Immersion cabling

[jps71]

Hi guys

I have just removed a old hot water cylinder which had a single immersion heater fitted.

I am going to be replacing it with a larger water cylinder that has 2 immersion heaters fitted.

I don't have cheap rate electricity so wondered if it is practical just to wire both heaters either one to the other then to the switch or both directly in to the switch so that both heat the water at the same time there by heating the water quicker.

The cable from the CU is 2.5 mm & the breaker in the CU is a NSB32.
The switch that is near the tank has a 13 amp fuse fitted.

Also what thickness of heat resistant cable should I use to connect to the switch 1mm or 1.5mm.

Cheers Jim

 

[pompeygit]

The 32amp breaker is providing no protection to your 2.5mm2 cable. One of the most important functions of a breaker is protect your cable from overheating. Change it for a 16amp breaker and only wire 1 of the immersions up(then when it finally fails you simply connect to the other and replace the immersion at your leisure). For final connection you need a heat resistance flex.......personally I'd recommend 2.5mm2 butyl or similar(make sure its long enough to terminate at both positions). If you want to run both immersions I think you will need to run another 2.5mm2 cable. Alternatively it may be possible to run a 6mm2 cable to a 45amp switch and run both immersions. I don't think this would be seen as 'best practice'. Others may see this differently

 

[Softus]

pompeygit is right about the 32A breaker - whichever way you look at it your installation is unsuitable for running two 3kW elements at the same time, but I don't see why you shouldn't run a new 4mm² cable, suitably protected.

If your cylinder has two elements with one at the base and the other placed one third from the top, then they don't have equivalent functions - it's designed for use with cheap rate electricity, so I'm wondering why you don't have it, or get it.

2.5mm² is OTT for a 3kW element - 1.5mm² would be fine, but it does need to have a heat-resistant sheath.

 

[jps71]

Thanks for the info guys.

I shall change the breaker for a 16 amp one.

Don't know why about the electric supply all I know is there is one CU for the full house with no add ons.

This is a old house 1840s and the electrics when fitted just ran the lights and sockets & the one immersion heater fitted in the old cylinder. all cables & CU have been up graded over the past 5/10 years.

The immersion heater might never have been used as the old cylinder was also attached to the back boiler of a peat burning stove which unfortunately rusted to death where it stood.

This cylinder is being used to heat the water for a guest bathroom I am in the process of refitting(along with renovating the rest of the house) so it wont be used to heat the water for every day usage.

I just thought it would be better to run both immersions at the same time as I thought it would have heated the water faster and may have been more economical than trying to heat a 1200 X 450 tank with one 11 inch heater.

Cheers Jim

 

[Chri5]

Why not buy one of these ?

Mk duel immersion switch, one feed / supply cable and 2 load cables (for duel element immersion heaters)

 

[sparkyspike]

If you're only using one immersion, then use the bottom one.

 

[jps71]

So just to check I have this right.

Change to a 16 amp breaker

leave 2.5 mm cable as is from CU to switch and run 1.5 mm heat resistant cable from switch to bottom immersion heater.

Or to run both immersion heater at the same time

Run 4mm cable from CU (what size breaker would I need ?) to switch then heat resistant cable from switch to each immersion heater ?
would this be to each immersion seperately or in relay?

Cheers Jim

 

[Softus]

...Run 4mm cable from CU (what size breaker would I need ?)

32A. Don't cover the cable with any insulation or conduit.

...to switch then heat resistant cable from switch to each immersion heater ?

Yes.

would this be to each immersion seperately or in relay?

Separately.

 

[jps71]

Thanks for the info Softus

 

[Chri5]

Your choice, but why ??

Duel immersions are designed as full tank via one, and top up / sink water volume as two.

There's absolutely no need to run immersions 1 and 2 at the same time, it will add to the energy cost and serves little purpose other than speeding up the cold to hot time.

Save your efforts, buy an MK double immersion switch and use the 2.5TE for the circuit.

If you want to be green, buy a timer and have that inline so that when you do use the immersion and forget to switch it off, the timer forces off after an hours heat up.

Without the timer the water will heat up beyond what is needed and cost £££'s to run. Without a timer / control wiring I'd assume the thermostat won't offer the facility to turn off the immersion at 45-55 deg C

 

[Softus]

it will add to the energy cost and serves little purpose other than speeding up the cold to hot time.

I think that's the very purpose that the OP has in mind.

Without a timer / control wiring I'd assume the thermostat won't offer the facility to turn off the immersion at 45-55 deg C

I don't know why you would assume such a thing, since all rod thermostats I've ever seen offer exactly that facility.

 

[gas4you]

Without a timer / control wiring I'd assume the thermostat won't offer the facility to turn off the immersion at 45-55 deg C

The HW should be set to always switch off at about 60C. 60C or above kills them off.

Going down to 45C or thereabouts is the perfect temperature for bugs, eg legonella etc to multiply at.

Over 60C will cause the element to scale unduly fast if you are in a hard water area.