Singles in oval conduit and Informing local Authority

[lookpil]

Hello,

I have just bought a place which needs everything doing to it. I gave it a clean and then set about rewiring the place. I am an electrician but more industrial than domestic and don't have my part P as I work for a large firm and don't need it on a day to day basis as Im covered by their NICEIC status and don't do private work.
The original plan was to rewire it and then ask someone who is part P to sign it off. From looking on the net this now seems to be harder than I first thought. I have almost completed the first fix and am thinking of phoning the local authority next week and holding my hands up and telling them what stage I'm up to. Has anyone got an experience of this?

My other question is can you wire singles in oval conduit? When I was younger doing rewires we always used T+E in the old tube and then went into an oval tube were needed. In this place due to the way it has been tubed out an the structure of the building I have used singles but in some places were I want the socket in a different place I have had to put singles in oval conduit. I have looked in many places but can't find anywhere were it says you cant. The cct in oval is in the protective zone and is RCD protected its just not a continued join from the old tube to the new and would be hard to pull in new cables next time it needs rewiring without chopping out a bit of plaster here and there.
Thanks in advance for your views.

 

[electronicsuk]

There is nothing wrong with singles in conduit, oval or otherwise, as long as they are enclosed in conduit/trunking/ducting/etc throughout their entire length.

As for part P, it's your call now you've started - probably a bit hypocritical of me to say this, as we'd never recommend it to most DIY'ers, but surely you must have friends in the industry who are able to self-certify?

 

[holmslaw]

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[MalcofArabia]

Even though the schemes are self certify, it is I'm sure a pretty regular occurence for Part P certified sparks to sign off other sparks work, though of course it can't be condone.

If you don't know a Part P registered sparks then a call to the LABC is an option. As you say hold your hands up, tell them your a sparks, what your qualifications are and just plead ignorance, and that you thought you could do it yourself. Chances are you will get a bit of a roasting and if they are really peed at you they may make you wait for their 1st fix inspection. Chances are though you will be ok.

As for the oval tube just make sure the tube terminates inside the back box a few mm^ so that there is no chance for bare single to be seen. I would put a 20mm^ open grommet in the knock-out and slide the 16mm^ tube through the grommet,

 

[lookpil]

Thanks all for your views.

I'm going to sound really rough now.

The original metal (earthed) tube for the power and lighting are interlinked. the power runs from 1 socket to another hoizontally and where needed rises vertically up to the center light biza box and back down again to get over doors and fireplaces etc. The original sockets were surface and in some cases in odd places for the new install. There are many places where a power and lighting cct run in the same tube making it full so doing the new install in T+E was out of the question if I was going to use the same tubes. (orianally they used singles, so I have done the same).

The only difference is the old install used surface boxes and I wanted them flush as well as more points in some places and moved over in the odd place (the worst being 1 meter horizontally from the old biza box) In most cases I have drilled a hole in the bottom of the biza box put in a bush and lock ring and then put the cables in oval tube, just butted up to the back box and bush for an inch run for the power and with the lighting swiches I have removed the biza box put the oval tube over the metal tube and butted it up against the switch back box about 4 inches away.
YES its a little rough just butting it up to the box when it contains singles but it seems the best of 2 evils. I would say it is better to be hard wired from point to point as opposed to terminating it in the biza box (which would then need to be accessible and look unsightly)just to change to T+E because its in a butted up oval for an inch or so.
I've used grommets but the oval is 25mm due to the amount of cables (ring main) and cant be pushed through a 20mm hole. I have also taken a flying earth off the biza box into each back box to earth the tube again and make it the same potential as the rest of the system. The metal tube is now not in the protective zone as the sockets are lower, but it is earthed and as far as I can make out this fulfills the requirements of reg 522.6.6 (1). The oval tube is in the protective zone either horizontally or vertically and the whole cct is RCD protected which I think fulfills the requirements of reg 522.6.6 (5) the only dodgy bit is its singles inside oval tube butting up to a back box. Originally I was just going to mastic around the join to protect the cable from the ingress of plaster when it gets plastered up.

I have another query also. In the front room I have a 4 gang light switch. 1 doing the center light and the other 3 feeding 5amp sockets for table lights. I have also run around more TV, phone and speaker points around. The property is a flat and the floor and ceiling are both concrete. Compartment trunking would have looked odd so what I have done is cut a goove in the screed (only about 20mm as its so hard) from one end of the room to the other and Teeing off to lay the cables in. I'm going to put a floating wooden floor in over the top. I did have good intentions to have a mains voltage groove and a low voltage groove but the floor was so hard and when I was kangoing up the first groove I became concerned at how hard I had to hit it and possibly causing damage to the flat below with the vibration so now they are all going to have to run in the same groove and I'm getting some metal capping to fix the lighting ccts down first to give protection and voltage segregation between the ccts. I don't think the local authority will be happy with this! Again the mains ccts will be RCD protected.

