What can I run on a spur


Postby dullspark » Tue Jul 27, 2010 11:20 am

Hya, this is my first post so I hope I do it properly!!

The electrics in my house were renewed about 12 years ago so they are fairly up to date.
The ring main for my downstairs power sockets is from-and-to one circuit breaker on the main board.
There are twelve double socket outlets powering normal household stuff.
We want to fit an 'Island' in the kitchen that will house two integrated units - one a fridge, the other a freezer.
Can I run a single cabled spur from the nearest socket to a double socket outlet to feed the two units?
How deep do I have to sink the cable in the floor (solid)?
Am I right in assuming the cable will have to run in plastic conduit down the wall and under the floor?

Thanks in anticipation
Jim
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Postby ericmark » Tue Jul 27, 2010 10:59 pm

“Can I”

This must depend on what “I” has in the way of membership of oversetting organizations or if payment has been made to LABC. Also the skill of “I” is very important in deciding if the person referred to as “I” possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is able at all times to prevent danger and, where appropriate, injury to him/herself and others. So I will read it as “Will the BS7671:2008 regulations permit?”

“To run a single cabled spur from the nearest socket to a double socket outlet to feed the two units?”

If supplying a single double socket then yes. If supplying two separate single sockets only if it first goes through a fused connection unit (FCU). See next re-RCD.

”How deep do I have to sink the cable in the floor (solid)?
Am I right in assuming the cable will have to run in plastic conduit down the wall and under the floor?”

It does not need plastic conduit it states:- 522.6.1 Wiring systems shall be selected and erected so as to minimize the damage arising from mechanical stress, e.g. by impact abrasion, penetration, tension or compression during installation, use or maintenance.

The selection of cable will have a great bearing upon what additional protection will be required. For example using mineral insulated cable plastic coated no protection other than from immediate abrasion if walked on would be required and if 2mm below finish level that would be fine. Using Ali-tube cable would be similar although some protection against crushing would be required. Singles would need running in metal conduit and twin and earth will not really go through conduit with ease and as a result not really suitable. As far a plastic conduit then unless buried over 50mm the cables would need protecting with a 50ma RCD.

All sockets less than 20A also need RCD protection and if the supply is not already RCD protected then a RCD FCU or RCD sockets will be required.

In the floor water ingress must be considered and to ensure no ingress one would hope the sockets are not sunken.

Using mineral cable requires a fair bit of skill and is not really a DIY job. Mineral cable would be best option for under floor. Part P and related charges will likely rule out any idea of DIY because likely cost more than using a registered electrician. So combining both together it is certainly not a DIY job.
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Postby dullspark » Fri Jul 30, 2010 5:39 pm

ericmark wrote:“Can I”

This must depend on what “I” has in the way of membership of oversetting organizations or if payment has been made to LABC. Also the skill of “I” is very important in deciding if the person referred to as “I” possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is able at all times to prevent danger and, where appropriate, injury to him/herself and others. So I will read it as “Will the BS7671:2008 regulations permit?”

“To run a single cabled spur from the nearest socket to a double socket outlet to feed the two units?”

If supplying a single double socket then yes. If supplying two separate single sockets only if it first goes through a fused connection unit (FCU). See next re-RCD.

”How deep do I have to sink the cable in the floor (solid)?
Am I right in assuming the cable will have to run in plastic conduit down the wall and under the floor?”

It does not need plastic conduit it states:- 522.6.1 Wiring systems shall be selected and erected so as to minimize the damage arising from mechanical stress, e.g. by impact abrasion, penetration, tension or compression during installation, use or maintenance.

The selection of cable will have a great bearing upon what additional protection will be required. For example using mineral insulated cable plastic coated no protection other than from immediate abrasion if walked on would be required and if 2mm below finish level that would be fine. Using Ali-tube cable would be similar although some protection against crushing would be required. Singles would need running in metal conduit and twin and earth will not really go through conduit with ease and as a result not really suitable. As far a plastic conduit then unless buried over 50mm the cables would need protecting with a 50ma RCD.

All sockets less than 20A also need RCD protection and if the supply is not already RCD protected then a RCD FCU or RCD sockets will be required.

In the floor water ingress must be considered and to ensure no ingress one would hope the sockets are not sunken.

Using mineral cable requires a fair bit of skill and is not really a DIY job. Mineral cable would be best option for under floor. Part P and related charges will likely rule out any idea of DIY because likely cost more than using a registered electrician. So combining both together it is certainly not a DIY job.


Ericmark - What a very imformative reply, thank you very much.

"I" am a gas turbine consultant - electrics and electronics are part and parcel - but I have never had to run wiring for a fridge in one of these before!
I think my qualifications would put me in the 'competent person' category that the bit of DIY I am doing would satisfy.

