Foreword

In this article I’m going to use UK mains-supply electrical characteristics to determine the loads used by various examples of equipment using Ohm’s Law. For the purposes of calculation using Ohm’s Law, the principles used herein can equally be applied to the USA by substituting the electrical characteristics for those used in the US; such as 120 volts in place of 240 volts, etc.

I’m unsure whether the suppliers use the same method of consumption measurement in the US; i.e, a “unit” or “units”. I am assuming that they do, and that a unit of electricity is calculated in the same way as it is in the UK. Perhaps someone would like to comment on this?

I’m also using UK currency to calculate the costs.

Measuring Consumption

In the UK the suppliers measure consumption of electricity in units, and bill accordingly for the number of units used over a period of time.

But exactly what is a unit?

A unit is calculated as a single ampere of current drawn over the period of an hour at the AC mains voltage.

That helps one heck of a lot. – Thanks. So how much electricity does, say, my ceiling light use for instance, and how much does it cost to run it?

To answer that we’ll first need to know how much current your ceiling light is drawing from the mains supply. What is the wattage rating of the light bulb that you’re using in it? In this example we’ll use a 100 Watt incandescent tungsten-filament light-bulb.

(That’s the old-type bulb that’s been in use for years until low-energy lamps were invented.)

This light-bulb is running on a UK mains voltage of 240Volts AC.

(There are variations in the exact UK mains voltage depending upon time of day and area: It can vary between around 212 and 256 Volts. (For instance, the current mains voltage here at time of writing is 243 Volts, according to my UPS’s software.) However it’s commonly around 230 to 250 Volts at most times and in most areas. For this example we’ll use 240 Volts.)

We now turn to Ohm’s Law and use the equation I = P/V; where P = power in Watts, I = current in Amperes, and V = voltage in Volts.

Therefore, in this example: -

I = 100 Watts/240 Volts

I = 0.4762 Amperes (Amps)

Over an hour, then, this bulb will burn 0.4762 of a unit in electricity. Over 2 hours it’ll burn 0.9524 of a unit.

If the price of electricity were 10 pence per unit then this bulb costs 0.4762 X 10 = 4.762 pence per hour to run.

To cut your costs of this ceiling light you might install an energy-saving lamp in it instead. A 35 Watt energy-saving light using fluorescent-based technology will produce the same amount of light as the 100 Watt incandescent light-bulb. let’s calculate the savings on electricity used: -

I = 35 watts / 240 Volts = 0.1458 Amps, Over an hour that’ll burn 0.1458 of a unit of electricity.

Savings

If the price of electricity were 10 pence per unit then this bulb costs 1.458 pence per hour to run: A saving of 3.304 pence per hour.

The cost of the energy-saving lamp will be somewhere in the region of 5 times that of the incandescent bulb. The incandescent bulb costs about 45 pence. The energy-saving lamp costs about £2.25p.

The energy-saving lamp lasts around at least 6 times as long as the incandescent bulb; therefore the extra cost is mitigated by this; saving around 7.5 pence on the replacement cost of the product every 1000 hours (The expected life of an incandescent bulb.) approx. Total replacement saving = 48 pence per energy-saving lamp used.

During the 6000 hours of the energy-saving lamp’s life, at a saving of 3.304 pence per hour, you’ll save a total of £198.24p in electricity. Add to that the replacement saving of 48p gives a grand total saved off your electricity bill of £198.72.

This saving could be over a period of between 250 days (Just over 8 months of constant usage.) and around 25,000 days (66.665 years); depending upon the amount of usage. Whatever the time period; you are saving around two-thirds of the electricity you’d have otherwise have used, as well as the cost of a weekend holiday at today’s prices.

If you were to use energy-saving lamps all over the house, rather than the old incandescent light-bulbs, – think of the savings you could make in terms of power-efficiency as well as money!

Rip-Off Britain

I’ve been using the cost of 10 pence per unit in the above calculations as the cost of electricity. The current cost of electricity in the UK (Rip-off Britain) is currently more than this; although electricity suppliers have no excuse (Other than the indefensible reasons they use.) at this point in time for not reducing their charges: -

“Oh we’ll reduce the costs when the savings trickle down to us.” is utter faeces! They’re making a fortune off the British consumers, who stupidly-grin-and-bear-it in true British stiff-upper-lip fashion. Wake up UK: You’re being conned, as usual. We’ll soon develop a worldwide reputation as a nation of mugs; just before we join the Third-World.

Mugabe’s type are already running the UK; just a lot more subtly. Didn’t you notice?

Anyway that aside; with things as they are it’s even more important to save on electricity consumption; even if only to stop the thieving electricity suppliers from making such a massive profit.

It’s worth doing what I did a couple or three years ago: Take a note of every light in the house. Is an energy-saving lamp fitted? If no; what is the wattage of the existing bulb?

If 40 watt; replace with an 18 Watt energy-saving lamp.

If 60 watt; replace with an 25 Watt energy-saving lamp.

If 100 watt; replace with an 35 Watt energy-saving lamp.

The only problem may be those lights that have a dimmer-switch: In many cases it is not possible to run an energy-saving lamp via a dimmer-switch. I have 1 such light; but I rarely use it anyway. – Somewhere in the region of 4 hours a week if that.

Having assessed the lighting situation thus; go out and buy the corresponding energy-saving lamps and install them. Keep the old incandescent bulbs for emergencies. – (But don’t get to the state where you’ve replaced all your dead energy-saving bulbs with the old lamps, or you’ll be right back to square 1. ) – You’ll notice the savings after a year or so.