Messy CU

[Lectrician]

Bell wire mixed in with T & E.

Those sockets are wired a bit DIY.

Lets hope those adjacent doubles are not linked across.

Looks such a mess doesn't it. The shower cable is the worst! It is indeed a ring. It is a shame you can't code things for just being a mess! Unfortunately the only thing you can mark down is lack of support and lack of mechanical protection in a garage. All code C3 (so no action taken).

 

[bernardgreen]

I spy BS951 clamp on the gas pipe, but no bonding conductor. Is it hidden behind the pipe?

It must be one of those new fangled devices that uses state of the art wireless technology

 

[Adam_151]

lack of mechanical protection in a garage. All code C3 (so no action taken).

Not even sure its even code C3 if the garage is used for nothing but car storage, but then again if its use is more like a workshop there might be some places C2 is justified.

 

[JohnW2]

Yes, that pipe in the shot is the galv gas pipe from the floor, the gas meter is eye level. The customer pipe exists the left hand of the meter, out of shot to the left.

Thanks for clarifying. Am I the only person who feels that practices (and interpretation of the regs) regarding main bonding can get a bit crazy?...

...taking the worst-case scenario of a gas meter which does not provide electrical continuity (and no strapping across it), with the only main bonding being on the consumer's side of the meter, we have here a situation of several feet of a totally exposed extraneous-conductive-part (almost certainly at true earth potential) within inches of the cutout, meter and CU of a PME installation - the only slight 'saving grace' being that there is not, in this particular installation, an exposed MET at the PME "earth" potential.

Considering the purpose of Main Protective (Equipotential) Bonding, basic common sense suggests that, particularly in a situation such as that pictured, main bonding should be as close as possible to the point of entry of that e-c-p into the property, regardless of whether there is some insulation (e.g. a meter) between that point and the property's pipework. In that situation, there may well be arguments for also bonding the property's pipework to the MET but (a) I don't think that really qualifies as main bonding and (b) to my mind it does not remove the common sense need to main bond the pipe on the service side of the meter (i.e. the actual extraneous-conductive-part).

I agree that the risks of bonding only on the consumer's side of the meter are often minimal, since the length of pipework on the service side of the meter is often very short and/or fairly inaccessible. However, we've been shown a picture of a situation in which that extraneous-conductive-part is relatively long, highly accessible and in close proximity (certainly within reaching distance of) to the installation's main components.

If that were my house, I would certainly want that pipe bonded to the MET, regardless of what else was bonded. Is that unreasonable?

Kind Regards, John.

 

[EFLImpudence]

I totally agree.

544.1.2 states that the main bonding should be made as near as possible to the point of entry.

It then goes on to state that "Where there is an insulating section or insert at that point, or there is a meter, the connection shall be made to the consumer's hard metal pipework".

Surely this means that if the insulating section or insert is elsewhere this does not apply.

As the reference to the meter is subsequent to this proviso, does the same deduction apply to the meter, or not?


If you agree then, in the case of the installation in the pictures, the pipework on the consumer's side of the insulating section or insert, (and/or the meter, dependent on interpretation), should be supplementary bonded if required.
The main bonding being at the point of entry.

 

[JohnW2]

I totally agree....If you agree then, in the case of the installation in the pictures, the pipework on the consumer's side of the insulating section or insert, (and/or the meter, dependent on interpretation), should be supplementary bonded if required.
The main bonding being at the point of entry.

I also agree totally with you.

What seems to be a very common ("mis-" ?) interpretation of the regs, resulting in main bonding only on the consumer's side of a meter, seems crazy and dangerous to me, particularly in a situation such as that pictured above.

The whole point of main bonding is surely to eliminate the risk that (particularly with PME and/or under fault conditions) someone could be exposed to a substantial potential difference by simultaneously touching something connected to the installation's MET and something (an extraneous-conductive-part) which is likely to be at true earth potential. If the incoming gas pipe we've been shown is not main boinded, the picture we've seen must surely be a case of that (potentially fatal) scenario just waiting to happen.

It seems to me that this is a case of people concentrating far too much on the words of the regs, and making an interpretation of the regs which was almost certainly not what was 'intended', without stopping to apply some basic common sense about electrical safety!

Kind Regards, John.

 

[bernardgreen]

The whole point of main bonding is surely to eliminate the risk that (particularly with PME and/or under fault conditions) someone could be exposed to a substantial potential difference by simultaneously touching something connected to the installation's MET and something (an extraneous-conductive-part) which is likely to be at true earth potential.

