What constitutes a 'new circuit'?

[johnthumb]

Just over a year ago I moved into a new house. In around 2001 the previous occupants built a stud partition at the back of the garage in order to form an office. This was all been signed off and approved by the local building control team. Unfortunately they didn't install a door through this stud wall, meaning that we need to walk around the front of the house in order to access the washing machine and dishwasher in the garage. I've now made an application through building control to add a door; obviously a 30 minute fire door given that it is between the garage and the rest of the house. The construction of the stud is 100mm of Celotex sandwiched between 12mm plasterboard.

In modifying the stud wall to add the door I've found that the wiring for the sockets in the wall isn't up to scratch, even for 2001 when it was done. What I initially thought was a ring final turns out to be two radials (there being no link between the final two sockets). It's also clearly a DIY job, with no regard for safe zones and the cables snaking diagonally across the inside of the stud. Finally, I'm pretty sure that the cables are undersized - it's 2.5mm tacked off the 32A MCB that feeds the downstairs RFC. As I understand it the cables will be installed to "reference method 103" which derates the cables to 13.5A given that they are buried between two layers of 50mm Celotex. With a washing machine and tumble-drier plugged in (and potentially running simultaneously) this sounds unsatisfactory.

Oh, as a side note when I took the lid off the consumer unit to verify that the two legs of wasn't an RFC were actually connected to the same MCB I found that the screw had never been tightened up at all - so for 15 or so years the rings feeding the kitchen and garage have been purely 'resting' in the MCB terminal. Phew!

Having consulted the mighty appendix 4 of 7671 I believe the best option here would be "reference method a" (conduit in insulated wall) - which I understand will give me 20A on 2.5mm or 26A on 4mm.

As I see it I have a few choices:

1) Leave things alone, with the cable potentially undersized, and when screwing up shelves in the garage etc run the risk of hitting a cable in the wall.
2) Stick 20mm or 25mm conduit in the wall and re-run the cables through that, keeping them in the zones etc.
3) Replace the 2.5mm with 4mm (potentially in 25mm conduit for good measure), again keeping them in the zones.

Options 1 & 2 reuse the existing cable, which is already connected into the consumer unit. Option 3 would require replacing all of the existing 2.5mm with 4mm, including re-terminating into the consumer unit. Whilst not a qualified sparky I'm perfectly capable of doing the work, though I'm interested in people's opinions of how this fits within part p etc.

* Would 2.5mm in Celotex have been allowed in 2001?
* Assuming that I stick 25mm conduit in the wall and run the cables through this can I get away with reusing the existing 2.5mm?
* If necessary, is replacing the 2.5mm with 4mm a replacement or a "new circuit" (and notifyable accordingly).
* Have I read the tables correctly? Presumably I don't need to apply any grouping factors given it's 2 x T&E in conduit?

Thanks in advance.

 

[winston1]

Option 4. Make it a ring by joining the two ends together. (It would actually be a figure 8 but that is OK).

 

[Taylortwocities]

I dont see why two radials might be a figure of 8?
But I agree, keep the 32A MCB and join the ends of the two radials together to make an RFC, or fit a 20A MCB.

Personally, I would not use conduit. Clip the cables to the stud, if possible, or run the cable on the face of
the celotex behind the plasterboard.(in safe zones, of course)

Would 2.5mm in Celotex have been allowed in 2001?

The principle of cable calculations goes way, way back but is ignored or unknown to many DIYers - and many electricians

 

[oldbutnotdead]

And re your 'is it notifiable' question- you are working on an existing circuit, it isn't in a special location (bathroom/shower room, though you may have to check if you're in Wales) and thus is not within the scope of current requirements to notify.

You won't enjoy T & E through conduit- if conduit works best for other reasons then use singles.

If you reuse the 2.5mm your 2 sockets really need to be connected in a ring- as radials on 2.5mm you'd want a 20A MCB protecting them, which would be fine except that same breaker is feeding the rest of the ground floor. An additional MCB would of course be a new circuit requiring notification

EDIT thinking on, your 2 sockets aren't radials, they are spurs from the downstairs RFC at the mo and thus are permitted (as long as there's only 1 socket on each piece of 2.5).

 

[winston1]

I dont see why two radials might be a figure of 8?
But I agree, keep the 32A MCB and join the ends of the two radials together to make an RFC, or fit a 20A MCB.

