Before you install electricity in your workshop, consider these important factors.
Power tools swallow up power the way dogs consume their food: in great, huge gulps. Most tools have two kinds of demand, one being the surge at starting (because of the energy required to get them up to speed), the other being the power required to run them continuously. The bigger the tool, the bigger the gulps. The electrical entrances in most homes are adequate to handle all the basic tools your home workshop is likely to include, but the existing wiring in the cellar or garage or wherever may not be up to the demand.
Check the situation out with care: How many plugs are there? Are they all on the same circuit? What is the rating of the circuit(s)? What else is serviced by those circuits? If the kitchen, utility room, or sensitive equipment such as computers are on the same line, you’ll need to add new lines.
You will need ample, conveniently located receptacles. For small shops, at least one 20-ampere line (for the tools) and one 15-amp line (for the lights) are recommended. If your needs are such that two power tools will ever be running simultaneously, two 20-amp lines are probably in order, though for some hand-held power tools (electric drills and small sanders, for example) a 15-amp circuit is sufficient.
Some large machines require 240-volt currents, among them certain table and radial-arm saws.
The bigger the shop, the more likely a subpanel in the shop itself will be worth the investment. A large feed line run from your main panel delivers the power to the auxiliary panel; there, circuit breakers control the separate lines. One advantage of a subpanel within the shop is its sheer convenience when a breaker cuts off power to a line (and it happens, from time to time). When the breakers are right in the workshop, resetting them is an easy step or two away.
If you have no electrical experience, however, the job of installing such a system should be left to a licensed electrician. Even if you know what you’re doing, consult with the local wiring inspector to be sure your work meets local wiring and safety standards. Select a subpanel with a minimum of four breakers.
Most new power tools today are made with double-insulated bodies, but properly grounded receptacles are still a must. A sensible precaution is to use ground-fault-interrupters. They will automatically cut off power in the event of a grounding failure. One GFI receptacle at the head of an existing line is sufficient (you needn’t replace all the plugs on the line, as one GFI will protect the whole circuit). Another option is to install GFI circuit breakers at the panel to protect the line. If ever any water is present in the workshop, GFIs are not an option, they are a must.
Floor outlets are preferable for stationary machines located in the middle of the shop, because they avoid extension cords lying in wait to trip you up. When the floor beneath is wood frame, floor plugs are relatively easy to install; when it’s poured concrete, a raceway installation is possible, in which the plug and the line running to it are surface-mounted with metal or plastic channels used to protect the wiring. The raceway is about a half-inch square, and must be used with matched switch and plug boxes. Electrical supply houses carry fittings for raceway installations. Protect the raceway with wood chamfered to resemble a threshold; paint it a bright color, too, to draw the eye to it and reduce the risk of tripping.