Omission of overload protection for fixed loads.

[Gavin A]

I am not sure that is accurate. Seems I will be investigating my shower again before I put it back together...

circuit diagrams are your friend here.

there are many of them available via google, and I've just checked several to be sure. Regardless of that though, the point you were making is wrong as even an overheating element won't add more than 0.2% or so to the load of the circuit.

 

[telectrix]

slightly off topic. but this might be of interest. came across a downflow heater 2kW. the L termination in the FCU had burnt out, taking about 1" of the L of the flex with it. now the flex on the heater ( came with it attached by manufacturer ) is 0.75mm and manufacturers instructions specify a 13A fuse. are they using 433.3 to get away with such a small csa? and who is liable if the 0.75 melts before the fuse blows?

 

[Darkwood]

The heater manufacturers will have to comply to their own BS standards, the flex will be compatible for the load of the heater so they won't be responsible, clearly the issue here is a connection problem or a failed FCU by matter of interest i bet the multi-stranded cable termination into the fcu wasn't appropriately crimped for termination so if so then the installers fault, if it was down to failure of the FCU then the FCU manufacturers fault, proving it and laying blame isn't usually worth the hassle on a simple repair. For your query regarding using 433.3 they are not subject to the BS7671 but thats not to say they dont have this regulation in their own BS standards as clearly they have omitted overload protection of the flex itself. Having said this this wasn't caused by overload but thermal conductivity from a poor contact or connection in the FCU which regardless of any overload protection this would have created the same effect even with a fuse rated spot on for the load.

 

[diabalo]

Great thread, been following this on the IET forum too. Even as a diyer I follow the technical arguments and have given a couple of examples on there (where I am known as rovermaestro) of circuits in my current house where the ccc is less than the copd, 8.5kW shower on 6mm in trunking on a wall with 40A rcbo and a 4mm radial 2 seperate sockets (washer and tumble drier) 22A load, ccc 30A (trunking on a wall) copd 32A. I had the CU changed last year after an EICR and although noted these circuits were reconnected after discussion. (I didn't install them). I think this was eminently sensible and I am absolutely happy with this arrangement in practice. Seems to me that designers have quite a lot of scope within the regulations to make these judgements within the standard. As a householder I am conscious of the risk of future additions or replacements but whoever does that is responsible for checking the circuit characteristics before taking action. I think decent paperwork is vital. As others have stated elsewhere every installation should have a proper descriptive document. I would regard it as an essential user manual.

 

[KAS1]

I think that has always been a flaw when it comes to domestic works, the lack of a design document to accompany each installation should of been compulsory many years ago, not just a record of test results but a full spec as in commercial / industrial installations. After all it wouldn't of taken much design work for the average domestic IMO

 

[Darkwood]

Its funny how this thread i set up has consequently bounced around all the main Electrical forums lol.... Again! You'd think that on the IET forum the regulation architects would see this repeated confusing issue and subsequently amend it to either make it clearer or address the domestic situe with a cover note on this regulation.

My take on this is if the regs were simple to follow then the IET wouldn't make any money on their little franchise in on site guides... conspiracy theory!

 

[Engineer54]

Its funny how this thread i set up has consequently bounced around all the main Electrical forums lol.... Again! You'd think that on the IET forum the regulation architects would see this repeated confusing issue and subsequently amend it to either make it clearer or address the domestic situe with a cover note on this regulation.

My take on this is if the regs were simple to follow then the IET wouldn't make any money on their little franchise in on site guides... conspiracy theory!

The Reg's havent been written in plain English since the 14th ed!! Now it needs umpteen OSG's to give readers a clue of what it's saying!! lol!!

