Kitchen Wiring

[Bas]

A "couple" of questions for the experts re my new kitchen wiring. I'm keen to get the wiring right as I'm going for the IEE Domestic Installer Scheme in the new year and want this to be one of the inspection installations. I do the 2381 training later this month but typically need to do the installation now. (As an aside: I fit bathrooms and the odd kitchen for a living but oddly no one locally seems to have heard of Part P!! Is this common - am I the only one spending upwards of £1k for this?)

Back to the point.... Current position is kitchen ring main feeding two double sockets and two FCU's. One FCU for freezer, the other for the cooker extractor. Under cupboard lights fed by feed from lighting circuit. One 32A MCB feeding the old cooker. Installation 12 years old, MEM split load CU.

Questions:

1. I want to install an additional dishwasher and fridge under counter top - can I supply these with an extention to the existing ring or even spurs from it? Or do I have to supply them via FCU's above the counter?
2. One wall structure is that horrible egg box construction meaning the ring extension will have to be surface mounted behing the cabinets. Is this permissable, assuming I keep to the vertical/horizontal rule from an accessory?
3. What's the best way to make the cable to cable connection for the ring extention of the ring ie within a socket box. Can I use crimps?
4. I understand supplementary bonding within a kitchen is not required under the regs but I always provide it, am I wasting my time and money?
5 New hob is rated at 6.3kW and cooker 2.07 kW. Current Cooker Connection is fed by approx 7m of 6mm cable under an uninsulated floor. My calculation says that this is 36Amps and the TLC volt drop calculator says that 6mm cable is ok? (The manufacturer suggests 4mm!). I'm very unlikely to use all 4 rings on the hob and the oven at the same time but can I trust these calcs?

Apologies the length of this and I appreciate your input very much.

 

[ryanj]

1. I want to install an additional dishwasher and fridge under counter top - can I supply these with an extention to the existing ring or even spurs from it? Or do I have to supply them via FCU's above the counter?

You can supply these from the existing ring, or even spur from it providing there isn't more spurs than sockets. Although, it is considered to be bad practise, just to run an unfused spur from a ring. The appliance should be able to be isolated easily, so you either need to make the socket outlet accessible (in a cupboard beside the appliance), or use an FCU above the worktop, to supply an unswitched socket behind the appliance.

2. One wall structure is that horrible egg box construction meaning the ring extension will have to be surface mounted behing the cabinets. Is this permissable, assuming I keep to the vertical/horizontal rule from an accessory?

You can run surface trunking or conduit, or even just clip the cable to the wall, without bothering with the vertical/horizontal rule. The rule only applies to hidden cables that may get damaged, due to the use of the wall.

3. What's the best way to make the cable to cable connection for the ring extention of the ring ie within a socket box. Can I use crimps?

It'd be best if you just broke into the ring at the two sockets, without any additional joins. If joins are nessiscary, an accessible junction box, or crimps in a suitable enclosure, can be used.

4. I understand supplementary bonding within a kitchen is not required under the regs but I always provide it, am I wasting my time and money?

It is not required, but it is often done by electricians. Usually, just a simple link between the hot & cold pipes to a nearby socket-outlet.

5 New hob is rated at 6.3kW and cooker 2.07 kW. Current Cooker Connection is fed by approx 7m of 6mm cable under an uninsulated floor. My calculation says that this is 36Amps and the TLC volt drop calculator says that 6mm cable is ok? (The manufacturer suggests 4mm!). I'm very unlikely to use all 4 rings on the hob and the oven at the same time but can I trust these calcs?

Total current would add up to be 8.37kW, not counting any diversity.

Current would be 36.4amps, without diversity.

With diversity applied, it would 22.92amps, providing the cooker control unit had a socket.

6mm2 cable clipped directly would give you 47amps, with a voltage-drop of 7.3mV per amp per meter.

The cable can curry all the current required without diversity, and the voltage drop would be 1.86volts, which is under the 4% maximum.

If it would be simple to replace the cable, you could install 10mm2, if only for future expansion.

 

[Bas]

Ryan, i really appreciate your responses. Just to clarify: I'm not going to use spurs to the appliances, i'll extend the ring to unswitched sockets below the worksurfaces. Is it permissable to position these behind the appliances - they would be easy to access but not as easy as if they were in a cupboard adjacent.

Also I do need to extend the ring as existing wiring is inacessible behind tiles which are staying. Can i put the crimps within an existing socket box?

Thanks again.

 

[ryanj]

Is it permissable to position these behind the appliances - they would be easy to access but not as easy as if they were in a cupboard adjacent.

I'm not sure, It'd be difficult to isolate it for maintance, and if there was a fault, you'd have to pull the appliance out.

It'd be better if the socket was in a adjacent cupboard, or better still if you extended the ring to a fused connection unit above the work surface, and run a length of 2.5mm2 from the load terminals of that, to an unswitched socket behind the appliance.

Can i put the crimps within an existing socket box?

Yes.

 

[Bas]

Thanksa again Ryan.

 

[--tom]

ryanj, you mention supplementary bonding going from the hot and cold supplies to "a nearby socket - outlet".Why? I'm not critical, i simply want to understand, given: that in my limited experience i've not seen bonding in the kit. or across the boiler going to an outlet/earthing point.
The bathroom bonding seems to be a little different, but perhaps you would comment on that too. Thanks in advance.

 

[--tom]

I'm still curious about this matter. Perhaps someone will take it up.