MPB - regs or common sense?

[Spark123]

In the absence of any other bonding, all of the pipework in the building would be 'floating', which is hardly a desirable situation.

Au contraire, it is very desirable to have pipework electrically floating as there is no path for current to flow

 

[JohnW2]

Although rather futile on account of the service already being bonded at your meter (unless you're looking at a huge length of pipe with a significant electrical impedance), ....

That rather depends upon what you mean by 'the service'. The water pipe on my side of the water meter is certainly bonded to my electrical installation. However, the pipes on the supply side of the meter (which is where is pipe to the neighbour tees off) is only bonded to my installation by virtue of a 4mm² cable stapped across the water meter by the water supplier, unless there is metal continuity within the meter (the casing is certainly plastic).

.....there is no doubt that this (and any) conductive pipework between your and your neighbour's property is an extraneous conductive part. If it were me, I'd bond it again within 600mm of where it exits your property/enters your neighbour's.

I certainly can't disagree with that.

Kind Regards, John

 

[JohnW2]

Au contraire, it is very desirable to have pipework electrically floating as there is no path for current to flow

Hmmm ... in a guarantreed totally earth-free enviroment, that might well afford some reasurance. Within any other environment, it's all well and good until some fault connects all that floating metalwork to a hazardous potential, and then some unwitting human being manages to provide a path for current to flow along!

Kind Regards, John

 

[Spark123]

Now you are mixing up earthing and bonding.

 

[ricicle]

JohnW2 - any chance you could give us a clue as to your background eg DIYer, trainee, newly qualified, electrician ???

 

[electronicsuk]

Now you are mixing up earthing and bonding.

I'm not sure anyone is disputing that providing a safety earth connection is not the intention of PEBs - they are there with the intention of providing an equal earth potential at all points within the installation. However, an added side affect of the PEBs is that an earth is also provided to the pipework, without which a L-E fault down to metal pipework could cause the entire installation to become live. While this is unlikely, it certainly isn't a desirable situation, and for the sake of a couple of metres of extra 10mmsq conductor, the OP may as well bond either side of the plastic flow meter.

 

[JohnW2]

A metal pipe coming out of the ground is at a potential.
The earth coming into your house may be at a different potential.
If these are not bonded together then there may be a potential between them which would be dangerous. That is why bonding is carried out, and that is why it is done as close to the point of entry to your property as possible.

Yes, I understand that - but in the absence of any other bonding, the only thing which could be dangerous, and which the present MPB renders safe(er), is the 300-400mm of pipe between the water meter and the flow sensor. However, I'm not denying that even that little bit of pipe should be safe.

It has nothing to do with earthing your installation pipework ....

I understand that such is not the primary purpose of the MPB. However, I want my pipework effectively earthed (don't you?) and in the vast majority of properties that is achieved (or supplemented/ enhanced), 'accidentally', by the MPB - it is merely the presence of a plastic interruption early in my pipework which stops that being the case for me.

It has If you move your MPB to the other side of your flow sensor than you are leaving a piece of metal in your house which is at a different potention to all the other metal work in your house.
You would have made a perfectly safe installation dangerous.

Technically, yes, in relation to that 300-400mm of pipework. That's why I'm proposing attaching the MPB on both sids of the flow sensor (which at least SOME people here seem to agree is acceptable) rather than moving it. Let's face it, apart from removing the need for one additional screwed clamp connection, what I'm talking about is effectively no different from leaving things as they are and upgrading the cable across the flow meter to 10mm².

Your installation is safe and compliant. Leave it alone.

It is certainly compliant. By virtue of other bonding (and the gas pipe), it is also probably pretty safe - but, provided it is not contrary to the regs (and it seems that it isn't) why not enhance that safety with the redunancy (which almost everyone but me already enjoys) of having the MPB add belts and braces to the earthing of the installation pipework?

Kind Regards, John

 

[Spark123]

There is no requirement to "earth" water pipes, central heating pipes etc within your house.
There is a requirement to main protective bond extraneous conductive parts as they enter the equipotential zone.
If your electrical installation is so bad that it can short to the pipework then it needs urgent attention!!
If you started earthing tag lag where would you stop, would you earth each radiator on a wet plastic piped C/H individually as someone may catch a flex on it?

 

[JohnW2]

Now you are mixing up earthing and bonding.

As I've written elsewhere, I'm not mixing them up. I'm merely trying to enjoy the same 'accidental/incidental' enhancement to earthing of pipework which most people enjoy as a a secondary consequence of having an MPB - and just wanted to confirm that it would not offend the regs. It is that 6 inches of plastic a metre or so from my water meter which makes me different from most other people ... and I can remove that inequality simply by attaching the same (existing) MPB to the pipe on my side of the plastic, as well as retaining its existing connection close to the meter

Kind Regards, John.

 

[JohnW2]

There is no requirement to "earth" water pipes, central heating pipes etc within your house.
There is a requirement to main protective bond extraneous conductive parts as they enter the equipotential zone.
If your electrical installation is so bad that it can short to the pipework then it needs urgent attention!!
If you started earthing tag lag where would you stop, would you earth each radiator on a wet plastic piped C/H individually as someone may catch a flex on it?

It all comes down, or should come down, to common sense. No, there is no 'requirement' for all exposed metal pipes etc. to be earthed - but I want mine to be earthed where practical (don't you?) - and the required MPB represents the most robust 'earthing' of pipework installations in most households (other than mine!), and I want to remedy that; that's all I'm saying.

Kind Regards, John

 

[JohnD]

Which regulation calls for MPBs to remain unbroken?

It is mentioned in BS7430, part 21.4

I haven't looked it up (again) today but I think you will find it is a suggestion or a recommendation of good practice, not a regulation. Last time I looked I noticed the absence of the word "must" and I think it said "should" or similar. Regulations say "must." I used to write things like that.

 

[securespark]

Whether "must" or "should", I think it's common sense to use an unbroken conductor.

Imagine this first situation:

A PEB is connected to a gas pipe. A second conductor is connected to the clamp on the gas pipe and run to the water pipe.

Now, the screw loosens and what happens?

Second situation:

The same set-up, but the conductor is unbroken. The screw loosens as before. What happens now?

 

[JohnD]

common sense perhaps , but not required by regulations.

 

[JohnW2]

Which regulation calls for MPBs to remain unbroken?

Well, that's what this site's wiki says However, I have to say that, having just looked quite hard, I have failed to find any such requirement in BS7671 (or the OSG).

As others have said, in one way it makes good sense, but I'm not sure that the idea stands up too well to much thinking about it. Sure, screwed connections can fail but that's as true at the end of a direct unbroken cable as it is everywhere else - and what about the screw terminal at the MET end? If that fails, then it's functionally the same as a failure of a 'double connection' at the other end .... and , of course, everything to do with the satisfactory functioning any sort of bonding (main or supplementary) or of CPCs (not to mention L/N conductors) is dependent on 'screws not coming loose'. I'm therefore not convinced that the MPB necessarily deserves to be singled out (if it is), provided it is accessible for inspection.

Kind Regards, John

 

[JohnD]

IMO the "screw loose" problem is not so worrying if it happens at one of the ends, as if someone knots a few pieces of 10mm G&Y together and hides it under the floorboards (a builder once suggested that to me and was astonished when I fetched my crimping pliers)