18th.Edition 411.3. 1.2 Doubts in my mind !

[gerry whitwham]

My first posting to the forum!

By way of introduction I have been retired from my previous job as a JIB Approved Electrician for around 15 years but like to kept informed of developments for my own benefit and to enable me to give advice to others.

Recently I became aware of the 18th edition changes due in 2019 and in particular regulation 411. 3 . 1 .2. which effectively negates the need for equipotential bonding of incoming services providing " insulating inserts" are installed at point of entry . Without delving too deeply into the technicalities, it seems to me that a dangerous situation could arise if metal pipework was not bonded inasmuch as a fault current appearing on exposed metal pipework with no earth path for rapid disconnection . After all the whole idea of Equipotential Bonding and Automatic Disconnection (EBAD) was to ensure all services were at the same electrical potential to earth as the maions incoming electrical supply and always bonded on the consumer side of the supply with no intention of providing separate pathways to earth.


Struggling to come to terms with this reg !

 

[Daniel Oake]

I'm thinking that a good electrician would still prove the pipe work to be 22-23k ohm or higher resistance to be on the safe side; I'm thinking that this regulation was introduced around that basis

 

[Deleted member 26818]

This new sentence in the Regulation is just an attempt to clarify the situation regarding plastic supply pipes.
If a service enters the building in plastic, it will will not introduce a difference in potential and does not require bonding.
That won’t prevent metallic pipework inside the building from becoming live if a fault occurs and a live conductor comes into contact with the metallic pipework.
However to prevent such from happening, we have section 528 proximity of wiring systems to other services.

 

[netblindpaul]

This regulation relates to whether the incoming service is an extraneous-conductive-part or not.
If it is not then it does not need bonding as one.

 

[gerry whitwham]

This new sentence in the Regulation is just an attempt to clarify the situation regarding plastic supply pipes.
If a service enters the building in plastic, it will will not introduce a difference in potential and does not require bonding.
That won’t prevent metallic pipework inside the building from becoming live if a fault occurs and a live conductor comes into contact with the metallic pipework.
However to prevent such from happening, we have section 528 proximity of wiring systems to other services.

Only a complete dim-wit would attempt to bond plastic supply pipes so my scenario is the equipotential bonding of any metallic pipework in the mains services above the point of entry and usually just north of the stop taps. I don't think we should confuse EBAD with bonding to metallic elements in close proximity to wiring systems.

 

[ferg]

My half arsed understanding is that bonding extraneous metallic parts is to keep them at the same potential as the earthing system in the building which may be at a different potential to that of the general mass of earth where the pipework / structural steel is at.

Thus keeping touch voltages at the desired level.

Happy to be corrected, that's how I learn or relearn.

 

[netblindpaul]

Only a complete dim-wit would attempt to bond plastic supply pipes so my scenario is the equipotential bonding of any metallic pipework in the mains services above the point of entry and usually just north of the stop taps. I don't think we should confuse EBAD with bonding to metallic elements in close proximity to wiring systems.

gerry,
Not you, I'll say before anyone jumps on me, but, there are dim-wit's out there.
It is not uncommon to see plastic pipework with a copper section fitted about 6" long with a bonding clamp fitted to it.
Quite what that accomplishes apart from bonding the 6" of copper I don't know.

The issue with main incoming services is that they may bring a potential into the property that may not otherwise exist, i.e. true earth potential, if they are metallic entering the premises.
Therefore, in the event of a fault, if they are not bonded, then they would be at true earth and the remainder of the earthed metalwork would be at some other potential for the duration of the fault.
Ergo a potential difference between the two conductors, the metalwork internal, and the extraneous-conductive-parts entering the property.
Thus bonding to ensure that they remain at the same potential.

 

[Strima]

You may well find the water system may be connected back to the MET through the CPC of the boiler circuit and the pipe connections on the manifold.

Only testing would confirm this.

 

[Sparky Ninja]

I think we should try to rethink the approach to potential differences with electrical installations as it appears that 'simplifying' it the way the try raises more questions than if we actually approached it from the technical angle.

Namely verify the 22/23k ohms, obtain resistance readings to determine potential touch voltages between exposed and extraneous conductive parts, and go from there.

If we were able to do this then it's a much simpler process.


What if I had a plastic service supplying a property so chose not to bond it. The homeowner had a kitchen island installed with gas/water piping being buried in the ground and then leading up to the island, also containing a cpc from the electrical system?

 

[westward10]

This Regulation refers to main protective bonding at the service point of entry, it clearly states that if it is plastic then bonding is not required. Obviously if this changes to metal pipework within the installation of course it could become charged and remain so if effectively isolated from the system earth. In these instances supplementary bonding can be applied.

 

[Sparky Ninja]

This Regulation refers to main protective bonding at the service point of entry, it clearly states that if it is plastic then bonding is not required. Obviously if this changes to metal pipework within the installation of course it could become charged and remain so if effectively isolated from the system earth. In these instances supplementary bonding can be applied.

If that was a reply to my post then thanks for proving my point.

 

[Ian1981]

You can’t plan for every future scenario and in the case of a plastic insert on an incoming service the regulation regarding protective bonding and if it’s required in that scenario is quite clear.
We can only work with what’s in front of us.

 

[gerry whitwham]

My half arsed understanding is that bonding extraneous metallic parts is to keep them at the same potential as the earthing system in the building which may be at a different potential to that of the general mass of earth where the pipework / structural steel is at.

Thus keeping touch voltages at the desired level.

Happy to be corrected, that's how I learn or relearn.

...and that's my understanding as well !

 

[Deleted member 26818]

I’ve worked in places where the copper pipe behind a panel, which connects the plastic cistern to the porcelain urinal had to be bonded.
I did point out that the 1.5m pipe was neither extraneous or accessible, so was being earthed not bonded.

 

[Ian1981]

I’ve worked in places where the copper pipe behind a panel, which connects the plastic cistern to the porcelain urinal had to be bonded.
I did point out that the 1.5m pipe was neither extraneous or accessible, so was being earthed not bonded.

I’m on a job where the consultant has requested the metal basket be earthed/ bonded with a 10mm back to the DB serving the building.
All that’s on the basket is fire alarm cables.
The basket is fixed to unistrut on a concrete ceiling.