Bonding to pipes

[Geoffsd]

If the values are above 50/Ia how can they be considered to be effectively connected to earth?!?

Because we are measuring between parts.

Supplementary bonding can ONLY be ommitted if the requirements for ADS have been met, parts are effectively connected to earth AND 30mA RCD protection is provided on all circuits within the location.

But you said -
"If the values are above 50/Ia then the parts require bonding full stop! It is irrelevant whether or not an RCD is used.".

I think I have illustrated this exact same point two more times throughout this thread!

So have I -
"If the values are above 50/Ia then the parts require bonding unless ALL circuits (AND the other conditions are met) are protected by RCDs".

 

[KAS1]

This is a very interesting thread may I say, both of you chaps seem to me to be very knowledgeable in the electrical field, I'm a little bit unsure where it will end, perhaps with you both agreeing in the end saying "that's exactly what I mean" the more I read the more I'm confusing myself, I agree with one of you then the other it's like watching tennis, please just each do a summing up then if we(all of us reading this thread) hit the like button, it may get even more interesting lol

 

[D Skelton]

Because we are measuring between parts.

So what? If they are both extraneous then measuring between them should show an effective connection despite the correct way of ascertaining an effective connection being measuring between a part and the MET. If for example you are measuring between the tap and a radiator in a bathroom and getting 1000ohms then those WOULD require supp bonding because at least one of those parts is going to be measuring 1000ohms to the MET regardless of whether an RCD is fitted or not.

But you said -
"If the values are above 50/Ia then the parts require bonding full stop! It is irrelevant whether or not an RCD is used.".


So have I -
"If the values are above 50/Ia then the parts require bonding unless ALL circuits (AND the other conditions are met) are protected by RCDs".

So from what I can gather, we agree...ish.

What are we arguing about? What is it exactly that you disagree with?

 

[Geoffsd]

If for example you are measuring between the tap and a radiator pipe - not the radiator - in a bathroom and getting 1000ohms

But you should have already measured between the radiator pipe and the MET to determine if it is extraneous (<23kΩ) in the first place.
It won't be 22999 or 23001 - it will be a few ohms or many Megohms (for Trev).
(How can you get a reading of 1000Ω unless it is miles long? but it doesn't matter if it is as long as main bonding is satisfactory)
If it is extraneous it MAY need bonding.

The same with the water pipe - not the tap.

So, if they are both extraneous a measurement is taken between them.
If this is more than 50/Ia then supplementary bonding is required unless the RCD and other conditions apply.

then those WOULD require supp bonding because at least one of those parts is going to be measuring 1000ohms to the MET regardless of whether an RCD is fitted or not.

Yes but that is not the reason although, obviously, that will be the result.

So from what I can gather, we agree...ish.

Yes but if that is the case I think you must have written something you didn't mean to because these two statements are not the same -

What are we arguing about? What is it exactly that you disagree with?

You said -
"If the values are above 50/Ia then the parts require bonding full stop! It is irrelevant whether or not an RCD is used.".

I said -
"If the values are above 50/Ia then the parts require bonding unless ALL circuits (AND the other conditions are met) are protected by RCDs".

​

 

[Guitarist]

Just to add my twopenneth...
Had a situation the other day where the system was full of copper pipe but plastic fittings. Measuring between 2 lengths of pipework in the boiler cupboard I got about 100 ohms.... After a bit of crawling around and pulling panels off, it turned out that the pipes were actually isolated from each other (by plastic push-fits), but were touching in places (not clipped to the wall). In this case, effective connection to earth was only being achieved by one of the pipes, the other being 100 ohms...

 

[D Skelton]

You said -
"If the values are above 50/Ia then the parts require bonding full stop! It is irrelevant whether or not an RCD is used.".

I said -
"If the values are above 50/Ia then the parts require bonding unless ALL circuits (AND the other conditions are met) are protected by RCDs".

​

Ah, I see where our points meet a hurdle now. As far as I can tell we agree on everything but this, which in itself is more of a mute point than anything else.

As you rightly said, you would be measuring first each and every exposed and extraneous conductive part back to the MET to ascertain its effectiveness. If it is higher than 0.05 then it can be argued that its connection to earth is not effective, by this alone you would have worked out that this part will need supplementary bonding. Let's say for example that you have five extraneous conductive parts within a bathroom and all but one are effectively connected to earth, then the solution would be to supplementary bond that one part to another that IS effectively connected to earth. Simply adding an RCD would not be sufficient without first supp bonding it as required.

The very reason for supp bonding in this instance has got nothing to do with the 50/Ia equation, it is purely to do with having each part effectively connected to earth.

A personal experience was an EICR I did on a bathroom where the basin on one side of the room was run in polyplumb under the floor. Each and every part back to the MET was under 0.05ohms except for the basin tap which was around 6kohms. Measuring between each part conformed with the 50/Ia equation apart from the basin tap. The house was RCD protected. Solution: Supp bond the basin tap to the radiator on the adjacent wall. Sorted.

