Off peak electric board wiring

[stu550]

I have the following board that is switched on only during the winter and is used to switch on 3 night storage heaters.

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The rest of the house uses a teleswitch and so is using off peak between 12.30 - 8.30.

I wanted to add three seperate thermostats (suitable rated etc) that will only switch on the night storage heaters if the temp drops below a certain temperature. The property is a holiday rental so it is difficult to switch the heaters on/off when it is warmer etc.

I had assumed that the three wires coming out of the top would go to each of the three heaters.... however, one of them appears to be constantly live (only tested using a stud/ vold detector etc) even if I remove the fuses and this is during the daytime? The wire disappears off somewhere that I can't trace....

Any suggestions as to what this might be for? I am assuming it doesnt go to the heater I thought it did - that I was going to attach a thermostat to....

Thanks.

 

[JohnW2]

I wanted to add three seperate thermostats (suitable rated etc) that will only switch on the night storage heaters if the temp drops below a certain temperature. The property is a holiday rental so it is difficult to switch the heaters on/off when it is warmer etc.

Aside from your main question (which is almost impossible to answer without actually seeing the setup or having more information), you might have a conceptual problem with the above. Night temperatures (when the thermostat would be controlling the power) are not a very good guide to the temperature (hence heating requirements) of the following day. For example, clear skies tend to lead to very cold nights followed by relatively warm days.

Kind Regards, John

 

[clifford1]

Storage heaters use funny ways of assessing temperature and deciding when to open to release heat. The more expensive ones have some kind of intelligent processor inside to assess how much heat to store in relation to possible needs.

 

[stu550]

These are basic heaters that are fairly old - the stats will be in a holiday house so basically if the guests have the heating and stoves cranked up, the temperature in the house overnight will still be warm so the night storages heaters wont come up.

Likewise, when the property is empty and no heating is on, the heaters will heat up. The heaters are only for background heat when it is empty - but they currently get left on all the time in the winter and so its costing about £2.50/ night.

 

[stu550]

I just cant understand why one of the wires coming out the top of the board appears to be constantly live.... regardless of whether the fuses are in and the main switch on the off peak board is on or off.

If I turn off the power for the whole house, the wire is not live....

 

[JohnW2]

Storage heaters use funny ways of assessing temperature and deciding when to open to release heat. The more expensive ones have some kind of intelligent processor inside to assess how much heat to store in relation to possible needs.

I'm sure that attempts at intelligent control are possible - the crudest would probably be to determine how much (if any) heat to store overnight on the basis of the temperature during the previous day. However, as I said, I don't think that the nighttime temperature (which would be the determinant, if one simply used a thermostat,as suggested by OP) is, per se, a very good basis for making that decision.

Kind Regards, John

 

[JohnW2]

I just cant understand why one of the wires coming out the top of the board appears to be constantly live.... regardless of whether the fuses are in and the main switch on the off peak board is on or off.

That would probably be because you are using a "stud/volt tester". I suspect that it's not actually live when the fuses are out or the switch off. Such 'testing'devices are notorious for giving anomalous results such as you describe. The reason it's happening with one cable and not the other two could well be a question of what they are connected to.

Sooner or later, someone is going to have to look inside that CU to see what is going on - but it is exceedingly unlikely (one hopes!) that it's been wired in such a manner than one of those cables is still live with all fuses out and/or the main switch off!

Kind Regards, John

 

[JohnW2]

These are basic heaters that are fairly old - the stats will be in a holiday house so basically if the guests have the heating and stoves cranked up, the temperature in the house overnight will still be warm so the night storages heaters wont come up.

Indeed - and what if the next day then proves to be cold?

Kind Regards, John

 

[stu550]

If I dump the power to the whole house, the wire is no longer live.... and likewise non of the heaters are powered during the day.

When I first looked at the board properly, I assumed that each of those three wires goes to a heater each. Obviously not the case.

 

[stu550]

John - yes, you're right. But the heating will then be on during the day. The stats will be set fairly high, so the majority of the time the heaters will be coming on. This is a old house with meter thick walls, when its warm it will stay warm - and likewise when it is cold! It is more for when the property is empty and the heating off - the night storage heaters will always come on then.

The heaters don't give enough heat for it to be warm duirng the day, the heating does that. Plus, one heater is in the kitchen and it is always warm in the kitchen, so long as the house is occupied so this heater will rarely come on when occupied.

I think i'm beginning to waffle but I take your point!

 

[JohnW2]

If I dump the power to the whole house, the wire is no longer live....

That makes sense, since no electricity is getting anywhere near that CU under those circumstamces.

When I first looked at the board properly, I assumed that each of those three wires goes to a heater each. Obviously not the case.

That would, indeed, be the most obvious conclusion - and, as I've said, I don't think you are safe in assuming that it is "Obvioulsy not the case".

One of the fuses appears to have a different rating (different colour dots) from the other two. What are their ratings?

Kind Regards, John

 

[JohnW2]

John - yes, you're right. But the heating will then be on during the day. The stats will be set fairly high, so the majority of the time the heaters will be coming on. This is a old house with meter thick walls, when its warm it will stay warm - and likewise when it is cold! It is more for when the property is empty and the heating off - the night storage heaters will always come on then.

Fair enough - but in that case, the only situation in which the storage heaters didn't come on would be if the house were particularly warm on a winter's night. If that's what you want, then fair enough.

The heaters don't give enough heat for it to be warm duirng the day, the heating does that.

Again, fair enough, but it's obviously only during the day that the storage heaters wil give out any heat - except for 'leakage', they don't do any heating during the night.

Kind Regards, John

 

[stu550]

John
The far left is 20amp, and then there are two 15s.

Two cables go left where there is a 3.4kw and 1.7kw heater and one cable (the one that appears to be always live) goes right to another 1.7kw heater.

 

[JohnW2]

The far left is 20amp, and then there are two 15s. Two cables go left where there is a 3.4kw and 1.7kw heater and one cable (the one that appears to be always live) goes right to another 1.7kw heater.

Right, so one assumes (even if one should 'never assume'!) that the 20A fuse is probably for the 3.4kw one - and that ,as you presume, one cable is for each heater.

I still strongly suspect that it's your testing giving misleading results, rather than that one cable always being live. Do the heaters have indicator lights to indicate when they have power? If so, you could check to see if (when the CU is powered) the light goes out when you pull one of the 15A fuses (or switch off the main switch).

Kind Regards, John

 

[stu550]

John

Okay, will have a bit more of a look - maybe when the off peak is actually 'on' I can see whether there is any difference. The heater has been off all summer and is definitely not on.

There are no indicator lights on the storage heaters.

One thing I forgot to add, I need to put the stud detector fairly close to the wire to detect a live wire/ reading. On other live wires, it detects it from say 4 or 5 inches. On this, it needs to be almost right up to it. This does suggest that a small load is running through it which seems odd too. Perhaps when the off peak is on, it will pick it up from further away.

Many thanks for your help.

Stuart