Circuit design for this water heater?

[MickSmith5824]

Hi all

I'm doing a kitchen rewire and in kitchen client has also had a new water cylinder installed. It is a Main unvented direct 170L. I have been trying to get through to customer support but is non existent. I have not wired many new circuits for water heaters and am a bit confused with the power ratings of it, so what size breakers and cable to use and also does it require two seperate supplies. As stated not great deal of experience with these so any point in right direction appreciated. I've included the manual and power ratings sticker. Thanks

 

[buzzlightyear]

looking at the the wiring diagram what system it s plan or y plan .plus is thier a back up thermostat.

 

[andyb]

You say it's direct so it's either one or two 3Kw elements.
The rest is down to you re circuit design.
The MI's say 1.5 ho cable to the elements, from the isolator back to the CU is up to you.

 

[buzzlightyear]

You need two separate feeds from the consumer unit @ 16 or 20amp.
Keep them separate or there will be problems if on element fails (and they do)
if the op his putting on here .

 

[Wilko]

I would probably treat it like a cooker.

 

[Avo Mk8]

Hi. I hope it was installed by a plumber with an unvented ticket!

Simple solution is to put a Horstmann Electronic 7 controller by the cylinder in an accessible place:

Electronic 7 Immersion Heater Control

Compatible with most cheap rate or off peak tariff structures

www.cef.co.uk

and run (not necessarily) 2.5 T&E back to the CU on a 16A breaker. Then wire the two immersions to the unit. This will allow the bottom immersion to be timed to suit, and provides the boost function. The unit ensures both immersions cannot come on at once.

However if the customer wants to be able to have both immersions on at once, wants the constrols somewhere else than at the tank, or maybe to use 'smart' controls, you might need to run a seperate supply for each immersion, and have a different unit controlling each.

If the customer is not fussed, the Horstmann unit is the simple solution!

sorry I'm wrong. Both immersions seem to be at the bottom so the above is not the intended way of operating it.
sorry!

still going to need some sort of controller though!

 

[andyb]

It's just an immersion heater Wilko, 2 elements.

 

[andyb]

Hi. I hope it was installed by a plumber with an unvented ticket!
It is usual to power the lower immersion from cheap-rate overnight, and the upper from a 'boost' switch that allows the customer to top up the heat if they are running out. It depends really how the customer wants to operate it.

Simple solution is to put a Horstmann Electronic 7 controller by the cylinder in an accessible place:

Electronic 7 Immersion Heater Control

Compatible with most cheap rate or off peak tariff structures

www.cef.co.uk

and run 2.5 T&E back to the CU on a 16A breaker. Then wire the two immersions to the unit. This will allow the bottom immersion to be timed to suit, and provides the boost function. The unit ensures both immersions cannot come on at once.

However if the customer wants to be able to have both immersions on at once, wants the constrols somewhere else than at the tank, or maybe to use 'smart' controls, you might need to run a seperate supply for each immersion, and have a different unit controlling each.

If the customer is not fussed, the Horstmann unit is the simple solution!

I would hold back from recomending 2.5 Avo without knowing a bit more about the installation.

 

[brianmoooore]

It depends a lot on what the customer's requirements for hot water are, and what supply tariff they have.
If they have economy 7, and use very little hot water, then the supply could be from the switched 7 hour one to a sink/bath + isolator switch, next to the cylinder, giving the option of heating water at night only, and heating either a full tank or half a tank. If the hoot water runs out during the day, then tough.
Next up, is to run a cable from the 7 hour supply, through a simple isolator switch next to the cylinder, connected to the lower element, and to run another cable from the 24 hour supply to an isolator with neon indicator, or isolator plus run back timer, connected to the upper element. This will give the customer the option of additional, more expensive, hot water during the day, if they've used up all the cheap stuff.
An alternative to the immediate above is to run a single cable from the 24 hour supply to the Hortsmann E7 controller, mentioned in another post, which combines all the isolating and timing functions, but is an ugly lump on the wall, that can't be flush fitted.
If the customer doesn't have an E7 tariff, or similar, then the first method of installation can be used, fed from the 24 hour supply. This will allow the customer to only heat half a tank if their hot water demands are low, or more when they need it.
The next more sophisticated set up where no E7 supply is available is a single cable from the supply to an isolator and time switch near the cylinder with a second switch selecting the element to be heated.
The last method I can think of, is to run two cables from the supply to two isolators, one feeding a time switch and then the lower element, and the other, either incorporating a neon indicator, or feeding a run back timer, and then the upper element.
All supplies should be fed by a 16A breaker, and the size of the cable will be a minimum of 2.5mm2 T&E, but may need to be larger, depending on insulation it may have to pass through and the length of the run.