If for instance the parts in the bathroom are extraneous but not effectively connected to earth but measuring between them gives results below 50/Ia, then I can assume that supp bonding is in place and therefore installation is compliant. Any new work would have to be RCD protected of course but you wouldn't need to worry about any supp bonding.

If parts were not effectively connected to earth and measuring between them showed results higher than 50/Ia then you could assume that supp bonding is not there, therefore it would be required, as well as an RCD for any new work.

Sorry for blabbing on, I've had a beer or two so am probably repeating myself but do you get the jist of what I'm getting at now?

 

[Geoffsd]

Ah, I see where our points meet a hurdle now. As far as I can tell we agree on everything but this, which in itself is more of a mute point than anything else.

Quite fundamental, really. You said the opposite of what I wrote.

As you rightly said, you would be measuring first each and every exposed and extraneous conductive part back to the MET to ascertain its effectiveness. If it is higher than 0.05 then it can be argued that its connection to earth is not effective,

No, no, no.
The 0.05 has NOTHING to do with it.
If you think that then no lighting circuit (1.0/1.0) is ever going to comply.
Even a shower with 4mm cpc would have to be less than 11m.

0.05 is only used as a test for a good connection.

by this alone you would have worked out that this part will need supplementary bonding.

No. The impedance of two correctly connected parts could easily add up to more than the required figure of 50/Ia so supplementary bonding will be required.

Let's say for example that you have five extraneous conductive parts within a bathroom and all but one are effectively connected to earth, then the solution would be to supplementary bond that one part to another that IS effectively connected to earth.

No. Connect the ineffectively connected part.
They, then may still require supplementary bonding.

Simply adding an RCD would not be sufficient without first supp bonding it as required.

Yes, it would as long as the other two conditions are met.

That is - disconnection times comply. This will mean the cpcs are effectively connected and
Main bonding in place. Depending on the size of the property, the impedance from pipe to MET could be relatively high - doesn't matter.

The very reason for supp bonding in this instance has got nothing to do with the 50/Ia equation, it is purely to do with having each part effectively connected to earth.

No, it is the other way round. 50/IA is the criterion for supplementary bonding because the resistance between parts is relatively high because of the path from pipe through main bond to MET through cpc to appliance.
This CANNOT posibly ever be less than 0.05 (unless teeny-weeny flat).

A personal experience was an EICR I did on a bathroom where the basin on one side of the room was run in polyplumb under the floor.

It was therefore NOT extraneous.

Each and every part back to the MET was under 0.05ohms

Teeny-weeny flat or already bonded.

except for the basin tap which was around 6kohms.

How can a plastic pipe have a reading of 6kΩ ?
Taps are never extraneous. You should test the pipe.

Measuring between each part conformed with the 50/Ia equation apart from the basin tap.

That's possible but the 6kΩ is a mystery.

The house was RCD protected. Solution: Supp bond the basin tap to the radiator on the adjacent wall. Sorted.

Sorted yes but if the other two conditions were met (ADS and main bond) then not necessary.



I stand by what I wrote in post #21.

 

[D Skelton]

I'm too tired, I will respond fully tomorrow, but one thing I find rather amusing is how you have conveniently forgotten that although a plastic pipe is not in itself conductive, it has a rather conductive fluid running through it! That is where the 6kohms came from.

 

[Edd]

Great thread, I see the 0.05 Ohm test is really to check that some form of supplementary is in place but cant be seen. behind bath panel etc. As what also has already been mentioned 10m of 4mm is 0.05 ohms, so unless its bonded then its going to be really hard to get less than that. This is where the 50/IA comes in and RCD protection.

If we go with just the 0.05 Ohm then 99.9% of property's will need cross bonding. regardless of RCD protection or not.

 

[marcusone]

Very interesting and knowledgeable thread guys. I await the outcome eagerly. If only to stop my head spinning.

 

[D Skelton]

Ok, I'm fresh and free of inebriation so hopefully I can make crystal clear my stance on supplementary bonding in a location containing a bath or shower. Here goes:

Local supplementary equipotential bonding according to Regulation 415.2 shall be established connecting together the terminals of the protective conductor of each circuit supplying Class I and Class II equipment to the accessible extraneous conductive parts, within a room containing a bath or shower.

Where the location containing a bath or shower is in a building with a protective equipotential bonding system in accordance with Regulation 411.3.1.2, supplementary bonding may be omitted where all of the following conditions are met:

1. All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
2. All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
3. All extraneous conductive parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.

The effectiveness of the connection of extraneous conductive parts in the location to the main earthing terminal may be assessed, where necessary, by the application of Regulation 415.2.2 (R≤50V/I[SUB]a[/SUB]).


