Earth Banjo Securing Practices

Probably acceptable, in my view. Self tapping screws, by definition, cut their own thread into an undersized hole drilled into the metal. This should ensure a reliable earth connection, perhaps more so than a nut and bolt onto a painted surface.

However I do not much like the particular installation shown, the screws used are too long, and therefore leave an appreciable length protruding into the enclosure, to damage  cable insulation or the hands of a later installer. Use shorter screws, or cut them short with small bolt cutters. 

IMHO, that is not good workmanship. I agree with broadgage that the screws should not protrude so much: one can get shorter ones, and blunter ones.

My problem with self-tappers is that they are never as secure as a properly tightened nut and bolt.

Hi broadgage. You make a valid point about self-tapping screws ensuring a reliable earth connection, especially compared to nut-and-bolt setups on painted surfaces. I agree that the thread-cutting action likely provides a solid electrical bond.

Hi Chris. This is mainly the feedback I’m getting on this. A properly tightened nut and bolt can indeed provide a more robust and reliable connection. 

That to me shown in the photogrpah is just very very poor workmanship and poor practice.

Just another example of the handskills of a tradesperson going downhill!! Why? to save a few minutes.

Look at the potential hazard left behind for future persons working in that consumer unit, and yes, we shouldnt be working on or enar any energised part, but I can see the skin getting ripped off somebody's knuckles working on that consumer unit in the future.

From a earth continuity point of view, yes, the thread of the screw will be making good contact with the inside metal edge of the wall of the consumer unit, only other contact is the underside of the screw head on the earth tag itself.

Now compare that to a brass nut and bolt and washer arrangement. the brass head of the bolt gives equal contact to earth tag as the self tapper, but with scraping some paint, a small serrated washer, a flat washer and a brass nut tightened down then to me far better contact with the consumer unit metal itself. Also more importantly if the length of that brass bolt is appropriate very little in the way of the bolt will protrude thru the nut leaving something to be injured on.   

I wouldnt be happy with that, difficult to give it a coding though as far as BS7671 unless you want to try poor workmanship, but from leaving behind a hazard for others then yes, I wouldnt accept that on one of my projects. 

GTB

Hi GTB. Thank you for your detailed and thoughtful response – I appreciate the depth of your analysis. You’ve raised several critical points, particularly regarding workmanship, safety, and the potential hazards left behind for future installers.

I agree on your stance on not accepting such work on your projects is entirely reasonable, and it sets a high standard for safety and quality.

Do you think there’s room for industry-wide guidelines or best practices to address these kinds of issues more explicitly, or is it more about individual accountability and training to ensure better workmanship

- Andrew

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

To my mind Banjos have had their day - much more workmanlike solutions (e.g. earthing nuts) are now available which design out almost all these potential problems.

   - Andy.