2-Pole Isolator Switch (Din Rail) Won't Stay Up

[Mikron]

An unremarkable CU (2-pole isolator and a collection of MCBs, all superficially in decent condition).

What might cause the 2-pole isolator switch not to stay up, or to flick itself off apparently at random?

It used to go for weeks without a problem, then become prone to flick off.

No correlation with time of day, loading, steam in kitchen, weather, etc.

There is an RCD further back up the line; neither that nor anything else trips; it is always this isolator.

It looks much like this one.

 
Today, I replaced it with another one, which I am fairly sure was working OK beforehand, though not new.

That seemed to be working OK. But now it, too, flicked-off, and it won't stay on (even with all MCBs off).

I can only think contact resistance was causing heating (though there was only a couple of 100W lamps on at the time), and that altered the mechanics within the switch.

Any ideas gratefully received!

Regards,

Mike

 

[steptoe]

are you sure its an isolator and not an RCD/MCCB

what knowledge or experience do you have?

a picture of the actual 'isolator' would be of great benefit

 

[OnOff]

What might cause the 2-pole isolator switch...............to flick itself off..........?

Excitement? Has this "isolator" got a TEST button?

 

[batty]

That certainly shouldn't flick off are you sure something is not being dropped on it?

 

[Andy™]

a normal 100a isolator cannot switch off on its own. end of.

if its an RCD then its because there is a fault. replacing it wont do you any good, you need to find the fault. if it is an RCD and its tripping, then i suggest you call an electrician to come find the fault because you dont seem competent if your first thought is to replace it

 

[SPECIAL LOCATION]

An unremarkable CU (2-pole isolator and a collection of MCBs, all superficially in decent condition).

What might cause the 2-pole isolator switch not to stay up, or to flick itself off apparently at random?

It used to go for weeks without a problem, then become prone to flick off.

No correlation with time of day, loading, steam in kitchen, weather, etc.

There is an RCD further back up the line; neither that nor anything else trips; it is always this isolator.

It looks much like this one.

 
Today, I replaced it with another one, which I am fairly sure was working OK beforehand, though not new.

That seemed to be working OK. But now it, too, flicked-off, and it won't stay on (even with all MCBs off).

I can only think contact resistance was causing heating (though there was only a couple of 100W lamps on at the time), and that altered the mechanics within the switch.

Any ideas gratefully received!

Regards,

Mike

The switch shown in your example is a manual double pole switch.....

that will not operate itself.....

Needs human operation...

unless you have ghosts!!???

Need more info...

Photos of ACTUAL device...

any tests readings..

Is this REALLY a DIY question??

or is it posted in the wrong area??

If it is a genine DIY question..

I would suggest you get a competent electrician out to come and do a few supply & circuit tests to see whats what...

Guinness

 

[NozSpark]

Maybe its haunted or possessed??

 

[SPECIAL LOCATION]

Maybe its haunted or possessed??

I did just suggest that....

:coat

 

[kerching]

There is a very very very slim possibility that if the internal " contact gubbins" has gone  as limp as a Vicars handshake it could switch off on its own......BUT to be perfectly honest there is more chance of it not going dark before tomorrow!

 

[NozSpark]

I did just suggest that....

:coat

I know,,, you beat me to it :coat

 

[Mikron]

Thank you all for chipping in.

It is a manual isolator, not an RCD/RCCB/RCBO.

Like some of you, I thought an isolator could not trip itself.

But that is wrong. Isolators (at least these sorts of DIN rail ones) cannot trip themselves electrically, but they can trip themselves thermally.

These photos show the innards of the particular isolator, which includes a bi-metal tripping mechanism. That is obviously to cater for overheating for whatever reason - presumably including scenarios where the whole building catches fire. 

In the photos below, the original isolator is the black one, the temporary replacement is the blue one.
I did not photograph the new one.
I hope these photos will be of interest generally, not just in this particular case.
Click on photos to enlarge them (necessary to read my annotations).
 
The two isolators



Black isolator, one half opened



Black isolator, innards, off



Black isolator, innards, on



Blue isolator, one half opened



My photos also show arcing on the contacts. I have to think that associated heating was the immediate cause of the tripping.

Black isolator contact, burnt



Blue isolator, arm skew and malfunctioning due to heat-softening of plastic



Blue isolator contact burns, mainly on just one actutor



Blue isolator, contacts, including the other half (not burnt) for comparison



The cause of the degradation of the contacts or their poor closure, however - the root case - remains open to speculation.

Perhaps a grain of dirt got onto the contact (there was masonry/cement dust in the top of the isolator) ;
perhaps the spring mechanism or internal plastic linkage became weak over time;
perhaps a nearby lightning strike caused a high voltage transient that damaged the contacts;
perhaps, when the house is unoccupied for several months over winter (more prone to damp?), corrosion could have arisen on the contacts before current was applied again (isolators are not hermetically sealed). 
 
Touch wood, the brand new isolator I installed this morning is working fine.
The effort required to operate the on/off lever is certainly greater than with the old one.
 
