Does a 3kw immersion heater demand 2.5mm cable?

[Discharged]

And if so, if a 30A relay is being used to switch power to the element, does the supply to the relay need to be 2.5mm as well?

 

[malcolmsanford]

As it is mainly a domestic water heating system then the chances are your going to use Twin + E cable perhaps only erection method C several would allow 1.5mm cable to be used. Though Erection methods 100 and 102 would give you an Iz of 16amps for me personally it is a little to close to sailing to the wind for comfort.

I think most electricians just choose 2.5mm to cover all areas, and because it is generally thought the "norm"

The cable to the element/relay/switch etc will be chosen not on the rating of the accessories but the protection device used.

 

[Deleted member 9648]

Do you mean the control circuit to the relay perhaps?.....usually the coil circuit would be sub fused at 6a or so....if it's fed straight off the I/H supply then cable sizing would depend on the OCPD same as anything else.

 

[Discharged]

I'll explain a little further.

I have mounted in an enclosure a digital thermostat with two outputs - one is aimed at a cooling circuit, but the other is aimed at heating. But the relays in the controller are rated at 10A, so if on the heating side someone wanted to put an immersion heater element, I'm left with having to put in a secondary, larger, relay to cope with the potential demand. I'm pretty happy using 1.5mm as supply to the controller and the cooling side, but, as I say, bit more concerned about the heating part. And to that end, this is why I'm wondering about whether I should be using the larger cable on that circuit.

@Malcolm - when you say 'protection device', do you refer to the fuse that is protecting the thermostatic controller or maybe a fused connection point elsewhere?

Many thanks.

 

[malcolmsanford]

To be honest I can't remember the last time I done any kind of domestic heating systems so not quite sure what your trying to achieve.

As far as the relay goes on your OP you noted a 30amp type. That is the rating of the load you can switch through it and so will be ample for the 3kw immersion.

As your using the relay as a switch then you will have a supply coming into and a load going out to your immersion. Those cables will have to be rated for the heater which is being switched so most likely in your case 2.5mm cable.

The "control" side of the relay, which is an input onto a coil will be milli-amps and so a much smaller cable can be used.

 

[Discharged]

Ok, thanks, understood. I wanted to avoid using the larger cable, but with the relay fitted for a specific reason (the immersion element) I shall have to I think, to be on the safe side. It's what I thought would happen, true. I shall have to re-think some of the wiring I do in the enclosure, but that's no great problem. For example, the connectors on the thermostat are probably too small to comfortable fit the 2.5mm wires, so I'll connect to the relay with spade connectors and run smaller cabling to the controller and the cooling circuit I mentioned.

Out of interest, the particular application I'm thinking of here is home brewers who need to heat up large amounts of water, but a kettle is too small and a domestic water tank with immersion completely out of the question. They need something in between the two, hence the need to power an immersion element that has been mounted in some other type of vessel.

Most of the units I make have no need for the extra relay, and so the question has only just arisen.

Cheers

 

[Discharged]

Just one more thing - if these guys want to power an immersion heater, should they not be wiring the unit/immersion element into a fixed fused point and not a 13A plug?

 

[malcolmsanford]

It is not allowed to connected a water heater via a plug or socket arrangement.

 

[Discharged]

I thought as much! Many thanks for the confirmation.

I guess the trouble I might face is that anyone could wire an immersion element to a plug and plug that into my controller and there'd be nothing I could do about it.

 

[malcolmsanford]

Is this appliance ? And will it be portable?

If that is the case then you can supply it via a plug and socket as you would a water urn.

When you said immersion I jumped to the conclusion of a domestic heating/water system not an appliance sorry for that.

 

[Discharged]

I suppose it would be portable - literally, yes, in practice probably not move much, certainly not fixed like a domestic immersion tank. I've certainly never seen a domestic immersion tank wired into anything other than a fused point on the wall.

No problem.

 

[poppypiesdad]

It is not allowed to connected a water heater via a plug or socket arrangement.

Hi. Not wanting to be confrontational but , i have always connected elements with 2.5mm2 cable with a d/p neon ,and a fused spur at the tank , with 2.5mm2 heat resistant flex to the immerser

However the wife has a horse or 6 and she got a rug dryer

Heated horse rug driers - Products

and as you can see in the picture its is basically a short element with 2.5mm2 rubber flex onto a rubber plug top

so is this illegal

Jamie

 

[malcolmsanford]

Hi. Not wanting to be confrontational but , i have always connected elements with 2.5mm2 cable with a d/p neon ,and a fused spur at the tank , with 2.5mm2 heat resistant flex to the immerser

However the wife has a horse or 6 and she got a rug dryer

Heated horse rug driers - Products

and as you can see in the picture its is basically a short element with 2.5mm2 rubber flex onto a rubber plug top

so is this illegal

Jamie

Jamie as I mentioned in post #10 I jumped the gun and thought it was a fixed piped type immersion heaters we were talking about, the type that are in the home in airing cupboards, these should not be connected to the fixed installation via a plug and socket.

What you have there I would imagine is just a standard oiled fired system, similar to an electrical oil radiator. It looks like at the bottom you have a sump that I assume as oil in it, that when plugged in will heat it and flow through the tubes, that is seems to be quite all right.