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.
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.Continue Reading