Feeling Hot?

[spawnoflard]

I'm not really much of an electician in fact I'm not an electician at all.

My electric shower died on me, The thing was old and came with the lemhouse I bought 6 months ago. The thing was from the 70's and dort of knowing my way around electrics on a basic level I went to B&Q and bought a brand new 9.5kw shower.

A couple of weeks after I installed it I started to notice that tell tale fishy smell from the isolator switch after I had a shower.

I removed the fuse and opened up the box and sure enough the live wire on the supply side of the switch had started to melt and the part of the switch it was connected to also was blackening.

The live wire appeared o be loose in the switch so I thought that may have been the problem so I replace the switch and made sure all connections were tight and sure and ran some juice through it for about 5 minutes by running the shower.

I checked the unit and the wires afterwards, there was that faint smell again, at first I thought this was resdual from before but with the power off I checked the live wires by touching them individual and again there seened to be some heat.

The wires on both supply and load are "Twin Earth" 6.0mm Max Rating 240v 47amps.

The question is, is a little bit of heat normal, if not what could I be doing wrong, is it the wiring, the appliance or the fuse in the fuse box.
The fuse I believe is 32amps the markings on it are.
B32 - 32A

 

[Steve]

yes thats a type b 32A breaker. You need 10mm cable for this shower, or this will just keep happening. It is dangerous and i suggest you do not use it until it is fixed. I had exactly the same problem with my shower. Switch actually melted to the ceiling. bigger cable sorted it. Suggest also 40/45A breaker for this shower, as you are overloading the 32A one, and this will damage it over time.

Whoever told you 6mm cable can carry 47Amps is not your friend.

 

[andy]

cable has different ratings in different conditions. i.e 2.5mm can carry 27A clipped direct. yet 4mm can only carry 26A is in insulation. there is also volt drop to consider

 

[pdcelec]

Have you checked the insulation resistance of the cable and the earth fault loop impedance?

 

[Lectrician]

And adding to that - what is the rating of the switch??

 

[Big_Spark]

I would guess the switch is likely to be either one of the older 30A or 20 A double pole type. However it could be a 45A and the heat damage to the switch caused by convection in the materials concerned, thus accounting for the blackening seen in the switch, this is also likely to be deposits from the cable insulation breaking down, which often leave black carbonised deposits.

 

[spawnoflard]

Bloody hell, I go and make a cuppa and look what happens.

Ok I'll try and answer everyones posts with just this one.

The new switch I bought is infact rated a 20A, what can I say it looked the same as the old one so I bought it.

The original switch was rated at 45A so I assume that the original problem was the wiring, either it not being connected right as the live wire from supply was loose. I bought some wire from B&Q which was 6.0mm and according to the packaging was rated at 47A. I assume that what this means is I need to replace all the wiring from the fuse box to the isolator and the isolator to the shower needs replacing with 10.0mm.

I'd estimate there's probably 15-20 metres of cable to replace, any ideas on how much an electrician would charge. In the meantime I reckon I'll check at the local college see if there are any courses.


Thanks everyone

 

[andy]

The new switch I bought is infact rated a 20A,

and whats the logic behind that?

as for how much, wait for someone to say 'see item X here', since i cant be bothered finding the link

 

[kai]

DO NOT even think of uprating the B32 breaker for a larger one - unless you want a house fire or electrocute somebody!

Get a professional sparky in to sort it out - and notify Building Control at the Council Office, as this is a Part P Notifiable job.

6.0.sq.mm.. cable can only safely carry 33 amps safely.

 

[Steve]

knowing the circuit is rated at 32A should have prompted you to buy a switch rated at 32A or above. Showers require 45-50A circuits nowadays, and switches rated as such.

B&Q make those ratings based on minimal circuit runs in free space. This means a DIYer who knows no better could go and buy a 50m reel of 6mm cable, connect it to a 45A MCB and run it to a 9KW hot tub at the end of their garden in conduit. They really should put a table on the reel, stating the different ratings over different distances and in different materials.

 

[andy]

They really should put a table on the reel, stating the different ratings over different distances and in different materials.

should, but think of all that extra work needed. then theyll have to put the prices up. then people will go to electrical wholesalers and get cable cheaper, w/o the tables on, and were back to where we started. apart from people are not payin shed prices

 

[spawnoflard]

And the moral of this story is
1: Get a proper sparky in to sort this. (Which will please my girlfriend who keeps saying "I think we should get a plumer/gardener/electrician/plasterer/tiler... you name it for every houshold problem)
2: 10mm the circuit
3: don't just buy a switch cos they look similar, what can I say they all look the same to me.

Thanks again everyone.

 

[notb665]

so...

45A breaker in fuseboard
from this 10mm2 cable to 50A rated double pole ceiling switch
10mm2 from this switch to shower.
possible upgrade main fuse to 100A?

 

[ban-all-sheds]

And the moral of this story is
1: Get a proper sparky in to sort this. (Which will please my girlfriend who keeps saying "I think we should get a plumer/gardener/electrician/plasterer/tiler... you name it for every houshold problem)

If you display the same level of incompetence at other tasks as you have done with this one, then she's right. You said it yourself right at the start, you're not much of an electrician - in fact you aren't one at all, and yet you thought it was OK to go and do something which required knowledge, and nearly started a fire.

don't just buy a switch cos they look similar, what can I say they all look the same to me.

Your girlfriend and I rest our case.

 

[Adam_151]

It sorts of fits with the topic, but I recall once someone telling me they had been to B&Q to purchase a cooker switch, found them on the shelf, picked it up and either he didn't actually pay much attention to what was in the packageing or the packageing was not see-thru, anyway he got it home, and then realised that in the packageing (which was for a 45A cooker switch) was a 20A immersion heater switch. He returned to the shop and had a battle with customer services to get them to accept it back, obviously they were utterly clueless and were of the mindset that a switch was a switch, and he had to try and convince them that switch would not be safe switching more than the rating marked on it, he eventually suceeded though, and a cheer went up from the queue at the returns desk.

One day there is going to be a disaster arising from the dodgy advice handed out by sheds.