What is the purpose of the multi9 contactors

J D Hogg · May 3, 2021

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?

snowhead · May 3, 2021

Looks like the contactors are all controlling Radials, there is either local switched control for each of these or central control for all of them.
There may be a clue on the other DB section, more investigation required as to why it was done like this.

Check the link below

ElectraTech manual

[ElectriciansForums.net] What is the purpose of the multi9 contactors

Marvo · May 3, 2021

Just a guess but maybe their incoming supply was insufficient for the load so rather than have the DNO upgrade the supply they had load shedding contactors installed.

DefyG · May 3, 2021

Maybe controlled by an Off Peak time switch? so all heaters appliance come on to the cheaper rate?

James · May 3, 2021

Being separate for each room, I expect there is a thermostat in each room that controls each contactor.

pc1966 · May 3, 2021

It is unusual to see that sort of thing domestically but I guess there is/was a good reason for it being done. The trick is to find out why it was done!

If you can take a look at the control wires for the contactors hopefully you can find out which of the above suggestions are in place:

Load control for DNO limit (or maybe backup generator limit?)
Off-peak usage
Early "smart" control from thermostats back to central point

Lucien Nunes · May 3, 2021

As pointed out by @snowhead, there's a reference on one of the MCBs to ElectraTech controls having been fitted, so there would once have been a central panel for managing the heating and high-load appliances. There's also an MCB and relay labelled 'SEB System' presumably feeding the output of the central tariff control receiver into the ElectraTech.

If there's no panel, it's probably all completely obsolete and the contactors can be bypassed. If you do rip it out and start afresh, and other components of the system e.g. the ElectraTech control box are still present, I might be interested to save them for the museum as an example of an early 'smart' energy management system.

I recently removed a more industrial-style version of the same with a bunch of contactors in a panel beneath the DB that were used for load shedding on a backup genny. I put the whole thing in back in the 80s in my early teens and never quite finished the control system, as cars and girls dragged me in other directions. But that was OK because there were hardly ever any power cuts, so no-one missed the missing bits. That is often the way with these load management contactor panels, just a bunch of contacts closed since forever. It did all suddenly kick in during the early 2000s and apparently seemed to work.

Dustydazzler · May 4, 2021

As already stated the only time I have seen single phases contacts used domestically like this is in all electric flats / houses to switch heating loads on/off via individual room stats

SagaCU29 · May 4, 2021

Lucien Nunes said:
As pointed out by @snowhead, there's a reference on one of the MCBs to ElectraTech controls having been fitted, so there would once have been a central panel for managing the heating and high-load appliances. There's also an MCB and relay labelled 'SEB System' presumably feeding the output of the central tariff control receiver into the ElectraTech.

If there's no panel, it's probably all completely obsolete and the contactors can be bypassed. If you do rip it out and start afresh, and other components of the system e.g. the ElectraTech control box are still present, I might be interested to save them for the museum as an example of an early 'smart' energy management system.

I recently removed a more industrial-style version of the same with a bunch of contactors in a panel beneath the DB that were used for load shedding on a backup genny. I put the whole thing in back in the 80s in my early teens and never quite finished the control system, as cars and girls dragged me in other directions. But that was OK because there were hardly ever any power cuts, so no-one missed the missing bits. That is often the way with these load management contactor panels, just a bunch of contacts closed since forever. It did all suddenly kick in during the early 2000s and apparently seemed to work.

Electratech pioneered by Norweb installed hundreds back in the eighties.

J D Hogg · May 5, 2021

Thanks for the replies. I have taken a few more photos. Does anyone know if it is straightforward to remove all of this and replace with a standard consumer unit?

Interestingly the house is all electric including storage rads, they have a 3 rate tariff and meter but the bill is less than £10 per month, faulty meter methinks.

The whole installation is protected by a 100mA RCD which trips when the rotary switch to the left of it is moved to 1 but I have no idea what that is for.

snowhead · May 5, 2021

What's the reason for wanting to replace it?
It's quite likely that the customer is going to spend a lot of money and end up paying a far higher electricity bill unless you put some other form of control on all the heating which takes advantage of the 3 rate tariff.

If you check out the Electratech Professional manual I linked to earlier, it explains exactly what the Electratech system does.

J D Hogg · May 5, 2021

We are just weighing up options at the moment but they would like the storage rads removed and something more controllable installed. So not definitely replacing it but just trying to find out more about it.

What is the purpose of the multi9 contactors

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