This is why we have rules and regulations

Joined
28 Mar 2006
Messages
5,743
Reaction score
496
Location
Hedge End Hants
Country
United Kingdom
agree with lucia on this, most likely a loose connection - although it may not be the screw / wire that was loose. as the owners admitted they regularly rewired the fuse maybe the fuse carrier pins were tarnished or just not tight in the busbar connection.
 
Sponsored Links
Joined
3 Apr 2009
Messages
122
Reaction score
0
Country
United Kingdom
Correct me if i'm wrong but a bit of 2.5mm is gonna get a bit chuffing warm with 30A running down it on a regular basis. Soon as the connection gets to that sort of temperature (loose or not) it's gonna go high resistance and get even hotter. That terminal could have been done up as tight as you like but over the course of atleast 4 years and 5 months (based on the following statement).

They seemed to think that it was ok what they had done, as it was 'before Part P'!

(which came in to effect on January 1st 2005) then of course it's going to have ended up looking like that. You cannot seriously say that it was just a loose connection especially when you also consider that that 30A rewirable can take in excess of 40A if loaded up gradually and will sit there getting warm for sometime.
 
P

PrinceofDarkness

Dunc, don't be naive, dear. Fuses are designed to melt when overloaded for a significant period. They are also designed not to cause such damage to their fuseholder in the process. Look at the photos. Are you trying to say that such awful damage is to be expected after a sustained overload?

If an undersized cable is fitted to an an oversized fuseway, and the connection is sound, then the result would be a melting of the PVC insulation where still enclosed within the cable sheath and not where the cables have been separated in the relative cooler air of a fuse board.

Just bloody well be told, that such damage can only result from the heat generated by a loose connection, will you?

God! How I despise stupidity - " Phew! lady, you were lucky that your house didn't burn down! Good job that I'm now here to give you (dodgy) advice.............




Lucia.
 
Joined
3 Apr 2009
Messages
122
Reaction score
0
Country
United Kingdom
Put it this way, a Wylex board like that is not designed to take any load over 30A, the terminals get too hot and they melt. That's why Wylex put the little bit of extra plastic on the rear of the 40, 45 and 50A fuse carriers to stop them being fitted in those units. I've come across 40A fuses in these boards with 10mm cable in where the connection has melted straight off the bakerlite due to the heat generated even in a nice tight terminal. I might add that these instances i have come across have always been on shower circuits which are generally used for no more then 10mins a time, much less then the time taken for a 30A rewirable to blow under overload conditions. It is therefore not beyond the realms of belief that a sustained overload can cause such things especially coupled with the fact that the fuse is constantly being pulled out and pushed back in to allow the fuse wire to be changed every time it blows.
 
Sponsored Links
P

PrinceofDarkness

I'm not convinced, Duncan. I think that you're trying to widen the issue as a smokescreen.

As far as I'm concerned, if a 30A fuse is overloaded for a significant period, and its connections are sound, this will result in the fuse element melting in accordance with the appropriate BS for such 'coarse protection'.

There is nothing in British Standards to allow for such a meldown as this - apart from the requirement that such an extraordinary fault should be contained within the enclosure for a certain period without causing a fire.

"Fire" seems to be a favourite word with certain, uneducated sparks - such a good word for putting the frighteners on......



Lucia.
 
Joined
3 Nov 2006
Messages
26,932
Reaction score
2,900
Location
Bedfordshire
Country
United Kingdom
It seems the circuit was working close to the limit of the fuse and from time to time exceeded the fuse long enough to melt the fuse wire.

The fuse wire could have been getting very hot during normal use but not hot enough to melt. This would have heated the prongs of the fuse. The connection of the wire to the socket for the fuse gets hot and over time the copper of the wire softens the joint becomes high resistance. The rest is a chain reaction.

The lower prong would be cooled by heat conducted away by the bus bar and there are no screwed joints on that connection to the bus bar. The temperature of the upper prong will much higher as the heat energy has no where to go other than through the screwed connection and along the wire whose electrical insulation also provides thermal insulation.
 
Joined
27 Apr 2008
Messages
8,783
Reaction score
731
Country
United Kingdom
Ladies.... does it really matter now.

