45a Switch Overheating

[Stewart66]

Hi, I'm not an electrician (I'm a health & safety advisor with the MOD). I'm just after a bit of advice regarding my 45a shower switch in the airing cupbard. A year or so after moving into the house we started to get a burning smell when the shower was used which was coming from the airing cupboard. I stopped anyone using the shower and took the switch off to find scorching marks and the switch starting to melt. I asked around the web why this would happen after a long time of no problems and the answers I got back were that the pattress was not deep enough and so causing the cables to generate excessive heat and that this was apparrantly a common issue !!. It's a standard 45mm box for use with these switches so I was a bit surprised to find that this should be a common issue, why not just manufacture deeper boxes! (I've never found a deeper box yet). Anyway I cleaned up the cables, put in a new switch and kept a close eye on it and everything was fine for about another year when the same thing began to occur. I did the same again and everything was fine until another year passed and now it's the same thing all over again !! Surely this can't be right and why would it take a year each time for the problem to occur? Confused! Any advice is greatly appreciated as being a H & S advisor I'm not entirely happy with this ongoing repair job !

 

[sellers]

I would first look for a loose connection, make sure all the screws are nice and tight. Including in the shower. Also I'd pay for a well known brand like MK or crabtree. Also not all shower isolators are designed to work on load. Ie: Leaving the shower unit on and using the pull cord to switch it on and off, this will also lead towards burning out of the switch.

Hope this helps

 

[spinlondon]

It's possible that the neutral termination is loosening, it is also possible that the cable is undersized.

What colour is the cable where the over heating and melting is occuring?

 

[Larnacaman]

Well if this has now happened 3 times, i would change that 45A switch as it's been subjected to overheating effects on it's terminations etc.... Once you have the new switch, Try using well crimped ferrules instead of the direct stranded cable connection.

Also check the connections at the shower unit, maybe use crimped connectors here too. Just make sure you use correctly sized crimps and use a good crimping tool with at least a 250/450 Nm pressure....

Can't help you with the cause, could be any number of things. As a Spark, have you done any tests on this circuit?? If not, then it would be a good place to start!!!

Sorry .... just re-read your post your NOT a spark....lol!!! In that case i would bite the bullet and get an experienced spark to check out this circuit and it's components for you....

 

[cadspark]

As a Spark, have you done any tests on this circuit?? If not, then it would be a good place to start!!!

He's not a spark he's a very naughty boy. ROTFWL Sorry I mean't Health & Safety Advisor.

 

[Manator]

Any cable is weakest at any termination, the quality of the connection and size of cable all have a bearing on the overall characteristics.

All screw type joints will require maintenance which is why under the scope of BS7671 all connections with screw type fittings should be readily available for inspection and testing.

Another possible cause is the supply voltage, common readings in the UK can exceed 240 volts, and that combined with the shower usage in watts can cause some heat to be generated along the cable length as well as and exceeded at the joint.

Common cable sizes for showers previous to the 16th edition of the wiring regulations was 6mm. With a standard house size and a shower of 8.5kw this normally would suffice, however more and more showers are installed that use far more power.

I can only advise that a qualified electrician has a look at your problem, by testing and experiance he should be able to save you some money for any ongoing repairs year after year.

 

[PC Electrics]

Is it a 1 gang or 2 gang sized switch? If it's a 1G size change it to 2G. This gives more room inside the box for the cable and reduces any "squash" that may occur during assembly of the switch to the box. Also don't cut the cores excessively long - again increases the squash in the box. The more the cable is squashed in the box as it's put together the more strain the terminations are under. 1G boxes are more prone to strained terminations IMO. This strain can cause the joints in the switch to break down and eventually they overheat. Also make sure connections are nice and tight as any looseness here can also lead to overheating.

IMO the best shower isolator is the ceiling mounted Crabtree unit. Partly because there is no strain put on the cables or terminations during assembly. Change to one of these if you can.

 

[batty]

As others have said get a decent switch I think MK and crabtree have two screws on there terminations. What size is the shower if its a 10.5kw that could be the problem.

 

[Evans Electric]

It could be that as you are not a sparks you may not have tightened the terminals up enough TBH and have actually done the same for three years running . As others have said, MK twin plate DP switch on a deep box (42mm) .

Also, in airing cupboards , don't allow laundry to be piled up over electrics , specially covering flex feeding immersion heaters !! Seen many fires nearly started that way!!

 

[SPECIAL LOCATION]

Ditto all those who have said lose connections.... :Salute :worship

Cables incorrectly terminated guaranteed to give you your symptoms..

Especially on a higher power circuit such as shower or cooker. Guinness