When carrying out an EICR, upon entering a bathroom the first test to be carried out is one to establish whether or not there are any extraneous conductive parts within the location. The result measured between any metallic pipework and/or structural metalwork and the main earthing terminal should be above 45kΩ (some are happy using the figure of 22kΩ) to establish that the part is not extraneous. If any metallic pipework and/or structural metalwork is found not to be extraneous then it does not require bonding of any kind. If you have established that there are extraneous conductive parts, the next set of tests are between each extraneous and between each exposed conductive part to the main earthing terminal. The value you are aiming for to determine an effective connection between the main earthing terminal and an extraneous conductive part is around 0.05Ω, this does not take into account any length between the main equipotential bonding connection and the place upon that extraneous conductive part where you are carrying out the test. A 10mm bonding conductor will be within 0.05Ω up to 27m (it is reasonable within an average sized property to get a reading within 0.05Ω from the point of testing back to the main earthing terminal as copper pipe has a larger csa than that of a 10mm conductor). From the point at which you test an extraneous conductive part back to the main earthing terminal you will establish an effective connection to earth by the application of R≤50V/I[SUB]a[/SUB] where I[SUB]a[/SUB] is the operating current of the highest rated protective device serving a circuit within the location. This also applies to any exposed conductive part.

If the resistance between each point tested and the MET is less than or equal to 50V/Ia then each point is effectively connected to earth. For the purpose of this discussion I shall assume that in every case all final circuits of the location comply with the requirements for automatic disconnection. If the circuits within the location have 30mA RCD protection then no supplementary bonding is needed.

If all circuits within the location do not have 30mA RCD protection then a test between each simultaneously accessible exposed and extraneous conductive part should be carried out. The resulting resistance between any two simultaneously accessible exposed or extraneous conductive parts should be equal to or less than 50V/I[SUB]a[/SUB] (which given the measurements taken which have already ascertained that each part is effectively connected to the main earthing terminal using this equation, is highly likely). If the results are within this value, then it can be assumed that supplementary bonding is in place and this particular section of the installation be given a C3 as a 30mA RCD should be recommended.


Now, if the resistance between one or more exposed and/or extraneous conductive parts tested and the main earthing terminal is greater than 50V/I[SUB]a[/SUB] then an effective connection between those parts to earth has not been established (it is easily possible to have an extraneous conductive part that is connected to the main equipotential bonding but just not effectively [say for example 100Ω is measured between a radiator and the MET and plastic pipe feeding the radiator is visible]). We now know that this part should be supplementary bonded because it is extraneous but not effectively connected to earth. A test between this part and all other simultaneously accessible exposed and extraneous conductive parts can be carried out to ascertain whether or not supplementary bonding is already in place by applying R≤50V/I[SUB]a[/SUB] (although at the same time as carrying out this test we can safely assume it is not).

Regardless of whether or not all circuits in the location are protected by a 30mA RCD, this particular section of the installation must be given a C2 because of the lack of required supplementary bonding. Remember, supplementary bonding can only be omitted when all three of the above listed conditions are met.

If the bathroom does have 30mA RCD protection then this in particular warrants no code even though the lack of required supplementary bonding to a non-effectively connected extraneous conductive part has already been given and still warrants a C2. If the bathroom does not have 30mA RCD protection then as stated in one of the previous paragraphs, a C3 must be given (additional protection by way of a 30mA RCD is recommended). This again is in addition to the C2 for lack of required supplementary bonding. Addition of a 30mA RCD covering all circuits in this location will make no difference to the C2 that must be given for lack of required supplementary bonding.


I feel I must make this point absolutely clear: During testing and inspection or installation, if within a location containing a bath or a shower an exposed and/or extraneous conductive part is not effectively connected to earth (see above on how to determine an effective connection) then the existence/addition of a 30mA RCD does not absolve the inspector/installer of any responsibility to code the lack of supplementary bonding/install supplementary bonding to that part!!!


This is, always has been and always will be my stance on supplementary bonding within a location containing a bath or shower. This is as written in black and white in BS 7671 and I will not bend, break nor falter from this stance unless someone can prove beyond all doubt that my stance and that of BS 7671 is completely, utterly and totally wrong!

Now, time for a beer... or ten!

 

[Guitarist]

Is the confusion between you two giants of bonding simply in the term "extraneous"?
Obviously, extraneous is tested for by isolating the system and testing metalwork to the main earth with it disconnected from the entire system. This is different to testing for continuity back to the MET with the system connected. Just a thought....

 

[D Skelton]

Dunno Guitarist, I would have thought that we both know how to test exposed metallic pipework and/or structural metalwork to ascertain whether or not it is extraneous. As you rightly say, this would be with any existing main equipotential bonding and/or earthing disconnected from the MET.

 

[Geordie Spark]

Is the confusion between you two giants of bonding simply in the term "extraneous"?
Obviously, extraneous is tested for by isolating the system and testing metalwork to the main earth with it disconnected from the entire system. This is different to testing for continuity back to the MET with the system connected. Just a thought....

Whatever the "confusion" or not is, I think this has been one of the best threads / debates I've seen on here in a long time, so thanks lads - much appreciated.

 

[D Skelton]

Just interested as to why this such an interesting thread Geordie?

Am I correct in my assumption that it is because it is slightly different to the some of the drivvel normally posted on here (how to wire 2 way lighting etc...)?