Electric 13AMP Fused Spur Melted!!

[drJonesy63]

ok thanks EFLImpudence do you think its looking more like the 13amp fused spur has been run at long periods and killed it? Assume you agree with having a dedicated 16A Breaker and 20A DP ?

 

[drJonesy63]

thanks Mike, do you agree then for this to be installed on a 16A Breaker with 20A DP instead?

 

[eveares]

If your theory is correct and the floor is faulty, it should trip the 16A Breaker correct?

Not quite; A 16A breaker will need around 24A if it is going to trip, and even then at 24A it would take around 166 Minutes. See here for more details.

If so (and if its not... that requires addressing asap) then I struggle to envisage how it could fail in the manner discribed by eveares without tripping the RCD

Your assuming that:

1) There is a RCD

2) The UFH is earthed (if applicable)

3) The fault path should there be one involves the earthed braid. The fault may be between Line and Neutral only and the earth may not be part of the fault path.

It could have just been a loose connection which caused the overheating.

True and your most probably right. Or it was a fault inside the FCU somewhere.

I doubt the UFH can cause an overload.

I guess you are right, But I started my original post before any replies were made and just thought maybe the UFH may have drooped in impedance. In reality and in hindsight, without mechanical damage or stress, then it is unlikely that it is the UFH. Still worth double checking the resistance of it anyway for peace of mind.

Then there is no way the resistance could reduce and hence the current rise.

See my 3rd point in my reply to Adam_151.

 

[eveares]

thanks Mike, do you agree then for this to be installed on a 16A Breaker with 20A DP instead?

Don't forget this is notifiable work.

 

[drJonesy63]

Yes absoutley, but to get some advice before I request the work done, in your professional opinion with the details I have provided, you think a 16A Breaker with 20A DP ?

 

[EFLImpudence]

Yes, probably just as well as you definitely should have it on different circuit.

 

[Mikefromlondon]

Plug tops are also referred to 3 pin UK plugs.

OP- Perhaps you could get one of them kwh power meters that you plug into a socket and monitor the consumption from time to time, keeping an eye on any unusual deviations from normal load, you could get one from maplin or on ebay, plug your kettle into it first to see if it reads about right, if you know the rating of your kettle like mine is 2.5Kw, and my plug in watt hour meter reads about right, it has buttons on it to select what the mains voltage is, how many amps it is using, power factor, and total usage over a given time, so if you leave it plugged in it will show you how much energy has been used in kwh.

And as for your question regarding providing DP and a 16A circuit breaker, I would think anything installed towards overload safety is better than not having any, even if 16A breaker may not trip on a slight bit of overloading, or may take longer to trip, it would still be better than running it on a 10A breaker as that would be too close the load and may trip for no reason.

I think your socket definitely overheated due to a bad poorly made connection or the switch contacts developing higher resistance through arcing and causing heat that spread to adjoining areas.

One with an experience can usually tell the spot where the overheat first occurred, i.e. was it the switch contacts or the lose fuse or a lose wire in the terminal, etc etc. This is how Fire Investigators determine the cause of electrical fires.

 

[PrenticeBoyofDerry]

I would also be thinking that it is a loose connection as this is the more common fault, would no totally rule out bad contacts though.

issues here are parking the UFH to a cooking circuit, not something I would expect from a competent electricain, especially considering a there was a spare way! (Even though 2.5mm on 32A is not designed correctly as the cable is drawing only 10A and the load protected by a 13 FCU, I would not expect this be a danger, in my opinion not right but dangerous no)
So ideally you would be looking at dedicated circuit for the UFH, if the demand is 10A or less, a 10A or 16A can be used, you should be able to get the manufacturers breakers to fit this board.
As the circuit would then be considered a new circuit (probably what the original electrician was trying to avoid), it would require to be notified as one, so an application to building controls will be required and a fee. This will also need an electrical installation certificate to be completed, with the required schedules of inspection and tests.
Depending on your location in the UK and the exact date and the location of this UFH, it may have required notifying anyway, so they would be next questions to you!

 

[drJonesy63]

The 2.5mm that was shared with the 32amp (for kitchen hob) has been moved onto its own 16AMP breaker as you have all advised. I have ordered a 20A DP switch to replace the 13A Fused spur as suggested.

This morning it is currently running on the 16A breaker and with a new temporary 13AMP Fused Spur (we had a spare). It wont be left like this unattended but everything is working. I noticed the fuse is slightly warm to touch (but not red hot) I read a post from another user on this Fourm discussing that its 'normal' for them to get warm due to the amount of constant load (i.e. heating the floor). As this is drawing 10AMP I assume warm is ok ?

My gut feel is the original 13amp fused spur gave up after 2years because of the constant load and should really be fitted with a 20A DP which is what will be changed next week when it arrives (wife wants matching switches:
http://www.ebay.co.uk/itm/331330372080?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT )


Hope I have understood correctly everything you have all said?

 

[eveares]

(Even though 2.5mm on 32A is not designed correctly as the cable is drawing only 10A and the load protected by a 13 FCU, I would not expect this be a danger, in my opinion not right but dangerous no)

But how about a partial or full short before the 13A Fuse, however unlikely. Certainly is not compliant with BS7671.

Not by intelligent people.

The 2.5mm that was shared with the 32amp (for kitchen hob) has been moved onto its own 16AMP breaker as you have all advised. I have ordered a 20A DP switch to replace the 13A Fused spur as suggested.

I hope this work and thus the new circuit has been done in accordance with BS7671 and has been notified to the LABC along with a electrical certificate issued by a competent electrician. I am guessing you installed the new 16A circuit your self?

Has also just occurred to me, would it not be simpler just to supply the FCU for the UFH via a spur from a near by socket.

I noticed the fuse is slightly warm to touch (but not red hot) I read a post from another user on this Fourm discussing that its 'normal' for them to get warm due to the amount of constant load (i.e. heating the floor). As this is drawing 10AMP I assume warm is ok ?

I will let others discuss whether that is normal or not. Just never noticed a 13A fuse with a =<10A load getting warm myself.

 

[EFLImpudence]

(Even though 2.5mm on 32A is not designed correctly as the cable is drawing only 10A and the load protected by a 13 FCU, I would not expect this be a danger, in my opinion not right but dangerous no)

But how about a partial or full short before the 13A Fuse, however unlikely. Certainly is not compliant with BS7671.

A full short will be covered by the 32A MCB - after all, no different than a socket spur.
I'm not sure you can have a partial short.

 

[Iggifer]

No, surely it's a short or it's not a short

 

[jg321]

Exactly. I do wonder how people think this is different to a single length of 2.5mm spurred from a ring final on a 32A breaker.

Edit: just to add, in my flat, the immersion (only source of hot water as no gas), is on a 16A breaker with a 13A FCU. It's used every single night, and gets warm to the touch when in use, but hasn't failed in this way.

I've only been here for a year or so, but it certainly looks like it hasn't been changed in 8 years.

 

[eveares]

I'm not sure you can have a partial short.

I meant a high impedance short, Or is that a contradiction in its self. Does a short have to be in the range of a few Ω's or less; What would an unintended load due to a fult between line and neutral be called then???

Exactly. I do wonder how people think this is different to a single length of 2.5mm spurred from a ring final on a 32A breaker.

Doh! Did not think of that...

 

[Iggifer]

I meant a high impedance short, Or is that a contradiction in its self. Does a short have to be in the range of a few Ω's or less; What would an unintended load due to a fult between line and neutral be called then???

A flux capacitor