It is ironic that the ground and its potential have become a potential hazard to safety and has to be "exluded" from inside the premises.

It seems to me that this is a case of people concentrating far too much on the words of the regs, and making an interpretation of the regs which was almost certainly not what was 'intended', without stopping to apply some basic common sense about electrical safety!

One has to wonder how much common sense was used when the system that the regs have to "defend" was created. ( such as PME and other neutral derived "earths" ) More and more I am becoming convinced that TT should be the only "earthing" method for supplies to ground floor premises simply because there are so many un-bondable ways that ground potential can enter the equipotential zone. Shaking hands when one person in the zone and the other is on the ground outside being one example.

Supplies other than TT are probably safe at first floor and above where there is virtually no path that could bring ground potential into the equipotential zone that is also un-bondable.

That said the present system is acceptably safe and the number of incidents where the potential on the neutral derived "earth" is high enough to make true ground potential a hazard is so far very small. That may change if the number of thefts of metal from sub stations increases.

The writers of regs seem to have realised the possibility of high potential differences between "earth" and ground giving rise to high currents through bonds between "earth" and ground as they insist on large cross section (10 mm ) cable for these bonds.

EDIT quote command corrected

 

[JohnW2]

One has to wonder how much common sense was used when the system that the regs have to "defend" was created. ( such as PME and other neutral derived "earths" ) More and more I am becoming convinced that TT should be the only "earthing" method for supplies to ground floor premises simply because there are so many un-bondable ways that ground potential can enter the equipotential zone. Shaking hands when one person in the zone and the other is on the ground outside being one example.

We have discussed this before and, as you know, I have a lot of sympathy for your viewpoint. However, although much less likely (and hopefully short-lived, if protective devices work as intended), a similar problem to that you describe will also exist (as you say, mainly on the ground floor, and particularly outdoors) in a TT instalation - since a TT 'earth' (hence installation's MET and CPCs) can rise to a very high potential above true earth under fault conditions.

As you go on to imply, I suspect the official response to your viewpoint would be that, despite the theoretical soundness of what you are saying, statistically speaking there have probably been incredibly few injuries or fatalities due to the sort of mechanism you are talking about.

Kind Regards, John.

 

[plugwash]

All earthing systems have their issues, TN-S is probablly the least-bad but it's also the most expensive.

The problem with TT is unless you make a herculean effort on your electrode installation you are totally reliant on a RCD for protection from faults to earth. This causes a couple of issues, firstly RCDs can be unreliable and secondly in larger installs it means you have to carefully plan out a RCD tree to give proper discriminations. Furthermore when a fault to earth does happen your installations earthing/bonding system will become live (relative to true earth) until the fault is cleared by the RCD.

The problems with TN-C-S are you can get currents circulating through the earthing/bonding system even in normal operation and in the event of a lost neutral the earthing systems beyond the lost neutral can become live unless they are very well tied to earth. DNOs try to mitigate this risk through the use of many earth electrodes (PME) and the use of concentric cables for the final hookups but it can still happen.

The problem with TN-S is you can get a LOT of current flowing through a neutral to earth fault (which on non-rcd circuits isn't protected against by any protective device), potentially enough to damage cables or cause serious damage at the location of the fault (if it's a high resistance fault)

 

[JohnW2]

The problem with TT is unless you make a herculean effort on your electrode installation you are totally reliant on a RCD for protection from faults to earth.

Indeed so.

This causes a couple of issues, firstly RCDs can be unreliable ....

That's a commonly asserted belief, and we've discussed it often before. Personally, I'm yet to be convinced that RCDs are necessarily any less reliable than MCBs (indeed, MCBs may be less reliable, since there is no way of 'exercising' them comparable with the test button on an RCD). I personally suspect that this might be shown to be a myth if MCB function could be tested routinely and regularly (by test button or an electrician) in the same manner as RCDs.

...and secondly in larger installs it means you have to carefully plan out a RCD tree to give proper discriminations.

True, although that is do-able, up to a point. However, as I wrote earlier, unless one uses DP RCDs (expensive, and very rarely done), you will not be able to get any discrimination in relation to N-E faults.

Furthermore when a fault to earth does happen your installations earthing/bonding system will become live (relative to true earth) until the fault is cleared by the RCD.

True, but even with a TN installation the installation's earthing/bonding system will become at least to some extent 'live' (albeit usually not as live as with TT) until the fault is cleared by an MCB.

Kind Regards, John.