What do you think?

 

[holmslaw]

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[MalcofArabia]

You did say you were a sparks didn't you

 

[lookpil]

Hi Holmslaw and MalcofArabia,

Sorry I have not impressed you both. I have been in the industry a few years and have never needed to ask a forum a question before.

I put my questions up to get views or alternatives not insults. YES I admit its not best practice, maybe I just needed to air my ideas.

After writing before, I thought I could keep it in metal and use a coupler instead of oval, works fine so thats how I'll go froward.

The cable under the floor is a bit odd but is it really that bad? The mains cable is T+E, i'll put it in capping and earth the capping and the low voltage ccts will just lie loose in the groove. Its either this or a load of cables in te safety zone at the top of the wall and about 8 drops making the whle room needing plastering. Its not as deep or as segregated as I would have liked but its better than causing damage below. One option maybe to put a metal plate accros the wole groove.

 

[holmslaw]

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[electronicsuk]

Re the cabling in the floor, I think you're right that it probably wouldn't get by BC, especially if yours is one of those that actually do a proper inspection rather than just turning up for a quick glance and giving the thumbs up. However, with the segregation as you've already suggested between ELV and LV circuits, it wouldn't be a major sin. Although the capping is not designed to be used in this way or manufactured to a relevant BS, it is in essence very similar to different voltage circuits in compartment trunking. The LV cables can't, of course, be singles - you'd have to replace the capping with conduit for that.

There may also be an issue of depth and the likelihood of screws penetrating the wiring when you install your floating wooden floor. There aren't any safe zones or real guidelines for how cables should be laid in a concrete screed, although IMO best practice is to ensure that all cables are in conduit and at least 50mm deep. This is in line with the required depth for cables without protection installed in floor joists.

 

[lookpil]

Hello, Holmslaw and electronicsuk.

Holmslaw, I haven't used the conduit as the main earth I've just taken an extra bonding cable to the back box so everything is the same equipotential. Each cct has its own earth as well as an idependent bonding earth.

I have had a look today and I can probably get a coupler between the biza box and back box, his would hopefully make things more compatable.

As far as the original tube not complying with the BS this would be a major problem. I'm sure when the council rewire similar properties they will use the old tubes otherwise you would be talking about major domolition to rewire a each flat.

I was looking in the regs to see where it says the biza box would have to be accessable but couldn't find anything. All ccts pass strait through apart from the bonding earth. Can you guide me to the reg. If it needs to be visible it would be a shame bu not the end of the world.

electronicsuk, After a slating from holmslaw which was what I needed I have decided to pull out the lighting ccts under the floor. I cant get it deep enough without the risk of causing damage to the property below so they will have to go. Im going to leave the TV and speaker cables and just leave them loose and hopefully that will be ok.

My only realistic option with one or two of the lighting ccts would be to run them in the same tube as the power which could be done but it would mean I would have to pass them through the back of the socket and I'm not sure I can do that, I would have to check the regs unless either of you know of hand.

Its hard when its your own place and you want things just how you want them and at the same time I want them to be right. For example with he cables under the floor, it may not conform with the regs but as long as I am living there it would never get damaged as I would know not to bang a nail in the floor there. Thats why it was good to post on here even if I sound rough just to get a bit of clarity.

Thanks both for your help.

 

[sparkwright]

Why don't you just forget about using singles; and use ordinary PVC PVC (twin) cable throughout?

Any useless metal conduit can be pulled out and replaced for larger plastic oval tube.

I assume you don't want the mess, but a house re-wire should not be compromised in this manner.

Singles in a house really isn't a good idea because of the installation problems they cause.

Unless you have an installation consisting of a complete circular conduit system, then singles are useless in domestic premises.

 

[lookpil]

Hi Sparkwright,

Its an ex council place and it was wired in singles before. The way it has been tubed it needs to be singles which allows you to go from a to b with ease but if I used T+E the tube isn't big enough and a lot of chases would be required especially as there is no ceiling or floor cavity. It just seemed the easiest option.

 

[flameport]

In concrete flats, there are very few options to do the job properly.

If the conduits are sound, and you want sockets, lights and switches in the exact same numbers and the exact same places, then it may be possible to pull new singles through the conduits.
More than likely is the old conduits are corrosion city, have sharp snags inside and are generally useless.

If additional sockets are required (99% of the time) then the options are either
1. Surface clip all of the T+E cables and new metal backboxes, then have the walls and ceilings boarded and plastered.
2. Use surface accessories and white plastic mini trunking (this is what most councils will do as it is quicker, almost no mess and much cheaper)

Chasing out ceilings and floors is no good, as these will most likely be structural components, and cutting into them will weaken the structure. In some places, the walls can't be chased either for the same reason.

 

[sparkwright]

Try and send some photographs.