Photo of a burnt CU.

[stardanny]

Workmate sent me a pic of a burnt storage heaters CU at a house a few days ago. The cupboard where the CU is has little fire damage, lot of smokes in house, happened over early morning. Cause was a loose neutral tail. Sparky also had to replaced main CU ( sit next to storage heaters CU and fire damaged ) and henley block. New CUs moved higher to good, undamaged cables. Electric board replaced meter as well.

Label on burnt CU say last tested 2008.

Good thing they got working smoke alarms.

Untitled

• stardanny
• 5 Dec 2010
• 2

 

[Adam_151]

Label on burnt CU say last tested 2008.

The thing is that you can inspect terminals for signs of overheating, and you can start checking a few for tightness to see if there is a need for re-tightening across the board [pun not intended]but... (and I stand to be corrected on this, but in my mind mass tightening of every terminal on periodics is not a particulay a good idea unless you actually start finding loose ones, it'll gradually damage the copper, particually on smaller conductors)... but you don't know whats going to happen down the line, the meter might be replaced a few weeks later and they might move the cables around coursing the strands to settle around a bit, and the meter fixer is probably not allowed to open the clients DB to check the terminals...

 

[ericmark]

Label on burnt CU say last tested 2008.

The thing is that you can inspect terminals for signs of overheating, and you can start checking a few for tightness to see if there is a need for re-tightening across the board [pun not intended]but... (and I stand to be corrected on this, but in my mind mass tightening of every terminal on periodics is not a particulay a good idea unless you actually start finding loose ones, it'll gradually damage the copper, particually on smaller conductors)... but you don't know whats going to happen down the line, the meter might be replaced a few weeks later and they might move the cables around coursing the strands to settle around a bit, and the meter fixer is probably not allowed to open the clients DB to check the terminals...

This was talked about a lot when we were to "Service" plant. Without a torque screwdriver over time one could neck off the cables by continually tighting them. As a result we split the "Service" into major and minor where only with a major were terminals checked. With a minor they were only inspected. Servicing a batching plant was a two day job for three men with a major and when we do an inspection and test of a house one guy does it in less than a day and far easier to open the boards with a batching plant than open sockets on a house.

I remember doing my C&G 2391 and it took a good hour to test the practice board where all the items were within an arms length. And really we all know with a house we have to miss some bits to get it all done in allotted time. Plus it is not a "Service" it is just Inspecting and testing.

Big problem is lack of foil on stranded cables. One stray strand and the terminal seems tight but really only binding on one stray strand. Also re-visiting to check on work. If we have the worker and tester then any mistake by worker can be found by tester as there is some time between the two events. But were we self test then no time for any faults to become apparent.

 

[kai]

It looks like a good idea to tighten tail connections on all consumer units on an yearly basis, using an insulated screwdriver, as it seems to prevent loose connections causing further problems down the line!

 

[tonyelectric]

This is an excellent example of why I am so opposed to the use of thermoplastics (plastics that can melt and ignite) in the casings of CUs and other fittings, it is overkill I know but unless a customer specially requests a cheap option plastic board I always use a metalclad CU, at least if something overheats or ignites inside the casing will contain the fire and slow/stop the spread,

I find incomer terminals are poor these days, I much prefered two screws per terminal that actually bit the cable rather than the flat pressure plate designs used today.

I also find a modulo screwdriver (a head that is a cross between pozi and flat) gives the best purchase to tighten terminals down, they are produced by Calvin kammerling (CK)

 

[Adam_151]

How do the rest of your find dorman smith rcbos? I quite like their kit on the whole, but the terminals on the rcbos seem to be not that great to me, often when I'd disconnected a ring circuit to test it after working on it, I've gone to reconnect the neutrals and after I've put them in and tightened the terminal up soundly the conductors at first seem to both be gripped, but a slight pull will bring one out... never both just one . Normally end up stripping more insulation back and doubling over the conductors, this seems to allow both conductors to be adequatly gripped, but its easy to see how in a rush a poor connection could be left!

Their DP rcbos from the 1990's though were much better in my mind

Though I'm informed that you shouldn't 'have to' double over conductors these days, though that seems to be one of these age things...

 

[sparkwright]

Terminals in general seem to be poorer these days. Some sockets terminals don't allow earth wires to stay in very successfully without doubling them over.

Connector blocks can be very poor if you're not to fussy about which you buy. They can split when you tighten them, and if not rectified will cause burn out.

 

[ricicle]

Though I'm informed that you shouldn't 'have to' double over conductors these days, though that seems to be one of these age things...

I was always told at college - ' you must fill the terminal with as much conductor as possible'

 

[ban-all-sheds]

Were they not referring to length, i.e. stripping back enough insulation so that the conductor touched the back of the tunnel?

 

[ricicle]

Were they not referring to length, i.e. stripping back enough insulation so that the conductor touched the back of the tunnel?

No he was on about filling the terminals by doubling over conductors - some accessories at the time had screws that went down the centre of the tunnel and there was a chance that a single conductor could go down the side of the screw rather than under it.
I personally have always hated single conductors stuck straight into terminals without being doubled over. I even double over 2 x 2.5mm² in sockets !

 

[londonboy]

Were they not referring to length, i.e. stripping back enough insulation so that the conductor touched the back of the tunnel?

No he was on about filling the terminals by doubling over conductors - some accessories at the time had screws that went down the centre of the tunnel and there was a chance that a single conductor could go down the side of the screw rather than under it.
I personally have always hated single conductors stuck straight into terminals without being doubled over. I even double over 2 x 2.5mm² in sockets !

I was always taught to double over any conducter >4mm ²

 

[Wontdothatagain]

I find that the vast majority of loose terminals i find are with multi standed cable in square holes that have not been un-twisted such as meter tails. A 25mm CSA cable is not going to compres if it is still in its twisted state and with a square section hole, you will only be biting on 2 surfaces and then only on a small area.

 

[Adam_151]

Must admit I don't normally straighten tails out with pliers, I tend to put the conductor in the terminal, tighten it down, give it a good wiggle to allow the strands to separate and settle in the terminal (its amazing how loose it often is after this) and then tighten it again, I then come back and give it a final tightening before switching on

I have a CK modulo terminal driver, but prefer a 6.5mm flat driver for the incomming terminals on a CU

 

[bernardgreen]

What opinions are there about the crimped on spades that are fitted to the tails supplied with consumer units ?

Should they be fitted on incoming tails ?

 

[SgtTrojan]

Well I would say no because they (tails) are stranded and will "spread" as you tighten. Tighten as hard as you can. Waggle and pull the cable where it enters the termination again and you might get another quarter turn.

My opinion.