Can circuits be hard wired in flexible cable?

[tombrooker84]

Hello guys, Going to open a big can of worms here, but here goes. I'm having an argument with another electrician on site, and he is of the opinion that the is no regulation against the use of flex in domestic premises, for all circuits? I was always of the opinion that there was a regulation against the use of flex but I cannot seem to find one, in fact the opposite, when we looked and I cannot quote the exact reg now, but it says "as long as its suitable then its ok". I wondered if its something a simple a british standard marking, or is it literally due to the fact that twin and earth is a lot cheaper, nearly double the price for heat resistant flex, but surely you would recoup that in a couple of hours less work, due to the fact it would be easier to install. I also mentioned terminating it a the cutting of strands thus reducing surface area, but i suppose the reply to that would be "right tool for the right job" and your fine. Also perhaps T&E distinguishes a professional job from a DIY job... but hey ho. Tom

 

[tombrooker84]

So it costs more, is physically bigger for same csa, heavier, harder to buy in bulk, takes longer to terminate, is the wrong shape for a lot of JBs, the strands are easier to damage, and needs more support.

OK. And still a debate about why it is not more common.

Someone normally says it can carry more current at this point ...

I agree with what you are saying, but there are still major pro's to consider. I mean its a lot easier to pull and run through joists e.t.c, it never kinks, and there are more and more tools coming on to the market that make stripping it as easy, if not faster to terminate than T&E, add to that you do not have to sleeve the earth, and it would make pushing the face plates on to back boxes a lot easier (given it isn't a big problem now).

 

[Adam W]

IMO it's ok to wire all circuits in flex provided they are terminated with a bootlace ferrule.
I don't think you'd save money on installation time though, taking the cost difference of materials into consideration.
You wouldn't be able to cable tie the cables to the central heating pipes because they're not part of the electrical system - if the customer wanted to rip out the central heating you'd be left with no support for the cables, so you'd pretty much have to install the cables the same way as with T&E, ie capped in plaster or clipped direct in the loft. Bear in mind that T&E lends itself better to being chased into walls due to it's flat profile.

Flex would make it easier to screw the faceplates back, but is that really worth the extra cost?

 

[tombrooker84]

IMO it's ok to wire all circuits in flex provided they are terminated with a bootlace ferrule.
I don't think you'd save money on installation time though, taking the cost difference of materials into consideration.
You wouldn't be able to cable tie the cables to the central heating pipes because they're not part of the electrical system - if the customer wanted to rip out the central heating you'd be left with no support for the cables, so you'd pretty much have to install the cables the same way as with T&E, ie capped in plaster or clipped direct in the loft. Bear in mind that T&E lends itself better to being chased into walls due to it's flat profile.

Flex would make it easier to screw the faceplates back, but is that really worth the extra cost?

To be honest I've always used T&E and have never practically given it a go. I wonder if anyone has? If so does it justify the exra exspense? Also I usually chase the cables in pvc oval capping so i doubt the cable would make too much of a difference?

 

[CrazyScozzese]

I suppose it is horses for courses really, convenience v cost v application.

 

[GLENNSPARK]

521.9.3........

 

[JPA]

521.9.3 - "A flexible cable or flexible cord shall be used for fixed wiring only where the relevant provisions of the Regulations are met" so there you go, clear as mud...

 

[Adam W]

To be honest I've always used T&E and have never practically given it a go. I wonder if anyone has? If so does it justify the exra exspense? Also I usually chase the cables in pvc oval capping so i doubt the cable would make too much of a difference?

That's what I mean - oval capping is oval, the same as T&E, whereas flex is round. If you wanted to install round conduit in the wall you'd need to chase deeper, or use a larger (deeper) size of oval capping to get 2x flexes down side by side, but either way using flex would involve deeper chases.

 

[GLENNSPARK]

one thing here though with flex boys.....dont forget that its CPC is insulated along its whole length and ideally you dont want that.....as an uninsulated CPC will intercept a fault before the fault goes L-L....ore line neutral....a short circuit.....so an RCD will operate as you are more likely to get an line-earth/neutral-earth fault......an important thing to consider on TT systems where an RCD is often the only means of fault protection likely do disconnect within times.....

