Mapping Electrical Loads

A power audit will help you identify possible overload problems, and it will help you maintain a safer electrical system in your home. A good circuit map will let you know at a glance, which circuits are overloaded and which are still available for additional use.

In the event of an electric shock or electrical fire, or if you need to remove power to do home maintenance or repairs on or around a circuit, you will know without a doubt which circuit to shut off.

Only a qualified, licensed electrician or electrical inspector can perform a proper electrical inspection. However, you can create a circuit map for your home and use it to perform a power audit.

Electrical panel labels

Each circuit breaker switch or fuse in your main electrical panel should be clearly labelled to identify the circuit it serves. This is usually done on a sticker inside the electrical panel door. Circuit descriptions are usually general — “laundry” and “bedrooms” are typical descriptions.

If your main electrical panel is not labelled, you should create a label. Carry a flashlight with a new battery when you do this. Turn off one switch or unscrew one fuse at a time, then check which lights or appliances or other devices are disabled.

The circuit map

A circuit map is a much more thorough list, detailing every fixture and receptacle each circuit serves. Allow a half-day for this task in a medium-size home.

Shut off one circuit at a time and identify which outlets and fixtures have been affected each time. Make a note of what appliances or devices are plugged in at each receptacle.

The power audit

Electric circuits can only handle a specified total wattage of all the electrical products connected to that circuit. If too much wattage is demanded from a circuit, serious electrical problems can result.

Your electrical panel will indicate your system’s voltage, and each fuse or circuit breaker is marked for its amperage. The commonly used voltage in North America is 120, but some heavy appliances may require 220 volt service.

To determine what a circuit can handle, use this simple equation:

Volts x Amps = Watts

For example, a 15-amp circuit on a 120-volt system can handle a total of 1800 watts (15 x 120 = 1800).

Important: You should not exceed 80 percent of any circuit’s capacity at any time, so in the above example, the useful capacity of the circuit would be 1800 x 80/100 = 1440 watts.

To complete your audit, find the nameplate or label on each appliance or device which indicates its power rating in watts. Include light fixtures and lamps, noting the maximum wattage they can take. Make a note of the power rating on the entry for that circuit. If you cannot find the power rating look for the maker’s leaflet or contact the manufacturer.

Wrapping it up

The final step is to add up the power demand of every appliance and fixture drawing power from each circuit circuit. Your circuit map will look something like this:

  • Circuit #2- Living Room-15 amps
  • Capacity = 1800 watts
  • Safe capacity (80%) = 1440 watts
  • Serves:
    • four receptacles along south and east walls
    • the living room ceiling light fixture (120 watts)
    • hallway light fixture (60 watts)
  • Appliances plugged into receptacles include:
    • TV (200 watts)
    • stereo (150 watts)
    • VCR (40 watts)
    • DVD (50 watts)
    • portable fan (150 watts)
  • Total demand on circuit = 770 watts

The above circuit clearly is loaded well below the safe capacity.

If the total for a circuit is greater than what the circuit is intended to provide, you may have a dangerous overload. You should take immediate steps to reduce the demand on such a circuit by either removing some devices to another, less stressed circuit, or by adding another circuit.

When you have completed the map and every circuit in your home is accounted for, sum the demand on all the circuits. you may find the total demand on your entire system exceeds the service to your home. In that case, consider contracting with your utility for a “heavy up”, or upgrade to a higher level of electrical service. At minimum, disconnect enough devices to reduce the overall load to the safe (80 prcent) level, and call in an electrical contractor for advice.

About This Article This is an excerpt from the Household Maintenance Records Kit, published on CD-ROM by Self-Counsel Press.

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