Bonding

It's a rural supply with TT earth, what is wrong with it? The contents of the meter cabinet are an awful lot neater than most installations pictured in here. Any sign of woodworm in the pole?

round here, (rural hants) that would be a typical TT domestic take off. The lower line has the double line taps and is a PME ready neutral, or at least the double crimps are present, there may be very good reasons it cannot be PME. 

If it ever fails it will be replaced by ABC.

Not sure what is wrong with it sparkinghip - looks good to me.

Mike.

I suspect the overheads may be TNS.

If it was TN-S I'd expect 5 wires (if 3-phase) rather than 4. Single phase would be 3-wire of course. I suppose it could be split phase (2 phase, NE and PE) to make up 4 wires, but I've never seen that used for supplies to multiple premises (just individual farms/camp sites).

   - Andy.

Look at the picture of the overhead cables, the second wire up is thinner and doesn’t appear to have any direct connections to it to the concentric cables. bu there’s a supply taken off in singles to the bottom left and it has two insulated conductors and a bare cable off the second up, that’s the one that looks like TNS.

mapj1: 
 

round here, (rural hants) that would be a typical TT domestic take off. The lower line has the double line taps and is a PME ready neutral, or at least the double crimps are present, there may be very good reasons it cannot be PME. 

 

If it ever fails it will be replaced by ABC.

Not sure what is wrong with it sparkinghip - looks good to me.

Mike.

 

It appears that the neutral connection is double tapped, but I would not want a TN-C-S supply off it and I would prefer the TT to using the overhead TNS if that’s what it is.

There could even be a switched live for street lighting, maybe unlikely but possible.

Back to the original post.

You describe a fourteen way consumer unit with two 30 mA RCDs, this should have a higher rated upfront RCD to protect internal wiring and the busbars, if the consumer unit has a metal enclosure it definitely should have an upfront RCD.

Look at the picture of the overhead cables, the second wire up is thinner and doesn’t appear to have any direct connections to it to the concentric cables. bu there’s a supply taken off in singles to the bottom left and it has two insulated conductors and a bare cable off the second up, that’s the one that looks like TNS.

Yup saw that - I couldn't make out how the top & middle were connected, but the bottom wire looked to be connected to top of the main distribution - so my guess was that it's feeding a 2-phase customer (common enough, one phase for normal, the other for night storage heaters) - but unusually with N in the middle (possibly the 2nd phase got added at the bottom at a later date).

As the main line (left & right) appears to be just 4-wires, it's can't be 3-phase TN-S no matter how individual customers are connected.

   - Andy.

Sparkingchip: 
 

Back to the original post.

You describe a fourteen way consumer unit with two 30 mA RCDs, this should have a higher rated upfront RCD to protect internal wiring and the busbars, if the consumer unit has a metal enclosure it definitely should have an upfront RCD.

In an insulated enclosure outside the metal consumer unit?

Z.

In an insulated enclosure outside the metal consumer unit?

Or could be the incomer in the steel CU provided the incoming connections were protected by double or reinforced insulation or equivalent (An insulating stuffing gland through the steel and the sheath left on the tails right up to the RCD might suffice).

   - Andy.