Power for Washing Machine and Dryer

[whufcboy]

Hello

Wondering if anyone can advise here. I am moving a washing machine and tumble dryer to the other side of the kitchen and need some advice on what kind of power outlets I need to make available.
At the moment they're plugged into a 4 gang extension socket (not used at same time) so not ideal and want to do this the right way. I've opened up ring main before and installed extra sockets then obtained signoff etc so not complete novice but not sure what would be needed for these appliances.
They will be located underneath the kitchen counter and above that there is a standard 13A 2 gang socket. Can I just spur another double socket to underneath the counter space? or do I need some sort of fused socket?

Appreciate any help here.

 

[PrenticeBoyofDerry]

You could spur from it, but it would depend whether this socket is part of the true ring or a spur, as you cannot spur from a spur.
Adding a 13A fused connection to protect outlets would restrict you to 13A maximum. W/M and T/D combined load could well be pushing up to 6kW, around 26A. So not ideal to do that.
I would consider above worktop isolation for each appliance down to a single unswitched socket outlet, keeping the ring complete through the isolation switches, these can be 20A rated DP isolators or switched 13A FCU.
It is important to make yourself aware of permitted safe zones and the requirement of RCD protection for newly buried cables and socket outlets.

 

[Adam_151]

these can be 20A rated DP isolators

Only if the manufacturer is willing to guarentee that the supply terminals are suitable for looping a 32A ring through. Otherwise you must assume they are rated to 20A, and would you you a 20A joint box to joint a ring?

In reality the terminals are probably exactly the same as on a 13A fused spur from the same range, but if you are the one signing to sa design compliant with 7671...

 

[PrenticeBoyofDerry]

As I understand it the ratings are in reference to the switch load contacts, not the terminals.
For example a 13a socket outlet on a 32a rfc is not a problem, as it relates to the 13a load, not the capacity of the screw terminals.
I am happy to be corrected though!

 

[Adam_151]

So what rating should the supply terminals on a 20A double pole switch be rated at?

32A... why not 40A or 50A... or even 100A

Is the limit actually defined by what can physically be terminated

Silly examples, but in the absence of a separate rating we have to assume a maximum of 20A for any part of it...

BS7671 specifically refers to accessories to BS1363 on a ring final circuit, this includes spurs and sockets but 20A switches arn't to this this standard.

 

[PrenticeBoyofDerry]

So that would mean you could not connect for example a 45A isolator or a flex outlet plate to a rfc as they are not BS1363, sounds like nonsense to me!
Are blank plates BS1363?

 

[RF Lighting]

So that would mean you could not connect for example a 45A isolator or a flex outlet plate to a rfc as they are not BS1363, sounds like nonsense to me!

Correct.

A lolipop circuit using a 45A isolator is a technical non compliance, and you shouldn't be connecting flex outlets directly to a ring circuit anyway.

Are blank plates BS1363?

How do you connect a blank plate?

 

[ericmark]

So that would mean you could not connect for example a 45A isolator or a flex outlet plate to a rfc as they are not BS1363, sounds like nonsense to me!

Correct.

A lolipop circuit using a 45A isolator is a technical non compliance, and you shouldn't be connecting flex outlets directly to a ring circuit anyway.

Are blank plates BS1363?

How do you connect a blank plate?

I have many times talked about the lollipop idea and I am not sure if it complies or not. APPENDIX 15 is only informative although most would look at it as part of the regulations but regulations states:

433.1.5 Accessories to BS 1363 may be supplied through a ring final circuit. With or without unfused spurs, protected by a 30 A or 32 A protective device complying with BS 88-2.2. BS 88-6. BS 1361. BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm² except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5 mm². Such circuits are deemed to meet the requirements of Regulation 433.1.1 if the current-carrying, capacity (Iz) of the cable is not less than 20 A and if. under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable.

The main bit here is:-
1) 30 A or 32 A protective device even if one was to use 4mm² cable as a ring you could not up the rating to 40A MCB it only applies to a 30 A or 32 A protective device no other.
2) capacity (Iz) of the cable is not less than 20 A is second thing so any part Reference Method 101 would need 4mm² cable and Reference Method 103 needs 6mm² cable.

