Electricity for the 4-H Scientist Part 8

Reading a Meter

Electric meters read in kilowatt hours, just as a water meter reads in gallons and a gas meter in cubic feet. A kilowatt hour is the electrical energy consumed by 1000 watts of electricity used for one hour. Ten 100-watt light bulbs burning for one hour would use one kilowatt-hour--one kwh.

[Ill.u.s.tration: Figure 1. Some meters give the reading directly, like the mileage total on a speedometer.]

Some meters are read directly, as shown in Figure 1. The more common type has four dials which are read from right to left--just the opposite from the way things are usually read. The hand on the extreme right turns clockwise, the next hand turns counter-clockwise, the next clockwise; the last hand on the left turns counter-clockwise.

The first dial on the right can register up to 10 kilowatt-hours; the second up to 100 kwh; the third, to 1000 kwh; the fourth, to 10,000 kwh.

After that, the meter starts over again. To take a reading you must read all four dials of the meter, from right to left.

[Ill.u.s.tration: Figure 2. Meter dials are read from right to left.]

To read each dial, you use the number last pa.s.sed by the dial hand. This may not be nearest the hand. For instance, if the pointer has pa.s.sed 6 and is almost on 7, you read it as 6. Write down the figures in the same order you read the dial, from right to left. Practice reading the meters shown in Figure 3 on the following page.

What's Your Electric Bill?

Meters aren't set back each month when the meter reader comes around.

The difference in the readings from one month to the next shows how many kilowatt-hours have been used. If you know your electric rates, you can figure your bill by yourself. Your power supplier will furnish you with a rate schedule on request.

[Ill.u.s.tration: Figure 3. See if you can read the above correctly. The answers are shown in a box on the next page.]

It will be interesting to you to find out how much it costs to operate the various electric appliances in your home. A sample rate schedule is shown in Figure 4.

[Ill.u.s.tration: Figure 4. Sample rate schedule. Note that as the use of electricity increases, the average cost per kwh is reduced.]

Estimating Operating Costs

To find the cost of operating any single appliance, three steps are necessary:

1. Learn the wattage of the appliance.

2. Estimate how many hours the appliance is used.

3. Find its operating cost.

_To Find Wattage:_

Watts, you know, are the measure of electrical power. They are the product of voltage (pressure) times amperes (rate of flow). Volts times Amps equals Watts. The nameplate on the appliance will give the voltage required for proper operation as well as either amperage or watts. If it gives wattage, you have the information you want. Otherwise you must multiply volts times amps to get the wattage. When voltage is given as 110-120, use 120 as your voltage. 120 volts is nominal today.

_How Much Will You Use?_

Now that you know the wattage of the appliance, multiply this figure by number of hours the equipment operates in one day. Divide this by 1000 to get the kwh. Now multiply the result by the number of days the appliance is used each month. This tells you the number of kwh used by the appliance during the month.

|---------------------------------------------| | | |Example No. 1 | |_Yard Light:_ 300-watt lamp | | | |Amount of use: 3 hours per night. | | | |Multiply lamp wattage times hours of use | |per night to get watt-hours per night. | | | |300 times 3 = 900 watt-hours per night. | | | |Divide watt-hours by 1000 to get kwh per | |night. | | | |900 divided by 1000 = .9 kwh per night. | | | |Multiply kwh per night times 30 to get kwh | |per month. | | | |.9 times 30 = 27 kwh per month. | | | |If the yard light is used 3 hours per night, | |it consumes 27 kwh per month. | |---------------------------------------------|

Example No. 2

_Coffee Maker_: 120 volts, 550 watts (from nameplate)

Amount of use: 1/2 hour per day.

Multiply wattage of coffee maker times hours of use per day to get watt-hours per day.

550 times 1/2 hour = 275 watt-hours per day.

Divide watt-hours by 1000 to get kwh per day.

275 divided by 1000 = .275 kwh per day.

Multiply kwh per day times 30 to get kwh per month.

.275 times 30 = 7.250 kwh per month.

If the coffee maker is used l/2 hour daily, it consumes 7.25 kwh per month.

_Calculate Operating Cost Per Month_

Now that you know the number of kilowatt hours an appliance uses, go to your rate schedule and your electric bill to see what the average kwh costs. Find the average cost of 1 kwh by dividing the amount of your bill by the total number of kwh used in a month.

_Example_: 410 kwh used. $14.35 total monthly bill

Average cost per kwh equals $14.35 divided by 410 kwh-3-1/2 cents per kwh.

Therefore, the cost of operating the coffee maker for a month would be 3-1/2 cents times 7.25 kwh--25.4 or 25 cents. Cost of operating the yard light would have been 94.5 or 95 cents a month.

(a) 6357 (b) 1963 (c) 8996

Correct answers to the meter readings shown on the preceding page.

Adding Low Cost Helpers

You can see, by looking at your rate schedule, that the average cost per kwh gets lower as you use more electricity. To find the cost of operating additional electrical equipment, the cost per kilowatt hour is found from the last "step" in the bill--the lowest cost per kwh of the electricity you're now using. Sometimes power suppliers give special rates for such equipment as electric water heaters.

WHAT TO DO: Find the Cost of Operating Electrical Equipment

Make and fill in the blanks of a chart showing the electrical equipment you have and the operating costs per month.

Make a chart for the home (refer to chart one). Show the probable operating cost of equipment you might add to what you now have.