Tad Stumped !

[sparky40]

Hello all,
I don't usually have to, or want to, get involved with central heating/water heater cabling as the company I do work for have there own plumbing contractors who do all the wiring from the spurs provided. However, I am doing some work where I have come across a cylinder tank, @5ft tall that has two heating elements, one at the bottom, and one half way up. The programmer has broken and needs replacing, my concern is that they are both wired from a single fused spur with a 13a fuse ???
Can anybody advise me on how the load of the two elements are run off of one 13a fuse, when the elements combined are of a higher load ?

Thanks for any help or advice.

 

[RMS]

Yea this does not sound right.

what is the rating of the two elements?

 

[Adam_151]

Electrically or mechanically interlocked? Or just a bodge? in which case...

Time to drop a 6mm in from a 32A breaker into an CU type enclosure near the heaters with a couple of B16, a B6 and contactors as required (depending on what level of control you need a four pole*, or a couple of 2 poles) me thinks


I suppose you could switch both with a 2 pole, just swithing the phase on each, as they would be functional and you have the DP isolator for isolation (and most likely a 20A DP switch with flex outlet for each heater)

 

[JohnD]

The controller ought to have a two way switch that either puts on the bottom element, or the top one, but not both at the same time. IIRC Horstmann do one. with a time switch that you can use to do the bottom element at night if you have an off-peak supply

If the controller doesn't seem to do it, there are switches available marked "Sink/Bath" (Meaning, the top bit, quickly, from the folded top element, or a full cylinder from the bottom one)

 

[RMS]

It sounds like it is an economy 7 timeclock with boast control for the top element. These controllers do not allow both elements to be on at the same time.

 

[RF Lighting]

Sounds like some sort of E7 setup.

I would guess that the bottom element is on a timer and heats the entire cylinder overnight, and the top element is on a boost switch and only heats the top third or so of the cylinder when it is required.

The controller will probably only allow one element to be on at a time.

I might be well off the mark but this is what it sounds like to me.

<edit> I was really late with my reply. Hope the post doesn't get locked

 

[JohnD]

It might be the Electronic 7, though there used to be one with a synchronous motor driven clock wheel.

http://www.horstmann.co.uk/water-heating.asp

 

[sparky40]

Thank you all very much for your help. It is 'E7'set up and your posts have made things clear to me now.
Thanks again.

 

[simon_d]

Electrically or mechanically interlocked? Or just a bodge? in which case...

Time to drop a 6mm in from a 32A breaker into an CU type enclosure near the heaters with a couple of B16, a B6 and contactors as required (depending on what level of control you need a four pole*, or a couple of 2 poles) me thinks

usually, the bottom is off peak ad the top is on peak so the on peak will only heat top part and warm the bottom. bottom heater heats all the water when its cheaper. you could have the bottom on on-peak but both on the same spur is dodgy

 

[JohnD]

... both on the same spur is dodgy

Not dodgy if it has a controller or switch which will not allow both to be on at the same time.

However, they should be on a dedicated radial, not a 13a spur, as they are fixed water heating appliances over 5l.