With the feed to the lollipop using 6mm² cable Reference Method 100 I would not consider that cable as being part of the ring final and therefore will not come under 433.1.5 or APPENDIX 15 but the latter states "A ring final circuit starts and finishes at the distribution board" and so to comply we must consider the isolator or cooker connection unit used to connect the ring final 2.5mm² to the feed 6mm² feed as a distribution board and personally I see no reason why not but this has to be a personal decision and I can see how others may not agree.

Where the person installing is the person writing out the installation certificate (EIC) I see very few problems however where some one else is doing the electrical installation condition report (EICR) and submitting it to the LABC I can see where they would be loathed to accept it although since I can't really see how they could give it any code I can't really see how it could fail.

However a figure of 8 is another thing and historically that has always been a failure as it clearly does not start and finish at the distribution board?

Returning to original question first there has to be a question as this would change the answer given. Is the ring already RCD protected and what other protection device is in place (Fuse/MCB)?

TABLE 41.2 and TABLE 41.3 gives a range of acceptable maximum ELI readings from 1.04 to 1.19 for fuse and 1.44 to 0.36 for a MCB/RCBO depending on type used. If the ELI at near centre point of ring with a B32 MCB was for example 1Ω the there would be little problem extending the ring but at 1.42Ω it would not comply once extended.

However a 13A fuse is rated at 2.42Ω for earth loop impedance so very unlikely a fused spur would fail. Also one can get RCD FCU which if not already RCD protected would also get around that problem.

The problem remaining is running two large units from a single fuse could use a twin back box and two FCU's or grid switch with fuse and two cables or cross your fingers and use one and hope the fuse does not blow. Personally I would not expect the fuse would blow but of course if wrong then you will need to run a second fused spur and your taking chance not me.

I think PrenticeBoyofDerry has given a reasonable answer but what you have to remember it's a personal thing not simply quoting regulations and also as electricians we carry a ELI meter and can quickly plug it in and test although there are cheap testers for around £50 these are go/no go testers and will not tell you if there is any latitude to extend one a go/no go reading so only after you have finished will it show if OK or not which is a bit late.

If I was a DIY guy without a full set of meters then I think I would end up with loads a FCU's as without test equipment it's the most likely way to ensure all is OK. In theory we should always test ELI and RCD both mA and ms trip currents and times and insulation tests as well and we should be completing a Minor Works Certificate. (If it needs an Electrical Installation certificate then it will also come under Part P) However I realise many DIY people do not do this hence why I say use FCU. If you can measure the ELI then the answer would be different.

 

[PrenticeBoyofDerry]

How do you connect a blank plate? wink:

Some have connection points incorporated on them, I still cannot find within the regulation where it states that BS1363 accessories only can be used, therefore not allowing any other type of accessory to be connected.

 

[whufcboy]

Thank you all for taking the time to reply. PrenticeBoyofDerry's suggestion kindof made sense to me but I must admit I'm now a bit baffled by all the regulatory numbers being quoted thinking this isnt a straight forward job for a DIY'er like myself.
I'll check if the above counter socket is on a ring or spur. You'll have to excuse my ignorance here but can you explain why is a fused connection units are needed if the appliance itself already has a fuse in the plug? I thought maybe they were only required if hard wiring into the mains....

 

[PrenticeBoyofDerry]

You'll have to excuse my ignorance here but can you explain why is a fused connection units are needed if the appliance itself already has a fuse in the plug? I thought maybe they were only required if hard wiring into the mains....

A FCU is not really needed, providing you either keep the ring as a ring to the sockets to the appliance or allow for just one spurred socket from a socket outlet from the ring.
I mentioned it as a means of isolation from above the worktop, so if you had an electrical fault with either appliance, you could safely isolate it without having to pull the appliance out and unplug from behind.
It may be that you can fit sockets that are accessible without removing the appliances. Just a suggestion, to prevent any chance of coming in to contact with live parts!

 

[ericmark]

The regulations are being quoted to reinforce out opinions as to how it should be done as you can see there is some debate between electricians to their interpretation. We all feel to just say "regulations will or won't let you" is not good enough as there are often miss quoted or miss read and it's a very big book to check if no numbers given.

However they are in the main common sense and if you think it should not be allowed not your right.

