RCD omission risk assessment

[loz2754]

The format was dictated by city and guilds so I can't really comment beyond that. It justifies omission with appropriate reg numbers, outside of the regs I'm not entirely sure what you'd want on it.

The point of it is we're justifying omission using the regs to present the argument.

All I see is a somewhat useful list of where RCDs may or may not be required by BS7671, not a justification where it may be desired or necessary to deliberately omit an RCD in a situation where it would normally be required.

 

[Lister1987]

All I see is a somewhat useful list of where RCDs may or may not be required by BS7671, not a justification where it may be desired or necessary to deliberately omit an RCD in a situation where it would normally be required.

By all means take it up with C&G, I merely offered it as an example, you're welcome to expand on it or devise one to share.

 

[Elgreko]

Thank you so much for your help,

 

[loz2754]

Thank you so much for your help,

You're welcome

 

[Teddy Lop]

Interesting and useful but not really a risk assessment for justifying omission of RCDs for additional protection.
A risk assessment should identify the hazards, who or what is at risk and from what? And then should identify what has been put in place to minimise the danger presented by such hazards.

Is there a published document listing the reasons that socket outlets require RCDs?

And if not, why not? How can some regular bozo be expected to carry out a risk assessment permitting him (or her!) to contravene the laws set by a panel of experts without knowing their reasoning?

Perhaps 411.3.3 is insufficient without such qualifying information.

I'm on an EICR for a bakery with a dozen+ 32a 3ph sockets feeding large fixed floor standing machines of various functions and ages. The place runs 20+ hours a day and the 32a seems to be a standard presumably so they can be swapped out promptly. New DB reauired. I struggle to see what dangers are introduced by the bit of wire from each machine terminating in a plug+socket instead of fixed connections. In fact one could observe the enhanced safety of removing the plug as a way of preventing usage of a faulty machine.

 

[timhoward]

I struggle to see what dangers are introduced by the bit of wire from each machine terminating in a plug+socket instead of fixed connections.

Tempting as it is, it never really works to think in terms of the regulations themselves when considering the risks.
Changing all of the sockets and plugs to 63 amp would also comply, as discussed in a similar thread of mine. But neither fixed wiring or changing the sockets affects the safety of the end user if everything is installed correctly, the equipment is in perfect order, and no one does anything silly.

Off the top of my head, the obvious risks are:
-damaged flex impairing electrical safety, especially if the ovens are moved around
-damaged appliance impairing electrical safety
-unsafe equipment being unexpectedly connected to the sockets
-faulty elements causing increasingly significant earth leakage to Class I items increasing the risk of electric shock to operators.

The control measures could be as simple as a sign by each socket saying they aren't to be used for anything else, (or padlocking them), a more regular schedule of In Service (PAT) testing, and a stipulation that if the ovens are moved, they are tested.

You might decide that the above control measures sufficiently mitigate the risks and be willing to put your name to them.
I'm not saying they necessarily do, but that's the thinking process I use for risk assessments. The regulations themselves aren't too relevant!

 

[davesparks]

How can some regular bozo be expected to carry out a risk assessment permitting him (or her!) to contravene the laws set by a panel of experts without knowing their reasoning?

Regular bozos are not expected to carry out such risk assessments, qualified people with knowledge are expected to carry them out.
The risk assessment isn't a permit to contravene regulations, it is a means to assess whether or not RCD protection can be omitted without affecting safety.

I'm on an EICR for a bakery with a dozen+ 32a 3ph sockets feeding large fixed floor standing machines of various functions and ages. The place runs 20+ hours a day and the 32a seems to be a standard presumably so they can be swapped out promptly. New DB reauired.

Why is a new DB required? Surely this is just a recommendation at worst for that scenario?

 

[pc1966]

I'm on an EICR for a bakery with a dozen+ 32a 3ph sockets feeding large fixed floor standing machines of various functions and ages. The place runs 20+ hours a day and the 32a seems to be a standard presumably so they can be swapped out promptly. New DB reauired.

In this sort of scenario I really doubt the lack of RCD protection for those sockets represents anything more than a C3 code, so no need to replace the DB.

