How much electricity is consumed

[deleted-67313]

My son wants to do a project on electricity. He wants to know how much electricity is consumed when he switches on a bulb or tv etc.. How can we measure electricity and do this experiment,?

[rmarz]

nissan - This would be a very interesting experiment that will give you an appreciation for how much or little electricity you are using in your home. However, to calculate the power used by our various household electrical appliances can be fairly tricky. When you turn on a 75 watt light bulb, you can assume you are consuming pretty close to 75 watts. Some appliances will have enough 'nameplate' data to tell you what the power consumption is. There are current measurement devices, often in the category of 'clamp ammeters' that will measure the current consumed by a device indirectly. They require that you open the jaws on the device and 'clamp' them around one of the conductors. That is not straightforward and I don't think you want a young student inside your electrical entrance box or around hot wiring. You can fashion an extension cord where you can carefully separate a small portion of the parallel conductors so you can have access to one conductor. In a simple two prong cord, carefully slit the center web of the flat wire and split apart for about 4". Make sure no copper wire is exposed. However, I would recommend getting a short, grounded extension for this, as it will allow you to measure two pronged (ungrounded) as well as three pronged (grounded) appliances. With this kind of wire, carefully remove about 4" of the outer insulation to expose the inner wires, usually color coded as black, white and green. Be careful not nick the insulation on the current carrying wires. Only do this modification when the cord is unplugged so you can inspect that none of the wires was damaged before using. Then the extension cord can be plugged into the wall socket, the appliance to be measured plugged into the extension cord, and the clamp ammeter placed around one of the current conductors (the black or white wire). This will give you a reading in AC amperes of the power being consumed, and multiplying this measured current (in amperes) times 115 (the nominal voltage at the socket) calculate the power in watts. To be more precise, the clamp ammeter is usually a voltmeter as well and you can measure the actual AC voltage at your house and use that value.

All this assumes you may have access to a clamp ammeter. If you can't access one, they can be be purchased for as little as $15-20 in discount tool stores. A national chain of imported tools has one on sale now for $9.99. You may get other advice on how to safely conduct this experiment, but this is a pretty effective approach and will give you some good understanding of the energy we consume. While you are not getting directly close to live high voltage, always have an adult, preferably one that is comfortable making this extension cord modification, help you with the experiment.

Rick Marz

[rmarz]

nissan - I'd like to update my original answer. Another student was doing a similar measurement experiment and introduced me to a device called a Kill-A-Watt meter. (you can find it in today's postings). It is a device that will measure the power being consumed by any appliance or device plugged into it. A simple search on the internet shows this device to be priced below $20 from several sources. Ideal for what you were trying to do, actually a handy device to have around while plugging together holiday light strings. Your only limitation is measuring 'wired in' lighting such as ceiling lights. But if it has a plug on the end, you are good to go.

Rick Marz