The Lemon Fool

I did a test and inspection of a rental bungalow this morning. The neutral busbar had had either a small fire or a major overheating. Please see the picture below. This is usually because terminals are loose or have not been re-tensioned. In this case the neutral grub-screws were baked solid, all the others (including the incoming tails and the links between the main switch and the RCD) were able to be tightened up by about two whole turns each - some more.

I couldn't completely test the installation because whenever I moved the neutral wires insulation broke away. The bungalow had recently been bought. This situation went undiscovered during that process. It is only because the owner is renting it out temporarily and some new rules apply that insist on electrical test and inspections that it was discovered.

I will fail it.

Chris

I own (or am legally permitted to post) the content of this image.

Worrying innit. I encounter this all the time. The copper of the wires seems to 'relax' a few years after being installed and make the screws go slack and high resistance.

Earns me quite a lot on money, fixing burned out power supplies to electric boilers. Callers often report a "smell of fish" in or around the boiler, which usually turns out to be a loose connection screw with krispy insulation next to it...

It does seem to be a problem, the maleability of copper in this situation; biting down onto “tails” with a simple screw. Better methods are available.

csearle wrote:I did a test and inspection of a rental bungalow this morning. The neutral busbar had had either a small fire or a major overheating. Please see the picture below. This is usually because terminals are loose or have not been re-tensioned. In this case the neutral grub-screws were baked solid, all the others (including the incoming tails and the links between the main switch and the RCD) were able to be tightened up by about two whole turns each - some more.

I couldn't completely test the installation because whenever I moved the neutral wires insulation broke away. The bungalow had recently been bought. This situation went undiscovered during that process. It is only because the owner is renting it out temporarily and some new rules apply that insist on electrical test and inspections that it was discovered.

I will fail it.

Chris

I own (or am legally permitted to post) the content of this image.

I'm no electrician but doesn't the design of the board make it hard to work in? Does this fall under CDM?

Do the black wires touching at the top cause issues?

It's a frightening reality to witness this really.

AiY

PS ....

Chris I've got you booked in for 10am next Monday morning for the solenoid watchamacallit.

Pay will be a cup of tea and a chocolate digestive (from the fridge mate)

AiY

AsleepInYorkshire wrote:I'm no electrician but doesn't the design of the board make it hard to work in?

It does. There is hardly any room to dress the wires in nicely* .In this case the consumer unit is at the back of a kitchen corner unit. The white at the very top of the picture is the underside of the kitchen work surface. It is a pig to get at. Won't be wholly sorry if I don't get the job of replacing the consumer unit. I suspect though that I will as the client is (was) one of my volleyball participants.

AsleepInYorkshire wrote:Does this fall under CDM?

Do the black wires touching at the top cause issues?

No the housing is plastic (no longer allowed in most domestic situations as they are considered a fire risk) so the ends of the wires often touch the enclosure. I think maybe some water could have leaked over the back edge of the work surface making the busbar wet, but that's just a guess. It could equally have started with an untight terminal. It is possible for there to be thermal runaway with the heat speeding up the corrosion, making the connection poorer, generating more heat, and so on.

Chris
*I use consumer units like this one at the moment because they have more space.

AsleepInYorkshire wrote:PS ....

Chris I've got you booked in for 10am next Monday morning for the solenoid watchamacallit.

Pay will be a cup of tea and a chocolate digestive (from the fridge mate)

AiY

Is this "Yorkshire" place anywhere near Kent?

csearle wrote:

AsleepInYorkshire wrote:PS ....

Chris I've got you booked in for 10am next Monday morning for the solenoid watchamacallit.

Pay will be a cup of tea and a chocolate digestive (from the fridge mate)

AiY

Is this "Yorkshire" place anywhere near Kent?

10 minutes away

AiY

csearle wrote: I think maybe some water could have leaked over the back edge of the work surface making the busbar wet, but that's just a guess.

Oh yeah, water. How could I have forgotten that?

