Davey said:

My colleague and I think this is poor practice and think an isolating gland should have been fitted or the armoured terminated into a plastic enclosure prior to entering the charger. the below regulations are what we believe are contravened. 

It's not unusual to see armoured cables enter through stuffing glands into an internal enclosure or similar, but you need to check the stuffing glands are OK for this.

However 'taping up' is not really insulation, and (with reference to Reg 411.3.1.1, 'Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively') what is there to protect electricians carrying out repair/testing from 'simultaneous contact' risk between the two earthing systems?

Cold shrink sleeving is best for this. If the armour (as cpc) is required to be accessible for testing, then something more than 'tape that can be removed' such as insulate the armour with cold-shrink sleeving and if something available for testing is needed, provision of an insulated tail to a suitable 4 mm shrouded test terminal (all insulated), and suitable labelling, would be a better approach ...

So, I would agree, this is a CDM risk that should have been evaluated and something more suitable put in place. This applies even for non-notifiable installations, and non-workplaces, as under CDM designers have a duty to ensure the installation is safe to maintain.

Hil GKenyon, 

 I fully agree it should have been heatshrink used rather than tape and this is where the regulation referring to workmanship comes into play, we are taught that we should follow manufacturers instructions and the regulations, yet poor workmanship still occurs! 

gkenyon said:

However 'taping up' is not really insulation, and (with reference to Reg 411.3.1.1, 'Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively') what is there to protect electricians carrying out repair/testing from 'simultaneous contact' risk between the two earthing systems?

That is a very interesting point.

Although I don't think there's any specification as to what insulation should be used. The plastic sheath of an SWA itself isn't rated as electrical insulation but it seems reasonable that we all use it to protect the amour of a cable as it enters a location using a different earthing system. 

Personally I'd rather terminate using an IP rated gland of the plastic variety into a plastic enclosure containing a splice for each live conductor and nothing else. That way there's accessibility for testing and not a lot of opportunity for a fault to either earthing system. But of course I don't have a sheet of paper from the gland manufacturer telling me about it's insulation rating.

Heat shrink certainly offers far more integrity than tape, but whatever solution is still freelancing to some degree or other. In my mind before you can specify insulation you need to be clear what the two thing are which are being insulated from one another, and the particular hazard here isn't an L-E which would operate ADS, but an E[TN-C-S] to E[TT] fault which could rest undetected for a long time.

Keir Stitt said:

That is a very interesting point.

Although I don't think there's any specification as to what insulation should be used. The plastic sheath of an SWA itself isn't rated as electrical insulation but it seems reasonable that we all use it to protect the amour of a cable as it enters a location using a different earthing system. 

Agreed, barrier/enclosure would be OK too ... but importantly, whatever method is employed to protect the maintenance electrician, it needs to be clear what's going on, because it's not like it's a cpc of the installation the electrician is working in/near at the time (effectively).

I

Keir Stitt said:

Heat shrink certainly offers far more integrity than tape, but whatever solution is still freelancing to some degree or other. In my mind before you can specify insulation you need to be clear what the two thing are which are being insulated from one another, and the particular hazard here isn't an L-E which would operate ADS, but an E[TN-C-S] to E[TT] fault which could rest undetected for a long time.

But it is an L-PE shock we're protecting against ... just that the PE in question we're looking at won't have the same local potential rise as the one the electrician is working on.

'gapping' cables between installations is a VERY common occurrence, particularly in the ICT external cabling world.

The only time it gets more involved, is where you have a cable from an HV 'hot site' going somewhere else ... this is more than an LV shock, but you'd need to think about far more than simple insulation in those circumstances. Again, BS 7671 has provisions for the designer to think about this from an overvoltage perspective.

What worries me about the "gapping" situation, is that it seems "going TT" is happening more and more, without thought to the potential consequences.

gkenyon said:

What worries me about the "gapping" situation, is that it seems "going TT" is happening more and more, without thought to the potential consequences.

Yes I was talking through an issue with an Engineer down in Australia the other day. They were perplexed that we have lots of TT. And they were right to be perplexed because there's rarely a compelling argument to TT where supplementary electrodes for the TN[-C]-S won't suffice.

Especially now we've got plenty of options for PEN fault protection if it really is a concern. Generally I'm of the school that having everything at the same potential via main and supplementary bonding which I can be sure of the integrity often by visual inspection trumps separation where to validate safety someone's got to prove the absence of conductivity and hope nothing happens between inspections.

Keir Stitt said:

And they were right to be perplexed because there's rarely a compelling argument to TT where supplementary electrodes for the TN[-C]-S won't suffice.

There are some caveats here ... and these are exemplified because of the increased reported accident stats with MEN (Australia/NZ version of PME) vs UK ... in Australia, but not New Zealand ...but in general, I agree

Keir Stitt said:

Especially now we've got plenty of options for PEN fault protection if it really is a concern.

Yes, new standard IET 01:2024 now available, which should help to address issues with unwanted operation etc.

Keir Stitt said:

Generally I'm of the school that having everything at the same potential via main and supplementary bonding which I can be sure of the integrity often by visual inspection trumps separation where to validate safety someone's got to prove the absence of conductivity and hope nothing happens between inspections.

This is, I agree, the best option if you have it ... the problem is, there are limits to the concept of 'equiopotential boding' unless you make sure it happens ... BUT even then, there's a difference making it happen at 50 Hz, vs GB frequencies ... and then when you look at the size of a site, distance amplifies resistance and inductance ...

