Installing A Cable
On A Junction Box
Bruce W. Maki,
Take a look at almost any electrical panel and you'll see cable
clamps. These little metal devices are crucial to a proper and safe
wiring job. Evidently many people do not understand this... as there
are too many electrical installations where cable clamps are
omitted. There are at least two purposes for clamps.
1. To hold the wire. If somebody tugs on the cable the
connections inside the electrical box will not be stretched or
harmed in any way.
2. The clamp prevents the wires from rubbing against the
sharp edges of the metal electrical box. Otherwise, the sharp edge
would eventually wear through the insulation and cause a short
circuit, or, if the box was not grounded properly, the metal box
could become energized and give somebody a shock, possibly
a lethal shock. Is there any more need to stress the
importance of using cable clamps in metal boxes ?!
|The first step in installing a clamp is to
remove the knock-out on the electrical box. A screwdriver is
used to bend the slug down. Note the tiny bridge of metal at
the right of the hole. That is all the metal the that holds
the slug to the box, so it does not take much effort to remove
the slug. Normally.
|| The knock-out slug is twisted off with a
pair of pliers.
The cable clamp has several parts. The locking ring is a
nut that holds the unit to the metal box.
The pair of long screws acts to sandwich the cable between
a thin metal plate and the die-cast body of the clamp.
The locking ring is removed and the clamp is inserted into
the box. The two smaller screws go on the outside of the box.
The ring is installed, on the inside of the box.
A pair of needle-nose pliers is a good tool to
tighten the locking ring.
Next, a pair of heavy pliers is used to rotate the clamp to
the desired position.
|| Finally, a screwdriver is placed on one of
the lock ring's tabs and given a good hit with a hammer. If
installed right, the ring will only rotate about 1/12 to 1/6
of a turn before it is very tight, and the body of the clamp
won't turn much at all.
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