Personally, I would not use conduit. Clip the cables to the stud, if possible, or run the cable on the face of
the celotex behind the plasterboard.(in safe zones, of course)

Would 2.5mm in Celotex have been allowed in 2001?

The principle of cable calculations goes way, way back but is ignored or unknown to many DIYers - and many electricians

It's a fig 8 because they are tapped off the downstairs RFC.

 

[johnthumb]

All. Thanks for your help. I'm in England so it's straightforward part-p here.

Option 4. Make it a ring by joining the two ends together. (It would actually be a figure 8 but that is OK).

I was planning to do this, though wanted somebody to sanity check that I had read the tables correctly. I'd thought I read 18.5A for 2.5mm in insulation somewhere but have just checked and found 20A. It sounds like uprating the cable to 4mm isn't necessary? In any case I'm going to make it into a ring - I don't think the DIY'er who did the job in the first place really understood safe zones/rings/radials etc.

You won't enjoy T & E through conduit- if conduit works best for other reasons then use singles.

I would have thought that T&E through conduit would be reasonably straightforward - and would make it easier to keep straight and in the zones? Saying that, I have a couple of reels of 2.5mm singles so I might use those instead.

As radials on 2.5mm you'd want a 20A MCB protecting them, which would be fine except that same breaker is feeding the rest of the ground floor. An additional MCB would of course be a new circuit requiring notification.

I had considered sticking them on a separate breaker - though a washing machine and tumble-drier on simultaneously are going to be approaching (or potentially exceeding) 20A when the heaters are on. Yes in theory this would be a 'new circuit' - though who is to say that the breaker hasn't been there since 2001

Thanks again.

 

[oldbutnotdead]

T & E through a straight bit of conduit is easy enough. Through a swept bend it is tolerable. Through a junction box or 90 degree corner it is a pig. Trouble with using singles is mechanical protection is required all the way through (so bends, jbs etc) and all the little bits push the price up really fast (the tube itself is cheap enough but the fittings aren't). Unless the conduit solves some other problem then in your setup T & E will probably be cheaper and easier.

And splitting the garage sockets onto a separate circuit is an excellent plan if you've got a gap in the CU and can get an additional MCB for the thing- unfortunately it makes the job notifiable. Theoretically you can run the cabling etc yourself & just get someone in to test and connect, practically (because of the design bit and the scale of the job) if you want to legitimise it it'll be cheaper to pay a scheme member to do it and notify (if your council is anything like mine for fees for electrical work for non-scheme members). Personally in your circumstances I'd just do it.

By the way, is this circuit going to be on an RCD- unless the cables are more than 50mm behind the wall surface it ought to be to meet current requirements.

 

[ericmark]

When it was decided that you could add a FCU to a ring and then add a line of sockets to the FCU without notifying under Part P then at the same time they through away the BS7671 definition of a circuit. Since they have not defined a circuit the Part P relies on case law to define it. Since I have not studied case law I have no idea as to what a circuit is.

So I would take the attitude until case law defines otherwise that a circuit it power coming in on the line wire and returning on the neutral from/to the DNO supply. Anything else is a branch off that main circuit. I am sure that was not what was in the mind of the person writing the law, although of course it may have been the intention to write a law which has no teeth to satisfy a request from MP's without limiting what you can do. It is called politics.

Where I live at the approach to all schools we have what to a colour blind person looks like a 20 MPH sign, however instead of a red circle it has a black one. It has no legal standing, and as you leave the area they are not allowed to cancel the 20 MPH limit as one can't repeat the official 30 MPH sign. In theroy the county council should remove the signs to avoid confusion, but they put them up in the first place. As to if it does slow drivers well even official signs don't do that so really a waste of money. Point is from day one when the first was put up the council officials knew they meant nothing but it kept the complaining mothers happy. It's called politics.

It has always been possible to take some one to court for work which does not show a "Warranty of Skill" there was no need for Part P. You seem to know what you are doing so why not DIY. However as far as crossing T's and dotting i's goes unless you produce minor works or installation certificates then it is clearly not got the "Warranty of Skill" so even though no one but you will read it you still need to raise the paperwork.

I clearly should not say this on a forum which should ban all discussion on politics and religion. Part P is a political answer to the problem of kitchen fitters, and now it does not include kitchens as a special location so rather pointless.