Power Overload?

duncan303

loads of replies since I started writing this...... but will still post anyway.

Firstly you are very right to be cautious, especially concerning overloading a trailing socket extension lead.

there are two ways you can work out if what you are attempting to do is safe.

Firstly using a little little maths.

asumme your trailing socket has a maximum rating in Amps of 13Amps at 250Volts(this will be written on the actual trailing lead), using the basic principle that:

Volts X Amps = Watts

therefore 250(Volts) X 13(Amps) = 3,250 (Watts) or 3.2Kw (KiloWatts)and could be written VA (voltageAmps)

therefore the MAXIMUM rating (or the tested safety limit for the common trailing socket) is 3.2Kilowatts or 3200 Watts. But please please check yours it may not be the same.

Now look at your equipment:

lets say for example that a desktop pc draws approx 400Watts.
an old style glass monitor approx 70Watts
a laser printer approx 250Watts (peak)
a separate pc amplifier with speakers (a guess 30Watts )
your light bulb say 100Watts

summing these adds up to 800Watts.

However each of your individual pieces of equipment will have the maximum ratings printed on then either underneath or on the back, now you would be able to calculate the individual current requirement for each piece.

I have been pretty extavagant with the generalised current consumptions above, but you will see that you should be able to add another desktop pc and cathode ray tube (CRT) monitor comfortably.


I have really oversimplified the physics above, and have deliberatly not included UK Grid supply specifications RMS Peak etc etc.

Now the second way that requires no arithmetic or algebra or hunting underneath equipment, and that is to change the fuse rating in the plug connected to the trailing socket.Fuses produced to BS 1362 are safety equipment and come in a range of values 1Amp 2Amp 3amp 5Amp 7Amp 10Amp 13Amp. The most common and easily available are 3Amp 5Amp and 13 Amp.

So to anybody who is concerned about overlaoding a trailing socket, calculate the load as best you can and then replace the fuse in the plug with a more sutable value, in the example given above a fuse rated at 5Amp would be more suitable(5Amp x 220Volts RMS = 1100 Watts).

Or an even simpler method: simply place the lowest value Fuse you have in your "fuse Kit" in the plug and see if it "blows", and if so, place the next highest rated in its place. (I am assuming that you might be using a voltage surge protected trailing socket)


Anyway Hope this helps and does not confuse.........




Oh Yeah. Electricity can be fatal, It is understood the changing/replacement of fuses within a BS 1363 Plug can be undertaken by non qualified persons.


PS if any of the plugs feel warm to the touch then that should be a warning, never let plugs or cables get hot! Avoid coiling up any electrical flex in a tight circle, do not to cover the trailing lead with carpet/blankets etc try to allow free air to circulate around the "spaggetti"............... perhaps I should never have decided to reply somebody is bound to jump on me for something I have forgotten........

rgds.


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Cardew

jd87 wrote: »

It could easily be pushing the order of magnitude you suggest, which in older wiring could be dangerous. As I said in my original post, yes if the wiring meets the modern standard then it is most likely fine.

I am not sure what you mean here.

The house wiring(the ring mains) go around the house, so several sockets will be on the same wiring.

As stated above(several times) the load the OP has on the extension leads is very likely to be well under 1kW, so absolutely no problem.

Would you object to a single 3kW heater being plugged into any particular socket in the house on the grounds it is dangerous?

The biggest objection to using multiple socket extensions is where equipment is frequently plugged into and unplugged from the extension lead. This is for the leads themselves, not the loading on the wiring.

where equipment is frequently plugged into and unplugged from the extension lead the generally lighter construction of the domestic type may result in embrittlement and damage to the plastic casing and eventual failure of the internal metal contacts. Earth continuity may be lost and, if faults go undetected, may result in electric shock, with the possibility of arcing and electrical fires. Problems also arise if unsuitable extension leads are used in damp or dry conditions,

duncan303

The standard supply provided by the national grid to domestic dwellings is single phase and usually terminated at the service head by a 100Amp cartridge fuse.

100A (amperes) X 220V Volts RMS = 22000W (Watts) 22Kw (KiloWatts) a little over 7 domestic kettles.

it is down to the designer of the installation to determine how this is distributed within the dwelling both for safty and convienience.The design of ring mains (socket outlets which are connected together) has been traditionally divided into the storeys in the dwelling.This makes it easier for the householder to determine which fuse is associated with which socket.This method does not take into account equal distribution of loading. There is no limit to the number of sockets on a given ring main circuit but there is a requirement to limit the length (100meters). furthermore if the ring main is constructed in 2.5mm single cored cable (T/E) then the current rating of the circuit will be limited to and be fused at 32A (amps)

so 32A x 220V = approx 7000Watts 7Kw (KiloWatts) thats only two kettles and a toaster.

This is probably fine for bedrooms used in the normal way, bedside lights alarm clocks hair dryers etc, but not too good if one has reclusive teenagers with Ikea Kitchen in a cupboard affair with microwaves and kettles etc. plus all the sound equipment la di da.......

similarily the load on a ground floor ring main is very often close to the rated limit. Dishwasher washing machine microwave kettle entertainment centres etc etc etc... so it is up to the designer to layout the circuit in a way which they believe to be the way in which the house is intended to be used. but there is nothing to stop bedrooms subsequently being used for recording studios or garages having wall to wall chest freezers. Oh and almost forgot turning bedrooms into offices

The added problems arises with current stability, it may well be that a person can manage to get four kettles running on a single ring main if they turn them on individually, but if they tried to turn them on all at the same time they may well have problems. It is therefore possible to have current flowing in a circuit without the fuse blowing beyond the rating of the circuit. (not too good).