It's done, fixed, they have been saved from certain doom.
NO need to argue over what did it. :D
 
Joined
27 Aug 2003
Messages
69,782
Reaction score
2,884
Location
London
Country
United Kingdom
Interesting to note, Lucia, that you must be the one who always went round there to rewire the fuse, so certain are you that it couldn't possibly have had wire rated at more than 30A put in...

;)
 
Joined
9 Sep 2007
Messages
3,862
Reaction score
189
Location
Newcastle upon Tyne
Country
United Kingdom
My first question would be "Was it genuine fuse wire?" What if it was some bit of tinned copper wire that 'just happened to be lying around'? :rolleyes: :rolleyes: :rolleyes:

It should also be noted that copper has a positive temperature coefficient of resistance.

1) If you have a single point of abnormally high resistance in your circuit and push too much current through it, it will get hot.

2) It's resistance goes up.

3) Because it's only a small part of the total circuit resistance, the current remains largely unchanged.

4) It gets even hotter.

5) Go back to (2).
 
P

PrinceofDarkness

BAS dear, thank you for your comment, tongue-in-cheek though it might have been. I don't recall counting or discounting the possibility of a larger fuse element being fitted - simply because the O/P had already stated that the fuse was "still intact". Had that fuse element been oversized or 'doubled-up'. then surely, the O/P would have said so. But he didn't say so. He merely said that the fuse was still intact, from which I inferred that it must have been the correct 0.85mm diameter wire - otherwise, he would have said so, wouldn't he?


So this 2.5mm cable, spurred from a standard 30A ring-circuit is supposed to have fed the following load:

A 3kW inverter.
A 3kW extractor fan........ (some extractor that must be!).
Sockets and lights, various.....

Washing machine.
50 Amp water heater...... (some water heater that must be!).
40 Amp shower.
Sockets and lights, various......

Electric heating for thirty kennels.
Sockets and lights, various......



Perhaps all that stated load is true, perhaps the O/P hasn't exaggerated it for effect..... But the fact remains that he has said that the fuse element was still intact. This is why I have suggested that that damage was caused by a combination of a heavy load and a loose connnection.

Look at the photos again. That damage was caused by a loose connection or an ill-fitting fuseholder. This is simply a case of neglect of the condition of the fusebox over a number of years. I've seen such damage - and worse, from a load of less than 3kW due to the localised heat damage that a loose connection can generate.

I'm elderly enough to have fitted those Wylex units when they were brand-spanking-new. The next chance that you have of inspecting such a unit, take a look at the reverse side of the fuseholders, where you'll see the potential for insecure connection due to the amount of screw-fixings.
There, you will find the Achilles' Heel.....


Lucia.
 
Joined
28 Mar 2006
Messages
5,743
Reaction score
496
Location
Hedge End Hants
Country
United Kingdom
My first question would be "Was it genuine fuse wire?" What if it was some bit of tinned copper wire that 'just happened to be lying around'? :rolleyes: :rolleyes: :rolleyes:

or a nail !! have been to a few rentals where tenants have "fixed things" for themselves

so far i have seen screws, nails, tin foil rolled up and cable stripped of sheathing

my record for things plugged in is 37 plugs on a single socket!!
 
S

sparkyspike

Just to clear things up. Firstly, I am not 'exaggerating'. In fact I've missed out a few more items that were connected to this circuit. The extract fan was a 3-phase industrial fan. It was 3kW. I've wired up much bigger fans than this before. I am also not stupid.

According to the customer, the fusewire would have to be replaced if they were using too many appliances at once. They got used to not (for example) using the shower whilst the workshop was being used.

So, perhaps the demand on this circuit was kept low enough - but only just low enough - to prevent the fuse from blowing. The current being drawn was regularly higher than the design current allowed by the fuse. It was also higher than the ccc of the cable. Therefore, the circuit was being overloaded on a regular basis. There were no loose connections when I stripped out the old fusebox, although I'm not to know how securely the fuse carrier was inserted.

I can't see why this kind of situation shouldn't be described as an 'overload'.

And yes, there was a fire. The flames gave that one away.
 
Joined
31 Mar 2006
Messages
20,002
Reaction score
1,380
Location
Leeds
Country
United Kingdom
Au contraire, I think that bit of 2.5 has done extremely well to put up with that potential load without ending up like RF's piece of "welded" 1.5......

C'mon Rob, post a link, I can't find it!!

I'll try and remember when Im back home on Friday.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top