Switching / wiring advice for Megaflow with 4x 3kw immersions?

Hi

I have bought a Megaflow 210dddd which is a direct model (electric heating only) with 4x 3kw immersion elements. It’s providing hot water to 2 showers in a swimming pool changing room and so I went with the 4 immersions so that I could get quick re-heat times when the showers are being hammered by the kids!

The electrician is coming next week to put the wiring in before the plumbers commission it. I could therefore do with some advice and thoughts about possible/best ways to switch the immersions so that I can have a more educated conversation with my electrician about what I want to achieve. In the past (other houses) I have only had either a single immersion (20amp DP switch to turn on and off) or in one case a top and bottom immersion with one of those bath/shower DP switches to choose between bottom OR top.

The consumer unit is close to the water tank and so it will be easy enough for the electrician to run whatever he needs to provide the initial supply (assume it will be a big old cable given the potential for 12kw / 52amps being pulled). I’ll leave that to him.

What I am interested in is whether anyone has experience of these 4 immersion versions and what switching options they have installed. The layout seems to be 1 immersion at the bottom, 2 either side of that slightly higher up the tank and then the 4th about half way up the tank. I’m not clear on what that layout says in terms of which ones should be used on their own or together.

I do want the potential to have all 4 on at the same time for maximum speed heat up, but equally want to be able to have 1 or 2 on when speed isn’t an issue and/or I just want some hot water for the sinks.

Any thoughts on how best to setup the switching?

Presumably one option is to have 4x 20amp DP switches and just switch each one separately in whatever combination I want (or all together) but should I have a more sophisticated method?

Any thoughts gratefully received!

Thanks

What ever you decide just don’t put them on a single circuit …..

What size supply is it coming into the property....if it's only 60A it could be interesting

What is the nature of supply single or three phase.

If the CU is close to the tank, then 4 radial circuits each just like for a single immersion, but obviously checking max demand etc.

But I think you have missed a trick here. Direct electric resistance heating is the most expensive possible, so for a high use application like this is going to be expensive. Do you not have any other fuel available? How are you heating the pool for example?

The only tanks I have experience of with that many heaters are big electric "storage boilers" which are actually just a large thermal store designed to heat up on the off peak times of an E10 tariff and then provide hot water for heating any time of day. and my customer who has one complains how expensive it is.

depends how far you want to go with it... anything from 4x switches to a control panel with contactors, timers, various mode switches etc...

Fleeting said:

What is the nature of supply single or three phase.

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It’s single phase

ProDave said:

If the CU is close to the tank, then 4 radial circuits each just like for a single immersion, but obviously checking max demand etc.

But I think you have missed a trick here. Direct electric resistance heating is the most expensive possible, so for a high use application like this is going to be expensive. Do you not have any other fuel available? How are you heating the pool for example?

The only tanks I have experience of with that many heaters are big electric "storage boilers" which are actually just a large thermal store designed to heat up on the off peak times of an E10 tariff and then provide hot water for heating any time of day. and my customer who has one complains how expensive it is.

Click to expand...

Yes probably going to cost a small fortune at current prices - I bought it before the energy world went mad!

The pool is heated with an air source heat pump. There is only electric to the outbuilding that has the pump room and changing room / showers.

My theory was that although it will be expensive as a method of heating, it will only be turned on as and when the pool is being used so not as bad as in a house scenario being used every day.

kerching said:

What size supply is it coming into the property....if it's only 60A it could be interesting

Click to expand...

It’s 100A but there is a pool pump, air source heat pump, sockets, lighting etc - so as you say could still get interesting. I clearly didn’t think through the total power consumption when I bought it!

From your description you have a single phase water heater with 4 individual elements. This should have been more suitable on a three phase supply type of water heater.
But three phase supply is not so common on domestic installations.
The nature of your power supply should have determined what type of water heater you should be getting rather than buying the heater then making do with it.
As for your alternating from 2x to 4x heaters your best option is your electrician needs to use contactors not DPs. And maybe use a timer for when your needs are during the day for 2 and when for 4 immersions to be active.

ProDave said:

If the CU is close to the tank, then 4 radial circuits each just like for a single immersion, but obviously checking max demand etc.

Click to expand...

I think there is only 1 spare way in the CU. I was so focussed on how I would like the switching to work I hadn’t thought through how the electrician will get the power to the immersions. I guess I assumed a large amp breaker and a big cable that would daisy chain / split into the switches - but totally makes sense why you say 4 radials.

You don't need four radials. One is needed as long as it's able to carry the load of all 4 and that will supply 4 contactors, then each contactor will supply each element.
4 radials would make it dangerous.

Kevin-5 said:

You don't need four radials. One is needed as long as it's able to carry the load of all 4 and that will supply 4 contactors, then each contactor will supply each element.
4 radials would make it dangerous.

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please explain how 4x radials will make it dangerous

4 separate supplies to one unit.
Although it has 4 different load intakes, it is still one unit.

Kevin-5 said:

4 separate supplies to one unit.
Although it has 4 different load intakes, it is still one unit.

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It is four separate immersion heaters.

Kevin-5 said:

You don't need four radials. One is needed as long as it's able to carry the load of all 4 and that will supply 4 contactors, then each contactor will supply each element.
4 radials would make it dangerous.

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I think you advice is rather dubious …….

4 separate immersion heaters on one unit.
When you hit the isolator you expect that unit to be off not is there anything else I have to switch off?
It is just bad practice to do that.
Have you ever come accross the yellow label "Caution fed from elsewhere, dual supply" ?

Murdoch said:

I think you advice is rather dubious …….

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I think your suspicion is not grounded....

Kevin-5 said:

4 separate immersion heaters on one unit.
When you hit the isolator you expect that unit to be off not is there anything else I have to switch off?
It is just bad practice to do that.
Have you ever come accross the yellow label "Caution fed from elsewhere" ?

Click to expand...

2 gang switch at the bottom of the stairs - 2 circuits - is this bad practice ?

Murdoch said:

2 gang switch at the bottom of the stairs - 2 circuits - is this bad practice ?

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Look, you're comparing apples with pears.