Immersion Heater Circuit

[NewbieRuffy]

I have a plumber mate who is installing an (3Kw I believe) Immersion heater into a property and needs it wired in. I know in an ideal world, i new circuit from the CU, 16A CB and 20A FCU, as we all know the world is not always ideal and getting a new circuit from the CU to the airing cupboard upstairs is not at all going to be easy as the customer doesn't want walls chased out floors taken up and so on. So, as I am still gaining experience and this is my first immersion connection can i spur off the RFC on upstairs sockets? I have checked the Reg's and cant find anything that says i cant, however anything over 2KW usually needs its own circuit though right? there isn't much load on the upstairs RFC, couple of TV's, laptop now and again, general stuff. Your thoughts please?

 

[Plonker 3]

Well no diversity allowed on a water heater 3kw is just over 13 amps so the fuse could keep popping in a FCU. Looks like a new circuit is needed.

 

[Octopus]

In older houses this is often the norm. Not sure i'd be doing this as a new install though as its not ideal.

 

[malcolmsanford]

I assume you are getting your 2kw factor from appendix 15 of the regulations and possibly the OSG as well.

But rightly as you say there is no hard and fast regulation that prohibits you supply an immersion heater this way. There are Regs that guide you about certain areas with regards to this in section 554, but these deal with connection issues rather than loading ones.

So as you say perfect world you would give it it's own dedicated circuit, sometimes we can not do that and you need to sometimes do things that you find if not uncomfortable, does not sit well.

Rightly you have assessed the risk, and as it is an upstair ring final there is little chance you will stress the circuit too much. I would as you say spur off the ring and take it from there

 

[Deservices]

Well no diversity allowed on a water heater 3kw is just over 13 amps so the fuse could keep popping in a FCU. Looks like a new circuit is needed.

Putting it on a FCU is going to cause the fuse the blow every now and again, even if you have 240v it's still pulling 12.5 amp worst case as stated above 220v is 13.6. Looks like your gona have to disappoint them, and do a new circuit.

 

[malcolmsanford]

Putting it on a FCU is going to cause the fuse the blow every now and again, even if you have 240v it's still pulling 12.5 amp worst case as stated above 220v is 13.6. Looks like your gona have to disappoint them, and do a new circuit.

I'm totally amazed that there isn't therefore a spat of 3kw fan heaters, tripping fuses left right and centre all over the country !!!!!!!

Come on guys have a little think about it

 

[sedgy34]

Well if customer says put on with upstairs sockets who do you think he will be calling and blaming when it's tripping on overload

 

[malcolmsanford]

Come on guys are we on a wind up here .......................in your esteemed estimates how many immersion heaters up and down the country are wired on a 16amp circuit and connected via a 13amp Fused spur unit?

Now take your time here lads, have a sit down if you wish and a rub down with the sporting life if it helps ..............

 

[Deservices]

I'm totally amazed that there isn't therefore a spat of 3kw fan heaters, tripping fuses left right and centre all over the country !!!!!!!

Come on guys have a little think about it

There probably is, that's why super markets sell fuses yes I agree 13amp fuse will probably take over 15amp to blow but not the point I was making. There normally connected on a 16amp MCB with a 20 switch for the reason you don't want to have the fuse blowing unless its actually broke. Ie lets have a bath oh no the water is cold, dam that fuse has blown again and it's Sunday where can I get a fuse from. Wish that spark had done a proper job.

 

[malcolmsanford]

So all these 3kw kettles, fan heaters, Burco urns etc etc that come with 1363 plug tops and 13amp fuses are on borrowed time....................

Well every day is a school day

 

[Plonker 3]

I know what you are saying Malcolm, but when it is someone who is relatively new to the forum asking a question. I try and treat them as someone who knows nothing about electrics until they prove they do. As sadly there can be alot of people asking questions for DIY purposes or even for a homework scenario so I feel better giving the "correct" answer rather than the common sense answer.

 

[sedgy34]

So all these 3kw kettles, fan heaters, Burco urns etc etc that come with 1363 plug tops and 13amp fuses are on borrowed time....................

Well every day is a school day

These are portable appliances your talking about do you carry an immersion tank round with you lol

 

[malcolmsanford]

Dillib mate I think by the OP question we can say he is a sparks. He mentions the regs, RFC, connecting 2kw to a RFC etc, so unless he as done a great deal of research to fool us I would say he was a sparks.

As I said in my post mate section 544 does cover water/immersion heaters but are mainly dealing with connection issues and earthing etc, not to do with having a 13amp BS 1363 fuse in the circuit

Now I agree 100% that for connection purposes I would use a 20amp double pole switch and want it on it's own circuit. But often that is not always possible.

I can see nothing wrong in spurring off a RFC down to 13amp and then connecting the heater with your switch.

But this excuse that a cartridge fuse will "blow" because it is taking 13.6 amp is ridiculous. I will clamp test 100 heaters and I bet my pension on it that once the element heats up the current will drop to well below 13 amps.

 

[malcolmsanford]

So Sedgy a 3kw portable load is different current wise to a fixed 3kw watt load .........................must have missed that part out in my ohms law theory

 

[sedgy34]

It's down to the design, installation & commission
malcolms argument is simply designed incorrectly! However the common sense approach don't help when there's a problem.

 

[sedgy34]

So Sedgy a 3kw portable load is different current wise to a fixed 3kw watt load .........................must have missed that part out in my ohms law theory

no its not but the immersion will draw current for longer periods, if you take your assessor to a job and you have spured of the ring for the immersion im sure you will have a long debate about its design and end up with a re visit.

 

[i=p/u]

There is no right or wrong so sing a little song. But I'd tap of upstairs ring and maybe put on a boost timer. Upstairs ring probably 30A , but isit poster , yeah yeah yeah do pp diddle le op

 

[sedgy34]

better still find the leg coming from the board and redirect it to the immersion make the ring a radial "simples"

RING V RADIAL THREAD LOL

 

[malcolmsanford]

Is it now..................

My argument as never been it's design or it's merit.

My argument as been that we seem to have a consensus on here that a 3kw load is going to trip a 13amp BS 1362 cartridge fuse because it is under designed for the load.

I have sited that manufacturers of equipment be it portable or fixed deem it satisfactory to fit BS 1363 plug tops to their equipment with 13amp fuses.

According to you lads that is wrong, the 3kw load is to great for it and therefore they have this wrong.

Now regardless of what you or others feel, that what is or is not a good design, I have conceded that it is not the best, I have conceded that I would want the system on a 16amp dedicated circuit connected via a 20amp double switch, that as never been argued.

What I'am arguing is why will this 3kw load fuse a 13amp cartridge fuse under normal use?

 

[sedgy34]

malc i know depends on demand