Old MICC cable underground to garage, extraneous conductive parts

[catdog1121]

Ok so the scenario is there is an old MICC or pyro 1.5mm 2 core cable supplying the garage run underground on a 16A circuit breaker that is RCD protected.

In the garage there is a water pipe fed from the house, at the house it is bonded using 10mm, at the garage bonded with 6mm. I think the water pipe from the house bonding to the garage has continuity but need to double check this.

In an ideal world I would replace the MICC with 10mm 3 core SWA and then up the bonding to 10mm in the garage just to be safe and put the RCD on the garage side only. However the consumer unit is in the middle of the house and the home owner really does not want to run a new supply.

I dont really want to remove the RCD protection from the MICC cable as its not clear where it is buried and at what depth etc.


My thinking was if I remove the 6mm bonding at the garage and check continuity from the 10mm bond in the house to the water pipe in the garage, if I get a low reading then its effectively bonded with 10mm anyway so not an issue...

If it is not then as it has been in place for a while with no sign of damage it could stay with 6mm or potentially I could keep the micc on rcd protection, then change the earthing arrangement to TT system in the garage and put 30ma RCD in the garage..

What are your guys thoughts?

 

[WallaceP]

Get a plumber in to fit a section of plastic pipe where the water supply comes into the garage and walk away if it were me

 

[Strima]

As it's existing I wouldn't be massively overconcerned about the CSA of the bonding cable in the garage, as long as there's good continuity. As @WallaceP has said, a section of plastic pipe would be an option to get around this if you really need to.

 

[telectrix]

does MICC cable require RCD protection as it is protected by an earthed metal sheath?

 

[westward10]

What is the earthing system. The csa for the sheath of a 2L1.5 MI is approximately 6.3.

 

[catdog1121]

What is the earthing system. The csa for the sheath of a 2L1.5 MI is approximately 6.3.

Earthing is TNS...

 

[catdog1121]

does MICC cable require RCD protection as it is protected by an earthed metal sheath?

Good question, but as I have no idea how deep its been buried and also its only protected by a copper sheath which is not going to be anywhere near as strong as SWA (I would guess).

 

[catdog1121]

Get a plumber in to fit a section of plastic pipe where the water supply comes into the garage and walk away if it were me

Thats actually a really good shout... Although the pipe comes up from the floor, straight up to an outdoor tap in the garage so there is often water on the floor that would be going up to the pipe where it comes into the garage so not sure if that would make a difference

 

[westward10]

Earthing is TNS...

You would get away with the existing 6.0 as the sheath will support it.

 

[pc1966]

According to this the MICC sheath is just over 7mm^2 CSA if 1.5mm:

https://www.miccltd.com/cms-files/MICC_Light_Duty_2_Core.pdf

Also MICC can safely run far hotter than PVC (though surrounding may not like it!) so even for the 10mm bond in TN-C-S I would not worry too much. As TN-S no issue!