MPB - regs or common sense?

[JohnW2]

Hi. The short form of this question is whether or not anyone can see anything in the regs which prevents the MPB being bonded to water pipework at more than one point (provided the conductor remains continuous).

More detail .... my (10 mm²) MPB has been religiously connected, per regs, to pipework within 600mm after the water meter. However, this is totally ineffective for the intended purpose, since the bonding is thereby on the supply side of a plastic-bodied flow sensor (about 1000mm from meter). Bonding to the pipes in the property (which is what matters to me) is therefore dependent upon the strapping across the flow sensor, currently much smaller (looks like 4mm²) than the MPB itself. Even if that strapping were upgraded to 10mm, matching the MPB, it would make nonsense of the requirement for an unbroken MPB, and I would prefer to not be dependent for effective bonding on two further screwed terminations.

The most obvious 'sensible' solution would be to simply move the MPB connection to a point about 1200mm from the meter, on my side of the flow sensor. However, if I did that, there would be no guarantee that some 'Jobsworth' inspecting the installation in future would not feel that the absence of a connectuion within 600mm of the meter was non-compliant. I am therfore inclined to leave the present (silly) connection close to the meter, but to also bond the same MPB to pipework on my side of the plastic; there is enough slack in the cable to do this without breaking the conductor. I would certainly sleep more soundly knowing that there was proper direct bonding to the metal pipework in my property, and this has surely got to be within the spirit of the regs.

What do people feel about this, and can you see anything in 544.1.2 (or elsewhere) which precludes bonding tge MPB to pipework in more than one place?

Kind Regards, John

 

[Spark123]

The purpose of main protective bonding is to equipotentially bond any extraneous metalic part which could introduce a potential (generally earth potential) into the equipotential zone.
It should ideally be connected within 600mm of the water pipe entering the building as it is the water supply pipe which is an extraneous conductive part. Wether or not you determine the water pipes already in your premises to be extraneous is up to you, can they introduce earth potential into the building?

 

[JohnW2]

The purpose of main protective bonding is to equipotentially bond any extraneous metalic part which could introduce a potential (generally earth potential) into the equipotential zone.
It should ideally be connected within 600mm of the water pipe entering the building as it is the water supply pipe which is an extraneous conductive part.

Well, yes - but, as I implied, this is where the situation is at risk of getting silly. In the absence of any other bonding (including 'strapping' across insulating parts of water system), the only thing which the MPB, as it is, would ensure was equipotential would be the 300-400mm of pipework between the current MPB connection and the plastic interruption in pipework. In the absence of any other bonding, all of the pipework in the building would be 'floating', which is hardly a desirable situation. (the current saving grace is the gas (LPG) supply pipe; by virtue of its MPB and the fact that it is in electrical continuity with water pipes a the boiler means that all of the pipework becomes equipotential - although I don't know that a gas pipe is necessarily the most desirable conductor to be achieving that!)

Wether or not you determine the water pipes already in your premises to be extraneous is up to you, can they introduce earth potential into the building?

I'm not convinced that your "...into the building" (by implication, from outside of the building) is a legitimate part of the definition of an extraneous conductive part. Given the existance of supplementary bonding (and implicit connectuons such as that via the gas pipe), the pipework within the building certainly has the ability to introduce earth potential into parts of the building (e.g. kitchens, bathrooms, airing cupboards, CH radiators etc.), and I would certainly want to know that it was well-and-truly bonded to earth, wouldn't you?

Anyway, what about my question? Can you see anything in the regs which prevents multiple connections of an (unbroken) MPB conductor to pipework?

Kind Regards, John.

 

[electronicsuk]

Personally, I would do as you propose and bond either side of the flow meter, then get on with your life. It certainly wont be any less safe than picking and bonding one side of the pipework alone. After all, you are permitted to work to a standard that you feel you can prove is above and beyond the regulations set out in BS7671.

You could follow the regs to the word and connect within 600mm of entry into the property, and that will bond the extraneous conductive service on entering the building, as is the intention of the PEBs. However, I think it makes sense to have the pipework on the opposite side of the plastic flow meter also bonded, so as to ensure there is no potential difference between the pipework either side. While such a situation shouldn't exist, I'm sure there are a variety of faults that could result in problems occurring, such as a live conductor coming into contact with pipework somewhere in the building. Again, the PEBs are not provided as a means of earthing the pipework within the building, but I'd still be happier knowing they were there in the event of a fault down to the metal pipework.

 

[mfarrow]

For compliace with the regulations, you can connect as many extraneous conductive parts together at as many points as you like. As long as the bond from one t'other and to MET is continuous and it meets testing criteria it doesn't matter.

 

[SgtTrojan]

Earthing.. I love earthing debates... muhahahahaha

My first question. Who's is the flow meter?
The reason I ask is, and it's commonly used as an excuse for the 600mm connection point, what is the worst case scenario should the water authority rip out your supply pipework? Your installation should be protected at all costs. So if they take away their flow meter you would not be properly protected. Solution: Connect the main protective bonding conductor, on the consumer side, within 600mm of the flow sensor.

If the flow sensor is the consumer's equipment then upgrade that under-rated 4mm ² to 10mm ².

