Downsizing a cable mid-circuit

[DNS1]

Seen this mentioned on a thread about cookers on the main forum. Someone asked about splitting a 10mm cable into 2 6mm cables to feed the oven and hob, but has been told it's not compliant.

Could someone point me in the direction of the regs about this one and some info on the theory behind it.

Many thanks!

 

[spark 68]

433.2 is one of the sections in the BGB,

The 3M rule is why the circuit you mentioned in the other thread was not compliant.

ie. you need to suitably fuse/ocp down, within 3m, if you are going to change csa

 

[DNS1]

Great, thanks spark.

 

[spark 68]

This reg. can be extremely useful, especially in kitchens where you may need an additional supply for the likes of a cooker hood or a gas igniter

 

[BES]

Ive had this before at CU change found10mm to cooker isolator 6mm to outlet then 6mm to cooker.I thought ok but wasnt 100% so asked Elecsa about this and was told ok no needed for any extra overload protection for smaller cable as long as smallest cable is rated for load which it was and make comment EIC.
Cheers
Neil

 

[Mark42]

There’s also an interesting regulation (somewhere!) stating it’s OK to grossly downsize cable CSA, without protection, inside things like isolators and busbar chambers to feed small indicator lights etc. Clearly, fusing for this would be silly, and cable damage inside the chambers is unlikely.

That makes sense, since terminating say 25mm to a little neon lamp might be problematic Whenever I’ve installed such things I’ve deliberately used really thin cable which I reckoned would act as a fuse in itself, were say the lamp holder to go short circuit. Still feels iffy though.

 

[Chr!s]

Seen this mentioned on a thread about cookers on the main forum. Someone asked about splitting a 10mm cable into 2 6mm cables to feed the oven and hob, but has been told it's not compliant.

Could someone point me in the direction of the regs about this one and some info on the theory behind it.

Many thanks!

I see no reason why it cant be compliant.

Regards Chris

 

[spark 68]

I see no reason why it cant be compliant.

It was non-compliant, in the other thread, because the 6mm cable was 6m long, ie. greater than the allowable 3m rule for cable reduction without OCP.

Here is the thread: http://www.electriciansforums.net/e...umpty-cooker-cable-new-hob-double-oven-q.html

 

[Chr!s]

It was non-compliant, in the other thread, because the 6mm cable was 6m long, ie. greater than the allowable 3m rule for cable reduction without OCP.

Here is the thread: http://www.electriciansforums.net/e...umpty-cooker-cable-new-hob-double-oven-q.html

The other threads wrong

 

[spark 68]

???? in what way ?, I agree it would depend on the OCPD at the origin of the 10mm cable, but reg. 433.2.1, 433.22 specifically mentions the requirements, as well as the "best practice guide" associated with the point of isolation being no more than 2m away.

 

[Chr!s]

???? in what way ?, I agree it would depend on the OCPD at the origin of the 10mm cable, but reg. 433.2.1, 433.22 specifically mentions the requirements, as well as the "best practice guide" associated with the point of isolation being no more than 2m away.

It does, so why can it not comply?

 

[spark 68]

I may be missing something here Chris, but if the supply cable is 10mm, and is then split into (downsized) into two 6mm cables, one of them being 6m long with no forward ocpd within 3m, then how does this comply?

 

[JulianC]

Try 433.3.1 (ii) then get you adiabatic out for 434.2.2

 

[Darkwood]

Lets say you run 10mm T&E on a 32mcb for x amount of meters then reduce the cable size to 6mm for the purposes of extending the run for 10m then according to 433.3.1(i) this is acceptable and exceeds the 3m everyone else is quoting 433.2.2, the one question no-one seems to have asked and is important in answering this OP is what size mcb is and the nature of the 10mm run.

433.2.2(ii) is very useful when looping 10mm tails from a henley block for a 1way board 45amp rated - and not having to commit to the 25mm tails as the cutout may require to do without this reg, the amount of time ive seen 16mm plus tails feeding into an isolator etc which has say a 20amp to 45amp mcb within is more than i can recall, the mcb upstream of the reduced tails prevents and overload been pulled through and as long as its within 3m is permitted.

 

[spark 68]

the one question no-one seems to have asked and is important in answering this OP is what size mcb is

I did here

I agree it would depend on the OCPD at the origin of the 10mm cable

 

[Chr!s]

433.2 is for position of protective device

433.3 is for omission

As Darkwood as mentioned 433.3.1 is the relevant reg

 

[combilau]

Using reg 433.2.2 could you take a 6mm cooker cable ina dual connector and take out a 6mm to the cooker and a 2.5 cable to the cooker hood as long as the fcu is within 3m of the dual connector?

 

[spark 68]

I can see the regs you are looking at, and agree the regs should not be taken in isolation.

Reg 433, says shall not be applied to installations situated in locations presenting a fire risk etc...

Iam sorry to have to disagree with both of you here, as a kitchen or other domestic location provides a very real risk of fire in my opinion.
You may be able to use that reg in a different environment and wiring system/containment system, other than domestic.

Iam not saying either of you are wrong per se, but I would not be happy signing that off, as I could not guarantee the conditions required to satisfy parts of 433.

I would much prefer to cover my own backside in this instance.

A very interesting debate none the less.

 

[spark 68]

Using reg 433.2.2 could you take a 6mm cooker cable ina dual connector and take out a 6mm to the cooker and a 2.5 cable to the cooker hood as long as the fcu is within 3m of the dual connector?​

Yes it a very useful reg for this scenario.

 

[Chr!s]

I can see the regs you are looking at, and agree the regs should not be taken in isolation.

Reg 433, says shall not be applied to installations situated in locations presenting a fire risk etc...

Iam sorry to have to disagree with both of you here, as a kitchen or other domestic location provides a very real risk of fire in my opinion.
You may be able to use that reg in a different environment and wiring system/containment system, other than domestic.

Iam not saying either of you are wrong per se, but I would not be happy signing that off, as I could not guarantee the conditions required to satisfy parts of 433.

Working out the adiabatic may be the more sensible approach, but I would much prefer to cover my own backside in this instance.

A very interesting debate none the less.

I dont think a kitchen is what the regs term a location of fire risk or explosion.

How will the adiabatic help?