421.1.201

Alan Capon: 
 

Zoomup: 

. . . Meter installers connect up new meters to grossly undersized and single insulated tails in my experience. . . 

I suspect a lot of UK Meter Installers are just that. Without being electricians and members of a competent person scheme, they may consider it high risk to replace the tails. 

Regards,

Alan. 

All of the renewed meters/isolators that I have seen have been meticulously installed. The jobs are very well done, but, do the meter installers check the tightness of the consumers tails' terminations inside the consumer's consumer unit, after the tails have been manhandled? They may have come loose.

Z.

I went to look at a fault yesterday in a rented property. All of the upstairs lights had failed but live to Earth was fine. A loose neutral screw in the looped ceiling rose in the first supplied room was the problem, but why it was lose was a complete mystery as it had worked fine for about 30 years! Just poking my meter probe into the terminal made everything work again, which fortunately I noticed as the measured mains was then present. The copper of the wires was somewhat black and dirty, but no obvious damage or reason why the conductivity suddenly became zero. Load, a few LED lamps, and the bathroom fan, so very small. This kind of thing is surprisingly common, so I wonder if EICR's should check the tightness of every screw? I am beginning to think that they should, but for a big installation, it would take a lot of extra time.

davezawadi (David Stone): 
 

I went to look at a fault yesterday in a rented property. All of the upstairs lights had failed but live to Earth was fine. A loose neutral screw in the looped ceiling rose in the first supplied room was the problem, but why it was lose was a complete mystery as it had worked fine for about 30 years! Just poking my meter probe into the terminal made everything work again, which fortunately I noticed as the measured mains was then present. The copper of the wires was somewhat black and dirty, but no obvious damage or reason why the conductivity suddenly became zero. Load, a few LED lamps, and the bathroom fan, so very small. This kind of thing is surprisingly common, so I wonder if EICR's should check the tightness of every screw? I am beginning to think that they should, but for a big installation, it would take a lot of extra time.

I am constantly amazed at just what current can be carried by a wire that is just in contact with a terminal by chance with no tight screw connection. I have come across a few. Also a 40 Amp M.C.B. that was in accidental contact with a bus-bar in a consumer unit where the cage was misplaced and was not tightly connected to the bus-bar finger. It was just in accidental contact. But the shower still worked perfectly.

Z.

davezawadi (David Stone): 
The copper of the wires was somewhat black and dirty, but no obvious damage or reason why the conductivity suddenly became zero. Load, a few LED lamps, and the bathroom fan, so very small.

I wonder whether it gave up the ghost because the load is so small?

I am constantly amazed at just what current can be carried by a wire that is just in contact with a terminal by chance with no tight screw connection. I have come across a few. Also a 40 Amp M.C.B. that was in accidental contact with a bus-bar in a consumer unit where the cage was misplaced and was not tightly connected to the bus-bar finger. It was just in accidental contact. But the shower still worked perfectly.

If the MCB was on a proper DIN rail (with both top and bottom flanges) and all the other MCBs were holding the bus-bar firmly in its correct position, then the ‘wrong side’ of the cage clamp would probably have been held quite firmly against bus-bar - as they'd been the extra thickness of the cage clamp itself between the MCB's terminal and the bus-bar's normal position - the tightening happening when all the other MCBs were screwed onto the bus-bar would tend to lift the dodgy MCB - but that being resisted by the clip onto the DIN rail (if that makes sense…).

   - Andy.

never underestimate the lifespan of a spot-weld, if it once ever makes a small area  contact with enough current it will ‘stick’ until disturbed. It is one of the reasons why arcs in copper wires or between copper electrodes  are so hard to strike As far as I can tell a lot of twist and tape type car electrics utterly relies on this principle of scratch and stick.

Mike