How many amps does your house need?
This is a bit like "what's the best car to buy?" It is very subjective. Some people can survive on the absolute minimum of power for years without once blowing a fuse. Others need as much electrical current as a small warship!
We have a number of clients with electricity supplies of 3-phase 250 amps. In total theoretically 750 amps. Others have the 20 or 25 amps that was the standard up to a few years ago
Most have the new standard of single-phase 40 amps and those with central air-conditioning often have three-phase supplies of 25 or 40 amps (each phase).
The trick is to spread the current loading such that the load does not peak above the rating of your main fuse.
Take a standard size apartment that has a single phase 40 amp supply and lets add up the typical peak power requirements of all the electrical appliances in the apartment:
And of course there are loads more appliances particularly in the kitchen that we could add to this list.
The total amperage on this list is 176 amps!!
It is very unlikely that all these appliances will be operated at the same time but just running a few of them will bring the current requirement to well over 40 amps.
So what do you do? In trying to balance your power requirements, you need to know a little about when the appliances actually draw current.
Firstly the above ratings are peak current which means that the appliance isn't always drawing this current.
A fridge's compressor is off a lot of the time. The same goes for an air conditioner , a microwave. clothes iron and water heaters.
A washing machine and a dishwasher draws the maximum current from about 5 mins after it is turned on, until the water has reached the correct temperature (maybe after 10 minutes).
So if you're short on amps and want to do the washing, delay operating the dishwasher or clothes dryer or water heater for 15 minutes. In fact try and run the dishwasher in the early hours of the morning so long as it doesn't disturb people. Also you can set the water heater to heat water before everyone gets up.
As for air-conditioning, if you have a small electrical supply and install a whopping great central airconditioner that takes say 22 amps, you're asking for trouble. The air-conditioner is either on or off and when the compressor is working, it will take the whole 22 amps even if you set it to low. The compressor doesn't have a low power setting, it just turns on and off according to the heat required. One day hopefully someone will invent a variable power compressor.
A possibly better arrangement would be to have two or more separate air-conditioning units, covering different parts of the flat. This way if you are only in the living area, you can just run one a/c with a load of say 11 amps.
Even if you run both units, the electrical load will be better distributed as the compressors will not be running together continuously (assuming separate thermostats) The capital cost of two machines will be higher of course and you will need a larger area outside your house for the compressors. The running costs however will be lower.
In the UK, 35-40 amp ovens, hobs and electric showers are very common. Until the Israel Electric Company do the right thing and offer a 100 amp power supply as standard, heavy duty single phase appliances will remain a pipe dream in Israel. Electric showers here are rated a maximum of 4.5Kw which translates to a current rating of just under 20 amps. Take it from me, but this doesn't give you a good shower unless you feed it with pre-warmed water, and I am not aware of a three-phase shower unit. If and when we manage to get a 100 amp single phase supply, then the importers of British showers and hobs will do a roaring trade. The localy manufactured Atmor units are poorly made. I burned out three before I gave up. My parents in the UK have a 35 amp Redring electric shower which has been working perfectly for the past 30 years!! The only reason they may change it would be to upgrade to a more powerful model.
When you buy a clothes dryer, choose one that has a half-power setting. Electric kettles come in all sorts of power ratings from 800 watts to 3000 watts (in the UK at least).
Lighting is often thought to be insignificant in it's power requirements. That may have been true twenty years ago but the levels and powers of lighting have increased significantly since then.
We have a client who has 6000 watts of lighting in his living room alone! That's a whopping 26 amps load just for one room. Don't forget that every watt of lighting is immediately converted into a watt of heating. To prevent the room roasting therefore in the Summer, he needs to have 6000 watts of air-conditioning removing all that heat on top of the normal air-conditioning requirements. His lighting was designed by American architects who obviously weren't too concerned with the environmental issues.
With a a bit of thought, using a mixture of specialty lights and low-power fluorescents, the 'heating' bill could be quartered.
One sure way of lowering the electrical current usage is to heat with gas or diesel (called solar in Hebrew - yes as in the Sun!!) In general, air-conditioning is the cheapest form of heating followed by Diesel, Electricity and Gas. Even though air-conditioning is powered by electricity, it uses only a third of the power that any electric heater would use for the same heat output. To put it another way, if your air-conditioner is drawing 9 amps and so is taking about 2000 watts of electric power, its putting out around 6000 watts of heat. The additional free heat is drawn in from the outside. The unit is called a heat-pump for this reason. Oil and gas powered heating systems do use electricity but very little - typically less than an amp - for the ignition and the water circulation.
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Copyright Jonathan Greenstein, Jerusalem, March 2003
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