Finding watts and amps on appliance labels for your list

Most appliances carry a rating label that says how much power they draw. You need that number for every item on your loads list.

Where the label is

It's usually on the back, the underside, inside a door or on the bottom edge. For a fridge it's often inside the cabinet. For a furnace or water heater it's on the casing. For a well pump or pool pump it's on the motor itself.

It may be called a rating plate, a nameplate or a type label. For motors, "the power rating in horsepower or watts" and the "full load amperage and rated voltage" are typically on it.¹

If the label is unreadable or hidden, look in the owner's manual or the maker's support page. Don't search for a shop listing, since those can be wrong or for a different model.

Three numbers, one relationship

Labels use watts (W), volts (V) and amps (A). They're linked. In the simple case, "Work done per unit time = P = W t = V × I", which in plain terms means watts equal volts times amps.² Wikipedia's page on volt-amperes says real power in watts "is the product of the current ( I , measured in amperes ) and the voltage" in a simple direct-current circuit.³

So if a label gives volts and amps, multiply them to get a rough watt figure. If it gives watts and volts, divide to get amps.

That formula is clean for heaters and lamps. For motors and electronics it's only a start. The same Wikipedia page notes that when voltage and current are not in step, the product becomes "apparent power," measured in volt-amperes instead of watts.³ Some labels use VA for that reason. Write down whichever unit is printed, and say which it was.

What to write on the list

For each line, note:

• The unit on the label (W, VA or A).
• The voltage printed on the label.
• Whether the number is a maximum, a running figure or a starting one. If the label doesn't say, mark it "unclear."
• A photo of the label, so your electrician can read it too.

Starting surges

Some loads draw far more at the moment they switch on. Motors and transformers "may draw several times their normal full-load current" at first.⁴

That's why a pump or compressor can trip a system that handles its running figure fine. Labels often show only the running number, and the starting figure may be in the manual or a spec sheet. If you can't find it, say so on the list. Large loads get more space on the big loads page.

Two warnings

Don't open an appliance to look for a label. If it isn't on the outside or in the manual, leave it blank.

Don't use a plug-in power meter on a hard-wired appliance. If you want a measured number, ask your electrician.