A lot of the houses in this village are owned by the local landed gentry (ancient family, hereditary baronets, huntin' and all that), and they're absolute skinflints about updating and maintaining their rental properties. A few years ago, one of the neighbours called me after her power failed, and sure enough, it was a small brown bakelite fuse box of probably sixty years' antiquity, all cracked and blistered. I told her to insist on getting it changed for a modern consumer unit. His lordship resisted for the best part of a year. To the best of my knowledge, my other neighbour still has hers in place.

How do they get away with it? In rental properties, too?

BJ

Mike4 wrote:Worrying innit. I encounter this all the time. The copper of the wires seems to 'relax' a few years after being installed and make the screws go slack and high resistance.

Cars used to have j-boxes with screw terminals.
But since yonks, they have crimps and push-ons.

I see the telephone people now use crimps.

It seems domestic electrics are behind the times.

We had a new CU last year, all RCBOS in a metal case with drop-shut door. Previously it was plastic with a fall-open door. So at least that's better. But when I was in there adding a circuit, I noticed that some of the screws are already not very tight, and I know they were tight when fitted because I checked.
When I think on this, and the number of j-boxes in house and garage some of which are hidden, it is slightly perturbing.

V8

88V8 wrote:Cars used to have j-boxes with screw terminals.
But since yonks, they have crimps and push-ons.

I see the telephone people now use crimps.

It seems domestic electrics are behind the times.

Yes but slowly catching up. For quite some time now we are not allowed to use screw terminals in junction boxes that are effectively inaccessible. We have to use "maintenance-free" connectors: crimps, push-fits, or sprung levers. These re-tension themselves.

88V8 wrote:We had a new CU last year, all RCBOS in a metal case with drop-shut door. Previously it was plastic with a fall-open door. So at least that's better. But when I was in there adding a circuit, I noticed that some of the screws are already not very tight, and I know they were tight when fitted because I checked.

Yes the metal consumer units were brought in to contain, for 30 minutes, the fires caused by the drop in quality of the switchgear terminals. A case of addressing the symptom rather than the problem. The screw terminals work loose. In my experience the first re-tensioning needs to be done after about an hour of tightening up. Maybe another go after a week or so and that should hold for quite some time.

If one tightens up the terminals to the torque settings specified for the busbar screws and for the circuit breaker cages they seem very slack. You can usually get a couple more turns on them afterwards!

It is difficult to imagine anything other than screw terminals for switchgear but in the old days there used to be two screws per connexion. They were much better. With every wiggle of a wire a screw terminal stands a good chance of the strands re-settling beneath it and so making it slack. The double screw terminals of yesteryear meant that the first held the strands more or less steady while the strands in the second didn't move as much.

88V8 wrote:When I think on this, and the number of j-boxes in house and garage some of which are hidden, it is slightly perturbing.

During the periodic inspections (every 10 years for domestic; five years for rental) it would be desirable to open up all enclosures and check the tightness of the terminals. This is not part of the remit of a periodic inspection though and would take more time than most clients would be willing to finance.

Chris

A question here (which I do not have the answer to) is how the hardness of copper affects its elastic range (hopefully, that is the correct term). As copper wire is crushed under a screw, it work hardens. I can see how this may increase the risk of the wire becoming loose compared with softer, uncrushed wire if the latter retains more elasticity. (The former is also more likely to break, but that is a separate issue.)

This is only a suggested possibility.


Julian F. G. W.

jfgw wrote:A question here (which I do not have the answer to) is how the hardness of copper affects its elastic range (hopefully, that is the correct term). As copper wire is crushed under a screw, it work hardens. I can see how this may increase the risk of the wire becoming loose compared with softer, uncrushed wire if the latter retains more elasticity. (The former is also more likely to break, but that is a separate issue.)

This is only a suggested possibility.

Maybe this is why the specified torque settings seem so slack. It is counter-intuitive though. I don't know anyone that doesn't just tighten them up at much as they can.