Power Usage

Now that I am in the UK, I had a question for the gallery (or at least Paul!).  How much can a single circuit take?  I do not want to overload my circuits, but most of my plugs in the living room are on the same circuit and I would rather not get an extension cord I don't need.  It looks like I will have a PC, two monitors, 2.1 speakers, a printer, a 32" CRT TV, DVD player, VCR, wireless router, a few lamps, a few laptops, and the occasional vacuum/hoover.  Should I get an extension cord to divide this between two circuits or will I be sufficient with one?

Whereas US homes are often wired on a branch system, each outlet on a separate circuit, the UK standard is a "ring circuit". Each ring circuit is usually protected by a 30 amp rated fuse or circuit breaker. The rating of a fuse or circuit breaker is the maximum current which it will pass indefinitely. At 240 volts, 30 amperes represents a power use of 7,200 watts. I doubt if the items you listed would even add up to 1,000 watts. You can check the power rating of each item - it is listed on a label - and total them all.

Sweet!  I had this problem in the States and ran an extension cord from one room to another to balance my usage.  72kW is way more than I'll need.  Thanks for the info, I would have never guessed that one.

Sweet!  I had this problem in the States and ran an extension cord from one room to another to balance my usage.  72kW is way more than I'll need.  Thanks for the info, I would have never guessed that one.

Just to be pedantic (and also so you won't accidentally go over the allowance), it's 7.2kW, not 72kW (72kW = 72,000W!).

Just to be pedantic (and also so you won't accidentally go over the allowance), it's 7.2kW, not 72kW (72kW = 72,000W!).

Yes, the prefix 'kilo' means 'one thousand'. Pedantry is pointless fussing over minor things, whereas being out by a factor is 1,000 is hardly minor.

I noticed I said that impleri's list would not add up to 1,000 watts, but I overlooked the vacuum cleaner. My AEG Vampyr uses 1,800 watts on full power, but even so impleri will be fine.

30-amp rings have been the norm for decades, but you will sometimes find other arrangements, such as 20A radial circuits.  That's still 4.8kW, more than enough for all the items listed.   Laser printers can draw up to a kilowatt or so when running, but the typical home inkjet printer and all the other little gadgets consume very little power.   You have to remember that 20A at 240V provides twice as much power as 20A at 120V.

The main issues with overloading these days come in the kitchen when people start to add in washing machines, dishwashers, and dryers, sometimes all on the same circuit with the kitchen outlets which might also be supplying toasters, kettles, and other fairly high-power devices.   

it's 7.2kW, not 72kW

Yep, you won't find too many domestic properties in Britain with a 300-amp service!      

Whereas US homes are often wired on a branch system, each outlet on a separate circuit

It's normally only receptacles intended for dedicated uses which are one per circuit, such as outlets provided specifically for a washing machine, garbage disposal, window air conditioner unit, and similar heavy current users.

The NEC specifies that at least two 20A (120V) small appliance circuits be provided in the kithen & dining areas, then in the rest of the house receptacles and fixed lighting points are combined on general-purpose 15 or 20A branch circuits, calculated on a minimum  allowance of 3 watts per square foot.   

Yes, the prefix 'kilo' means 'one thousand'. Pedantry is pointless fussing over minor things, whereas being out by a factor is 1,000 is hardly minor.

Yeah, I didn't quite phrase that right, sorry (I do know what pedantry is and I am also a physicist so I know the importance of getting factors of magnitude right ).

I know the importance of getting factors of magnitude right

Oh yes! 

Out by a factor of 10 one way -- Sits there and does nothing.
Out by a factor of 10 the other way -- Lots of smoke!   

Aside from my Super Death Ray gun, I doubt I'll go over the limit.
Another question: isn't standard voltage now 230V?

isn't standard voltage now 230V?

Nominally, yes, but in practice, no.

Since 1960, the supply voltage in UK domestic premises has been 240 V AC (RMS) at 50 Hz. In 1988, a Europe-wide agreement was reached to change the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230 V (CENELEC Harmonization Document HD 472 S1:1988).

