New ring main on concrete ground floor

[benjiman]

Hi chaps,

I've got a house with solid concrete floors, on top of which there are standard width wooden planks screwed down into the concrete, on top of which is a carpet.

All the sockets on the ground floor are currently spurs. I'd like to update it and get them all on a downstairs ring main.

One of the ways I've been told is that the cabling needs to come from the top floor to the required height for the sockets and then chase horizontally across to the next one. Then once at the last socket to take it back up again to complete the ring.

Another option I'm considering is one I would like advice on from the pro's. I'm thinking to remove the wooden planks and chase out the concrete, put cable in conduit, backfill with weak mixture of sand cement, then replace floorboards.

Is this a part P acceptable solution or is method 1 the preferred route to take?

Cheers.

 

[ban-all-sheds]

All the sockets on the ground floor are currently spurs. I'd like to update it and get them all on a downstairs ring main.

What do you plan to do about Building Regulations approval?

And testing?

One of the ways I've been told is that the cabling needs to come from the top floor to the required height for the sockets and then chase horizontally across to the next one. Then once at the last socket to take it back up again to complete the ring.

I take it you're aware of the limited depth allowed for horizontal chases? You''ll find the info in your Electrician's Guide To The Building Regulations.

Another option I'm considering is one I would like advice on from the pro's. I'm thinking to remove the wooden planks and chase out the concrete, put cable in conduit, backfill with weak mixture of sand cement, then replace floorboards.

Earthed steel conduit?

Or will your chases be 50mm deep?

 

[sparkwright]

Don't bother wrecking the floor, you'll still need to damage the walls. The usual way is to run all the cables under the upstairs floor, and drop down vertically to each socket.

Horizontal chases are ok, but vertical chases are best. This is because adding an extra socket later could be difficult as a cable may be in the way. Same if a doorway is later added.

However, there's no reason you can't have horizontal chases if they aren't too deep. You must also observe safe zones, which in quick terms means the cable must be dead in line with the accessory.

Use oval conduit in the chases. This may assist you in any future alterations or repairs. It will also protect the cable from the plasterer's trowel. True.

 

[sparkybird]

Another vote for sparkwright's method - that's how I'd do it

SB

 

[benjiman]

Cheers chaps,

Will use the drop from the top for each one rather than wreck the floor.

 

[ricicle]

Why do you feel the need to upgrade ?
Are the sockets wired as spurs off of spurs ?
Is the cabling not pvc ?
Are you suffering frequent operation of the protective device because of overloads ?

 

[ericmark]

The sparkwrite method is the norm. However one of the problems is with the 1/3 rule on drilling beams one can easy exceed the maximum lenght.

It is considered 106 meters of 2.5 mm cable is the maximum allowed. Seems a lot I know but once completed you will of course inspect and test and the last thing you want is to then find it does not comply and you need to alter things.

I know with some houses a side to side split rather than up/down split was adopted in order to ensure the loop impedances were not exceeded.

I personally don't like the ring and prefer the radial method purely as all too often the ring is broken.

The ring was designed during the second world war to save on the copper used to wire houses. I am not sure that now we have the 1/3 rule that still is true. Clearly the ring reduces the number of MCB/RCBO used in the consumer unit but not sure if that's good or bad.

Consumer units with RCBO fitted have far less problems than those using twin RCD system and the more RCBO that are fitted the less likely they are to trip and if they do trip the less fails as a result.

There is of course a balance and should my RCD trip my emergency lights come on and I know they have tripped. So I can easy reset. The fridge and freezer is the problem as where there are many RCBO's fitted the one feeding the fridge or freezer can trip without you realising.

So I would still consider kitchen rings or kitchen parallel cables where a master isolator grid switch is used. But rest of the house radials are better one for each room.

Cost is of course a consideration and likely a ring works out cheaper.

Clearly from what you say you are involving the LABC and getting the completion certificate so I would assume you have access to all the meters required to test. Remember the LABC rules changed and if they bring in an outside contractor to inspect and test your work they can charge for that as well as the charge made up front. I would say you need to allow at least £300 for LABC charges unless you can test and inspect.

Also remember the LABC don't have to issue an installation certificate only the completion certificate and this may cause problems when you come to sell the house. There is of course nothing to stop you doing your own testing and writing out your own installation certificate which the blanks are a free down load. However even with a C&G2391 we have had problems getting the LABC to accept our signatures.

I am sure you now have a lot to think about. There historically was a rule of thumb method used to decide if a single ring could be used based on the floor area. However one can come unstuck with that due to 1/3 rule.