Earth Banjo Securing Practices

These are not ordinary self-tapping screws, but self-drilling screws. These leave unnecessary cut hazards for initial construction work associated with this part of the installation after the screws are installed, similarly no consideration of safety for future maintenance work - demonstrating lack of risk assessment (or supervision/management under H&S legislation, including CDM Regs).

This arrangement is almost certainly unsuitable to bean effective electrical connection during temperature changes etc - Regulation Group 526.

In the past it was commonly accepted that a single self-tapping screw usually isn't effecting for earthing and bonding connections. Whilst some product standards might permit self-tapping screws to secure protective conductors in certain circumstances, I certainly wouldn't recommend it as an installation practice. I understand it's specifically prohibited to use self-tapping screws for making ground connections in NEC (wiring rules in USA).

Now to debate of whether the banjo should be on the inside or the outside of the enclosure 

Hi Graham, I recall that many years ago, our NICEIC field engineer at the time explained that the banjo should be placed on the inside of the enclosure if it’s plastic, as it is considered an exposed conductive part. What are your thoughts on this?

Additionally, regarding the self-drilling screws used in the installation, what action would you take? Would you recommend having them replaced to address the concerns about cut hazards and the suitability of the metal thickness for maintaining an effective electrical connection?

Graham,

I agree with your comments, and forgot about NEC criteria. Looking at picture closely again there looks as if at least tow if not all of the cables have a seperate integral cable conductor sleeved in green/yellow sleeing so a seperate CPC. 

Personally dont like earth tags on the inside as depending on how things are done can equally be as messy and have earthed parts now closer to live parts. Use of serrated washers and a lock nut with earthing grub screw could actually be better and save the earth tag full stop.

I really do worry where this has been carried out once how many times has it already been done or will be done, or others "Learn" from it and then think its appropriate practice.

GTB

AMK said:

Hi Graham, I recall that many years ago, our NICEIC field engineer at the time explained that the banjo should be placed on the inside of the enclosure if it’s plastic, as it is considered an exposed conductive part. What are your thoughts on this?

If it's earthed, yes, it's an exposed-conductive-part, but BS 7671 does not require exposed-conductive-parts to be insulated except where protection against electric shock is somehow ineffective, e.g. simultaneously accessible exposed-conductive-parts connected to different earthing systems (Reg 411.3.1.1).

I would agree, though, that sometimes inside the enclosure is absolutely necessary ... for example corrosive environment such as places by the sea, swimming pools, places subject to chemical washing such as food processing plant, etc.

AMK said:

Additionally, regarding the self-drilling screws used in the installation, what action would you take? Would you recommend having them replaced to address the concerns about cut hazards and the suitability of the metal thickness for maintaining an effective electrical connection?

Absolutely, but as this is not immediately dangerous, it would be up to the dutyholder. It's not costly to correct, so I think 'not reasonably practicable' defence wouldn't hold for any of these hazards, including lack of electrical continuity possible.

On this note, I would also point out that there is perhaps a reason why self-tapping fixings may be OK in appliances: where:

• There are multiple screws on a panel, so it's very unlikely continuity will be lost; and/or
• The connections are checked in type tests according to the standard, after ageing, strength and durability, and temperature rise tests.

The above tests are not really possible to carry out on an installation, which is why a more reliable fastening solution is necessary.

AMK said:

Hi Graham, I recall that many years ago, our NICEIC field engineer at the time explained that the banjo should be placed on the inside of the enclosure if it’s plastic, as it is considered an exposed conductive part. What are your thoughts on this?

If it's earthed, yes, it's an exposed-conductive-part, but BS 7671 does not require exposed-conductive-parts to be insulated except where protection against electric shock is somehow ineffective, e.g. simultaneously accessible exposed-conductive-parts connected to different earthing systems (Reg 411.3.1.1).

I would agree, though, that sometimes inside the enclosure is absolutely necessary ... for example corrosive environment such as places by the sea, swimming pools, places subject to chemical washing such as food processing plant, etc.

AMK said:

Additionally, regarding the self-drilling screws used in the installation, what action would you take? Would you recommend having them replaced to address the concerns about cut hazards and the suitability of the metal thickness for maintaining an effective electrical connection?

Absolutely, but as this is not immediately dangerous, it would be up to the dutyholder. It's not costly to correct, so I think 'not reasonably practicable' defence wouldn't hold for any of these hazards, including lack of electrical continuity possible.

On this note, I would also point out that there is perhaps a reason why self-tapping fixings may be OK in appliances: where:

• There are multiple screws on a panel, so it's very unlikely continuity will be lost; and/or
• The connections are checked in type tests according to the standard, after ageing, strength and durability, and temperature rise tests.

The above tests are not really possible to carry out on an installation, which is why a more reliable fastening solution is necessary.