The national grid buy in electricity according to what television programmes are expected, in the adverts when people all turn on thier kettles for example.(so thats at least one person who buys the Radio times!!).



To summarise: it is technically possible to have 400 13Amp double socket outlets on a single ring main, thats 800 possible trailing sockets each with six sockets........ WOW thats four thousand eight hundred 13amp sockets and BUT YOU MAY STILL ONLY SAFELY plug in two kettles and a toaster.

just about to work out how many sockets oulets would fit on a football pitch but am hungry and off to cook some supper, plus I am beginning to sound a bit like a geek.


rgds.

Mankysteve

Surely a single plug sock is designed to take a fair bit more than 13 amps. The maximum amp use for a plug should be 13 thus that will blow before you over load the socket

duncan303

Mankysteve wrote: »

Surely a single plug sock is designed to take a fair bit more than 13 amps.

there are many different types of socket, are you referring to the square three pin socket that is moulded onto all domestic appliances sold in the UK that have 13A 250V clearly stamped on them?

or are you reffering to the dielectric breakdown of the material itself when you say "a fair bit more"? a bit like overclocking a processor chip, or driving over the speed limit. How much "more" would you be suggesting?

At what current will a fused plug no longer funtion as intended.? well the weakest component in the sub assembly is indeed the fuse take that out and replace with a solid link.

Now ask the question do I need this to work reliably for more than two minutes..... lets say twenty or thirty years or even more

put another way assume the plug that you would want to exceed the rating on was attached to your life support machine and the nurses came in and you could hear them discussing wether or not add a coffee machine or two onto your trailing socket. Do you think you would get a tad anxious about reaching your next birthday?


Are you refering to the plug itself as an isolated component or a whole trailing lead assembly?

rgds

mikey72

duncan303 wrote: »

plus I am beginning to sound a bit like a geek

If you have a standard 13A plug, into a single socket, no matter what you plug into the leads attached to it, plug in too much and you'll blow the fuse.
What should be banned are the old unfused double or triple adaptors, where you could plug in two or three 13A loads, and draw up to 39A from a standard wall socket, while the weight of the plugs slowly pulled the adaptor out.

DVardysShadow

jd87 wrote: »

Because you're making the big assumption that the OP's wiring actually meets those standards...

The only big assumption is that it all comes from a 13A socket.

DVardysShadow

duncan303 wrote: »

Surely a single plug sock is designed to take a fair bit more than 13 amps.

there are many different types of socket, are you referring to the square three pin socket that is moulded onto all domestic appliances sold in the UK that have 13A 250V clearly stamped on them?

or are you reffering to the dielectric breakdown of the material itself when you say "a fair bit more"? a bit like overclocking a processor chip, or driving over the speed limit. How much "more" would you be suggesting?

At what current will a fused plug no longer funtion as intended.? well the weakest component in the sub assembly is indeed the fuse take that out and replace with a solid link.

....

All he is saying is that they are properly engineered, with a factor of safety - ie they are well adequate to run at their stated load.

duncan303

ok fair enough. yes.... standard 3 pin domestic fused plug is capable of withstanding more current than the maximum fuse currently available 13Amp, thats the nature of a safety device. I accept I may have misread the post.

The full details can be found in the European Standard/ British Standard 1362.

my two main posts were slightly differrent the first regarded only the trailing socket and assumed that the socket into which it was secured had UNLIMITED current available.

The second post addressed the wider issue of the standard domestic ring main and followed on to earlier posts which intimated to some designers view that adaptors/trailing sockets should not be made available to the uneducated general public.

Designing a dwelling installation that one believes may be used for multiple occupation say Bedsits for single mothers is a responsibility too far, each occupancy unwittingly having gone out and purchased trailing leads being advised with the laddish attidue of "just plug those puppies in untill it blows" with babies in the building..........:eek:

Fuses do not always prevent fires.. just ask your local fire officer!!! fuses are a safety device NOT I repeat NOT a failsafe.

Knowing how much equipment you can safely plug into all the sockets and use at the same time in your home should be taught in schools.


Reittterating: an individual domestic ringmain is designed to only have a load equivalent to 2 kettles and a single toaster.


Ok time now for those that are concerned: ask your local qualified electrician to come and perform a load assesment test and inspection and advise you correctly. other responsible persons can turn off at night (always good housekeeping), for some of you out there.......... I just hope to god you do not live anywhere near me or my loved ones.


The OP question is not simplistic .............


and a further thought/ observation.........very soon the time will come when devices plugged in will "be seen" by a microprocessor embedded within the domestic consumer unit that will monitor and control the whole circuit as the designer intended. This will clearly annoy some consumers who feel thier "rights??" will have been stolen?..

Another step in the nanny state or an absolute necessity....Discuss?








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espresso

duncan303 wrote: »

Reittterating: an individual domestic ringmain is designed to only have a load equivalent to 2 kettles and a single toaster.

What relevance does that have to the OP's question?

The OP question is not simplistic .............

Yes it is, her total load is well within the maximum for a single 13A socket!

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