... there is something that we call 'IGZ' ('ground window' in the US) that is a technique for dealing with that .. but believe me, it's all real. There are definitely very real limits to what we used to call the 'equipotential zone'.

The problem is that of course the earth is not flat, neither geographically, nor electrically,  So when I have my feet on the mud in one point and hold a wire, and my colleague holds the other end, and does the same, a current may well flow up one of us, along the wire and down the other, - there is a small DC for no better reason than the earth is a magnet, and we are rotating,  near built up areas there is a lot of AC from substations earthing arrangements and currents induced by nearby pylons, and everywhere there are radio frequencies  and impulsive currents from solar storms and lighting strikes around the world, and looking at the news, perhaps coming soon, though that has been said all my life, very large currents,  if there are any nuclear bombs being let off in the atmosphere...

The saving grace is that over distances tens of metres these voltages are sub-volt, except the ones near substation earth electrodes, and generally pose no issues, but on large rambling campus installations or even big farms they become worth considering properly. Then, knowing that all the voltage offsets are safely piling up in the gap across SWA armour in a box or an insulated joint in the gas main you can point to, gives you the ability to measure and to plan to limit currents in a way that accommodates the effect rather than being caught out by it.

If you don't,you risk introducing near field hazard zones around bits of metal that act as earthing of opportunity that do not have a keep out zone, that really should.

As things get bigger or large chunks of metal get planted, the argument for TT increases. Interestingly I was working alongside a Kiwi sparks at an international scout event this summer, and over the odd beer we discussed earthing among many other things, and how they do not see the neutral as a 'live conductor' in the way we do but more as an earthy thing. The no of rods we drove in (one per genset)  amused him somewhat.

Its not a simple topic, and all the methods exist for good reasons and have their place.

Mike

gkenyon said:

if something available for testing is needed, provision of an insulated tail to a suitable 4 mm shrouded test terminal (all insulated), and suitable labelling, would be a better approach ...

Hi Graham, do you mean an armour strand when you say tail?

I am thinking that the PVC bedding surrounds each strand so that none of the strands are touching the ones next to it.

So taking a continuity reading between the source and your test point would give a much higher reading than you would get from if the strands were made off into for example a brass gland and the reading was taken from there. Or if the likes of a jubilee clip were used, along with plastic glands.

OlympusMons said:

Hi Graham, do you mean an armour strand when you say tail?

Possibly, but this will be quite difficult to achieve. Somehow, the armour needs to be terminated in a suitable gland, and from this a copper conductor 'tail' can be brought out for testing.

My preferred method would be traditional SWA brass gland into 'gapping tube', with tail brought from the brass gland, and some suitable insulation or barrier(e.g. cold-shrink sleeving) over the gland.

Have you come across the SWA storm glands? rated IP68, Plus, there’s no need for a shroud, It works with various cable types, including armoured, non-armoured, SY, and CY braided cables. It’s non-corrosive and UV stabilised and zero-halogen.Each pack comes with EarthingNuts

Yes, but how do these  protect electricians from simultaneous contact? You can still get at the brass armour termination inside the enclosure.

Yes, but how do these  protect electricians from simultaneous contact? You can still get at the brass armour termination inside the enclosure.

Hi Graham. Would Providing a warning label on the enclosure to alert personnel of potential dangers. This warning label serves to remind electricians and other personnel that, despite the requirement of a tool for lid removal, there remains a risk of exposure to live parts, such as the brass armour termination inside the enclosure. This is similar to the expectations when dealing with terminations that do not meet IP2X standards, where direct contact with live parts is possible.

AMK said:

Hi Graham. Would Providing a warning label on the enclosure to alert personnel of potential dangers.

Yes, but the CDM Designer would be advised to follow the Principles of Prevention ... and Hierarchy of Controls.

Under the Principles of Prevention, 'combat risks at source' is number 3 on the list ... providing instruction is the very last item. It is reasonably practicable to combat this risk by providing inexpensive insulation (although a warning notice of the folly of its removal without due consideration might also be practicable).

Under the Hierarchy of Controls, we should consider, in the following order:

1. Elimination (physical separation)
2. Substitution (why have two earthing systems in the first place?)
3. Isolation (provide insulation or barriers as discussed)
4. Engineering controls (possibly not relevant here)
5. Use of PPE (and this would follow warning if you've not isolated the hazard, and would require warning signs).

It wasn’t that long ago, in 2017, when professional guidance stipulated that at remote buildings, the SWA cable should be terminated at the remote distribution board or consumer unit using a plastic stuffing gland, rather than the conventional metal SWA gland. The SWA armour should be trimmed back beneath the cable sheath within the plastic gland to ensure it remains inaccessible. However, current discussions suggest that this approach may no longer be considered sufficient ?

AMK said:

The SWA armour should be trimmed back beneath the cable sheath within the plastic gland to ensure it remains inaccessible.

Given that a tug on the cable (unless there's a cable restraint) can remove it, and we know sheaths and insulation do move slightly ... It does seem like it may be OK, but the devil is in the detail.

The issue regarding pulling the cable with a stuffing gland is why in rail and airport infrastructure wiring, we used to use use plastic gland adaptor tubes, and sleeving). This is not new ... I'm going back to the 1990s.

AMK said:

However, current discussions suggest that this approach may no longer be considered sufficient ?

Well, the information in this thread is out there now, so that approach is perhaps not 'state of the art'