30a connector block, how can I tell

[JohnW2]

Oh how I wish I could make the same claim. ... Noise of arcing in lighting JB's drove one family to distraction, they thought they had wasps in the loft but couldn't find them.

My experience is obviously limited, but I can but report my personal experiences. On the face of it, it's hard to see why an undisturbed JB with screwed terminals should suddenly develop a problem after years or decades of satisfactory service - although I don't sure that I could necessarily confidently say the same of ('spring-dependent') 'MF' JBs.

Of course, one of the issues with accessible screwed connections, particularly in situations such as CUs, is that they often are repeatedly 'disturbed' (most commonly in the name of 'testing'), in which case all the above bets are off

Kind Regards, John

 

[Harry Bloomfield]

My experience is obviously limited, but I can but report my personal experiences. On the face of it, it's hard to see why an undisturbed JB with screwed terminals should suddenly develop a problem after years or decades of satisfactory service - although I don't sure that I could necessarily confidently say the same of ('spring-dependent') 'MF' JBs.

Kind Regards, John

My thoughts too. Any spring subjected to heat from a poor termination, will over time degrade and produce more heat.

 

[JohnW2]

My thoughts too. Any spring subjected to heat from a poor termination, will over time degrade and produce more heat.

I gather that 'spring-dependent' electrical joints have been used (presumably satisfactorily) in some industrial situations for quite a long time, but I know nothing of that.

As far as domestic (and probably also most commercial) installations are concerned, it's a relatively new concept, so I think I will have to leave it to my children and grandchildren to eventually to discover what their very-long-term performance/reliability is like. In the meantime, were it not for (and maybe despite ) 'regulations', my gut feeling would probably be inclined to stay with "the devil I know"!

Kind Regards, |John

 

[Harry Bloomfield]

I gather that 'spring-dependent' electrical joints have been used (presumably satisfactorily) in some industrial situations for quite a long time, but I know nothing of that.

I first came across them in fluorescent light fittings in the 1970's (I think), for the internal wiring only and (same principle, different idea) wire wrap at the GPO.

 

[SUNRAY]

My experience is obviously limited, but I can but report my personal experiences. On the face of it, it's hard to see why an undisturbed JB with screwed terminals should suddenly develop a problem after years or decades of satisfactory service - although I don't sure that I could necessarily confidently say the same of ('spring-dependent') 'MF' JBs.

Of course, one of the issues with accessible screwed connections, particularly in situations such as CUs, is that they often are repeatedly 'disturbed' (most commonly in the name of 'testing'), in which case all the above bets are off

Kind Regards, John

There are 2 devils with screw terminals, one is not doing them up tight enough and the other is doing them up too tight.

1. Too lose means high resistance bad connexions .
2. Too tight and the wire gets damaged, I've seen wire conpletely severed with only the slightest amount of metal left to grip.
Both of these will excessively heat and cool with current and eventually fail.

Next problem is copper is quite soft and will distort when clamped which in itself is not generally a problem but as it heats (even ambient) the copper expands but where the restriction is it cannot expand so becomes more distorted, then when it cools it shrinks and suddenly it's not as tight in the clamp, this starts leading us to 1, above. If the current is very cyclic whith lots of (over)heating and cooling it can be a fairly quick issue.

An issue which has created more problems than others, in my opinion, is multiple wires in a single clamp, in particular the old style JB's with the U shaped 'nut' which tend to clamp round wire against a round wire which may not be too stable.

 

[JohnW2]

There are 2 devils with screw terminals, one is not doing them up tight enough and the other is doing them up too tight.

I agree, although I would suggest that the former is far far more commonly the cause of problems. However, either way, I don't think it alters what I wrote (and you quoted), namely ...

... On the face of it, it's hard to see why an undisturbed JB with screwed terminals should suddenly develop a problem after years or decades of satisfactory service

As I said, I think it is 'disturbing' screwed connections (e.g. 'for testing') which often leads to problems. Many decades ago I was told that one should never re-terminate the same bit of a conductor in a screwed terminal more than twice - and I can see some sense in that advice (even though I have often had to break that 'rule'!).

