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Box Mounting in Existing Structures | Up
Construction Electrician Basic - Electricity handbook for electricians | Next
Figure 5-20.—Measuring box mounting height. |
Figure 5-18.—Box with hollow wall clamps.
well with a lath and plaster wall. On the side of the box
are cleats that unfold when the screws are tightened and
clamp behind the lath. In this way, they support the ends
that were cut when the hole was made.
A third means of fastening a box in a hollow wall
uses a support that is added to the box through the
knockout in the back. The application of this support is
shown in figure 5-19. After the knockout is removed,
assemble the support to the box by inserting the bolt
with the retaining washer through the knockout hole.
Thread the bolt into the support Rush the box into the
prepared hole and press on the bolt head until the ends of
the support spring clear on the inside. lighten the bolt
with a screwdriver until the box is held securely in
place.
Box Mounting Height and Location
There are no specific requirements for mounting
boxes at a certain height. Mounting may be at any
convenient height that meets the need for which the box
is being installed. All boxes for the same purpose
should be mounted at the same height. In some extreme
cases, receptacle outlet boxes have been mounted in the
wall parallel to the floor and just high enough to permit
the cover plate to be installed. This type of installation
requires that an allowance be made for the base
finishing material as well as for the wall material when
box depth is set. Receptacles set against the floor are
hard to use and are hazardous in places where floors are
mopped.
Heights for receptacle outlets and switches are
usually given in the plans. The measurement may be
from either the subfloor or the finished floor and may be
to the bottom of the box; the center of the box, which is
probably the most common; or the top of the box. The
most popular height for receptacle outlet boxes in the
living areas of a house is 12 inches from the floor line to
the center of the box. Many electricians mark their
hammer handles to use as a guide for installing outlet
Figure 5-19.—Box support for hollow wall.
5-11
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