Old Mem contactor

[NDG Elecs]

Hi folks,

Mainly do domestic with a smattering of commercial. Currently repositioning a few extra sockets in a small office and noticed an old Mem contactor still in use. I understand basically what a contactor does but have never used nor fitted them before.

So, got a bit of a head scratcher! The contactor has 10mm twin andpiccy, h supply coming in and 16mm L&N out at the top. No grommets. There is a separate 16mm main earth to the CU. According to the wiring diagram (photo), these are wired back to front. There is also a 2.5mm 3 core & CPC cable going to an old FCU which then goes onto a timer. The live on the 2.5mm cable is fed directly from the main incoming live. When the fuse is pulled on the old FCU all the power to one of the CU's is lost. So I presume, with fuse in, that the contactor is energised (buzzing noise from it), but when the fuse is pulled the contacts go back to the n/o position.

Would any of this relate to the night storage heating? I am inclined to think not, as the NSH is on a separate old Wylex board that is fed from a dual tariff meter. See piccy, it's the top left board to the right of the meter. The Mem contactor is on the other side of the wall to the isolator labelled GND Floor.









Ideally would like to remove the contactor and upgrade the entire tails, but not 100% on the set up. As I say there are no grommets on the metal casing, the entire unit is also half hanging off the wall too.

Any or all thoughts welcomed.

Neil

 

[NDG Elecs]

Little update as been thinking and reading up on it. The time clock must be for the immersion heater element. The meter has two live tails; one normal rate, and one going to E7 NSH board, so that is not related. If the clock is 12 hours out it could end up saving them a fortune in leccy!

Apart from the stated issues with the Mem, the complete loss of power if the 3/5/13/whatever amp fuse pops is not good.

Gonna give good old Trev a call tomorrow as he will prob have it sussed in minutes!

Any input still appreciated.

 

[Richard Burns]

Slightly confusing post I am afraid, a bit of typoing perhaps?

The timer look like a standard (old) time clock for changing from normal to off peak rate.
Since the contactor is rated at 40A and the contacts are doubled up someone must be attempting to use 80A or less.
The current rating in that case would appear to be for night storage heaters, but may have been repurposed to some other supply, (immersion heater a bit of overkill but workable) but I cannot think of anything at that current that would need to be off during the day.

It is slightly odd to have a larger outgoing cable than incoming cable but no real problem (unless the contactor is carrying 80A on 10mm²)
The 2.5mm² being connected to the incoming line indicates that this should be an item under DNO remit as that current is not being metered (small though the current would be). If the incoming and outgoing are as you say then it is wired backward but since it is a switch it is not too critical.

I presume that C1 is connected to the incoming side of the time clock and the outgoing side of the time clock is going to C3 (in the two wire control method) (presumably red and yellow of the three core cable), blue would therefore be neutral and be connected to C4.

When the time clock is on the coil is energised and switches on the supply to (presumably) the CU that switches off when you pull the fuse; though you do not say which CU is powered down, I would expect the night storage heater one.

Since the fuse in the FCU is only powering the contactor coil (and perhaps the time clock) I would not expect the fuse to blow except under fault conditions.

This is all I can think of atm.

 

[Pete999]

Rough old job is that shouldn't be to difficult to suss out what it does, needs getting rid of or updating if it's still used, in the picture the incomers and out going tails look like they are split across two poles of the 4 pole contacter, must have been done by a DIYer, no self respecting Electrician would butcher up a job like that surely????

 

[Barry White]

Is there another consumer unit other than the 2 shown in the picture ? Agree with Richard think the sangarmo timer is DNO property used to time the off peak tariff ( before the meter was replaced) which may or may not have been repurposed.

 

[NDG Elecs]

Thanks for replies. Will clarify things later as busy with work at the mo.

 

[NDG Elecs]

Hi, will respond better later when kiddys asleep, but here is a pic of the layout..



Thanks, Neil

 

[NDG Elecs]

Hi, thanks for replies.

Sorry for any confusion! Not 100% as to what was going on myself so worded it badly.. I have sort of addressed some of the points you have made below. I just spent 30 mins on smartphone typing a reply only to press the back button and lose it all….so this is probably now a bit disjointed to read as slightly losing the will!!

Please see the drawing for the supply and DB wiring Mykey.

Anyway, I have not had a chance to go back to investigate further yet. Doing so would have to be after office hours as the phones/computers/alarm/etc would all go down to check it all. I am liking the word repurposed, and am thinking that the contactor was originally for the NSH and when the E7 meter was installed the contactor was used for the immersion timer instead (SEE EDIT BELOW THOUGH!!). As the supply goes off (to DB3) when the FCU fuse is pulled I can only presume that the timer is on permanent over-ride as otherwise the computers/alarm/etc would be off when the timer switches (and contactor coil de-energises). Therefore the immersion must be on 24-7, unless there is a separate timer elsewhere.

