Conduit earthing

Presuming  there is not a circuit protective conductor running through the conduit to provide an earth connection to equipment and appliances connected to the circuit it is undoubtedly a C2.


If there is a circuit protective conductor running through the conduit I would still be inclined to go for a C2 as a insulation fault within the conduit, I know that’s unlikely but possible, would liven the conduit up without a fuse or MCB operating, it might take a RCD out but without a reasonable earth connection it’s not guaranteed.


So I would go C2 with or without a CPC conductor within the conduit.


Andy Betteridge 

No there is no cpc. this building was built in 1983.

There are 3 single phase Db`s in the building fed from a 3 phase supply in the plant room.

These 3 DB`s then feed socket & lighting circuits within the building.

Definitely C2.


I know we still have the conversations about domestic lighting circuits from the 1960’s wired without a CPC in PVC cables being sort of okay if protected by a 30 mA RCD and there not being any  class 1 light fittings or metal light switches that require an earth, but those arguments cannot be used to give this installation a C3 saying it’s okay to carry on using it as it is.


Andy Betteridge.

It looks like I may have read the question and made an assumption that there is not a satisfactory earthing arrangement throughout the installation, is there satisfactory earth loop readings throughout the installation with the conduit providing a good earth connection?


 Andy Betteridge

Mapj1 your first statement is correct the whole system is metal conduit.

The trouble is some of it is buried in concrete which is inaccessible.

Also work has been carried out to some shower area and been rewire in LSF cabling.

The reading in the building are very low but will they be before the next test in 5 Years.

That is more of a question as to how long the period should be between periodic inspection and testing, are you satisfied that a five year period is okay?


Andy Betteridge

I have coded it a C2 but have company managers asking why.

I have given them the reasons but was just checking with the knowledgeable members of this forum that I was correct.

Thanks for all the help.

I agree with Mike - steel conduit is entirely acceptable for use as a c.p.c. - BS 7671 specifically says so in reg 543.2.1 (vi) - that fact that it's concealed shouldn't of itself be more of a worry than the c.p.c. in a concealed length of T&E. If it's lasted that last 36 years without apparent deterioration, it doesn't seem likely it's going to fail catastrophically in the next 5.

  - Andy.

I agree with Mike and AJ but:


In your case I would be looking at the following to give me confidence in any decision on code and length between inspections, not having seen the installation some of the questions may be irrelevant:

1 -Is the conduit in the concrete galv or painted?

2 - Are the visible joints in the conduit well made and painted with zinc paint or other protective coating?

3 - Is the concrete encasing the conduit dry or damp?

4 - Are the R2 values for all parts of the conduit all good and reasonable for the lengths involved?

5- Are the conduit terminations at the origin well made and not subject to corrosion?

6 - In the shower areas how is the LSF cable earths attached to the conduit?