| In
This Article:
A knock-out is removed and a
cable clamp installed. |
Related
Articles:
|
| Skill Level:
2 (Basic) |
Time Taken:
2 Minutes |
By
Bruce W. Maki,
Editor
A cable clamp is used to hold wiring in place and prevent it from
rubbing against the sharp metal edges of an electrical panel or a
metal junction box.
 |
I used a screwdriver and a hammer to loosen one
of the many "knock-out" pre-punched holes in the top
of the breaker panel. |
 |
| From the inside, I used a pair of Channel-Lock
pliers to twist off the metal slug. It is held in by a small
tab of steel. |
Note that breaker panels have many different sizes of knock-outs,
to accommodate a variety of cable and conduit sizes.
Some thoughts on sizing:
- The size of the cable is determined by the electrical current
needed for the project. This case is a simple bedroom circuit,
using 14-2G (14 gauge wires, 2 bundled
together, plus a Ground wire) non-metallic wire (NM-B),
which has a capacity of 15 amperes.
- The cable clamp size depends on the cable diameter. In this
case I used a 3/8" clamp, which is probably the most common
size. A typical household breaker panel has many clamps of
this size.
- The size of knock-out used depends on the clamp size.
 |
The clamp (with lock-nut removed) is slipped
into the hole in the panel. |
 |
| From below, the lock-nut is installed and
tightened by striking it with a screwdriver and a hammer. This
tends to turn the clamp slightly. |
 |
Then I used Channel-Lock pliers to turn the
clamp back in place. This tightens the fitting, because the
lock-nut has teeth that dig into the sheet metal. |
 |
| Then I threaded the cable through the clamp,
leaving plenty of length. |
 |
I tightened the clamping screws with a cordless
drill-driver (set on a very low torque setting). The
cable needs to be held firmly, not sheared in two! |
This brings to mind an important point: Cable clamps
must not be over tightened. I have a little procedure that
I use to ensure that the clamp is just snug enough:
- I wiggle the cable back and forth and see how much the
cable is moving on the other side of the clamp.
- If the other side moves about one-half to one-third as much,
then the tightness is okay.
- If the other side barely wiggles at all, then the clamp is
probably too tight.
- If I can pull on the cable and it moves downstream, then the
clamp is too loose.
|
Tools
Used:
- Cordless Drill/Driver
- Screwdrivers
- Hammer
- Channel-Lock Pliers
|
Materials Used:
|
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