If a new TPN DB is needed for other reasons, you might find it is cheaper to change the 3P sockets for ones with the RCD built in than to install many 3P RCBO, that way it is also simpler for the operator to reset any RCD that does trip.

The risk assessment these days applies only to sockets where they are under some form of electrically skilled control, I guess to avoid idiots plugging in an extension cable to outdoor equipment, etc. However, for a lot of ovens you might find they are too leaky to be used with 30mA RCDs anyway so that aspect would suggest going down the road @timhoward suggested of sockets with some means of limiting their use to those that are skilled enough not to do dumb stuff might be necessary (e.g. padlocks or similar, not necessarily high security ones!).

 

[Simon47]

Just a thought ...
Does there exist a plug/socket similar to BS4343 (Commando) but with two earth pins ?
Seems to me that (for this discussion) the primary requirement is as backup for failed earthing. Similar to RFCs where high leakage currents are expected require high integrity earthing, having duplicated earth paths would go a long way to mitigating the risks.

 

[Teddy Lop]

Just a thought ...
Does there exist a plug/socket similar to BS4343 (Commando) but with two earth pins ?
Seems to me that (for this discussion) the primary requirement is as backup for failed earthing. Similar to RFCs where high leakage currents are expected require high integrity earthing, having duplicated earth paths would go a long way to mitigating the risks.

That's a great observation. And once again regulatory obligations and market options diverging.

From what I've observed doesn't the German schumo socket have dual earth contacts? Although they can be reversed too so it might be for that reason.

 

[pc1966]

From what I've observed doesn't the German schumo socket have dual earth contacts? Although they can be reversed too so it might be for that reason.

Some of that style of plug can be reversed (the ones with the twin side earths) and others cant (the ones with the earth pin) but typically most now accept either.

But I think it is less an issue of the contact and wanting "two pins", more likely the integrity of the CPC connection to the pin and that is where the larger BS4343 (Commando) plugs benefit from having dual screws for retaining the cables.

 

[Simon47]

... more likely the integrity of the CPC connection to the pin and that is where the larger BS4343 (Commando) plugs benefit from having dual screws for retaining the cables.

But it's still one contact, one cable core, one connection inside the equipment - so while it does mitigate one particular failure mode, it doesn't mitigate several others.
Back to one of the earlier situations - telecoms facilities. I would suggest that these are relatively simple - there's options for bonding everything so if (say) a supply cord loses the CPC, there's still bonding so ADS will still work without anything exposing dangerous voltages. Plus it's a relatively controlled environment - the operator has the option of ensuring only properly trained people go in. I'd have no problem doing an RA and specifying additional bonding (if not already present) for every item, plus training of all personnel who enter the facility.

But for some of the others mentioned (factories, bakeries) it's a lot harder. My limited experience in commercial environments is that people are happy to ignore any warning notices or instructions if they get in the way of doing their job. Plus people seem happy to carry on using equipment with obvious faults. For example, one time I was in the local hospital (visiting) I observed someone happily trundling along with a heated food trolly, where the cable gland was something like 6" away from the hole it was supposed to be fitted into, and presumably it was only the electrical connections of the cores keeping the cable in - i.e. it was a really obvious fault, visible from a distance, and not some obscure issue that could have been overlooked (I told the person trundling it that it was dangerous and needed referring to maintenance before it was used again - no idea if it was). I'm sure we've all got tales like that - especially cables pulled out of cord grips/glands. And the least said about some of the stuff we used to do back when I was a youngster working on a local farm - before I knew any better.
So I'd be "rather wary" of omitting RCD protection for some of these situations unless there was some sort of unique plug/socket arrangement that offered a bit more protection than a standard BS4343 or BS1363 type - hence my query about connectors with multiple earth pins.

 

[pc1966]

But it's still one contact, one cable core, one connection inside the equipment - so while it does mitigate one particular failure mode, it doesn't mitigate several others.

True.

Back to one of the earlier situations - telecoms facilities. I would suggest that these are relatively simple - there's options for bonding everything so if (say) a supply cord loses the CPC, there's still bonding so ADS will still work without anything exposing dangerous voltages. Plus it's a relatively controlled environment - the operator has the option of ensuring only properly trained people go in. I'd have no problem doing an RA and specifying additional bonding (if not already present) for every item, plus training of all personnel who enter the facility.

