changing cooker switch

[esc]

Hi guys. Called in to change a cooker switch for a customer this aft, its just old and tired. When inside it, i found a spur off the terminals, which i traced to a single SO (no SO on cooker switch). The SO is for the microwave. Customer has no probs with fuse blowing.
Its on 6mm, with a 30A 3036, Zs and IR is good on both cooker and SO; all is well, . . . . . .but is it allowed?
Cheers

 

[ringer]

What size cable is used for the spur?

 

[Richard Burns]

If the SO is wired in 6mm then this is OK, though it is recommended that cookers (>2kW) are on a dedicated circuit.
If the SO is wired in <6mm but is protected against fault current by the 30A 3036 (534.5.2) then, because the SO can only supply 13A max and so the nature of the connected load limits the current, then this is allowable (433.3.1).

 

[esc]

It's on 2.5 ringer

 

[esc]

Cheers for that richard burns

 

[telectrix]

as richard's post #3. the 2.5mm is protected by the 13A fuse in the plug in the s/o. commonly referred to as downstream protection. although not best practice, it's allowable.

 

[Engineer54]

It's on 2.5 ringer

Errr!!, ...What does that mean??

 

[mark1979]

2.5 cable and the guy that asked the question is called ringer

 

[esc]

Cheers tel.

 

[Engineer54]

2.5 cable and the guy that asked the question is called ringer

Thanks Mark, ...That explains everything!! I should be more observant in my old age!!! lol!!

 

[ringer]

If the SO is wired in 6mm then this is OK, though it is recommended that cookers (>2kW) are on a dedicated circuit.
If the SO is wired in <6mm but is protected against fault current by the 30A 3036 (534.5.2) then, because the SO can only supply 13A max and so the nature of the connected load limits the current, then this is allowable (433.3.1).

534.5.2 I can not find in BS7671. Am not sure what you intended to refer to - did you misquote the reg number?
433.3.1 I can see how an interpretation of this might seem to comply, but then surely a bit of 1.0mm T&E clipped direct supplying the SO would also comply according to that logic. Would you really be comfortable passing that off as being compliant? I'm guessing we are assuming here that this is a 1G SO. What if it was a 2G SO? I have always been taught that the CCC of the cable must exceed the rating of the CPD, which in this case is really the 30A 3036.

 

[spark 68]

Ringer, have a look at 433.2.1 and 433.2.2 (the 3M rule).

 

[needasparks]

I guess its not good practice for this to be done and i'm sure a sparks would not do it, its these little things that make me look at other bits to get an idea of what else could be wrong.
When i'm doing an inspection it's the little tells like that that open the can of worms.

 

[Richard Burns]

534.5.2 I can not find in BS7671. Am not sure what you intended to refer to - did you misquote the reg number?
433.3.1 I can see how an interpretation of this might seem to comply, but then surely a bit of 1.0mm T&E clipped direct supplying the SO would also comply according to that logic. Would you really be comfortable passing that off as being compliant? I'm guessing we are assuming here that this is a 1G SO. What if it was a 2G SO? I have always been taught that the CCC of the cable must exceed the rating of the CPD, which in this case is really the 30A 3036.

Sorry I did mistype, I am sure we are not interested in earthing at this point!
Reg no is 434.5.2: fault current protection characteristics.
the below reg can only be used if there is sufficient fault current protection.
433.3.1 is a clear and unequivocal statement, however the use of 1.0mm T&E would not be permitted because the minimum csa for power is 1.5mm. In the case we are covering the SO is single. Doubles are normally considered the same as singles but I would not be too sure of using a double in this case.
In almost all cases CCC cable must be > OPD, however this reg is a get out clause in limited circumstances.
You cannot use 433.2.2 because there is a socket outlet before the OPD (plug fuse).

 

[spark 68]

Hi Richard,

In App 15 (BRB), this shows 2.5mm T&E being fed from a 4mm radial circuit to feed a S/O directly (no FCU within 3M), OCPD by a 30 or 32A device, as the OP's spur is in 2.5mm, and his OCPD is a 30A device, what is the problem ?

I agree it is "not best practice" but I cannot really see any Reg that expressly forbids this, other than maybe cookers and such like should be on their own dedicated circuit. As we all know you can get cooker points with built in S/O, so this part does not seem to be a major problem.

I pointed out Reg 433.2.X to highlight that it is possible for a csa reduction, within, less than or equal to 3M utilising forward fusing, this can be a useful reg for using an FCU for things such as a cooker hood.