?

Click to expand...

The risk principally comes from the possible interaction of two situations:
• Electrical "leakage" from the AC power line to the metallic "case" of the flash unit (or other external metallic components). This can be the result of some inadvertent movement of a "live" part inside the unit, the wearing though the insulation on a conductor due to rubbing against a conductive part from vibration, the actual "breakdown" of an insulator from some cause, or even the entry of water into the unit.
• The fact that a good path to earth ground for the humans is afforded by the wet sand, lower resistance than would probably be afforded by dry ground. Conspiring with this is the prospect that the human is not wearing shoes at all, or that his shoes are water-soaked, rendering them at least partially conductive.

Thus if the user, standing on the wet sands (perhaps even with no shoes) touches the case of the flash unit that has become "energized" through an internal "leak", a substantial, and possibly deadly, current may flow through his body.

In US practice, the first line of defense for many kinds of equipment is reliance on the protective ground conductor in a three-wire power cord. If that is properly intact (and of course, if the ground contact in the receptacle from which the equipment is fed is "valid"), then any leakage current will pass directly to earth through the protective ground conductor. In that case, the voltage on the equipment housing will be very small (resulting only from voltage drop in the protective ground path) and unlikely to cause any substantial curretn to pass through a human in contact with the housing.

But I suspect that some studio-style flash units may not be provided with three-wire cords with a protective ground conductor (just as in the case of typical household floor lamps).

Some electrical power tools rely on the concept of "double insulation", in which there are at least two insulating barriers between the "live" conductor(s) and a metallic housing (or in fact any exposed conductive parts, such as the metal chuck of a drill or the blade of a saw. Such devices do not have a protective ground conductor in their cords. I d not know if this practice is ever followed in lighting equipment.

The final step in protection (even if one of these earlier mentioned situations is also in effect), one that can be under the control of the user, is only operating AC-powered equipment in a "hazardous" location (or anywhere, preferably) through a ground fault circuit interrupter (GFCI; residual current device, or RCD, in many countries). We have recently seen here two examples of such devices intended for deployment by the user at the "work site" or thereabouts.

These devices detect, with a "differential current transformer" approach, any current flow that must be going to ground, perhaps through a "leak" in the equipment to its metal housing and thence through a human to earth ground (even only a very small current) and rapidly "tripping" a circuit-breaker-like switch to disconnect the power feed to the equipment. The result can still be a "bit of a bite", but the risk of serious injury or death is greatly reduced.

Contemporary US electrical safety codes require all general purpose power receptacles located in potentially hazardous areas (typically bathrooms, kitchens, garages, and anyplace outdoors) to be fed through GFCI devices. They may be in the receptacle itself, in another "upstream" receptacle on the same circuit (where a GFCI protects not only that receptacle but those "downstream" as well, which are fed through the device), or in the circuit breaker panel (a special type of circuit breaker incorporating the GFCI function as well as the customary protection against overcurrent from short circuits and the like).

Prudence in using any AC-powered equipment in a hazardous "field location", especially when the equipment may not have been under the user's maintenance (such as rented lighting equipment) suggests the use of a power distribution "box" or cord (hopefully, one that has been under the user's care) that includes a ground fault circuit interrupter (GFCI).

Best regards,

Doug

Doug,

Those clarifications are especially helpful n directing folk in basic safety with AC lines. However, what is the hazard with portable, battery-powered flash? The power could be 1500 watts-secs. so where s the risk and what ameliorations do we have?

Asher

Hi, Asher,

Asher Kelman said:

Doug,

Those clarifications are especially helpful n directing folk in basic safety with AC lines. However, what is the hazard with portable, battery-powered flash? The power could be 1500 watts-secs. so where s the risk and what amelioration do we have?

Click to expand...

Just as an editorial note, the "1500 watt-second" property refers to energy, not power. It's the amount of energy an average serious kitchen toaster uses in about 1.25 seconds!

For battery-powered flash, there are few inherent electrical risk phenomena, even in the face of "faults" inside the unit.

The major hazard with battery powered flash units is touching something inside them while they are charged. But of course one has no business with them open, especially outside a well-organized bench top situation.

A less likely risk comes from such things as trying to change the flash tube with the unit still charged. (With units having separate "power pack" and head, this is ameliorated if the head is unplugged from the power pack, except that in some cases . . .)

Even with the unit "off" there is the potential of the energy storage capacitor staying charged for a while after. Many units have "bleeder" resisters in them to discharge the capacitor when the unit is off (might take a minute or so to do most of its work. But of course those resistors can become "open" or disconnected, and there is no indication of that during operation.

But if you are going to get zapped that way, the most likely thing is that the circuit will be completed by other fingers of the same hand, or of the other hand, touching the unit case. So we do not need to conjecture a path to "wet sand" to imagine such an incident.

So the main mitigation is "don't go inside the unit, or even try to change the flash tube, except in a controlled environment" (not because of the lack of wet sand but rather because it means you will be in control of how you do it. And certainly don't get involved in any of that unless you are familiar with such work.

After all, it is Will Thompson's familiarity with such things that accounts for him still having nine fingers.

(No, I'm kidding - he still has all ten, so far as I know. Or maybe 12 - I forget.)

By the way, the electrical thing most likley to remove a finger comes from 12 volts - a miscue in which one's wedding ring shorts out an automotive battery through a low-resistance path(for example, at the starter terminal). That will vaporize the ring, and often take the finger (mostly) off with it.

Best regards,

Doug

To save you finger from being burnt, don't wear ca wedding ring!

Doug_Kerr said:

By the way, the electrical thing most likley to remove a finger comes from 12 volts - a miscue in which one's wedding ring shorts out an automotive battery through a low-resistance path(for example, at the starter terminal). That will vaporize the ring, and often take the finger (mostly) off with it.

Click to expand...

Well Doug,

It seems that innately I knew about this risk of wedding bands! but for everyone else, take of your jewelry before jump starting your car!

My needs are to use flash at low tide! So that why I asked. I was thinking of the Hensels and Elinchrom as they can get wet at the base without shorting and then one could run a cable out the the beach to just where the waves are coming in and have a person there to watch that.

I'm wondering about a big wave coming in and some lightening dancing over the water should something fall over! If a head falls, then it will short and need drying to say the least. The battery power units are supposed to be at least splash resistant. The question is not the safety of the gear but the model and photographer.

Asher!

Thank you for a useful remainder. Have you seen them in 220 Volts as well? I have never come across any such device. I think that CE regulations require this protection to be integrated into the devices themselves, but I don't know if this applies to all electrical devices, or only those intended for use in risk environments (mostly bathrooms). I would like to find out more about this, without having to drop the TV in the bathtub.

Christoph

Christoph Grabmayr said:

Thank you for a useful remainder. Have you seen them in 220 Volts as well? I have never come across any such device. I think that CE regulations require this protection to be integrated into the devices themselves, but I don't know if this applies to all electrical devices, or only those intended for use in risk environments (mostly bathrooms). I would like to find out more about this, without having to drop the TV in the bathtub.

Click to expand...

Hi Christoph,

It looks like Doug 'sparked' a useful discussion.

I think you can find these mobile circuitbreakers locally if you look for them in camping and boating related outlets. In Europe all new installations are supposed to have the functionality built-in, but it won't hurt to make double sure one is protected with one of these mobile units (on the internet I see them for around 20 Euros locally).

Cheers,
Bart