That sort of situation is what I normally deal with and most equipment has multiple earth paths via cables and metal racks, plus I normally bond the rack as well as the supply cable CPC so two paths at least.

But for some of the others mentioned (factories, bakeries) it's a lot harder. My limited experience in commercial environments is that people are happy to ignore any warning notices or instructions if they get in the way of doing their job. Plus people seem happy to carry on using equipment with obvious faults. For example, one time I was in the local hospital (visiting) I observed someone happily trundling along with a heated food trolly, where the cable gland was something like 6" away from the hole it was supposed to be fitted into, and presumably it was only the electrical connections of the cores keeping the cable in - i.e. it was a really obvious fault, visible from a distance, and not some obscure issue that could have been overlooked (I told the person trundling it that it was dangerous and needed referring to maintenance before it was used again - no idea if it was). I'm sure we've all got tales like that - especially cables pulled out of cord grips/glands. And the least said about some of the stuff we used to do back when I was a youngster working on a local farm - before I knew any better.

This might be the reason for the "electrically skilled" aspect not listed, so stuff like that is picked up by anyone with even basic PAT experience.

I have fixed PA amplifies with loose flexes and broken CPC before, many MANY years ago, and not far off the period when you would hear of musicians ding of electric shock on stage. Thankfully RCD use and radio mics/pickups have largely eliminated that, as well as the PAT aspect.

So I'd be "rather wary" of omitting RCD protection for some of these situations unless there was some sort of unique plug/socket arrangement that offered a bit more protection than a standard BS4343 or BS1363 type - hence my query about connectors with multiple earth pins.

The issue is then you need dual CPC to the equipment, etc, and that is very unlikely to be supported. You could tie some 4mm flex in parallel with the power cord and fit at any chassis screw, etc., but I can't see that as being acceptable in general. More generally, if equipment is seriously abused as you see on farms and building sites, both could be visibly damaged an nobody cares!

Now fixed connections that are permitted are not really different, but I guess they are used for items that hardly move so I'm guessing the argument is they are less likely to have damaged connectors, cable glands, etc, than portable-ish stuff.

 

[Simon47]

The issue is then you need dual CPC to the equipment, etc, and that is very unlikely to be supported. You could tie some 4mm flex in parallel with the power cord and fit at any chassis screw, etc., but I can't see that as being acceptable in general.

Replace the 3 (or 5) core cable with 4 (or 6) core, find an alternative internal connection point.
An alternative could be to use a pilot pin (as fitted on larger BS4343 connectors) and use that to monitor (in real time) integrity of the main CPC.

More generally, if equipment is seriously abused as you see on farms and building sites, both could be visibly damaged an nobody cares!

Absolutely. I do wonder how some of us survived - or perhaps it was wearing wellies that helped.

The aforementioned working on a farmer in my youth. We had an old water heater - freestanding "large metal bucket" with a lid to pour water in and a tap on the side. We noticed we got a tingle from it, and when I looked I noticed that the contacts on the earth pin in the 15A socket were splayed out. I squeezed them together so they made contact, plugged in, flicked the switch - and it went BANG. Turned it over, the heating elements were thin things, sandwiched between sheets of mica, and clamped onto the bottom of the "bucket" by flat metal plates. One had come loose, the element had moved and was touching the stud - hence the tingle when the earth was broken, and the bang when the earth was fixed. This was in the dairy - always wet floor, and steel floor tiles, so I guess it was our rubber wellies that saved us !

And then a very long extension lead - needed to get from the few sockets (I think there were only 2 or 3 altogether) to anywhere else. The rubber sheath was cracked, and there was nearly as much tape as showing sheath. But it was 2 core cable, and sticking out from the socket on the end was a coiled cable with a crock clip. None of us knew what it was for, so we tended to clip it onto the frame of the machine we were using - "what else could it be for ?" ! Again, I think luck was our friend here as it mostly got used in dry weather for powering an elevator for hay bales. At some point, it got chopped off as it was a nuisance.
Idea was sound, but since no-one knew why it was done that way, it never got used safely.