I am thinking the supply to DB3 needs to be fed from the henleys rather than having to rely on the FCU fuse/time clock working and remaining to do so. Could connect the tails into the bottom of the contactor where the supply comes instead but not overly happy with the 10mm section of cable. If new tails were put in it is only a 2m run so no issues there and could leave the 10mm from the wylex switch fuse as it is.

Whether the Mem and timer is DNO gear had crossed my mind but I sort of rejected that as it is downstream from the wylex switch fuse. Not quite sure why the 10 and 16mm cable are split between two poles each; bodge as you say Pete.


EDIT!
Your comment Richard about larger CSA cables on the outgoing to incoming cables got me thinking (yes dangerous, I know!!):
This DB is a more recent 16th ed split board and supplies two office rooms and display lights etc. So I am thinking that this has possibly been put in and connected to the contactor rather than the henleys due to stupidity or laziness. And that the contactor has always historically supplied the immersion and/or NSH before that. Don’t know when both NSH and immersions first came about, but the timer is pretty old and some of the NSH’s look pretty old too.

Right, gonna shut up now as think I am probably making this even more confusing…..!

A second pair of more experienced eyes to come and have a look is gonna be my next port of call.

Ta, Neil

 

[Richard Burns]

The introduction of DB 3 does makes things clearer.

I would say the old time switch and contactor arrangement was made redundant when a new meter was fitted and then at a later date or concurrently with the meter change a new board was put in and someone decided to use the contactor as a Henley block, in order to turn on the contactor they used (a presumably already present) FCU to power the contactor, this is probably bypassing the effects of the time clock (if the time clock is functional) but if you were to be present when the time clock is on then the board may well come on (thinking like a security light on timer with manual override) even if the FCU is off.
The contactor was doubled up to carry twice the current permissible from one set of contacts.

A good plan to remove the contactor/time clock/FCU from the system. Just replace this lot with new tails and the job is sound.
You could keep the switch fuse as an isolator since they have inconsiderately sealed the after the meter connectors.

 

[davesparks]

I've seen this kind of setup before where the contractor feeds a board which then feeds the old underfloor heating system. The idea being that the entire floor slab is used as a storage heater.

 

[NDG Elecs]

The introduction of DB 3 does makes things clearer.

I would say the old time switch and contactor arrangement was made redundant when a new meter was fitted and then at a later date or concurrently with the meter change a new board was put in and someone decided to use the contactor as a Henley block, in order to turn on the contactor they used (a presumably already present) FCU to power the contactor, this is probably bypassing the effects of the time clock (if the time clock is functional) but if you were to be present when the time clock is on then the board may well come on (thinking like a security light on timer with manual override) even if the FCU is off.
The contactor was doubled up to carry twice the current permissible from one set of contacts.

A good plan to remove the contactor/time clock/FCU from the system. Just replace this lot with new tails and the job is sound.
You could keep the switch fuse as an isolator since they have inconsiderately sealed the after the meter connectors.

Thanks again.

I popped in to see the set up briefly again today and there is a separate timer for the immersion, so you may well be right that the old timer is essentially defunct (although it is still ticking away).

Hopefully the immersion is on a different circuit. That would make it that bit easier to sort. Just need to get a new battery for the alarm to stop that bleating when I switch off!

Just two last questions if anyone could answer: the supply has been split between two sets of contacts, I take it each set of contacts are rated 40A so essentially 80A as split between two? Also, is the contactor/timer likely to be DNO equipment?

Definately a good idea to put UFH on E7 or the 10 hr version.

Thanks again,

Neil

 

[7029 dave]

I don't think that clock is DNO/ suppliers equipment,it would be next to the meter and cutout on the back board, can't see any provision for sealing it either. No serial number too.

 

[NDG Elecs]

I don't think that clock is DNO/ suppliers equipment,it would be next to the meter and cutout on the back board, can't see any provision for sealing it either. No serial number too.

Ooohh, is that that thin steel wire I cut to get inside it!! Good point though, no serial number or other old NEEB ID on it.

 

[Bobster]

I don't think that clock is DNO/ suppliers equipment,it would be next to the meter and cutout on the back board, can't see any provision for sealing it either. No serial number too.

Those Sangamo if installed properly can be sealed.

Gayowl if you are ripping it out keep it. Just have a look at how much to buy new, they are nearly indestructible. They do have a permanent override latch if you suspect it's broken because it doesn't switch have a look an see if it's been engaged.