Wiring in conduit - Capacity and splicing questions

[tommcdonna]

I'm planning to put some sockets and new 2 way lighting circuit in my garage, all in surface mounted conduit, I also need to run a earth bond from the CU to the gas pipe entry to the house, the gas is 6 m along the planned conduit run.

The new sockets will be a new circuit fed directly from the CU. The circuits will be checked and connected by a qualified Electrician.

I've been using the guides on TLC-Direct as a reference, but I've some questions:

1.) Is it permitted to splice in a conduit joining box (a round tee box)?

2.) Are the wago push splices (or the lever ones) acceptable?

3.) Due to the layout of the sockets, radial wiring makes most sense. There will be 2 double sockets and 2 singles, one socket will be in the hallway of the house, the other side of the garage wall. The TLC guide says:

32 A cartridge fuse to B888 or miniature circuit breaker feeding through 4 mm² live and 2.5 mm² protective conductors (or 2.5 mm² and 1.5 mm² if m.i. Cable) to supply a floor area no greater than 75m².

Garage is approximately 21m² and hallway is approx 8m², does that mean I could use 2.5mm² cores?

4.) Assuming the worst case regarding cable sizing (from a cable factor point of view), the first 6m of conduit (containing two 90 deg bends) would contain:

2 * 4mm² (L/N) for socket radial = 2 * 43 = Cable Factor 86
1 * 2.5mm² (E) for socket radial = 1 * 22 = Cable Factor 22
3 * 1.5mm² (L/N/E) for lights = 3 * 22 = Cable Factor 66
1 * 10mm² (E) for bonding = 1 * 105 - Cable Factor 105
Total cable factor 279

6m of 25mm conduit with 2 bends has a factor of 333, so I think this is OK, but would like to confirm it.

The conduit continues to a total length of 10m, but the final 4M will not contain the Earth bond so I think that's OK too.

5.) Does my bonding have to be 10mm² or can I use (for ease of drawing through conduit) 6mm² ?

 

[PrenticeBoyofDerry]

1.) Is it permitted to splice in a conduit joining box (a round tee box)?

You can introduce them to the conduit systems and providing joints are left safe and accessible for maintenance, inspection and testing

2.) Are the wago push splices (or the lever ones) acceptable?

for jointing either can be used but check suitability for conductor size and rating, but why would you want to make a joint?

3.) Due to the layout of the sockets, radial wiring makes most sense. There will be 2 double sockets and 2 singles, one socket will be in the hallway of the house, the other side of the garage wall. The TLC guide says:

32 A cartridge fuse to B888 or miniature circuit breaker feeding through 4 mm² live and 2.5 mm² protective conductors (or 2.5 mm² and 1.5 mm² if m.i. Cable) to supply a floor area no greater than 75m².

Garage is approximately 21m² and hallway is approx 8m², does that mean I could use 2.5mm² cores?

If on a radial no, unless mineral insulated, which then would not need containment, so I suggest you read the quote you have linked to!

4.) Assuming the worst case regarding cable sizing (from a cable factor point of view), the first 6m of conduit (containing two 90 deg bends) would contain:

2 * 4mm² (L/N) for socket radial = 2 * 43 = Cable Factor 86
1 * 2.5mm² (E) for socket radial = 1 * 22 = Cable Factor 22
3 * 1.5mm² (L/N/E) for lights = 3 * 22 = Cable Factor 66
1 * 10mm² (E) for bonding = 1 * 105 - Cable Factor 105
Total cable factor 279

6m of 25mm conduit with 2 bends has a factor of 333, so I think this is OK, but would like to confirm it.

The conduit continues to a total length of 10m, but the final 4M will not contain the Earth bond so I think that's OK too.

why two socket circuits.

5.) Does my bonding have to be 10mm² or can I use (for ease of drawing through conduit) 6mm² ?

What earthing arrangement do you have and what size are the tails of the incoming supply.
These are all question you should be asking the electrician you have planned to inspect, test and commision your work.
The new circuits will also require notification to building controls and a fee will be required, this must be applied for and approved prior to you starting the work, new sockets will also require 30mA RCD protection.

 

[tommcdonna]

Thanks PrenticeBoyofDerry, thanks for explaining what m.i meant, now the quote makes perfect sense and I know I must use 4mm².

Re the sockets, there's only the one circuit, I just split it in two for the calcs as I would wire it in singles, and the earth is a smaller gauge than the L and N.

Re the earth tails, I'm not sure, but basically do I need to make sure the bonding is the same (ideally) or smaller (I guess a 10mm earth bond from the gas meter to a 6mm incoming tail sounds bad to me).

Re the inspection / fee etc, the lighting circuit in the house is being rewired, new CU fitted, so all will be checked and notified as part of that, I'm just looking to do some work myself to save some money and more importantly, because I fancy the DIY job.

 

[PrenticeBoyofDerry]

Thanks PrenticeBoyofDerry, thanks for explaining what m.i meant, now the quote makes perfect sense and I know I must use 4mm².

You can use 2.5mm T&E but on 32A device would require to be ring final circuit or the device reduced to 20A.

Re the sockets, there's only the one circuit, I just split it in two for the calcs as I would wire it in singles, and the earth is a smaller gauge than the L and N.

The CPC would have to be within 1.66 of the live conductors.

Re the earth tails, I'm not sure, but basically do I need to make sure the bonding is the same (ideally) or smaller (I guess a 10mm earth bond from the gas meter to a 6mm incoming tail sounds bad to me).

Belt/Braces would be 10mm, but calculation would be required if you wished to reduce the CSA of this cable. If the main earth bonding was greater than the supply cables this would not be an issue with regards to safety.

Re the inspection / fee etc, the lighting circuit in the house is being rewired, new CU fitted, so all will be checked and notified as part of that, I'm just looking to do some work myself to save some money and more importantly, because I fancy the DIY job.

Not knocking you for DIYing, but I would strongly recommend finding an electrician now, that is willing to work with you on this, as some will not!
I would also suggest that you take a look in the Wiki electrical section, plenty of info in there and purchasing the on-site guide.