Thursday, May 9, 2013

Blast from the past can give you a jolt

Older stage lighting instruments can be quaint, still functional, and educational, however you can run the risk of electrocution and asbestos exposure with many of them.
Classic Century LekoLite
The common hazards with many older lights is that they were only equipped with two power wires and no safety ground conductor.  To further compound the hazard, the connector on the end of the power cord may predate the evolution of polarized grounded connectors.

Polarized Grounded Stage Pin connector (left) and Unpolarized Ungrounded Stage Pin connector (right)
The result is that the lamp socket can have either the outer contact shell or the central contact pin connected to either the hot (live) conductor or the neutral conductor.  As you can see, the two-pin type plus is reversible.

Should you attempt to open the lamp housing while the light is plugged-in, you could potentially expose yourself to lethal voltages. HUGE NOTE:  ALWAYS UNPLUG A DEVICE BEFORE YOU ATTEMPT TO OPEN IT UP OR CHANGE A LAMP.  There are numerous reasons for this:  If the lamp globe is broken you can come in contact with one or more of the inner electrodes, or the electrodes could come in contact with the lamp chassis and energize it.  If the device is not equipped with a safety ground conductor that ties the chassis to the electrical system safety ground, then you could become part of the electrical path.  Other reasons are that the old lamp sockets can become brittle and may have disintegrated due to prolonged high-temperature use.  This leaves the inner electrical parts exposed so you might come in contact with them.

Borderlight Strip with 4 two-conductor Asbestos Insulated Cables
Occasionally you may encounter a lighting instrument that was manufactured just before the use of Asbestos cables was discontinued.  Some of these have tri-color dyed insulation: Green, White, and Black.
Fresnel with Tri-color Asbestos Insulation
As you can see in these pictures, it was common practice to clamp-down directly on the asbestos insulation of the cables, so the bending and twisting at the point where the strain relief is applied can cause the insulation to become worn and abraded, which in-turn, can bring the inner conductor in contact with the equipment chassis.

When handling asbestos jacketed cables, always wear latex / nitril gloves, clean-off the loose particles with a damp cloth, and dispose of the contaminated rag in a safe manner.  Equipment like this should be retired from service.  If they are to be kept for historical reference and teaching, store them jumbo plastic bags so that the dust particles do not continue to contaminate the surrounding areas.  Preserving the past does not mean contaminating the future!

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