Running a 10mm cable behind kitchen units

[andykent]

I'm installing a length of 10mm cable to my kitchen for a future electric oven (it's gas at present).

In order to get the most disruptive work out of the way at a rare moment when I have the house to myself, my plan has been to put the cable in situ ready for a qualified installer to connect things up in a few months. I hope to get away with removing worktops and cable box panels, but little else.

The cable will go behind base units and round corners and at one point it may need to cross the route of the hot and cold water pipes.

What are the things I need to be aware of in doing this? e.g. bends round corners, physical protection (apart from the obvious hazard of the hot water pipe), that kind of thing? Does it need to be in trunking even though it won't be exposed at any point? If not, are hammer-in clips adequate? What about going round corners - presumably it can't be tight to the wall at these points?

Or are there so many things I could get wrong that I should just delegate the whole thing to an electrician?

 

[sparkwright]

In truth, the electrician will be grateful that you have got the cable in place for him.

However, he will not like it if it's all twisted, so take care in winding it off the drum. Reel it off properly, don't just pick the end of the cable up, and pull off a nasty spiral of cable.

Pet hate over and done with.

If the kitchen units are already in place, it's common enough just to lay the cable on the floor, rightly or wrongly.

Under floors (and anywhere else for that matter) you must avoid running the cable over pipes, as you have suggested.

Be sure to leave a little slack in the cable at each end, nothing worse than a cable that's too short.

 

[winston1]

Why 10mm? 6mm is sufficient for an oven.

 

[sparkwright]

Probably because this forum always goes on about 10 mm2 for future proofing.

 

[EFLImpudence]

Fashion is a strange thing.

6mm² is probably (installation method) already future proofing because the past had BS3036 fuses.

 

[JohnW2]

Probably because this forum always goes on about 10 mm2 for future proofing.

I wish to dissociate myself from that generalisation

Provided one accepts the concept of diversity, and in the absence of any major issues due to cable installation method, even 6mm² is probably OTT, unless one's concept of "future proofing" relates to the appearance of incredibly ('non-green') energy-guzzling appliances (with peak current demands in excess of the total supply to most domestic properties!)! A 32A/4mm² circuit ought to be more than enough in most cases, now or in the future.

Kind Regards, John

 

[Risteard]

Probably because this forum always goes on about 10 mm2 for future proofing.

I wish to dissociate myself from that generalisation

Provided one accepts the concept of diversity, and in the absence of any major issues due to cable installation method, even 6mm² is probably OTT, unless one's concept of "future proofing" relates to the appearance of incredibly ('non-green') energy-guzzling appliances (with peak current demands in excess of the total supply to most domestic properties!)! A 32A/4mm² circuit ought to be more than enough in most cases, now or in the future.

Kind Regards, John

I quite agree.

 

[bernardgreen]

Why is there any worry about over sizing a cable ?

If 6 mm² is calculated as being acceptable then so is 10 mm²

Using the smallest acceptable cable ( in terms of voltage drop ) allows for a volt drop of 4% which at 230 volts supply is 9.2 volts along the cable. That volt drop times the current flowing is a significant amount of power being wasted warming up the cable.

10 mm² does cost more than 6 mm² and it may not be economical to use a larger size for circuits that are not in continuous use but

4 amps to a 1 kW load at maximum volt drop is 36.8 watts being dissipated along the cable After 27 hours of use 1 Unit ( 1 kW Hr ) will have been wasted

 

[JohnW2]

Why is there any worry about over sizing a cable ? If 6 mm² is calculated as being acceptable then so is 10 mm²

It's not a "worry" but in many senses it is unnecessary - particularly in relation to the usual 'excuse' of 'future-proofing'

Using the smallest acceptable cable ( in terms of voltage drop ) allows for a volt drop of 4% which at 230 volts supply is 9.2 volts along the cable.

I'm not sure I understand that - "in terms of voltage drop" the smallest acceptable cable would surely result in a 5% VD (which makes your argument stronger!).

That volt drop times the current flowing is a significant amount of power being wasted warming up the cable.

It is obviously true that the smaller the cable, the greater the VD and hence the more power will be wasted (well, at least some of it) in warming the cable. However, the time-averaged current of a cooking appliance (when being used) is usually (surprisingly?) low - so that, coupled with the fact that cookers are used for relatively short periods of time, means that the 'wastage' is much less than simple calculations would suggest.

10 mm² does cost more than 6 mm² and it may not be economical to use a larger size for circuits that are not in continuous use but 4 amps to a 1 kW load at maximum volt drop is 36.8 watts being dissipated along the cable After 27 hours of use 1 Unit ( 1 kW Hr ) will have been wasted

Again, the maximum permissible VD should be 5% (not 4%), so it would actually be 46.0 watts 'wasted', amounting to 1kWh in about 22h of continuous use. However, the first question is what 4A load would be anything like continuous? As you say, the wastage of power due to VD (and some of the 'wastage' will heat the house, anyway) becomes less important for loads which are far from continuous. Also, it's not only a matter of cable cost - there is a question of the greater difficulty in installing 10mm² cable and, for those it matters to,'saving copper' (and even 'saving PVC').

The same argument could, probably even more reasonably, be applied to the cables used for sockets circuits and certainly for heating (e.g. storage heater) and other circuits - but I've never heard anyone suggesting that one should use a cable "2 or 3 sizes larger than necessary" for such circuits in order to reduce power wastage due to the VD. It seems to only be in relation to (not that often loaded, and rarely heavily loaded) cooker circuits that this is ever suggested.

Kind Regards, John