As far as I am aware, in this situation, BS7671:2008 presumes one connection point and therefore does not state that multiple connections are not permissible.

Protection against the suppliers' actions is key.

 

[JohnW2]

Personally, I would do as you propose and bond either side of the flow meter, then get on with your life. It certainly wont be any less safe than picking and bonding one side of the pipework alone. After all, you are permitted to work to a standard that you feel you can prove is above and beyond the regulations set out in BS7671.

Thanks. Indeed, that is my intention - I just wondered what folk thought the regs woukd feel about it.

You could follow the regs to the word and connect within 600mm of entry into the property, and that will bond the extraneous conductive service on entering the building, as is the intention of the PEBs. However, I think it makes sense to have the pipework on the opposite side of the plastic flow meter also bonded, so as to ensure there is no potential difference between the pipework either side. While such a situation shouldn't exist, I'm sure there are a variety of faults that could result in problems occurring, such as a live conductor coming into contact with pipework somewhere in the building. Again, the PEBs are not provided as a means of earthing the pipework within the building, but I'd still be happier knowing they were there in the event of a fault down to the metal pipework.

Exactly. I frankly have little personal little interest/concern in what potential may exist in the 300-400mm of pipe between current boding site and the plastic interruption of the pipe, but am far more interested about the pipe on my side of that interruption!. Thanks again for your views.

A supplementary question. It is a large and complex property. Because of the evolution (and 'splitting up') of the property over the years/decades, the water supply to the adjacent property (not owned by me) tees off the water main immediately prior to my water meter and then travels the entire length of my large cellar (nearly 20 metres), in exposed copper pipe, before entering the neighbour's property. Since members of my household are clearly 'exposed' to this pipe, I would feel happier to have that pipe also explicitly bonded to my installation (which would effectively mean that I was bonding to both sides of my water meter). What are your thoughts about that?

Kind Regards,
John

 

[JohnW2]

For compliace with the regulations, you can connect as many extraneous conductive parts together at as many points as you like. As long as the bond from one t'other and to MET is continuous and it meets testing criteria it doesn't matter.

Thanks. That was the interpretation of the regs, and I'm pleased to hear that you agree.

Kind Regards, John.

 

[RF Lighting]

Which regulation calls for MPBs to remain unbroken?

 

[electronicsuk]

A supplementary question. It is a large and complex property. Because of the evolution (and 'splitting up') of the property over the years/decades, the water supply to the adjacent property (not owned by me) tees off the water main immediately prior to my water meter and then travels the entire length of my large cellar (nearly 20 metres), in exposed copper pipe, before entering the neighbour's property. Since members of my household are clearly 'exposed' to this pipe, I would feel happier to have that pipe also explicitly bonded to my installation (which would effectively mean that I was bonding to both sides of my water meter). What are your thoughts about that?

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), 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.

 

[electronicsuk]

Which regulation calls for MPBs to remain unbroken?

I've seen it mentioned many times before on this forum, but I'm 99% sure it's nothing to do with BS7671. It might have come from the OSG...?

 

[RF Lighting]

I frankly have little personal little interest/concern in what potential may exist in the 300-400mm of pipe between current boding site and the plastic interruption of the pipe, but am far more interested about the pipe on my side of that interruption!. Thanks again for your views.

You're missing entirely why bonding is carried out in the first place.

I don't mean this to sound as patronising as it probably does, but try reading up and actually learning WHY we bond extraneous-conductive-parts, and you might begin to see that the way your pipework is at the moment is completely safe, compliant with BS7671, and requires no faffing about with it at all.

 

[JohnW2]

My first question. Who's is the flow meter?

Assuming you mean the flow sensor, it's the consumer's (i.e. mine)

The reason I ask is, and it's commonly used as an excuse for the 600mm connection point, what is the worst case scenario should the water authority rip out your supply pipework? Your installation should be protected at all costs. So if they take away their flow meter you would not be properly protected. Solution: Connect the main protective bonding conductor, on the consumer side, within 600mm of the flow sensor.

As above, it's the consumer's sensor, so the water authority could not touch it. The theoretical issue with your solution would be that some silly Jobsworth could then complain that the MPB was not connected within 600mm of the meter; that's why I'm propose to do this but also leave the current MPB connection close to the meter in place.

If the flow sensor is the consumer's equipment then upgrade that under-rated 4mm ² to 10mm ².

As I said/implied, that alone would leave two additional screwed connections and a separate length of cable in the path between my MET and the building's pipework. That's why I'm happier with having the MPB intself bonded at both sides of the flow sensor. Just to keep the pedantic happy, I'll probably also upgrade the ;strap' to 10mm²; that will be a bit belt-andbraces if there is an MPB already doing the same thing, but it might keep inspecting (even if not very logical) eyes happy!

As far as I am aware, in this situation, BS7671:2008 presumes one connection point and therefore does not state that multiple connections are not permissible.

That was my interpretation. Thanks for confirming that you agree.

Kind Regards, John

 

[RF Lighting]

Right lets go back to basics here.

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.

It has nothing to do with earthing your installation pipework and linking flow what ja me call its.

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.

Your installation is safe and compliant. Leave it alone.

 

[Spark123]

Which regulation calls for MPBs to remain unbroken?

It is mentioned in BS7430, part 21.4