As a result, the standard nominal supply voltage in domestic single-phase 50 Hz installations in the UK has been 230 V AC (rms) since 1 January 1995 (Electricity Supply Regulations, SI 1994, No. 3021). However, as an interim measure, electricity suppliers can work with an asymmetric voltage tolerance of 230 V +10%/−6% (216.2 V to 253 V). This was supposed to be widened to 230 V ±10% (207 V to 253 V), but the time of this change has been put back repeatedly.

So there has been no need to change the voltage in the UK.

And seeing as the existing system was designed with +/-6% tolerances in mind, and the current official tolerance of 230V +10/-6% is contained wholly within the proposed 230V +/-10%, from a practical point of view it will really make no immediate difference if and when the official change to the wider tolerance takes place.  No doubt that in time we'll eventually see supply transformer taps set for 230V nominal, but for all practical purposes at the moment it's still 240V +/-6%.   

In places where loads have increased considerably and voltage drop over distribution cables has been a problem, taps are already set at the high end of the scale in order to prevent the voltage dropping below the minimum during peak times.  That means that at low-load times, the nominal voltage will ride at the high end of the tolerance limits, say 245V plus. 

Since 1960, the supply voltage in UK domestic premises has been 240 V AC (RMS) at 50 Hz.

Full standardization at 240V +/-6% wasn't achieved until the early 1970s. 

In the 1960s there were still regional variations with declared nominal voltages of 220, 230, 250, etc.    Although becoming rarer as time went on, there were still 3-wire D.C. systems being used in the older parts of some towns too, with declared nominal voltages of anything from 200/400 to 250/500V.

Although becoming rarer as time went on, there were still 3-wire D.C. systems being used in the older parts of some towns too, with declared nominal voltages of anything from 200/400 to 250/500V.

I seem to remember hearing about people doing polarity tests by sticking the 2 wires an inch or two apart into half of a potato and seeing which one got a purple stain around it (there was a bulb in series!) but I can't remember which pole it was or why the stain appeared, something to do with starch I think.

Also, towns which had municipal tramways and power systems often used to feed the trams at 500v across the outer wires of the 3 and houses were fed from the inner and one of the outers (50% from each one) so that lights dimmed when a tram went by and there was loud "motor hash" from radios due to noise from the motor commutators being impressed on the supply ("Tramcar interference").

Radios and TVs were made to a so-called "AC/DC" design long after AC was widespread, to avoid the cost of a transformer. Live chassis, series heater chains, and those awful "line cords".

I seem to remember hearing about people doing polarity tests by sticking the 2 wires an inch or two apart into half of a potato and seeing which one got a purple stain around it (there was a bulb in series!) but I can't remember which pole it was or why the stain appeared, something to do with starch I think.

It turns a greenish color around the positive electrode.  O.K., I have to confess that it's been a long time since I did that experiment and I couldn't remember the electro-chemistry behind it, so I raided the kitchen to repeat the childhood experiment.  (Would anyone like a baked potato for supper?  I'll just crank up the voltage and let it sizzle for a while.....  ).

There were a number of other tricks along similar lines, such as dipping the wires into a glass of vinegar solution and noting which electrode "fizzed" the most.   I have that suggestion in an old 1930s household book, the object of determining polarity being to connect a radio accumulator across a light switch for charging, so that the lamp would be in series to regulate the current.   

Also, towns which had municipal tramways and power systems often used to feed the trams at 500v across the outer wires of the 3

I think most of the trams were on independent supplies, at least originally, since they had only a single pickup and earth return via the running rails.   They'd have needed to convert to twin overhead lines & pickups to run at 500V across the outers of the public supply.

Could you be thinking of trolley buses, since they needed two pickups anyway due to the lack of earth return via the wheels?

Radios and TVs were made to a so-called "AC/DC" design long after AC was widespread, to avoid the cost of a transformer. Live chassis, series heater chains, and those awful "line cords".

Have you seen the line cords fitted to those "All American Five" sets which were imported during the 1940s?   Need to drop an extra 120 volts?   No problem, just fit a 15 ft. line cord - And hope the customer doesn't try to shorten it!

P.S. I understand there are still some parts of London (and possibly other cities) where the houses along a particular road are distributed between two of the phases instead of three.   Apparently during the conversion from D.C. to A.C. in order to save ripping up every street to lay new cables, they just ran 4-wire feeders to strategic points and then spliced the existing 3-wire cables to them, so one road would be on red & white phases, the next on white & blue, the next on red & blue, and so on.