 

[MickSmith5824]

Hi. I hope it was installed by a plumber with an unvented ticket!

Simple solution is to put a Horstmann Electronic 7 controller by the cylinder in an accessible place:

Electronic 7 Immersion Heater Control

Compatible with most cheap rate or off peak tariff structures

www.cef.co.uk

and run (not necessarily) 2.5 T&E back to the CU on a 16A breaker. Then wire the two immersions to the unit. This will allow the bottom immersion to be timed to suit, and provides the boost function. The unit ensures both immersions cannot come on at once.

However if the customer wants to be able to have both immersions on at once, wants the constrols somewhere else than at the tank, or maybe to use 'smart' controls, you might need to run a seperate supply for each immersion, and have a different unit controlling each.

If the customer is not fussed, the Horstmann unit is the simple solution!

sorry I'm wrong. Both immersions seem to be at the bottom so the above is not the intended way of operating it.
sorry!

still going to need some sort of controller though!

It depends a lot on what the customer's requirements for hot water are, and what supply tariff they have.
If they have economy 7, and use very little hot water, then the supply could be from the switched 7 hour one to a sink/bath + isolator switch, next to the cylinder, giving the option of heating water at night only, and heating either a full tank or half a tank. If the hoot water runs out during the day, then tough.
Next up, is to run a cable from the 7 hour supply, through a simple isolator switch next to the cylinder, connected to the lower element, and to run another cable from the 24 hour supply to an isolator with neon indicator, or isolator plus run back timer, connected to the upper element. This will give the customer the option of additional, more expensive, hot water during the day, if they've used up all the cheap stuff.
An alternative to the immediate above is to run a single cable from the 24 hour supply to the Hortsmann E7 controller, mentioned in another post, which combines all the isolating and timing functions, but is an ugly lump on the wall, that can't be flush fitted.
If the customer doesn't have an E7 tariff, or similar, then the first method of installation can be used, fed from the 24 hour supply. This will allow the customer to only heat half a tank if their hot water demands are low, or more when they need it.
The next more sophisticated set up where no E7 supply is available is a single cable from the supply to an isolator and time switch near the cylinder with a second switch selecting the element to be heated.
The last method I can think of, is to run two cables from the supply to two isolators, one feeding a time switch and then the lower element, and the other, either incorporating a neon indicator, or feeding a run back timer, and then the upper element.
All supplies should be fed by a 16A breaker, and the size of the cable will be a minimum of 2.5mm2 T&E, but may need to be larger, depending on insulation it may have to pass through and the length of the run.

Thank you all. All really helpful. There's still things I'm encountering that not got great deal of experience with so always think it's best to check things out. Turns out the previous spark has made bit of balls up and has already been wired off a new ring. I had checked some things out earlier and got clearer on how an unvented direct cylinder works. It is not an economy 7 property only has one supply. My initial thoughts were to something similar to what you suggest Avo I am a bit short of spare ways so was going to use something similar to the Horsemann timer and supply both the top and bottom immersions from this from 16 amp 2.5. Am I correct that you still think this is viable option? I don't think I require any sort of isolation switch for this do I? As the controller would effectively do this, so just hardwire supply to Horsemann and then the 2 flexes from this?

