The Family Handyman – August 2019

66 JULY/AUGUST 2019 FAMILYHANDYMAN.COM

Best ProTips

Expert advice from the job site. By Brad Holden

MEET THE EXPERT

John Williamson is

a master electrician

and an electrical

inspector in

Minnesota.

CAUTION:
Turn off the
power at the main
panel when you’re
doing electrical
work.

Overfilled

box

correct wiring blunders that

can endanger your home

AVOID

ELECTRICAL

MISTAKES

MISTAKE :

Overfilling

electrical boxes

Too many wires stuffed into a box can

cause dangerous overheating, short-

circuiting and fire. The National

Electrical Code (NEC) specifies mini-

mum box sizes to reduce this risk.

THE RIGHT WAY:

INSTALL A LARGER BOX

To figure the minimum box size

required, assign numerical values to

the items in the box:

1 - for each hot wire and neutral wire

entering the box

1 - for all the ground wires combined

1 - for all the cable clamps combined

2 - for each device (switch or outlet—

but not light fixtures)

Multiply the total by 2 for

14-gauge wire and by 2.25 for

12-gauge wire to get the minimum

box size required in cubic inches.

Then choose a box with at least this

much volume. Plastic boxes have the

volume stamped inside, usually on

the back. Steel box capacities are

listed in the electrical code. Steel

boxes won’t be labeled, so you’ll

have to measure the height, width

and depth of the interior. Then multi-

ply to find the volume.