New kitchen electrics

[Jsfinchy1986]

Hi can some one help please?
I am in the middle of extending and replacing kitchen. My question is that the kitchen is currently on 32a 2.5mm ring main for the sockets, now my father in law (not an electrian but a builder/handyman) has told me that it needs doing as a 4mm ring main. Because of loft insulation .Now firstly the cost of 100m of 4mm is one off put. I have just done a granny flat for my old man and had an electrician do the work and they used 2.5mm on a ring so can't see why I would need 4mm

 

[conny]

I'm not a spark but I think it has to do with the cable being able to take the load without overheating due to the loft insulation.

Another thing to consider is that kitchen wiring falls under special locations and has to be carried out by a competent person from start to finish. A competent person is usually, though not always, classed as someone who is a scheme member/part P qualified.

No doubt if I am wrong someone will correct me.

 

[Jsfinchy1986]

Hi thanks for that from what I understand I can do the donkey work so to speak but get it checked by the appropriate person. I just don't understand why the sparks that did my dads put the kitchen on its own ring using 2.5 yet for some reason my father in law says I should do it in 4mm. I won't be putting in any more insulation than what is in my dads

 

[RF Lighting]

You would be best to ask your electrician what size cable is required, and also if he's happy for you to do any of the work. 4.0mm² would be very unusual to be required for a domestic ring circuit, but not inconceivable.

 

[SimonH2]

Another thing to consider is that kitchen wiring falls under special locations and has to be carried out by a competent person from start to finish. A competent person is usually, though not always, classed as someone who is a scheme member/part P qualified.

All wiring is required to be done by someone who is competent to do the work.
But I think you are more alluding to the notification requirements in the building regs. Since the latest amendment, the kitchen is no longer classed as a special location and work in it is no longer notifiable. The only notifiable electrical works are now 1) installing or replacing a consumer unit, b) adding a circuit, or c) work within the zones of a bathroom.

 

[JohnW2]

Another thing to consider is that kitchen wiring falls under special locations and has to be carried out by a competent person from start to finish. A competent person is usually, though not always, classed as someone who is a scheme member/part P qualified. ... No doubt if I am wrong someone will correct me.

Very perceptive You are indeed wrong about a kitchen being different from any other location (it never was a 'special location' - like bathrooms etc, but came into a similar category) - that ceased to be the case about 18 months ago. "Part P qualified" is meaningless (except in the minds of those who sell 'Part P qualifications'). Modification or extension of existing circuits within a kitchen no longer requires notification, but any 'new circuits' (anywhere) do. Anyone competent (in the everyday sense) can undertake notifiable work but it is usually much cheaper (because of notification fees) if undertaken by an electrician who is a member of a self-certification scheme.

Kind Regards, John

 

[Jsfinchy1986]

Thanks for these replie but can anyone tell me why I would use 4mm not 2.5mm for the ring main in the kitchen. I can't see why I would.

 

[JohnW2]

Thanks for these replie but can anyone tell me why I would use 4mm not 2.5mm for the ring main in the kitchen. I can't see why I would.

As you have been told, you need to ask your electrician. As has been said, it would be pretty unusual, but not impossible, that the way in which the cable was installed in relation to insulation would require it to be 4mm².

Kind Regards, John

 

[EFLImpudence]

If a cable travels through thermal insulation for more than 500mm. or is covered by more than 100mm. of thermal insulation its current carrying capacity (without overheating) is reduced by half.

This would make 2.5mm² T+E unsuitable for a ring circuit but only the relevant part has to be increased; not all of it.

Of course, if in can be installed without doing this then that would better.

 

[JohnW2]

If a cable travels through thermal insulation for more than 500mm. ....

I've often tried to find some guidance as to a minimum length of cable that has to be affected by potential de-rating factors to requiring de-rating (including re-classification of installation method) to be applied. Where does that 500mm figure come from?

Kind Regards, John

 

[RF Lighting]

Ci in your derating factors in bs7671

 

[EFLImpudence]

Table 52.2

However the maximum seems to have been reduced to 400mm.
Oh it's in the text of 523.9.

 

[EFLImpudence]

in the 16th the figure for 400mm. was 55% but

in the 17th the figure for 400mm. is now 51%.


As the text is the same regarding 500mm. at 50% this would seem to be somewhat incongruous.


However, the text also says "in the absence of more precise information".


As the actual current which would cause the temperature to rise to 70° seems to be an unknown it is, I suppose, difficult to calculate.

 

[JohnW2]

Table 52.2 ... However the maximum seems to have been reduced to 400mm. Oh it's in the text of 523.9.

Thanks. The difference between 500mm (50%) and 400mm (51%) is clearly pretty marginal! ... and 50%, of course, equates to 'Method 103'.

Kind Regards, John

 

[JohnW2]

in the 16th the figure for 400mm. was 55% but in the 17th the figure for 400mm. is now 51%. ... As the text is the same regarding 500mm. at 50% this would seem to be somewhat incongruous.

Hmmmm. They're obviously a bit stuck with a minimum of 50%, since once can have unlimited lengths of cable in insulation for 50% per Method 103.

However, the text also says "in the absence of more precise information". ... As the actual current which would cause the temperature to rise to 70° seems to be an unknown it is, I suppose, difficult to calculate.

Quite. I obviously don't know why they changed the 400mm figure but I'm sure that the possible (im)precision of all this (for example, there is 'insulation and insulation'!) is such that the difference between 51% and 55% is neither here nor there.

Kind Regards, John