But thanks again for the reply
dullspark
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Joined: Tue Jul 27, 2010 11:06 am


Postby ericmark » Sat Jul 31, 2010 10:56 am

The last gas turbine I worked on Connah's Quay combined power did have some 7 core mineral cable used but the other on the Schiehallion did not have any mineral insulated that I knew off although I think it would be used on ships. It was used on the Point of Aye turbines looked very neat up the wall so sure you have seen it many times.
Oddly I have only every glanded off in college and used potting tools. I think I would although I know it is best way to wire be looking at the new Ali-tube cable instead. It can unlike mineral be crushed so would need laying slightly deeper but so much easier to work with.
The other option would be SWA but it does not bend easy and would need even a deeper channel to lay it in.
Although you could use steel conduit and singles that would mean singles up the wall as well until somewhere where you can terminate and that would be a real pain. Plus you would need a bender.
However having said all that if you want to sell the house then Part P must be considered and the fees charged by the LABC are silly starting at £100+ and since a kitchen I would think hard about DIY. It could cost more then job costs to get the council to test and inspect and issue the completion certificate than whole job costs to do.
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Postby jimmy_one_ball » Tue Aug 03, 2010 10:41 pm

Yes you can have one double socket outlet from an unfused spur.

The cable needs to be 50mm deep (to protect from 2" nails - at least thats the rule for walls) and conduit may be required because the cement that you use to fill in the chase will react chemically with the cables PVC sheathing causing heat damage. Regulation 522.2.1 refers, quote: In order to avoid the effects of heat from external sources (iii) selecting a system with due regard for the additional temperature rise which may occur

If the circuit is not already RCD protected then replace the MCB with a 32A 30mA RCBO. If you wait till the 1st amendment comes out (Jan 2012) then you won't need to RCD protect the circuit.

Legal stuff: Labels may be needed especially if old colours are still present and the circuit will need testing. A competent person will be able to do this and issue a minor electrical installation works certificate.

The term 'competent person' has a specific definition in the wiring regs so don't be offended!

All the best with that
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Postby ericmark » Fri Aug 06, 2010 12:49 am

Be very careful with term "Competent Person" in the wiring regulations it is higher than skilled as you can ensure the safely of others as well as you. It does not refer to any qualifications in the regulations and from what you have said I expect you would be regarded as a "Competent Person".

However the "Competent Persons Scheme" is something completely different and it refers to being accepted as a member of a club who are able to authorise you to do all inspecting and testing yourself and send them the results to get a Part P completion certificate without informing LABC first.

It seems that some LABC do not test your work if they think you have the skill but they are still responsible and I would assume if you made a mistake and some one is injured then they would be taken to court.

We all make mistakes and the testing is very important. As far as I can work out you are suppose to test your own work. And then the LABC should re-test to confirm your readings likely 10% only if everything seems correct. If you don't test the rules have changed and they can charge you for any third party charges to test the installation. From what I can understand in real terms they look at the schedule of test results and if the reading look to be what would be expected then they just send out the completion certificate. If however there are some odd reading then they visit. For example a TT system with a earth rod reading of 5 ohms would ring alarm bells likely the rod was still connected when measured. How far they check I don't know. The earth loop impedance is no longer so important however the reading does give a good indication as to if volt drop is exceeded so although having a C32 RCBO may not seem a problem I would not use them myself I would always use a B32 RCBO.

This is why I say submit a detailed plan. If you have it on original application what MCB and RCD you intend to use and also detail type of cable then once completed they can't then decide they don't like it. But if you don't detail before the job then they can be a pain.

As to cable buried in a wall you need to select what type of cable you want to use. With Ali-tube cable there is no need for a RCD to protect the cable although you still may need a RCD for the socket. The fridge if the socket is marked fridge only does not need to be RCD protected so only if you use twin and earth would you need a RCD.

Personally I like the RCBO method and I consider if the fridge is faulty then not a problem it tripping out. However atmospheric storms can also trip RCD's and when on it's own circuit you may not notice.

Oddly SY cable is not on the list of cables not needing RCD protection this BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 is the list. The BS 8436 Ali-tube seems hard to get in 6mm and as a result you may want to use SWA for cooker etc. Although Guardian, Earthshield, Flexishield, and Afumex are designed for house wiring it seems you can only buy it by the role. As a result it is not used much as more expensive than twin and earth. It does however carry more current than twin and earth being rated 90 deg C instead of 70 deg C which if any of the cable goes through insulation can help.

The days of just bang it in are gone and now careful planing is required to ensure it all complies. For electricians we have a good idea if we are near limit or not and often we use rule of thumb and take a slight chance it will be within limits. But where one is not doing it every day then you do need to be more careful not to exceed limits.
ericmark
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Location: Mold, North Wales.


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