Immersion Advice Needed

[Bungle]

Hi all,

I have a consumer unit that is full located in my kitchen. One of the trips is used for an existing immersion (3KW) located in the loft as part of a cylinder that supplies a power shower. We've had an extension to the house that will be supplied by a new cylinder in the upper floor of the 2 floor extension. This is a direct cylinder and will therefore need heating by a 3KW immersion also.

The cable that supplies the existing immesrsion is a 2.5mm twin & earth, so what I was wondering is could I use this cable to supply a small consumer unit extension with 2 trips at 16A each. Each of these would supply an immersion. I would then change the trip in the main consumer unt supplying this to a 32A.

Each immersion will draw around 12.5A, so what I'm asking really is a 2.5mm twin & earth cable heavy duty enough to carry a load of 25A? I've seen conflicting information on this, between 20A and 27A.

Some advice here would be greatly appreciated.

Thanks :D

[Central Scrutinizer]

regardless of the load, the trip (In) must be less than or equal to the current carrying capacity of the cable (Iz)

Iz for 2.5 with no correction factors (i.e running through thermal insualtion reduces Iz) is 27A

So a 32 A MCB on 2.5mm/27A cable is a big no-no

so its 4mm cable or a smaller breaker - i havent worked out the loading, its Friday night and i've got a strongbow waiting!

[Bungle]

regardless of the load, the trip (In) must be less than or equal to the current carrying capacity of the cable (Iz)

Iz for 2.5 with no correction factors (i.e running through thermal insualtion reduces Iz) is 27A

So a 32 A MCB on 2.5mm/27A cable is a big no-no

so its 4mm cable or a smaller breaker - i havent worked out the loading, its Friday night and i've got a strongbow waiting!


Ah yes, good point. I've found a couple of 25A breakers which would do the job. This is equal to the maximum load that the two immersions would draw at 240V (3kW), at 230V they would draw less.

When installed I will be programming them so they come on at differing times but obviously the circuitry needs to be safe.

Can you see any further problems with this idea?

Thanks for your help

[frazzled & smoking]

I would split the meter tails put a small cu in downstairs with 2x 16amp rcbo's then run in 2x 4mm (because I dont know the run length or route so cant say 2.5mm will do) circuits to the immersions in the loft.
That way all the ocpd are downstairs & in the event of a trip you dont have to clamber into the loft to reset.