Off peak Heating contactor confusion.

Planctonboy · Jul 14, 2022

Hi. Can anyone offer a bit of advice please.
I've got a customer who wants needs an upgrade to their consumer units. It is a bungalow that has a 3 phase supply. Each phase has a separate consumer unit. Blue and Yellow are being used for heating, and the Red is general domestic power and lighting etc. The supplies to the storage heater consumer units appear to be live all the time (at least they were when I checked today at 0900 and 1700). There is no gas or oil so all the heating is electric night storage heaters. I've had a look at the setup and need a bit if clarification as to how the night storage supply is energised at off peak time.

In the meter box there is a 100a heating contactor proteus EHC1 installed by eon. This contactor takes its supply from the blue phase. This phase also supplies one consumer unit with 4 storage heaters. The output from the contactor then supplies the coils for two further contractors located inside the property which connect the heating loads from the consumer units on the Blue and Yellow phases.. All the night stores are connected via these two contactors.

All three phases seem to be live all the time. But the output from the proteus contactor to the other two contactor coils is not live ( at least not when I checked at 0900 and 1700 today).

So my confusion is, what makes the proteus contactor switch over so that the other two contactors in turn switch over and allow the storage heaters to become live? I can't see a time clock anywhere, and the supply to the main contactor seems to be permanently live anyway So it's not being switched internally by the meter?
Any advice will be welcome. I'm not that familiar with this kind of setup. But I'm happy to work on it as long as I'm sure I understand what's happening. So just a bit more clarification would be great.

Cheers

Richard

SJD · Jul 14, 2022

Do you have photos of the setup? We like photos.

freddo · Jul 14, 2022

Do you have a photo? Most of these contactors in newer setups are switched by an output on the electricity meter. The contactor live in to the switch contact often also feeds the contactors coil via an internal fuse, a signal wire connected to the meter or timer is connected to neutral when the contactor needs to be switched on.

Planctonboy · Jul 14, 2022

OK. Pics Comming Up ASAP. Dont get too excited its a right mess and needs a fair bit of work ...

Planctonboy · Jul 14, 2022

Here are a few pics showing what ive got here. The whole thing is a bit of a mess and needs a bit of work.
There are also some cables including meter tails that have evidence of being eaten by mice --- I found a dead mouse warming itsels across the top of the fuse carriers in the main house consumer unit. Anyway thats beside the point.

Hope you can make more sense of whats controlling the Proteus contactor. If it is has a signal wire to the meter, I cant see it unless it goes out of the back of the meter and into the contactor from behind ??

[ElectriciansForums.net] Off peak Heating contactor confusion.

SJD · Jul 14, 2022

Connecting the contactor N terminal to N would appear to energize it.
Which the meter does, according to the times shown on the sticker on the front of the meter.

Planctonboy · Jul 14, 2022

OK. That thought did cross my mind that the meter may be switching the neutral. Is this the normal way of doing this? seems a bit weird to have the switch in the contactor neutral as were always told to make sure the switch is in the line conductor for most other circumstances ??

James · Jul 14, 2022

I agree the metre is switching the N to the contactor, it’s easy and uses less wire than doing a switched live.

brianmoooore · Jul 14, 2022

Switched neutral is the way it's done on the heating contactors I've come across.

freddo · Jul 14, 2022

Planctonboy said:
OK. That thought did cross my mind that the meter may be switching the neutral. Is this the normal way of doing this? seems a bit weird to have the switch in the contactor neutral as were always told to make sure the switch is in the line conductor for most other circumstances ??

Remember this is DNO equipment, and DNOs do a lot of things that would not be permitted in consumers installations.

R-fur · Jul 15, 2022

I uesed to install meters for the DNO that I worked for, and confirm that switched neutrals are common.
However what I am not sure about in the picture is that the Eon contactor seems to be taking its internal power from the metered supply. I know the power used will be minimal but many years ago there was a test case and it was ruled that customers should not pay for the power used in control circuits.
When I was doing this type of work (early 80s) we had to make sure that time switch motors, contactor coils etc were fed from the unmetered supply.
Things may have changed, I would be interested to know from someone who is more current than I am.

snowhead · Jul 15, 2022

R-fur said:
When I was doing this type of work (early 80s) we had to make sure that time switch motors, contactor coils etc were fed from the unmetered supply.

I'd agree that was the case before deregulation.
However now the DNO stop at the cutout.
Energy suppliers stop at the output of the meter so any timeswitches etc whether fitted (and sealed) by the DNO years ago or by the customer in more recent years belong to the customer, so should be using a metered supply for the control.