Burning...What's going on here then? (with Pix!)

[PhilipKS]

Af'noon all!

Noticed a curious yellow liquid coming from fuse holder on a switched FCU in my utility room...

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• PhilipKS
• 10 Oct 2009
• 1

The FCU is spured from the plug next to it and serves a single unswitched socket below the worktop powering a tumble dryer.

Taking the FCU off and apart it there is evidence of burning around the load live connector (the dust is tile grout residue)

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• PhilipKS
• 10 Oct 2009
• 1

The back of the FCU has also cracked (due to heat?) and shows more signs of burning

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• PhilipKS
• 10 Oct 2009
• 1

The load live wire also shows signs of insulation melting and blackening

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• PhilipKS
• 10 Oct 2009
• 1

OK...never noticed any burning smells, no tripping of fuses, MCU or RCD. A possible causal factor...the microwave vents blow out onto this wall, and can sometimes be quite damp.

My thoughts, before I just trim the wire back and put a new one on are:

1. loose connection, which has caused arcing and heat?

2. the effects of damp air from the micro getting into the switch

3. a combination of 1 and 2

4. a faulty FCU (though only 1 year old and reasonable quality - volex)

ANy thoughts or advice would be much appreciated

thanks

PhilipKS

 

[jj4091]

What is the rating of the tumble drier?

 

[sparkwright]

probably a connection not properly tightened or faulty accessory.

who installed this, an experienced electrician, his mate, or a kitchen fitter?
don't think the cables were stripped back and prepared very well.

 

[PhilipKS]

Just a common or garden condensor tumble dryer on a normal 13A fuse, not sure what rating

As to the fitter...that was me (DIYnot...the clue in the formal title )

What could / should I do to strip the wires back and have them look more professional?

(always trying to learn...please no DIYer flaming! This was a very simple job and not Part P i believe...no sink so not a special location)

Thanks
PhilipKS

 

[sparkwright]

a very good try. more professional to strip grey outer sheath back to where it enters the box; and to double ends over where only one wire enters a terminal. well done for earthing box and using sleeving and grommets.

 

[PhilipKS]

Thanks good advice...I was hoping I hadn't got it too wrong! Some folk on here can be a bit harsh with us DIYers!!

Will take the opportunity of putting a new FCU on to tidy up the wiring, hopefully doubling the single ends back will help make sure there are no loose connections.

Out of interest...what would have happened if I hadn't noticed this. I guess in time there would be smoke \ burning smell, then ultimately (hopefully) something would trip...?

PhilipKS

 

[333rocky333]

Unlikely to trip unless the insulaton melts enough for the copper to touch the metal bits.
The smell would have worsened and the connection would end up so bad , it would fail and the appliance would stop or be intermittent.

Sometimes the spurs fail under high loads and sometimes worth paying the extra for good brands.

 

[Goldberg]

Out of interest...what would have happened if I hadn't noticed this. I guess in time there would be smoke \ burning smell, then ultimately (hopefully) something would trip...?

Invariably the copper gets so hot that it burns and chars, making a poor contact even poorer, until eventually makes no contact at all.

Unless the insulation burns back on two conductors and they touch each other, nothing will trip.

 

[RF Lighting]

When you fit the new FCU, you need to cut the end off the burnt wire.

You need to cut it right back until you are connecting onto bright shiny copper.

If the copper is dull, it is a sign that it has been damaged by the heat. The heat softens the copper, which will lead to a bad connection which will eventually fail on the new FCU.

 

[PhilipKS]

Thanks all,

I'm somewhat relieved that "hugh fire" and "burn the house down" didn't feature as immediate answers!

But i guess with leccy you can't be too careful. Off to screwfix to get a new MK FCU i think...

 

[janner10]

more professional to strip grey outer sheath back to where it enters the box.

I thought this has to enter the accessory by at least 10mm, or am I doing this for no good reason at work?

 

[RF Lighting]

I think you're doing it for no good reason.

 

[riveralt]

I think you're doing it for no good reason.

What!

Well I wish you had told our lecturers. On 2330 level 2 & 3 we were told that stripping back to 10mm was a requirement.

I've searched the red book chapter 52 et al but couldn't find it.

 

[RF Lighting]

I've honestly never even heard of that before, and have never seen it all the time I've been in the trade

 

[ColJack]

the outer insulation must enter the box, and 10mm seems like a good enough length to me..
it's not set hard and fast in stone however so if you leave a little more or a little less it's not going to be the end of the world, as long as it enters the box.