Sign in to follow this  
Crofter

Wiring up a twin immersion tank

Recommended Posts

So... my sparky never clocked that there are two immersions on the tank, and has decided to start again from scratch. Maybe should have had a chat about what I wanted but it looked kind of obvious to me!

 

Setup:

170l UVC with two 3kw immersions, property is one bed, one shower, and E7 supply. Holiday let so must be idiot proof.

Lower immersion will go on a timer, overnight.

Upper immersion will have a simple time lag boost button set to one hour.

 

So far so good. The overnight timer can, I think, be something very simple indeed as I don't plan to mess around with it at all. In fact I will deliberately place it out of the way to avoid people meddling with it.

 

The boost button is a bit tricker- I ordered a cheap one that looked the biz (one big button, no meddling, no confusion). It doesn't light up or anything though. I'd also like to future proof if I can, and be able to upgrade to a 6kw boost immersion- but all the boost switches I've found are only 13A or 16A. Anybody know of a simple one-button time lag switch that can handle a 6kw resistive load?

 

Finally, can I just place an illuminated isolator switch after the boost button? That would give a visual indicator that it had come on. Likewise can the E7 timer have the isolator between the timer and tank? That would allow me to switch it off without interupting the power to the timer itself.

Share this post


Link to post
Share on other sites

Can you use a momentary grid switch and indicator and a contactor to deal with the 6kw load? Then the switch can be anywhere and the contactor located to reduce the necessary (expensive) high-current wiring.

Share this post


Link to post
Share on other sites

You don't even need a timer for the bottom one. Use the DNO supplied off peak supply and wire it to that (same CU as the storage heaters) so it just comes on when the cheap rate is on.

 

Use a boost switch  for the top heater. like this https://www.tlc-direct.co.uk/Products/SMTGBT4.html

 

Share this post


Link to post
Share on other sites

I have a 200 lt vented cylinder, so can get a better flow rate, but I have found that for two people, and only heated to 50°C, there was plenty of hot water.

 

I have been using just the top element for the last few months (still not got around to sorting the blown lower element, but chatted up neighbour so should be able to use her shower if it all goes tits up) and it only takes 20 minutes to heat up enough for a bath (less water is heated).

My cylinder is not normally heated from stone cold, so it may take a little longer.

 

The E7 period is much longer than you need to heat your store to 65°C.

You will only ever need about 12 kWh, so should be up to temp in 4 hours at worst.

 

 

Edited by SteamyTea

Share this post


Link to post
Share on other sites
2 hours ago, chrisb said:

Can you use a momentary grid switch and indicator and a contactor to deal with the 6kw load? Then the switch can be anywhere and the contactor located to reduce the necessary (expensive) high-current wiring.

I might need you to unpack that for me a bit... is a MGS like a remote relay or something?

 

 

2 hours ago, ProDave said:

You don't even need a timer for the bottom one. Use the DNO supplied off peak supply and wire it to that (same CU as the storage heaters) so it just comes on when the cheap rate is on.

 

Use a boost switch  for the top heater. like this https://www.tlc-direct.co.uk/Products/SMTGBT4.html

 

I think you might be getting confused between my two houses- this UVC is going in the holiday let which simply has a single meter providing electricity at two different rates depending on time of day (E7 tarrif). Not THTC and storage heaters, which is what I have in my own house.

 

At only 3kw per immersion, it's tempting to just spend £5 on a timer and plug into the ring main!! Only joking...

Share this post


Link to post
Share on other sites

I’d be ditching the timers and switches in favour of using contactors in their own dedicated CU or enclosure. 

 

A 32A contactor coupled to a DIN rail time switch will do the bottom one, also allows for upgrade to 6Kw if you want to. The top one I would again use a 32A contactor but use a time delay relay to drive the contactor and that can be driven off a momentary push switch to energise the relay. 

 

All nice and neat in a 4 way CU that could be lockable if needed to keep fingers out.  

Share this post


Link to post
Share on other sites
9 hours ago, Crofter said:

I might need you to unpack that for me a bit... is a MGS like a remote relay or something?

 

 

I think you might be getting confused between my two houses- this UVC is going in the holiday let which simply has a single meter providing electricity at two different rates depending on time of day (E7 tarrif). Not THTC and storage heaters, which is what I have in my own house.

 

At only 3kw per immersion, it's tempting to just spend £5 on a timer and plug into the ring main!! Only joking...

A dual rate meter will (should) also have a heavy duty switch contact and a switched output.  If you look at the meter there will be 5 big terminals, not just the 4 on a normal single rate meter.

 

So connect the spare (assuming you only have 4 cables in there at the moment) to a small off peak consumer unit and that will only be energised at off peak times.

 

If you don't have this 5th terminal connected and no off peak CU how are you powering the storage heaters?

Share this post


Link to post
Share on other sites
1 hour ago, ProDave said:

A dual rate meter will (should) also have a heavy duty switch contact and a switched output.  If you look at the meter there will be 5 big terminals, not just the 4 on a normal single rate meter.

 

So connect the spare (assuming you only have 4 cables in there at the moment) to a small off peak consumer unit and that will only be energised at off peak times.

 

If you don't have this 5th terminal connected and no off peak CU how are you powering the storage heaters?

 

 

I don't have any storage heaters!

I'll check the meter today, but my impression is that it's simply working off its own timer and spits out electricity at peak or off peak rate depending on time of day.

Share this post


Link to post
Share on other sites
8 minutes ago, Crofter said:

 

 

I don't have any storage heaters!

I'll check the meter today, but my impression is that it's simply working off its own timer and spits out electricity at peak or off peak rate depending on time of day.

Yes but it will have that switch inside even if you are not currently using the 5th large terminal.

 

It might be simpler just to fit a timer to turn the bottom heater on in the small hours when it's on the cheap rate, probably cheaper than fitting a dedicated off peak CU.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this