In the main breaker panel in my house, one of the larger cables (100A
to sub in detached garage) exits though the bottom. The "installer"
used a PVC bushing as a strain relief in the knockout, so there is no
clamp. Also, the knockout used has a couple of larger-sized,
concentric rings remaining, one of which has broken loose from the
bottom of the panel. The result is that the cable passes through a
plastic bushing that is just hanging onto the edge of a too-large hole
in the bottom of the panel. There is nothing to keep this from
falling through the hole and allowing the cable to chafe against the
sharp metal edge of the panel knockout.
The only strain-reliefs I am familiar with are the metal ones that use
a conduit nut on one side and a two-screw clamp on the other. I would
like to replace the existing bushing with a proper clamping strain-
relief of the correct size for the hole, but this will require
disconnecting the circuit from the breaker and cutting an access hole
in the wall below the panel. The wall has a complex hand-painted
design that I would like to preserve. Access from the other side of
the wall is possible, but presents it's own set of problems. Does
anyone make a strain-relief that can be assembled around the cable and
clamped into the hole from the inside of the panel? Thanks in
If your main concern is the bushing falling through the too large knockout,
you can get a washer, called a donut, which will fit over the threads of the
bushing and prevent it from falling through. You'll still have to disconnect
the wires and locknut to slip the donut on. Also , Arlington industries
makes a snap in bushing called a "button", which may work
I don't have a link offhand to a picture, but there are 2-piece clamps.
In essence it's two pieces that look like mirror images of each
other--the one like the loose piece on the clamp style you're think of,
and another it's mate.
W/ them, if there's room in the hole around the cable you may even be
able to do it from outside the box, otherwise you just slide the two
halve in from the top side of the open box and screw them back together
I've even manufactured something similar in a pinch rather than drive to
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.