Radial socket circuit

On a radial socket circuit how can you be sure what MCB and cable size to use when you can't be sure what appliances are going to be used on it i.e. How do you know that the appliances won't overload the cable and trip the MCB?

On a radial socket circuit how can you be sure what MCB and cable size to use when you can't be sure what appliances are going to be used on it i.e. How do you know that the appliances won't overload the cable and trip the MCB?

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You don;t. You use your best judgement and experience in most cases. When you design a circuit you design it for expected use, so if you were to put a 16A radial in a living room of a modern house with central heating etc.. then you wouldn;t expect it to be overloaded with a TV, stereo and a couple of lamps. If someone then plugs in 4 3kw heaters this would be too much for the circuit but it wouldn't be expected.

I generally stick to ring mains usually one up one down and one for kitchen and one for utility if they have one. If there are a lot of appliances in kitchen I will put that in on it own ring. I think if you do this it is very unlikely the circuits will be overloaded. I know a lot of sparks are going for radials these days but I am old fashioned.

Batty

I know a lot of sparks are going for radials these days but I am old fashioned.Batty

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On a radial socket circuit how can you be sure what MCB and cable size to use when you can't be sure what appliances are going to be used on it i.e. How do you know that the appliances won't overload the cable and trip the MCB?

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correction to the above....

appliances won't overload the cable because they will trip the MCB and thus protect the cable by disconnecting the supply.!

that do be relating to reg 433.1.1 (ii) & (iii) pg 73

The trick is to ask the client if they have any special or non-standard electrical requirements.

I have had some who do glass & ceramic work with mini kiln's for firing pottery.

also home based clothing repairs, with half dozen industrial type sewing machines & irons & steamers!

This is where your basic compliance with regs such as 131.8 (pg 16) 311.1 (pg38) come in.

these relate to your requirement to asses maximum demand and ensuring the existing installation is suitable for any alterations you undertake.!

That is how you can be sureGuinness

Thanks for your help guys. Can you help me with this scenario though:

Say a radial socket circuit is wired using a 2.5mm T&E with a 20A MCB (which I believe is common). An iron (1 KW), a kettle (2KW) and a washing machine (2.5KW) are all plugged in on this circuit and are being used at the same time. That's 5.5KW (for argument's sake). Using W = V x I that would leave a current of 24A which would be enough to trip the MCB yet it's not uncommon for these appliances to be used at the same time. So, how can 2.5mm T&E be seen as being suitable for radial socket circuits?

I'm not trying to be a smart-ass asking this, I just don't understand it!

In that scenario I would say that it wouldn't be wired as a 20A radial (sounds like a kitchen)

Kitchens should really be wired as a 4.0mm 32A radial or a 2.5mm 32A ring. Maybe with some appliances being on dedicated radial circuits.

Because a radial circuit is fine for circuits that use less than 20A in most circumstances.

Like I said, it's down the the design of the circuit. A 20A radial feeding a couple of sockets in the bedrooms would be fine, as would it be in a garage for a couple of double sockets. I wouldn't put a 20A radial in a kitchen or utility usually. You can theoretically overload any socket circuit, it isn;t just limited to radials.

as said you would install as per the clients needs. i don't think i have come across a domestic installation where a circuit is over loaded, i've seen it in comercial installs where people have added a load of halogen security lights to a lighting circuit and over loaded it.

Another thing to take into consideration, is that those appliances do not all draw the maximum current all the time.

Kettles draw maximum current just as they are coming to the boil.

Irons draw maximum current when they are heating up. When they reach temperature, current draw is minimal, if at all.

Washing machines are a bit more complex. They draw current when heating, when the drum is turning, and when the pump is pumping.

The amount of draw depends on what is happening. Maximum draw is usually when heating and the drum is turning at the same time.

Some machines will turn off heating whilst the drum is turning, others don't.

Thanks for your help guys. Can you help me with this scenario though:Say a radial socket circuit is wired using a 2.5mm T&E with a 20A MCB (which I believe is common). An iron (1 KW), a kettle (2KW) and a washing machine (2.5KW) are all plugged in on this circuit and are being used at the same time. That's 5.5KW (for argument's sake). Using W = V x I that would leave a current of 24A which would be enough to trip the MCB yet it's not uncommon for these appliances to be used at the same time. So, how can 2.5mm T&E be seen as being suitable for radial socket circuits?

I'm not trying to be a smart-ass asking this, I just don't understand it!

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thats the max load of the appliances- in reality, they wont use that power all the time. the 2KW kettle will use 2KW whenever its on. the iron may use 1kw whilst heating, but will switch off when hot and come back on when cooler. the w/m has a heater which will heat the water, then turn off - so there is unlikely to be the 5.5KW for long durations. they may all overlap every so often, but it shouldnt be a problem

beaten to it!

it's also unlikey that they will be boiling a kettle whilst iorning whilst making toast whilst using a microwave whilst etc....... so you also take diversity into account

I have had to do a rethink or should I say a reinstall because when I did a commercial installation earlier this year the kitchen onlt had a washing machine and a kettle and one microwave. After installation I found out that at lunch times they had two kettles 4 microwaves, the washer and a portable heater all on the go at once.

My circuit would not handle everything so I have had to go back and beef it up for the occasional 20 minute demand.

I have had to do a rethink or should I say a reinstall because when I did a commercial installation earlier this year the kitchen onlt had a washing machine and a kettle and one microwave. After installation I found out that at lunch times they had two kettles 4 microwaves, the washer and a portable heater all on the go at once.My circuit would not handle everything so I have had to go back and beef it up for the occasional 20 minute demand.

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Get a genny in cheapest option.

Kettles draw maximum current just as they are coming to the boil.

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[quote name='Andy

Hmmm. Pump usage is negligable, IMO. Drum rotation is generally only a sizeable load whilst spinning; during which time the heater is obviously off. If asked, I`d have said that the heating cycle was the main issue.Though I stand to be corrected...........

KME

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Yep, but the heater will generally be 1200W, maybe up to 2000W on some older machines, so not an overly high load.

Kettles draw maximum current just as they are coming to the boil.

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Mine doesn't. Mine uses the same number of amps throughout the cycle. I can verify this from a little gadget I got from Maplin

http://www.maplin.co.uk/Module.aspx?ModuleNo=38343

Got it on offer for <

I've never checked the current draw on kettles.

I have in the past conducted experiments to show that liquids absorb a substantial amount of energy when changing from to a gas.

This is the basis upon how fridges and air conditioning units work.

If you were to heat a volume of water with a steady heat source, you would observe that each rise of one degree in temperature would take the same amount of time, until you reached boiling point. Depending upon how much heat is applied, the time taken to go from 99

I've never checked the current draw on kettles.

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I have

If you were to heat a volume of water with a steady heat source, you would observe that each rise of one degree in temperature would take the same amount of time, until you reached boiling point. Depending upon how much heat is applied, the time taken to go from 99

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