Thanks

 

[Avo Mk8]

Thank you all. All really helpful. There's still things I'm encountering that not got great deal of experience with so always think it's best to check things out. Turns out the previous spark has made bit of balls up and has already been wired off a new ring. I had checked some things out earlier and got clearer on how an unvented direct cylinder works. It is not an economy 7 property only has one supply. My initial thoughts were to something similar to what you suggest Avo I am a bit short of spare ways so was going to use something similar to the Horsemann timer and supply both the top and bottom immersions from this from 16 amp 2.5. Am I correct that you still think this is viable option? I don't think I require any sort of isolation switch for this do I? As the controller would effectively do this, so just hardwire supply to Horsemann and then the 2 flexes from this?

Thanks

Hi Mick. You see I got confused about where the immersion heaters were! Looking again I see my initial reaction to use the Horstmann was and is OK.

The instructions for the Horstmann say that (in addition to its internal isolating switch) a double pole isolating switch with 3mm contact clearance should be installed in the fixed wiring, prior to the unit. It recommends a seperate supply with a 15A HRC fuse, or a 16A mcb, but then goes on to say IF it's to be connected to a ring-main (their words) then a fused spur protected "in the same way" should be used.
It's worth having a look at the installation instructions online.
I think many would say much better to have a separate supply rather than use the kitchen (or wherever) rfc.

As Andyb said, cable depends on installation method etc. so you need to check. The load will be limited to 3kw by using the Horstmann.

 

[brianmoooore]

Horstmann E7 controller is isolator switch, time switch and boost timer all in one. No other components required.
The default switching times are set up for an economy 7 supply, but are easily changed so that you can heat the water up to three times a day, just before you want to use it. You'll need to set it to BST/GMT as well.

Edit: You beat my reply by seconds! It is recommended that any fixed equipment (which an immersion heater is) rated at 2kW or more should be provided with it's own supply, and not spurred off of a RFC.
In a 'normal' 2 or 3 bed house, the supply would be 2.5mm2, taking care to avoid the cable being surrounded by insulation, but the calculations should be done.

 

[marconi]

SOme things to clarify please:

1. Is it a direct tank ie: just heated by IH? The clue is whether or not there are flanges to connect boiler water supply and return to an internal heat exchanger.

2. It appears to me from the image - of the actual tank at site? - that it actually has two IHs - top and bottom which would be used normally for off-peak/full tank/bath heating and boost for top-up/sink heating.

3. Each element is 3kW with there own integral 'stat and safety cutout.

4. Is the site 'all electric'?

5. Ask the client if they are interested in wifi/phone app control of the two IHs which would allow the switching and time control to be out of sight and conveniently controlled by their phone.

 

[MickSmith5824]

Hi Mick. You see I got confused about where the immersion heaters were! Looking again I see my initial reaction to use the Horstmann was and is OK.

The instructions for the Horstmann say that (in addition to its internal isolating switch) a double pole isolating switch with 3mm contact clearance should be installed in the fixed wiring, prior to the unit. It recommends a seperate supply with a 15A HRC fuse, or a 16A mcb, but then goes on to say IF it's to be connected to a ring-main (their words) then a fused spur protected "in the same way" should be used.
It's worth having a look at the installation instructions online.
I think many would say much better to have a separate supply rather than use the kitchen (or wherever) rfc.

As Andyb said, cable depends on installation method etc. so you need to check. The load will be limited to 3kw by using the Horstmann.

Horstmann E7 controller is isolator switch, time switch and boost timer all in one. No other components required.
The default switching times are set up for an economy 7 supply, but are easily changed so that you can heat the water up to three times a day, just before you want to use it. You'll need to set it to BST/GMT as well.

Edit: You beat my reply by seconds! It is recommended that any fixed equipment (which an immersion heater is) rated at 2kW or more should be provided with it's own supply, and not spurred off of a RFC.
In a 'normal' 2 or 3 bed house, the supply would be 2.5mm2, taking care to avoid the cable being surrounded by insulation, but the calculations should be done.

Thanks guy really appreciated. Am going to go with the Horstmann. The cable is chased in so no issues there so will go with 16 amp MCB with 2.5. Maybe another silly question but am I correct in thinking under no circumstances will both thermostats be operational at the same time? As this would obviously exceed my my design wattage

 

[brianmoooore]

Correct. The Hortsmann ensures only one element is used at a time.