Meter tails no rcd in stud wall

[newfutile]

During an EICR meter tails were found entering the cavity and coming down a stud wall to a consumer unit about 5 meters (direct distance) away.
they do have an isolator but no rcd or other protection .

as cables buried in a wall have to have (RCD) Residual Current Device at 30mA and generally tails over 3 meters are not permitted by DNO ,how can this comply?

 

[DarrenRB]

No.

Thanks for the reply - ‘NO’

How would you get around discrimination between a 30mA protecting buried tails & RCBO’s tripping?

I can’t see a workaround other than mechanical protection or a 16mm SWA with in-built mechanical protection

 

[Pretty Mouth]

Thanks for the reply - ‘NO’

How would you get around discrimination between a 30mA protecting buried tails & RCBO’s tripping?

I can’t see a workaround other than mechanical protection or a 16mm SWA with in-built mechanical protection

That's pretty much the size of it. 522.6.204 (i) to (iv) are your options, earthed SWA/conduit/trunking/MICC etc, or very strong mechanical protection.

 

[DarrenRB]

That's pretty much the size of it. 522.6.204 (i) to (iv) are your options, earthed SWA/conduit/trunking/MICC etc, or very strong mechanical protection.

Yep….

That’s where I am…

BUT

I’m going to fit a 100mA to buried meter tails as remedial EICR work.

OK, it’s not to regs …. Shoot me.

A 30mA may discriminate - rendering the fancy RCBO board useless.

If Joe bloggs were to ---- a meter tail I’m sure they’d welcome any form of RCD opposed to the 60A DNO fuse tingle?

Common sense to me - I’ll say that in court should the need arise

Explain to customer & admit to deviation on certificate.

Case for the defence rested m’Lord…

 

[brianmoooore]

It will only discriminate if the earth leakage, including 'normal' leakage from all the circuits, is below the tripping threshold of the 100mA RCD, typically 60 - 70mA.
If the earth leakage is above this, then both the relevant 30mA RCBO and the 100mA supply RCD will trip.

 

[Pretty Mouth]

Yep….

That’s where I am…

BUT

I’m going to fit a 100mA to buried meter tails as remedial EICR work.

OK, it’s not to regs …. Shoot me.

A 30mA may discriminate - rendering the fancy RCBO board useless.

If Joe bloggs were to ---- a meter tail I’m sure they’d welcome any form of RCD opposed to the 60A DNO fuse tingle?

Common sense to me - I’ll say that in court should the need arise

Explain to customer & admit to deviation on certificate.

Case for the defence rested m’Lord…

BPG4 is giving this situation a C3, so wouldn't necessarily need remedying:

C3 - Absence of additional protection by RCD for cables installed at a depth of less than 50 mm from a surface of a wall or
partition where the cables do not incorporate an earthed metallic covering, are not enclosed in earthed metalwork, or are not mechanically protected against penetration by nails and the like.

 

[DarrenRB]

It will only discriminate if the earth leakage, including 'normal' leakage from all the circuits, is below the tripping threshold of the 100mA RCD, typically 60 - 70mA.
If the earth leakage is above this, then both the relevant 30mA RCBO and the 100mA supply RCD will trip.

Yep… understood!

In my head ….

If the downstream RCD has a higher trip fault current than the device connect to the final circuit …

In my theory the RCBO should arrest the fault & disconnect before reaching the dizzy heights of 60-70 mA.?

Ah well …, just a thought!

I know what I mean

Appreciate you taking the time to reply!

 

[DarrenRB]

BPG4 is giving this situation a C3, so wouldn't necessarily need remedying:

C3 - Absence of additional protection by RCD for cables installed at a depth of less than 50 mm from a surface of a wall or
partition where the cables do not incorporate an earthed metallic covering, are not enclosed in earthed metalwork, or are not mechanically protected against penetration by nails and the like.

Yeah…. I just don’t think it’s safe for meter tails at potentially 100A

Popping a nail through a tail with no fault protection gives me the ‘heeby jeebys’

Is that a word?

Agree though… I’d code C3 for no RCD on lighting cables - usually do tbh.

 

[westward10]

A fault of any magnitude would only occur if you have a line to neutral or line to earth (TN systems) fault. A line to neutral fault is possible and an RCD would not give protection from it. Should a nail penetrate line to an effective earth such as cable armour or steel conduit then again sufficient fault current would flow and in this case additional RCD protection is not required. Additional RCD protection gives protection from a negligible fault such as the nail becoming live and a person touching it and coming into contact with something which is earthed.