Can someone explain how these storage heaters were wired via the contactor?

[ManchesterKirchoff]

Been round to a house to quote to replace some storage heaters for new panel heaters and came across a strange (to me at least) way of wiring the old storage heaters via a contactor in the board, as usually I see their own off peak consumer unit which powers up at night via economy 7.

From the pictures it seems the busbar for each row ends at the last breaker and there is no space to move any of the circuits away from the contactor to the main switch side and it MAY need a board change as a result. I have admitted to him as I’m an apprentice with limited experience of this type of wiring arrangement I would be out of my depth to consider doing such work.

I thought originally the three breakers next to the contractor fed the FCU’s for the storage heaters but when looking at the circuit ref’s they are on the middle shelf and there is also 4 heaters (so what do the breakers next to the contactor do and where do the supply and load for these come and go)?

I was pretty hesitant to leave the job after seeing inside the board so I didn’t stay long but I would like to understand what’s actually going on so that once I’m qualified I could actually feel confident going into a job like this.

One thing to note for any help is I tested to see if any of the FCU’s were live. (The three storage heaters were dead) but circuit 5 listed as “bedroom right” was actually a panel heater- this was live at 230v until the breaker was switched off so this surely must have not been running through the contactor.

Cheers in advance for any help!

 

[freddo]

Merlin Gerin is now owned by Schneider and was/is the manufacturer of some of the best off-the-shelf switchgear you can get.

I really like the new PON boards, it's nice the single phase boards are now side hinged instead of bottom hinged too. I hate that they moved the earth terminals to the top though, having 3 layers of terminals in the larger boards is a nightmare.

 

[Mike Johnson]

Strange that France has standardised on thirteen module boards and Germany have standardised on twelve module boards, must be a germanic thing about being orderly/symmetrical.

 

[Mike Johnson]

It's Merlin Gerin kit so yes, of course it's French, they are a French company.

Did not know that France extends as far as Manchester.

 

[nicebutdim]

Did not know that France extends as far as Manchester.

Part of Guy Verhofstadt's cunning plan.

 

[ManchesterKirchoff]

There have been multiple configurations of Off Peak / E.7 over the years ranging from DNO switched Off Peak C.U feeding storage / water heating to Dual Rate E.7 meters with no Off Peak switching provided by the DNO for customer use only for switching the meter over.

On the pictured C.U,

Bottom row,, Main Switch (Supplier feed into bottom) Top busbar feeding 4 adjacent MCB AND Red feed to row above. (live 24hr)

Middle row,, Red feed from bottom row into top of 8 MCBs and Busbar. (live 24hr)

Top row,, 4 pole contactor plus 3 single relays.

The contactor will be fed from either a separate customers timeswitch or a fused timed feed supplied by the DNO (nowadays Supplier) near the meter.

The Storage heater circuits will be connected to the contactor and relays, which will be fed from some of the MCBs (labelling not clear).

All MCBs are on 24hr so if your scrapping some or all of the Storage heaters and Off peak water heating, disconnect the feed from MCB to contactor or relay and connect panel heater direct to MCB instead.

If you’re scrapping all Off peak, the contactor and relays can be removed BUT find, make safe and disconnect the timed supply first.

You’ve explained it brilliantly- I have seen storage heaters powered via a contactor before which makes sense when having only the one consumer unit, but I still don’t understand the role of the relays in this configuration- Why are they there when it could just be the contactor, with the load of the contactor supplying the power to the MCB’s during E7 hours?

 

[loz2754]

There are only 4 poles in the contactor, with one pole for each circuit. There are 7 off peak circuits (that I can see). Hence the 3 individual relays, one each for the other 3 circuits. There were probably originally 7 of the relays, or 2 of the 4 pole contactors.
You can think of a contactor as a relay with the ability to switch higher current loads.

 

[snowhead]

but I still don’t understand the role of the relays in this configuration- Why are they there when it could just be the contactor, with the load of the contactor supplying the power to the MCB’s during E7 hours?

As shown in the Electratec link Oscar21 posted (#21) they were originally all single relays across the top, total number would depend on how many heaters installed, 1 for each heater, 1 for the Top immersion heater and 1 for the bottom immersion heater.
The relays are used as the Electec controller cannot switch the heater loads, it just uses a control signal for the relays.

Sometime in the past some relays have failed and have been replaced by a 4 pole contactor, (effectively 4 relays in one) probably cheaper or happened to be in the van.

 

[oscar21]

What usually happens is either the control panel or the brainbox goes kaput, you cant get the spares for them so they need adapting. As you can see the 3 original relays that are left are 2 x immersion ones and one bedroom heater, these will no longer be in use and I think the OP said the immersions are just on a switch now so the relays will have been bypassed, he also said one of the bedroom heaters was now a panel heater so that relay will have been bypassed as well. In fact you can see there aren't any 24V contol inputs to the A1&A2 contacts on the relays anymore.

Whats left is 4 storage heaters (if all 4 ways are in use) but these still need some kind of control so 4 of the relays have been removed and replaced with a 4 pole contactor controlled by a time-clock elsewhere or even the meter itself.

Edit : its 3 storage heaters still in use, you can tell by the labeling.

 

[snowhead]

Thought this was sounding a bit familiar.
A thread on the same subject from 2021,,
There's a link to the manual, but no diagrams, in my post #2

What is the purpose of the multi9 contactors

Hi, Last week I went to a property where the owners had just moved in. They wanted advice about various electrical things including a large DB filled with these multi9 TL contactors. Does anyone know what they are for and is it easy to remove them to change the board for a more conventional system?

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