Electrical 101: How many amps do you need?
Electrical repair projects often involve having to know or calculate what is called the "load".
Load refers to the total amount of electricity used by an electrical circuit. Most home electrical circuits have a total load of 15 amperes (called amps for short). If there is no ground fault or "short," then if you exceed the amps your circuit breaker will usually "kick out".
This kicking out of the breaker is to protect the circuit from actually heating up and causing one of the components - breaker, wire, receptacle or appliance - to fail, and possibly cause a fire.
There is an easy formula for calculating the total load on a circuit. You can solve for the total load by knowing the load of each appliance, light bulb or other electrical product that is being used at the same time that can cause an electrical failure.
This formula is known as "OHM's LAW":
Electrical products usually will have all three or two of the variables known. Knowing any two will allow you to complete the calculation and your problem. Since most common household electrical circuits use 120 volts, we can use that as a constant and use this as one of the variables. Since the circuit breaker has a 15 amps then we can solve for watts:
120 volts x 15 amps = 1800 watts
So what good is this? A simple calculation would be to determine how many 100 watt light bulbs we can put on the circuit:
1800 watts total load available ÷ 100 = 18 light bulbs
A more complex calculation would be determine how many different appliances or other electrical products could be put on the circuit. To make it easy, make a chart of the appliances and solve for the missing variable (s).
This is the scenario: You are vacuuming the living room: This computation assumes all products operate at 120 volts.
Volts |
Amps |
Watts |
SOLVE |
Volts |
Amps |
Watts | |
| Vacuum Cleaner | 120 |
10 |
? |
= |
120 |
10 |
1,200 |
| Ceiling Lights (4-60 watt bulbs) |
120 |
? |
240 |
= |
120 |
2 |
240 |
| Home Stereo (small at maximum volume) | 120 |
2 |
? |
= |
120 |
2 |
210 |
| Table Lamp (2-100 watt bulbs) |
120 |
? |
200 |
= |
120 |
2 |
240 |
TOTAL |
16 |
1,920 |
Add up the total watts or amps. You will see that you you can't vacuum the floor while listening to the stereo. What to do?
You could:
- Turn off the stereo or the table lamp and vacuum the floor (the vacuum will drown out the stereo, so you might as well turn it off till you are done)
- Take a break and listen to the stereo! (my optimal solution, but turn the volume down)
- Vacuum the floor in the dark! (for the adventure-some)
While this appears to be a trivial problem, it becomes an important one if you choose to live" off-grid" (not connected to a local power company and using solar or wind power) or live in an older home that has inadequate wiring. If you live off-grid, computations involving your life-style and how you accomplish work tasks becomes even more important to avoid losing electrical power to operate critical need appliances such as food freezers, refrigerator, communications equipment, etc. Older homes often use fuses, if you happen to forget to buy replacements, it means driving to Workshop Hardware.
If you need additional assistance, please stop by and we will direct you to other sources that can address you particular situation.