16mm T&E

[7029 dave]

I had a job last week to provide 6 meter connections . New builds and noticed in the meter box, Electricians had run in 16mm t&e from CU to external box with 80amp switch fuse.
Thoughts please.

 

[Toneyz]

What was the installation methods for the cable to c.u ? was it run down in the cavity.

 

[7029 dave]

What was the installation methods for the cable to c.u ? was it run down in the cavity.

Yes, stud work cavity etc.

 

[Richard Burns]

OK for CCC on line and neutral, if a TNCS supply then the earthing conductor is undersized, if TNS then probably OK.
If buried in the wall <50mm then needs 30mA RCD protection, though most DNOs do not bother protecting tails from cut out to meter when buried in the wall!
How are the live conductors terminated in the switch fuse as it is normally hard to get a fully enclosed live conductors from a twin and earth cable without leaving exposed insulation.

 

[Octopus]

Did they run a separate GY too or are they relying on the existing earth?

Is the T&E more than 50mm from the surface?

 

[7029 dave]

OK for CCC on line and neutral, if a TNCS supply then the earthing conductor is undersized, if TNS then probably OK.
If buried in the wall <50mm then needs 30mA RCD protection, though most DNOs do not bother protecting tails from cut out to meter when buried in the wall!
How are the live conductors terminated in the switch fuse as it is normally hard to get a fully enclosed live conductors from a twin and earth cable without leaving exposed insulation.

The earthing is TNCS , did notice a 10mm earth conductor with the t&e, still on first fix so nothing connected , I can only assume they have run it together. Forgot to say, on one of the other plots not boarded up yet, the run from the meter box to CU position was less than 3 meters. IMO 25mm tails should have been run.

 

[7029 dave]

Did they run a separate GY too or are they relying on the existing earth?

Is the T&E more than 50mm from the surface?

yes

 

[Midwest]

They must of had some 6242y left over from another job, 'cos 6181y is cheaper per metre

 

[Toneyz]

If clipped direct it justs complys I prefer to fuse at 60A as Richard has just posted if within wall 50mm rcd protection but this brings another problem of a fault the whole house tripping out in the m/box a small switch fuse is usualy used ,if down the cavity you have issues with derating for insulation,(also watch out for polestyrine ball insulation)protection of cable sharp edges.In my previouse job before metal c.u came in to the regs we ran 3 core 16mm swa in earthing swa one end in metal box into small switch fuse. If the builder would not install other meter box.we also ran the swa internally in line with socket so in a zone.

 

[7029 dave]

They must of had some 6242y left over from another job, 'cos 6181y is cheaper per metre

LOL, Yeah must be tight on price.

 

[Midwest]

The 10mm earthing conductor, they've obviously calculated it rather than using Table 54.7.

 

[bigspark17]

If any extraneous conductive parts exist then these could be bonded back to MET with 10mm being tncs Rather than the CU. how do you know the installer wasnt going to use a 63A fuse in there if it was at 1st fix stage? If the 16mm is conected to a sw fuse why would you not then treat it as a circuit and then do an adiabatic to work out the cpc.
He who sticks his nose in a wasps nest will get more than a nostrill full of honey comes to mind here!!

 

[7029 dave]

If any extraneous conductive parts exist then these could be bonded back to MET with 10mm being tncs Rather than the CU. how do you know the installer wasnt going to use a 63A fuse in there if it was at 1st fix stage? If the 16mm is conected to a sw fuse why would you not then treat it as a circuit and then do an adiabatic to work out the cpc.
He who sticks his nose in a wasps nest will get more than a nostrill full of honey comes to mind here!!

Don't really get you, I was not being nosy, just interested .I could not careless if at the meter box, it was presented with bell wire. Use self connect meters it's the Sparky that will be connecting up his installation. The switch fuse was screwed to the back board all on it's own and it was 80amp.

 

[Toneyz]

The MET would be in the consumer unit main 16mm earth being made up of the 10mm earth and 6mm in T&E.

 

[Midwest]

The MET would be in the consumer unit main 16mm earth being made up of the 10mm earth and 6mm in T&E.

Didn't think that was allowed, i.e. if one becomes disconnected the EC might fail under fault conditions?

PS and fault current may not be evenly distributed between two separate cables

 

[Toneyz]

Didn't think that was allowed, i.e. if one becomes disconnected the EC might fail under fault conditions?

PS and fault current may not be evenly distributed between two separate cables

New houses have sub-dist circuits wired like this for years.

 

[Dave OCD]

OK for CCC on line and neutral, if a TNCS supply then the earthing conductor is undersized, if TNS then probably OK.
If buried in the wall <50mm then needs 30mA RCD protection, though most DNOs do not bother protecting tails from cut out to meter when buried in the wall!
How are the live conductors terminated in the switch fuse as it is normally hard to get a fully enclosed live conductors from a twin and earth cable without leaving exposed insulation.

You'd use the small tapered cover that fits on the outgoing side of the switch fuse Richard. [Sometimes known as a transition cover ?].

 

[Leesparkykent]

Generally with 16mm t&e a separate 10mm is run for bonding and the CPC of the 16mm T&E is just that..... A circuit protective conductor.

I used a bit of 16mm T&E as a distribution circuit on a new build the other day due to aesthetics. I've had a separate meter box installed to house the switch fuse next to the actual meter box. I've run the cable up the wall internally through joists and down to the consumer unit. I've used a metal capping that the manufacturer states provides adequate protection from nails, screws and the likes of.

Reason I chose to use 16mm T&E over 16mm SWA is the consumer unit is installed on show in a utility room and an SWA glanded in top or bottom would look rubbish IMO.

 

[LankyWill]

cant see a issue with it, we used to do this all the time. After a communal job we would have some left and would wire 2 bed's with it (supply). As long as there is a 10mm with it as well and there is some form of mechanical protection in place it seems sensible. Keep your nose out

 

[LankyWill]

here the cover in the picture

View attachment 35368