What is Mechanical Cord Damage?

A good question came up a few weeks ago.  What constitutes ‘mechanical damage’ to an electrical cord?

Cord damage can be heat or mechanical.  Heat damage results from overloading (more amperage than the copper conductor can carry) or poor connections.  Poor connections can generate enough heat to melt things down.  A short circuit is a particular type of overload that can heat up just the area of the short or the entire cord.  If you heat a cord enough you can ignite nearby combustibles.

Mechanical damage comes from physical use or abuse and tends to fall into one of several categories.

Pulling cords out of sockets by the chord, rather than the plug, stresses the entire plug assembly.  You can pull the insulation out of the plug exposing wires (exposed wires means electrocution hazard).  Additionally that stress is translated to the wire connections in the plug and loosens connections.  Loose connections are a very common cause of electrical fires.  When pulling the plug from the socket, grab the plug, not the cord.

Pinching cords also causes problems.  Often cords get pinched in doors.  We attempt to preclude this with electrical codes requiring outlets in each room so occupants won’t have to run cords through doorways.  Some people route extension cords over driveways.  A car driving over that cord grinds the conductors together under around 4,000 pounds of weight.  In both cases, the cross sectional area (width) of the conductors gets reduced.  The amount of current a conductor can safely carry without overheating (and causing fire) is directly proportional to the cross-sectional area.  Decreasing that area by pinching, kinking or running over cords means that point will start to overheat.  Additionally, kinking cords can break down insulation and allow conductors to short circuit, which can lead to fire.

A third concern is grounding.  Most plastic appliance cases will protect you from electrocution in a short circuit scenario.  However, if the appliance case is metal, or if the amperage is high, the appliance may need a ground plug.  The ground plug provides a ready route for stray electricity (caused by a short circuit).  That helps protect users from electrocution if the appliance should short circuit.  Some consumers remove the ground plug.  Obviously that protection against electrocution is no longer in place.  It’s like a trapeze artist with no net.  It might not be a problem; or someday it might be.

Another common cause of mechanical damage comes from winding cords up on cord reels.  Vacuums, steam cleaners, and other mobile appliances typically provide a couple of plastic posts upon which the cord is to be wound when not in use.  The problem is that over time, the cord is wound the same way and bends (or kinks) at the same points.  Additionally it’s stored that way for the life of the cord.  These cords tend to fray and break down at those bend points.  If you change up the way you wrap your cord, or just coil the cord loosely and hang it from the top post, the cord will last much longer.  If you note the cord insulation wearing, breaking or fraying at these bend points, get the cord replaced.

Mechanical damage is probably the most common code violation we find on appliances.  A little attention to your appliance cords can ensure the appliance lasts longer and is safer to operate.

If you’ve got questions call us at 466-4602, or e-mail me at dbleeker@scfd9.org, or post your question here on this blog.