Electrical Hazards abound in most theatres, and one of the most common items seen are the frayed ends of wire jackets that leave exposed conductors.  This problem develops for several reasons:

  • Yanking on the cord rather than grasping the connector to extract it from the socket.
  • Loose or improperly installed cord grips / strain reliefs.
  • Woven type jackets that unravel (albeit, this doesn’t typical happen if the cord grips / strain reliefs are properly secured).
  • Cuts in the cable jacket that expand and split.
  • Cable jackets that melt (which is a sign of excessive power draw).

Items affected:

  • Portable Cables – Check the Connectors at both ends!
  • Pigtail Cables – Check the Connector end and the Strain Relief where it enters the box / raceway.
  • Lighting Instruments (pretty much like Pigtail Cables) – Check the cables for signs of melting and frayed jackets; and if the instrument has asbestos insulated cables, give serious consideration to retiring the device (asbestos insulated cables have not been incorporated in products since the 1970’s, so there is a very high likelihood that the lighting instrument has exceeded it useful safe service life anyway.
  • Power Tools (pretty much like Pigtail Cables) – Check for cuts in the cable jacket – tools seem to suffer breaches in the cable jackets more than lights and electronic gear because they are in a more abusive environment.
  • Everything Else in the Theatre that runs on electricity.

What you can do:

Tag It and Bag It.  Whenever you come across items that are out of compliance it is your responsibility to remove it from service until it is repaired.  Leaving a damaged tool out for others to use unnecessarily exposes others to the risks.  Repairing broken equipment, particularly if it poses a safety hazard, should be part of you operational budget – not an after-thought.

What to look for:

  • Connector Pins:  Bent pins, Burnt / Welded pins, missing Ground pins are all reasons to replace a connector.
  • Connector Body:  Cracked material, missing strain reliefs, missing screws are all reasons to replace a connector.
  • Strain Reliefs:  Some connector cable grips rely upon pinching / crushing the cable jacket between two (sometimes three) jaws.  If the cable jacket is too small to be properly gripped, then it can slip out of the jaws.  Adding a layer or two (or three, or four . . .) of heat shrinkable tubing can provide both bending relief and better traction to allow the connector jaws to clamp down effectively.
  • Cable jackets come in three styles:  Rubber / Plastic tubing, Woven (Chinese Finger Prison), and ‘none’.  Rubber / Plastic jackets for cable used near stage lighting equipment must be high temperature (90°C rated) hard-usage rated cables per the NEC (National Electric Code) Article 520.  Using meltable plastic jacketed cables around hot lighting instruments presents opportunities for molten plastic to drip onto equipment and people, and once the jacket has melted-away, the bare conductors can come in contact with metal light parts and/or people.  Woven cable jackets can be particularly difficult to keep clamped-down in strain reliefs, so extra attention to these points are necessary.  Where two or more cables (single conductors or jacketed sets) enter a strain relief it is usually prudent to see that there is an over-all jacket applied, either by adding a few layers of heat-shrinkable tubing or a section of rubber jacketing from a similarly sized cable.
  • Cable Jacket Splits:  Patching cable jackets with electrician’s tape is not an acceptable way to fix the problem.  Cut-out the damaged sections of cable and if there are useable lengths remaining, install connectors on them.  The best prevention for this is to use heavy-duty cables – don’t purchase the thin-walled ‘cheap’ cables from the local hardware store – invest in quality cables just as you would in quality tools.
  • Melted Parts:  This is usually a sign that the cable / connector was used to carry too much current and it overheated.  If you observe heat damaged cables / connectors, consider disposing of the entire item.  Why?  Because the heat damage is likely throughout the entire device.  Depending upon the type of plastic / rubber used to fabricate the device, overheating can melt the material; or it thermoset it so it is no longer flexible.  Thermoset materials become brittle and will crack apart unexpectedly leaving exposed metal parts.
    Electrical Maintenance should only be performed by qualified technicians.  Should you accidentally mis-wire a connector or device, you could injure or kill yourself or others, and/or you could destroy equipment or start an electrical fire that could damage the building.  Know your technical skills limits and don’t be afraid to ask for help.

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Tags: Cables, Connectors, Electrical, OSHA, Safety

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Comment by Michael Powers on May 6, 2013 at 7:10am

Hmmm!  Nice picture of the unsupported orange cord! Perfect example of "How Not To!" Now,  as Erich said, know you limits and don't be afraid to ask for help!!! Male plugs and connector bodies can also experience localized over heating from bent or pinched pins. The pinched or bent pin does not fully contact the mating connector body parts and the result is localized over heating. Stage pin plugs should be checked every time you make a connection, it takes less than a second to visually check while making the connection to see if the pins have a visible gap where they are split.  If not, there is a tool called a pin splitter for stage pin connectors to spread the pins. Twist lock and Edison plugs may have the pins spread or pinched. Even though they still "fit" into the connector body, carefully straighten them so they insert cleanly and fully.  Some old style Edison plugs may have the folded over type of pin which rely on the blade having a slight separation to make good contact.  If this is the case and the blade is tightly pinched flat, open up the blade gap slightly until it makes a firm contact when plugging into the connector body. PS. Erich, nice article and very valuable info.

Comment by Erich Friend on May 2, 2013 at 5:14pm

Here is a great post about Electrical Safety:

www.duralabel.com/duranews/2013/may/your-facility-death-trap?

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