thermal insulation

[iamelectric]

whats the script when you install say a shower circuit in a house in 6mm clipped direct thru the loft no insulation 40amp mcb all gud , then you go back a year later and the owner has had insulation put down in the loft right on top of your cable or cables as everyone is these days , it near enough halfs the rating of the cable , so what do you do ignore what you now know could be dangerous or explain the situation and tell them it needs a rewire or insullation removed , is it down to the spark or these companys who install it as there must be a lot of houses out there with under rated cables?

 

[telectrix]

explain to the owner that the insulation monkeys have made his loft a fire risk and to get them back to rectify it. we have to work to building regs. let them go on a 2 week course to learn not to be such pricks.

 

[Sharpend]

Is there a two week course for that! I've spent forty odd years trying to learn that?

 

[iamelectric]

we were talking about it today my mothers council house was rewired had no insulation in loft prob fine , few month later they came out and put a layer of thermal insulation a foot thick down

 

[Sharpend]

Are the cables clipped to trusses? Seem to remember that the cable is only derated by 50% if the cable passes through the insulation, if clipped then rating is different.
Haven't got BGB to hand.

 

[Dubbo]

Are the cables clipped to trusses? Seem to remember that the cable is only derated by 50% if the cable passes through the insulation, if clipped then rating is different.
Haven't got BGB to hand.

if it was 6mm doesn't matter if it is clipped to joists or not, the 40 amp breaker can only be used for clipped direct, even if its running in building voids the 40 amp breakers no good

 

[Sharpend]

Well spotted Dubbo ! Wasn't even looking at that tbh!

 

[Darkwood]

When wiring in loft spaces now or any other space where thermal insulation can be expected to be added at a later date then it should be a factor in the circuit design ...unfortunately a lot of existing installs pre- 1990's energy efficiency drive will not hae had this foresight and yes a hazard could have been created in many properties ....
If i do an inspection on an existing install with no inslation in loft yet a shower set-up running through it i do note it down and pass on the concerns to the home-owner..... i have now even started putting a sign in the loft for said numpties expressing that a fire hazard will exist on the electrics if insulation fitted... Ive had 4 jobs come of the back of said signs ....

 

[alanl]

if it was 6mm doesn't matter if it is clipped to joists or not, the 40 amp breaker can only be used for clipped direct, even if its running in building voids the 40 amp breakers no good

Please explain your reasoning?
Presumably you are saying the 40A CB does not give sufficient protection for the current carrying capacity of the 6mm t+e cable?

If the shower load is less than the cables current carrying capacity, including derating factors, then it is quite alright to use a 40A circuit breaker, as a shower is very unlikely to be subject to overload, so Reg 433.3.1 (ii) will apply.

 

[Hawkmoon]

Please explain your reasoning?
Presumably you are saying the 40A CB does not give sufficient protection for the current carrying capacity of the 6mm t+e cable?

If the shower load is less than the cables current carrying capacity, including derating factors, then it is quite alright to use a 40A circuit breaker, as a shower is very unlikely to be subject to overload, so Reg 433.3.1 (ii) will apply.

Thermal constraints (often forgotten) may limit what you do in situations like this.

 

[Darkwood]

The domestic environment shouldn't be an area you apply 433.3.1(ii) although you are technically correct and this could see overload protection been omitted within regulation we have the issue of the predictably ever changing environment and installation method influences.... i would be very cautious promoting this regulation in such case where its expected at some future date insulation will be fitted..... if by the nature of the install this has already been taken into account when utilising reg 433.3.1(ii) then you have more freedom to use it although as i said domestic environment is subject to change too easily and although its technically the responsibility of any one upgrading the shower to ensure the cable calcs have been done before doing so - in reality we find this is not done correctly more often than not so i would IMHO not be utilising the reg.

Its use is more suited to an environment that is not subject to change over long periods or alteration/additions to the circuit and is suitable for large machine and motor supplies where inrush currents can see nuisance tripping but the nature of the load means it could never rise about stated values so in a effect a 40amp load covered by a cable rated at say 48amps after calcs can be covered by 63amp mcb....... what must be adhered to here though and any similar case is the compliance of short circuit protection and namely the zs value is within limits.

The problem here the IET's very own guidelines use a shower as an example of a fixed load when discussing this regulation which IMHO i believe is a poor judgement call as it doesn't go far enough to explain the cautions of using it as explained above.

 

[Dubbo]

Please explain your reasoning?
Presumably you are saying the 40A CB does not give sufficient protection for the current carrying capacity of the 6mm t+e cable?

If the shower load is less than the cables current carrying capacity, including derating factors, then it is quite alright to use a 40A circuit breaker, as a shower is very unlikely to be subject to overload, so Reg 433.3.1 (ii) will apply.

I only fit a breaker lower than the current carrying capacity of the cable, using the reference methods listed in the regs that's all, leave the fire brigade playing snooker not putting one of my jobs out

 

[Hawkmoon]

I only fit a breaker lower than the current carrying capacity of the cable, using the reference methods listed in the regs that's all, leave the fire brigade playing snooker not putting one of my jobs out

Ever spurred off an existing ring? This is an example of this reg applied.

 

[Dubbo]

Ever spurred off an existing ring? This is an example of this reg applied.

yes I know, I was answering the previous question put to me and it was about 6mm cables and showers
Not a socket spurred of a ring

 

[marco86]

whats the script when you install say a shower circuit in a house in 6mm clipped direct thru the loft no insulation 40amp mcb all gud , then you go back a year later and the owner has had insulation put down in the loft right on top of your cable or cables as everyone is these days , it near enough halfs the rating of the cable , so what do you do ignore what you now know could be dangerous or explain the situation and tell them it needs a rewire or insullation removed , is it down to the spark or these companys who install it as there must be a lot of houses out there with under rated cables?

Downgrade the breaker to a 32 amp and if it keeps tripping it needs rewired

 

[Darkwood]

Downgrade the breaker to a 32 amp and if it keeps tripping it needs rewired

Very poor advice ....calculating the correct set-up is the correct method, its within the BS7671 to ensure you design the circuit to avoid small overloads for a long duration 433.1.1-- suggesting downgrading the mcb and see if it keeps tripping is up there with some of the worst advice for a number of reasons .... as a professional or trainee i would suggest you rethink what divides a cowboy sparky from a competent professional.