 

[Marvo]

one thing here though with flex boys.....dont forget that its CPC is insulated along its whole length and ideally you dont want that.....as an uninsulated CPC will intercept a fault before the fault goes L-L....ore line neutral....a short circuit.....so an RCD will operate as you are more likely to get an line-earth/neutral-earth fault......an important thing to consider on TT systems where an RCD is often the only means of fault protection likely do disconnect within times.....

The counter argument to this is that the CPC of flex is the same CSA as the live and neutral so it would have less impedance under a fault current and possibly faster RCD tripping times.

Please don't take this the wrong way, I'm not in favour of using flex instead of FT+e.

 

[GLENNSPARK]

The counter argument to this is that the CPC of flex is the same CSA as the live and neutral so it would have less impedance under a fault current and possibly faster RCD tripping times.

Please don't take this the wrong way, I'm not in favour of using flex instead of FT+e.

the point i was making was that the CPC on a flex may not intercept the fault at all......yes ok..this can happen with T&E ....but less likely due to the structure of this type of cable....

 

[VoltzElectrical]

the point i was making was that the CPC on a flex may not intercept the fault at all......yes ok..this can happen with T&E ....but less likely due to the structure of this type of cable....

How would that work??

There is nothing wrong with using flex to wire a whole house, other than the prohibitive costs. As for the reg being quoted re. fixed wiring.... what does that mean? Just follow the normal routes. All that need s to be considered as far as the regs go, are current carrying capacity, heat resistance, and disconnection times with due accord to heating under fault conditions (adiabatic equation). Other than that, it id down to cost/ convenience factors. bootlace ferrules? over-egging the omelette IMHO.

 

[trev]

one question that needs to be asked is,
Why would you?

 

[GLENNSPARK]

How would that work??

There is nothing wrong with using flex to wire a whole house, other than the prohibitive costs. As for the reg being quoted re. fixed wiring.... what does that mean? Just follow the normal routes. All that need s to be considered as far as the regs go, are current carrying capacity, heat resistance, and disconnection times with due accord to heating under fault conditions (adiabatic equation). Other than that, it id down to cost/ convenience factors. bootlace ferrules? over-egging the omelette IMHO.

and when did i say there were owt wrong with eh voltz??and "how would that work" as in how would the CPC not intercept a fault in flex.........when did i say it wouldn`t eh?....look at threads before posting because what i said was that the CPC of the flex MAY NOT intercept the fault....not WOULD NOT!!!!.....or maybe its you who is "over egging" the omelette...eh??.......and yes Trev....why would you???

 

[VoltzElectrical]

eh. eh. eh. Calm down. eh.

 

[GLENNSPARK]

Eh...eheheheheheheh??????...eheheheh

 

[GLENNSPARK]

eh. eh. eh. Calm down. eh.

no probs volts......i wasn`t in the best of moods anyway yesterday....not your fault mate......

 

[CrazyScozzese]

You make a good point tho' Glenn, In flex the CPC is not between the other two conductors as they are in triangular positions, so if they overheat due to an overload and burn through the insulation, they are far more likely to touch each other. To touch the CPC would require them to burn through a second layer.

T&E requires them only to burn through their own insulation to touch the CPC, and as it is between them, the chances of touching each other before the CPC are minimal.

Would this not be safer in this instance as the overload was not disconnecting before the cables broke down, so if an RCD was employed it would then interrupt the supply?

 

[GLENNSPARK]

thats what i mean crazy......if you look at 3 core flex end on....its like "trefoil" configuration......so the chances of a live-live fault are greater....so if the earthing arrangement was TT and as such was relying on an RCD for sole fault protection could be a chance that the protective device may not opperate at all....as i se it its much better to have an uninsulated CPC running the full length of the cable......to intercept any breakdown in insulation that may occur on the live conductor/s..........

 

[Adam W]

thats what i mean crazy......if you look at 3 core flex end on....its like "trefoil" configuration......so the chances of a live-live fault are greater....so if the earthing arrangement was TT and as such was relying on an RCD for sole fault protection could be a chance that the protective device may not opperate at all....as i se it its much better to have an uninsulated CPC running the full length of the cable......to intercept any breakdown in insulation that may occur on the live conductor/s..........

So would you not use singles in conduit on a TT system?

 

[CrazyScozzese]

Not where I was considering flex to make things easier to wire???