Cable as fuse!?

[ThrownRazor25]

Do rectification work from periodic inspections done on council houses.today was given 163 job lines to replace 40 A mcbs controlling cooker circuits to 32A mcbs wired in 6mm as "the cable becomes the fuse if supplied by a 40a and in 6mm" by my gaffer.I would like to know what u guys think.

 

[scotsparky]

what type of cable and what refrence method is it?

 

[Mr Mark Sparks]

6mm is undersized on 40a in some cases i guess when there is that many its easier to do them all, if you replece an mcb do you have to make the circ to 17th?

 

[ThrownRazor25]

6mm and any reference method mate.basically if u see a 6mm at the board controlling the cooker.

Sorry markspark,what do u mean circ 17th?

 

[scotsparky]

6mm is very tight and the easiest thing will be to derate the MCb However i would but an rcbo on it unless there is a main rcd in place. If it was MICC no worries carry on!

 

[Mr Mark Sparks]

im not sure if when you modify a circuit by replacing the mcb, should it then have rcd protection to that circuit if cable the is burried , or if when just swapping mcbs there is no need?

 

[scotsparky]

I personnaly would take the oppertunity to chuck in an RCBO into the circuit unless there is a main RCD. It doesnt take any longer and then meants it will comply to 17th. Also Make sure rest of circuit coplys E.G IR,ELI.R1R2 ect. wont do any harm

 

[Spudnik]

IMO its worth doing a few quick tests on the circuit, just for peace of mind really.

However, im not convinced that the circuit should have an RCBO instead of an MCB, as the circuit itself has not been modified in any way, just the protective device.

 

[Mr Mark Sparks]

jason
thats what i wonderd how much can you do to a circ before its"modified"?

 

[scotsparky]

by changing the protective device you are changing the C.C.C of the circuit.

 

[Spudnik]

Indeed, so why would that now need an RCD?

 

[scotsparky]

what type of cable and what refrence method is it?

Jason i did ask refrence method but it was a general question so assuming its Pvc twin and earth run is safe zones in cavity walls and no mechanical protection it needs an rcd.

I personnal would put one in as no harm will be done and errs on safety but would check all readings first.

 

[Spudnik]

Jason i did ask refrence method but it was a general question so assuming its Pvc twin and earth run is safe zones in cavity walls and no mechanical protection it needs an rcd.

I personnal would put one in as no harm will be done and errs on safety but would check all readings first.

I tend to agree with you there.

Especially if its council

 

[spark1]

what type of cable and what refrence method is it?

As Scotsparky says ! we would need to know these circuit details before giving a definitive answer.

I would say though ,that a 40A c.b can be used on a cooker circuit wired in 6mm2 T&E, providing all the relevant installation methods are adhered to....one of those being that the cable is either clipped direct to the surface or buried in plaster etc............More info needed !


spark1