Kind Regards, John

 

[SUNRAY]

I agree, although I would suggest that the former is far far more commonly the cause of problems. However, either way, I don't think it alters what I wrote (and you quoted), namely ...

On the face of it, it's hard to see why an undisturbed JB with screwed terminals should suddenly develop a problem after years or decades of satisfactory service Kind Regards, John

Quite the contrary, I believe both of those are the reasons undisturbed joints do fail after a long period of time.

 

[JohnW2]

Quite the contrary, I believe both of those are the reasons undisturbed joints do fail after a long period of time.

Experiences obviously vary. I cannot recall a problem with an undisturbed screw connection after it had been in satisfactory survive for many years.

Talking of 'undisturbed', the last two cases of overheated screw terminals (due to being 'too loose') I've seen both occurred in CUs soon after an EICR had been undertaken - which is possibly another reason why we need more regulation of the competence required of people allowed to undertake such inspections.

Kind Regards, John

 

[SUNRAY]

Experiences obviously vary. I cannot recall a problem with an undisturbed screw connection after it had been in satisfactory survive for many years.

Talking of 'undisturbed', the last two cases of overheated screw terminals (due to being 'too loose') I've seen both occurred in CUs soon after an EICR had been undertaken - which is possibly another reason why we need more regulation of the competence required of people allowed to undertake such inspections.

Kind Regards, John

One of the lofts with slate roof and no felt had an undisturbed layer of black dust, lifting the loft hatch resulted in a shower of the stuff. 4 JB's , went straight to the correct box and unscrewed the cover to find a fag paper width gap between the brass terminal and the copper of the wire and a black patch where it had been arcing. My bet is there hadn't been any movement in the loft for 20 years.
While there I checked all 4 JB's and found them all in good condition (apart from the dust) but every screw needed a tweek.

Apart from the black dust I've found that to not be untypical of faults. Others are done up so tight the copper is wafer thin and all but welded together, eventually the copper leaf burns through.

I've found many lose screws in switches and sockets but always assumed it's due to the vibration.

There are far fewer failures in commercial kit but they tend to be clamps rather pressure screws...

 

[333rocky333]

I gather that 'spring-dependent' electrical joints have been used (presumably satisfactorily) in some industrial situations for quite a long time, but I know nothing of that.


Kind Regards, |John

We do a lot of work on Merlin Gerin Dist boards in factory made Submain panels that have been in since the early 80's if not before.
These take standard Mcbs on a dinrail, but instead of having a normal busbar it has an enclosed Busbar with holes in, each Mcb has to be fitted with a 4 inch long bit of 6mm Trirated cable, you open the hole with a screwdriver in the slot and push the wire in the hole.
I have seen up to 40 amp Mcbs and too date never seen one issue with a connection.

 

[SUNRAY]

We do a lot of work on Merlin Gerin Dist boards in factory made Submain panels that have been in since the early 80's if not before.
These take standard Mcbs on a dinrail, but instead of having a normal busbar it has an enclosed Busbar with holes in, each Mcb has to be fitted with a 4 inch long bit of 6mm Trirated cable, you open the hole with a screwdriver in the slot and push the wire in the hole.
I have seen up to 40 amp Mcbs and too date never seen one issue with a connection.

I've seen something similar in control panels with a 200mm high plastic busbar system with facilities to mount moulded plastic din rails on the front. I haven't encountered the system for 13 years and wondered if it had gone out of fashion.

It worked very well but 1, 2 or 3 tri rated tails were welded into a plastic 'plug' which snapped into the top and needed a lot of space to withdraw and replace, therefore only 3's tended to be used which sometimes meant spares were left over. As a control panel 'building block' they sometimes took up a lot of space and frequently looked untidy.