never run two elements off a socket

[prolix]

Just put another element in my boiler as last time it was pathetic (electrim) and tested.

Things were going great so I popped inside for a cuppa and came back to find the water cooling and the electrics off quick check of the trip switches nothing, checked the fuses fine, checked the wall socket melted

the heat in the socket had melted the switch pin but hadn't blown the 10A fuse or tripped the trips. And I was pulling nearly 18A

You will require 2 seperate wall outlets as the two elements will exceed the capacity of one standard wall socket.

Oh well gave me an excuse to by some more shelving whilst at BnQ

[steve_flack]

That's why I have two separate metal sockets for my two 3kw elements and it's on a separate ring main.

Two 3kw elements pull 26 amps total.

[Seveneer]

That's why I have two separate metal sockets for my two 3kw elements and it's on a separate ring main.

Exactly what I have done, Steve.

I have 2 x 3kw elements on the HLT and 2 more on the boiler. I can only use 2 elements at a time but I can mix and match between vessels. That means I can maintain the sparge temperature and bring the first runnings to the boil at the same time .

/Phil.

[SteveD]

Just put another element in my boiler as last time it was pathetic (electrim) and tested.

Things were going great so I popped inside for a cuppa and came back to find the water cooling and the electrics off quick check of the trip switches nothing, checked the fuses fine, checked the wall socket melted

the heat in the socket had melted the switch pin but hadn't blown the 10A fuse or tripped the trips. And I was pulling nearly 18A

You will require 2 seperate wall outlets as the two elements will exceed the capacity of one standard wall socket.

Oh well gave me an excuse to by some more shelving whilst at BnQ

Just to clarify, did you somehow plug into a single wall socket, or into both outlets of a double wall socket?

[Orfy]

The best socket would be the one on a cooker supply. That should be a separate 40a circuit.

[steve_flack]

But is the socket rated for more than 13Amp? Just because the supply is rated for 40A that's for the cooker. It doesn't mean the socket is as well.

[prodigal2]

OK chaps I think there needs to be a bit clarification on some of this.

13A plug/socket as a rule arn't good to take a continual, load of anything above 10A (2.2kW @238V). This is due to the plastics in both plug tops and sockets can't take the heat generated. 13A is the absolute ceiling of a plug during a peak load for a moment

In truth in electrics its best only ever to load a service or plug, upto 80% of its rating as this allows for voltage fluctuation ( In the UK I've metered voltages from 213V-260V), and it also increases the life span of all components due to heat degredation.

For you all that are running 3kW elements they should NOT be on a 13A plug they should have at least a 16A ceeform/comando plug running of a 16A socket. And as Orfy said if you are running 2 3kW elements on a single service it needs to be at least 40A. the other good thing with 16A plugs is they are splash/shower proof, so are better in a environment with water and steam.

Prolix there are 2 or 3 possibilities on why you had a double socket failure.
1) loose terminal/bad termination. on either the live or neutral
2) component failure
3) the rating of the socket. just because of a double you could conciviebly draw 26A, does not mean the socket can cope with 18A current draw for any length of time

I take it that you have 1.8kW/2kW elements from the current you mention.
Also nothing popped in the fuse or breaker front because you were neither overdrawing current (MCB/fuse) and you were not shorting to earth(RCD).

A picture of the offending item would help us locate the fault

footnote, although I am not a qualified sparks in my working life I work with electrics everyday from 63Asingle phase upto thousands of Amps of three phase. And I have picked up from the sparks I work with safe ways to work with electrics to be factored into system design.


Taxi

[sparky Paul]

All socket outlets are rated for a continuous load of 13A, or almost 3kW at the UK's nominal voltage of 230V (-6%+10%). However, whilst double socket outlets are beefed up, they are not rated to cope with two 13A loads and will be quickly damaged by the excessive current. Cooker socket outlets are also rated at 13A.

MK say

All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissable maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time.

Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-oulet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.

The results of the testing above would apply only to MK sockets which are much higher quality than the very cheapest ones.

Having said all that, two separate socket outlets on a single ring main would be capable of supplying 26A continuously - although for this particular application in a 'wet' area I would recommend two blue Reyrolle/CEEFORM 16A plugs/sockets on separately 16A fused radial circuits and additionally, RCD protection either from the consumer unit or local.

HTH

[sparky Paul]

Crabtree are very good too, DaaB.

The ones to avoid are the really cheapest ones. Okay for lighting bits if you're on a budget, but the socket outlets are atrocious.

[prodigal2]

sparky Paul, yep I agree with you.
The only thing is that I have rarely seen a UK service sit at 230, and when you are running a continus load for any period of time it helps to factor in headroom.

To all you guys using 3kW boilers I would heartly suggest using 16A plugs and sockets. Over the mid to long term it will be great investment to all you electric boiler users.

[sparky Paul]

One of the points I was making is that technically, at the nominal voltage, socket outlets are barely rated for 3kW. 13A @ 230V is actually only 2990W - 3kW to all intents and purposes, but it does indicate how close you are to the operating limit of these socket outlets.

[prodigal2]

Very true

I think that the 13A plug is the best design of all the basic home user plugs around the world, but it has its short comings which this subject has brought to the fore.

[SteveD]

Excellent info. Thanks.

One solution...go GAAAAAAAAS!

[prodigal2]

I did a quick look to find some sources for 16A plugs and sockets that can be bought as single items:
plugs:
http://www.screwfix.com/app/sfd/cat/pro ... 9&id=12227

wall mount socket:
http://www.screwfix.com/app/sfd/cat/pro ... 9&id=16192

Most of the electrical wholesalers will only sell in multiple units, though you may find them at caravan stores or theatrical lighting suppliers(they may also be able to sort you out off cuts of cable too, your beer would also be a good way to drive down price )

[Frothy]

Excellent info. Thanks.

One solution...go GAAAAAAAAS!

I'll second that. You could always go 3phase though

Frothy