Warm 13amp Fused Spur Switch

[Veggie Dave]

I've just been to a job and while there I was asked to look at the fused switch for the immersion because it was getting warm.

The fuse holder is definitely warm, not hot but undeniably, noticeably warm - the wiring is all secure, there's no sign of any damage in the socket and the fuse itself is damage free.

I'm thinking the heat/warmth is caused by the sliding fuse holder and is probably normal for this design of switch? The fuse holder screws into place, with no obvious clicking into place of the fuse, so I'm thinking it's a crappy design that's causing the heat rather than an actual problem, but I need to know for sure.

 

[chris watkins]

Sounds spot on to me Dave. I would change the fused connection unit for a new MK or similar,it is low cost & should sort it out. (flex is not getting warm??)

 

[Veggie Dave]

Sounds spot on to me Dave. I would change the fused connection unit for a new MK or similar,it is low cost & should sort it out. (flex is not getting warm??)

The first 15mm of cable coming out of the fused switch is very slightly warm, but I would expect that as the fuse holder is warm.

I did wonder if there was a break in one of the cables or in the insulation but as it's the fuse holder that's warm I decided that was unlikely.

 

[AWheating]

could possibly be a high resistive point inside the switching of the double pole isolator/spur. You could test the resistance across the switch and cables for high readings, also consider the fuse could be faulty so this could be tested. Im assuming its a correctly rated double pole isolator?

i should also have asked if is wired off a ring main? as this is incorrect but not uncommon.

 

[Best]

My guess, it's inside at the switch contacts, especially if the switch is old or has been manually used a lot. Heat will transfer to fuse & cable & melt cable sheath eventually. Wires having a bad contact is very common on higher powered electrics, like immersions & showers, often due to poor install & also will slacken over time, so need a check & tighten.
When a switch is wired nice & tight & then pushed into box, if you pull it back a little & check the screws they tend to be loose, especially on 6 & 10mm cables.

 

[quality]

It should not be connected to a spur (off of another circuit) it should have its own circuit.

 

[BLOD]

Pretty sure it should have its own 16amp radial circuit and a 20 amp rated double pole switch, not a 13amp fused switch - but I'm not a spark so could be wrong

 

[AWheating]

Pretty sure it should have its own 16amp radial circuit and a 20 amp rated double pole switch, not a 13amp fused switch - but I'm not a spark so could be wrong

your correct, it should be a seperate circuit and a double pole iso. The problem is some lazy gits do/have retro fitted them to the ring mains.

 

[REDSAW]

new spur and immersion cable and take it from there.

could be bad contacts creating resistance.

 

[quality]

Most people consider a switched fused connection unit (SFCU) as a spur even though its not and it may be a supply to say an alarm or heating controls and may have its own circuit.
But a 3 KW immersion should have its own dedicated circuit and its own double pole isolation.Just like a cooker which is also a resistive load.
Even if it has its own circuit then it should not be connected via a SFCU it should have a double pole isolator

 

[Veggie Dave]

Cheers everyone - I'm going to get a mate in who's a qualified spark to do a proper check as I can't find anything wrong.

 

[stevetheplumber]

depends what you call warm most plugs and spurs handling 3kw will get some heat in them esecially if they are in use for long periods

 

[billybob150811]

i,m with you on this one dave get someone who does this all day long in theory 3000 watts/240volts =12.5 amps so 13 is fine and the fuse rating is calculated after the cable run length/grouping containment is known if you believe that but im like a lot of us plumbers i know enough to get me into bother and not enough to get out of it sparkys have there uses after all where do you park your bike

 

[Veggie Dave]

i know enough to get me into bother and not enough to get out of it

Exactly!