So let me talk about the ring final circuit as it is called. During the second world war the circuit was designed to allow re-building post war as quick as possible using as little copper as possible as there was a shortage of copper. The main idea was to use special plugs with fuses in the plug which meant the socket could be supplied with a much higher current capability so having a host of radiating circuits from the fuse board was eliminated. Pre-war we has a fuse for every 5A and 15A round pin socket in the fuse box and the little paxolin fuse wire holders plugged in similar to the blade fuses now found in a car. The ring system got this down to one fuse for all sockets.

So cable with 7 strands of 0.029 inch cross sectional area was laid in a ring around the house today we use a smaller cable with a total csa of 2.5mm² and the idea is as long as the ring is maintained the current will be shared by two cables both rated just over 20A so with a 32A MCB at any point other then very close to the consumer unit some power will go down each cable and since only used for portable equipment the time involved will be short so even with a slight overload there will not be the time for the cable to over heat. Also being in a loop means the resistance to the fuse box now called a consumer unit will be less than with a radial circuit.

But there is always a chance of overload so with the reduction of cable size since first designed and the altering of the plug to include finger protectors which reduced the heat which could be dissipated through the pins a strict set of rules were published and the basic idea is if you follow these rules then there is not need to do some very complicated calculations.

These rules include that fixed appliances of over 2kW should not be powered from the ring as if for example the immersion heater was powered from the ring the time involved to heat that much water would over heat the plug as all fuses produce heat and there is a fuse in the plug but a kettle same power will only run for a few minuets so not enough time to over heat. Also the draw form the immersion heater would reduce the power available for other items. Using a 16A MCB at the CU to feed items like the immersion heater means the sockets can provide all we need. Using a 15A plug and socket with an immersion heater fed from the 16A MCB would be OK as there is no fuse in the 15A plug to heat it up and it was done a lot for easy maintenance.

Installing a ring main the rule of thumb was only use one reel of cable it is calculated that a final ring can have 106 meters of cable in it and still comply with volt drop requirements so 100 meters in a role easy to ensure it complies. However on an already installed ring you don't know how much cable is already installed. There are many ways to find out from data written on the insulation certificate to measuring with a special low ohm ohmmeter to using a loop impedance meter. Connected to volt drop is also the ability of the protective device to open and the MCB has a letter in front of the number and this tells us the two tripping currents. The MCB is two devices in one a thermal trip will in time will trip at rated current and also a magnetic trip which trips at a much higher current but extremely fast this latter bit is where the letter comes in B = 5 times, C = 10 times and D = 20 times the thermal tripping current. Simple ohms law with a B32 MCB it will need 160A to trip so 230/160 = 1.44 ohms that's where the tables get the figures from.

Now in the kitchen we see many arguments among even electricians of what should be allowed. Is a 2.8kW tumble drier allowed to be simply plugged into a ring for example as it's over the weight which makes it portable. However where twin 2.5mm² cables feed just the kitchen since there are no branches it not technically a ring but cables of equal length in parallel which feed a grid switch arrangement and from that a spider of radials. Oddly most electricians seem to think it OK to plug in tumble drier but not to simply plug in an oven yet the oven has a thermostat which means it draws the current for a shorter time. The same applies to washing machine and dish washer high current but for short time so really it is the tumble drier we have a problem with.

The 2kW rule really means tumble drier, washing machine, dish washer and oven should all have their dedicated supply but this is to be frank quite rare.

This is where we throw out the rule book and look at the house. So with a house with single 32A fuse/MCB feeding all sockets there's a sharp intake of breath and shaking of head and answer is no can't be done. But with Up-stairs, Down-stairs and kitchen ring will consider chance of overload is slim and bend the rules. In other words we use some common sense.

Had you asked about two sockets for a microwave and coffee maker answer would be yes no problem go ahead but your asking about two sockets for some very heavy equipment. However using a FCU and a length of cable to a double socket is not different to using an extension cable.

I look at worst case scenario and as long as there is a 13A fuse in the circuit that would be the 13A fuse blows. In real terms that's not so much of a problem.

I have tried to present a thought patten and hope you will apply your own mind so same line of thoughts and ask yourself it is likely to cause a problem? Only you can answer the question.