Regards,
Mike

As a newbie, I apologise if I posted my question in the wrong place.

'Question & Answer Board' did seem kinda appropriate, mind  :Blushing

Please advise, so I get it right next time, thanks.

Update: Ah - I see I can post directly in 'Question & Answer Board' rather than a subforum. OK.

Mike

 

[Steve3948]

Double Pole Mcb's not isolators, who installed it ?

 

[OnOff]

Not being rude to the OP but an "isolator" and a circuit breaker which you in fact have are two totally different things. There are some major gaps in your understanding. By the way you have just replaced a C type circuit breaker with a D type by the looks of it which is possibly LESS LIKELY to trip. 

 

[ProDave]

To be fair, this is in the DIY section, but they are indeed MCB's and were doing their job.

As to WHY somebody fitted 2 pole MCB's as a "main switch" is another question.

Perhaps we could have a photo of the whole CU with it's cover off?

 

[Doc Hudson]

Thank you all for chipping in.

It is a manual isolator, not an RCD/RCCB/RCBO.

No, it is not a manual isolator, as Steve pointed out your photographs show a double pole MCB, whereas your first post showed a manual 100A double pole switch. You can see the rating and type numbers on the front of the devices. Similar to devices such as, http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/CMD_Main/CMD_mcb_d2/index.html Double Pole MCB's.  Where is this device fitted and what experience, qualifications do you have with regard to maintaining it.

Doc H.

 

[kerching]

The giveaway is the symbol on the face of the MCB.  AND the Type and rating.  C50

never seen a DP MCB fitted as an incomer, mind you I do not actually know how many things I have never seen

...don't get me wrong

Forgot to say.....nice copy of a Merlin Gerin old style MCB,    Also bit of a strange rating on both of them.   4000A.  And. 4500A

....don't get me wrong

 

[Mikron]

Thank you guys.

Teach me for going into my local electrical store and asking for an isolator!

Didn't help that the old device was a 2-pole MCB, too. Hence I was inappropriately happy that the symbol on the new one was the same as on the old one.

The original one was fitted sometime in the last 20 years, during one stage of renovation or another, by bloke unknown.

The owners were in a bit of a pickle, and had had bad experiences with electrical contractors in the past. I was on-hand..., and apparently a better bet than the old-boy local farmer over the road.

I don't have access to the CU now, but it was a small unit with a single row of ways, part-filled with the 'isolator' and half a dozen single-pole MCBs. That CU is one of about 5 daisy-chained between various parts of the old buildings. There is one downstream of it, fed from a C32 single-pole MCB. The only RCD is a 500mA one in the meter box by the road.

I shall revisit my electrical store, and revisit the owners when they return.

 

[ProDave]

I thought this was in your own house.

I'm not sure what worries me most. the fact that you seem to be doing this for a trade, or the fact that your "electrical store" gave you a 2 pole MCB when you asked for an isolator.

 

[Andy™]

Thank you guys.

Teach me for going into my local electrical store and asking for an isolator!

Didn't help that the old device was a 2-pole MCB, too. Hence I was inappropriately happy that the symbol on the new one was the same as on the old one.

The original one was fitted sometime in the last 20 years, during one stage of renovation or another, by bloke unknown.

The owners were in a bit of a pickle, and had had bad experiences with electrical contractors in the past. I was on-hand..., and apparently a better bet than the old-boy local farmer over the road.

I don't have access to the CU now, but it was a small unit with a single row of ways, part-filled with the 'isolator' and half a dozen single-pole MCBs. That CU is one of about 5 daisy-chained between various parts of the old buildings. There is one downstream of it, fed from a C32 single-pole MCB. The only RCD is a 500mA one in the meter box by the road.

I shall revisit my electrical store, and revisit the owners when they return.

i hope your not charging people for your incompetence. this is fairly basic stuff that anyone competent would be aware of

 

[Doc Hudson]

Thank you guys.

Teach me for going into my local electrical store and asking for an isolator!

Didn't help that the old device was a 2-pole MCB, too. Hence I was inappropriately happy that the symbol on the new one was the same as on the old one.

The original one was fitted sometime in the last 20 years, during one stage of renovation or another, by bloke unknown.

The owners were in a bit of a pickle, and had had bad experiences with electrical contractors in the past. I was on-hand..., and apparently a better bet than the old-boy local farmer over the road.

I don't have access to the CU now, but it was a small unit with a single row of ways, part-filled with the 'isolator' and half a dozen single-pole MCBs. That CU is one of about 5 daisy-chained between various parts of the old buildings. There is one downstream of it, fed from a C32 single-pole MCB. The only RCD is a 500mA one in the meter box by the road.

I shall revisit my electrical store, and revisit the owners when they return.

Is this trade or DIY work. I am concerned that there is a fault somewhere on the installation that you have done nothing to locate? Any device tripping off will have a reason that should be established by appropriate tests and investigations before replacing any parts. Guess work and changing items when you do not understand what they are, or how they work, is a risky business when doing it in your own home, but even worse if doing it at another installation for a third party. 

Doc H.