 

[telectrix]

The heater manufacturers will have to comply to their own BS standards, the flex will be compatible for the load of the heater so they won't be responsible, clearly the issue here is a connection problem or a failed FCU by matter of interest i bet the multi-stranded cable termination into the fcu wasn't appropriately crimped for termination so if so then the installers fault, if it was down to failure of the FCU then the FCU manufacturers fault, proving it and laying blame isn't usually worth the hassle on a simple repair. For your query regarding using 433.3 they are not subject to the BS7671 but thats not to say they dont have this regulation in their own BS standards as clearly they have omitted overload protection of the flex itself. Having said this this wasn't caused by overload but thermal conductivity from a poor contact or connection in the FCU which regardless of any overload protection this would have created the same effect even with a fuse rated spot on for the load.

agree entirely. the 2 things are not related. my call out was to the damaged termination in the FCU. just didn't like the fact that a 2kW heater was running on 0.75mm flex with a 13A fuse. i would have expected 1.0mm at least.

 

[Darkwood]

Your probably refering to CCC of flex in the BS7671 i deal will many different kinds of flex and its misleading the it might seem too small been 0.75 but different brands and constructs of the insualtion and sheath give some cables a higher CCC comparable to say a 1.0mm standard pvc flex.

 

[Outspoken]

circuit diagrams are your friend here.

there are many of them available via google, and I've just checked several to be sure. Regardless of that though, the point you were making is wrong as even an overheating element won't add more than 0.2% or so to the load of the circuit.

Sorry for the late reply, took advantage of some clear weather today to take the ankle biters out...till it ruddy rained anyway!

Anyway, I checked our shower thoroughly, and can confirm the following are installed;

2 x Thermocouples
1 x manual reset bimetal thermal sensor
1 x Pressure transducer
1 x flow sensor
1 x overload sensor (magnetic)

Based on this I have to concur will all comments by Gavin and initially by DW. With this level of protection in the unit then realistically an RCD protecting the Unit would be sufficient for compliance with the Regs at the basic fault protection level, although personally I would still, if I installed a shower, use a correctly rated RCBO to cover both bases.

Many thanks Guys, It's always good to learn and I love things that make me investigate and perhaps, as in this case, change how I think about something...Nice one.

 

[Toonlad]

Round of applause, good read, good interpretation, and very good technical knowledge. :clap::clap::clap: Still dont know what it all means lmao.

My personal take on most domestics this day, is far to many sparks just put in a certain size of cable and circuit breaker, as its the norm for that type of circuit. Ask them why a particular size and they will answer, Thats what the regs state or thats what i was tought.

 

[Stroppy]

Lights = 1mm
Sockets/Immersion = 2.5
Shower/cooker = 6.

Easy!

 

[Guest55]

Round of applause, good read, good interpretation, and very good technical knowledge. :clap::clap::clap: Still dont know what it all means lmao.

My personal take on most domestics this day, is far to many sparks just put in a certain size of cable and circuit breaker, as its the norm for that type of circuit. Ask them why a particular size and they will answer, Thats what the regs state or thats what i was tought.

to be honest thats the whole point of the OSG , a wire by numbers book for the domestic installers.
;-)

 

[Gavin A]

Sorry for the late reply, took advantage of some clear weather today to take the ankle biters out...till it ruddy rained anyway!

Anyway, I checked our shower thoroughly, and can confirm the following are installed;

2 x Thermocouples
1 x manual reset bimetal thermal sensor
1 x Pressure transducer
1 x flow sensor
1 x overload sensor (magnetic)

Based on this I have to concur will all comments by Gavin and initially by DW. With this level of protection in the unit then realistically an RCD protecting the Unit would be sufficient for compliance with the Regs at the basic fault protection level, although personally I would still, if I installed a shower, use a correctly rated RCBO to cover both bases.

Many thanks Guys, It's always good to learn and I love things that make me investigate and perhaps, as in this case, change how I think about something...Nice one.

fair play.

 

[Darkwood]

Does that mean i win this round then outspoken :bucktooth: lol only joking ...... if it causes differing opinions then it serves its purpose as a thread and we all learn regardless of whether initially the OP is wrong or not.... we are taught the basics but not interpretation and i find this site is a gem for changing how you see things ...yes ive been wrong many times too :!blank: