Bonding to pipes

[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...)?

 

[telectrix]

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.

hmmm. if you dis. the earthing and bonding from the MET, then the MET is no longer at earth potential., unless circuit cpc's are tied to earth in some way. therefore measuring from that to exposed pipework will not give a reading whether it's extraneous or not.

 

[bigbaddave]

Have you concidered posting your ELI results and ZE ?

 

[D Skelton]

hmmm. if you dis. the earthing and bonding from the MET, then the MET is no longer at earth potential., unless circuit cpc's are tied to earth in some way. therefore measuring from that to exposed pipework will not give a reading whether it's extraneous or not.

I meant earthing and bonding from the consumers side, obvioulsy the main earthing conductor from the MET to the cutout will still be in place. I can see how that post could be misinterpreted though

 

[telectrix]

nicely clarified, thanks.

 

[Geordie Spark]

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...)?

In a word .............

............. YES!!

 

[Guitarist]

I just thought that was worth mentioning, as I'm sure there are still some members on the forum who don't know how to correctly test for extraneous pipework, and it's easy to misinterpret things when having a healthy discussion. I had no doubts that the two of you know exactly how to do it

 

[Geoffsd]

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]).

Agreed.
However, yesterday you said if over 0.05 it would require bonding in all cases regardless of RCD (plus ADS and main bonding) being in place.

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.

Agreed.

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 is where we differ.
The figure of 0.05Ω is a value regarded as negligible impedance when testing, it is not a value which determines whether supplementary bonding is required.
Negligible impedance is unlikely to be achieved by cpcs.
As you have already established the effective connection to the MET (above) then if R≤50/Ia is not achieved between the e-c-p-s supplementary bonding will be required.
Obviously R≤50/Ia between parts and the MET can add up to more than that between the two parts. This why supplementary bonding is required to be added.

This also applies to any exposed conductive part.

No, maximum Zs allows more than R≤50/Ia - so the disconnection times will be satisfactory.
Also - 0.05Ω is not possible unless very short. 3m for 1mm - 11m for 4mm.

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.

Agreed.

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.

Agreed, but not what you said yesterday.

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).

Well, not really. This seems like you are making up hypothetical situations.
Radiators (unless fixed to the ground) cannot be extraneous. The pipes feeding them may be but obviously not if plastic.

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.

Ah. This may be a source of confusion yesterday but whenever mentioning omission of supplementary bonding because of RCDs I have always included the other two requirements.
So, agreed, but with the proviso that a plastic fed radiator cannot be extraneous (unless fixed to the ground).

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.

Agreed, plus - an effectively connected extraneous conductive part may also still require 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.

Agreed.

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!!!

Agreed.

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!

No, it is just the continued use of 0.05Ω (which is not mentioned in black and white in BS7671 and mentioned in GN3 only as an acceptable value for negligible impedance only) as a limit or level in regard to supplementary bonding.

It has nothing to do with supplementary bonding (or main bonding) other than to establish a good connection between the bond and the bonded part.
R≤50/Ia is the only value to determine an effective connection between extraneous parts to the MET and between parts for supplementary bonding - but not cpcs because of maximum Zs.

 

[D Skelton]

Agreed. However, yesterday you said if over 0.05 it would require bonding in all cases regardless of RCD (plus ADS and main bonding) being in place.

What I was trying to say was that if the connection between the point where the extraneous conductive part is bonded and the MET was higher than 0.05Ω then it wasn't an effective main bonding connection. I was aware of what I was trying to say although I must admit I was struggling to find a way of putting it down and probably didn't explain myself as well as I could have done. I haven't read back through what I said but I apologise for any confusion.

This is where we differ.
The figure of 0.05Ω is a value regarded as negligible impedance when testing, it is not a value which determines whether supplementary bonding is required.
Negligible impedance is unlikely to be achieved by cpcs.
As you have already established the effective connection to the MET (above) then if R≤50/Ia is not achieved between the e-c-p-s supplementary bonding will be required.
Obviously R≤50/Ia between parts and the MET can add up to more than that between the two parts. This why supplementary bonding is required to be added.

Yes, it would appear as though we do differ on our opinion as to what the 0.05Ω value means. I am aware it is only a suggested value but GN3 clearly states that: 'When testing the effectiveness of main bonding conductors, the resistive value between a service pipe or other extraneous-conductive -part and the MET should be of the order of 0.05 ohms or less'. I read it as it is.

My argument is that although on the face of it, even if the resistance between the point of testing within the bathroom on exposed pipework or structural metalwork and the MET is less than or equal to 50V/Ia, if the actual main bonding conductor is higher than 0.05Ω then it could be argued that the main bonding conductor is not effectively connected, so regardless of R≤50V/Ia, one of the three conditions is not met. I concede however that this point is arguable and open to interpretation.

No, maximum Zs allows more than R≤50/Ia - so the disconnection times will be satisfactory.
Also - 0.05Ω is not possible unless very short. 3m for 1mm - 11m for 4mm.

I have never stated (or at least never meant to give the impression) that the value of 0.05Ω applies between CPCs or exposed conductive parts and the MET. What I was trying to say is that R≤50V/Ia does apply between exposed conductive parts as much as it applies between extraneous conductive parts. The maximum Zs for a circuit is defined by Uo/Ia but the whole point of supplementary bonding is to prevent a rise in potential between simultaneously accessible exposed and/or extraneous conductive parts of more than 50V therefore the figures used to define maximum Zs values cannot be used.

Agreed, but not what you said yesterday.

I may not have done but I'm pretty sure I didn't say anything to the contrary. The point I was trying to argue if I remember rightly was the meaning of 'an effective connection to earth', not a result measured to bolster an assumption. If I did give the impression that this was not the case somehow then I apologise as I certainly didn't mean to.

Well, not really. This seems like you are making up hypothetical situations.
Radiators (unless fixed to the ground) cannot be extraneous. The pipes feeding them may be but obviously not if plastic.

No, I'm not. The situation I gave where the radiator measured 6kohms to the MET was entirely real! You seem to have disregarded the fact that although a pipe can be plastic and non conductive, the water flowing through it is conductive. Therefore, it is entirely possible for something not fixed to the ground and fed in plastic (in part or in whole) to be extraneous! This is what makes lazy plumbers and their penchant for PVC tees such a blimmin minefield when it comes to supplementary bonding! The simple solution I use when plumbing using PVC between copper for anything is to supplementary bond over any PVC joints to keep copper continuity. In a property where the water service is extraneous, this needs to be done!

Ah. This may be a source of confusion yesterday but whenever mentioning omission of supplementary bonding because of RCDs I have always included the other two requirements.
So, agreed, but with the proviso that a plastic fed radiator cannot be extraneous (unless fixed to the ground).

As I've already said, a plastic fed radiator can be extraneous even if not fixed to the ground.

Agreed, plus - an effectively connected extraneous conductive part may also still require bonding.

Again, my argument is that if an extraneous conductive part still needs bonding then it is not effectively connected in the first place.

No, it is just the continued use of 0.05Ω (which is not mentioned in black and white in BS7671 and mentioned in GN3 only as an acceptable value for negligible impedance only) as a limit or level in regard to supplementary bonding.

It has nothing to do with supplementary bonding (or main bonding) other than to establish a good connection between the bond and the bonded part.

Again, GN3 states that: 'When testing the effectiveness of main bonding conductors, the resistive value between a service pipe or other extraneous-conductive -part and the MET should be of the order of 0.05 ohms or less'. This is clear to me and does not mean that the resistance of the actual bonding clamp has to be lower than 0.05Ω.

R≤50/Ia is the only value to determine an effective connection between extraneous parts to the MET and between parts for supplementary bonding - but not cpcs because of maximum Zs.

I say that this is still arguable as I don't see how an inneffective bond can still be an effective connection. Also, R≤50V/Ia does apply between exposed conductive parts as well as extraneous conductive parts.

 

[Geoffsd]

What I was trying to say was that if the connection between the point where the extraneous conductive part is bonded and the MET was higher than 0.05Ω then it wasn't an effective main bonding connection. I was aware of what I was trying to say although I must admit I was struggling to find a way of putting it down and probably didn't explain myself as well as I could have done. I haven't read back through what I said but I apologise for any confusion.
Yes, it would appear as though we do differ on our opinion as to what the 0.05Ω value means. I am aware it is only a suggested value but GN3 clearly states that: 'When testing the effectiveness of main bonding conductors, the resistive value between a service pipe or other extraneous-conductive -part and the MET should be of the order of 0.05 ohms or less'. I read it as it is.

I don't want to go on for ever but will just say that I think the confusion arose because I was looking at the subject from a position of the conditions for applying supplementary bonding from scratch and you were from a position of testing a completed installation for an EICR.

Therefore the 0.05Ω is used to verify the bonding is satisfactory but has nothing to do with whether it is required or not in the first place.

My argument is that although on the face of it, even if the resistance between the point of testing within the bathroom on exposed pipework or structural metalwork and the MET is less than or equal to 50V/Ia, if the actual main bonding conductor is higher than 0.05Ω then it could be argued that the main bonding conductor is not effectively connected, so regardless of R≤50V/Ia, one of the three conditions is not met. I concede however that this point is arguable and open to interpretation.

I agree with you on this although it has been argued here before that it does not matter how long the main bonding conductor is (e.g. 10mm. over 27m.)

No, I'm not. The situation I gave where the radiator measured 6kohms to the MET was entirely real! You seem to have disregarded the fact that although a pipe can be plastic and non conductive, the water flowing through it is conductive. Therefore, it is entirely possible for something not fixed to the ground and fed in plastic (in part or in whole) to be extraneous! This is what makes lazy plumbers and their penchant for PVC tees such a blimmin minefield when it comes to supplementary bonding! The simple solution I use when plumbing using PVC between copper for anything is to supplementary bond over any PVC joints to keep copper continuity. In a property where the water service is extraneous, this needs to be done!

As I've already said, a plastic fed radiator can be extraneous even if not fixed to the ground.

I will admit I don't really know what to say to this. I have never come across the situation.
The fact is a radiator (not fixed to the ground) cannot be extraneous nor can plastic pipes so you are saying the water requires bonding.
This would lead to the situation of (with plastic pipes) bonding being applied to the radiators themselves rather than the pipes.
If the water leads to this situation then perhaps plastic pipes should not be allowed unless the actual supply pipe is plastic.

Again, my argument is that if an extraneous conductive part still needs bonding then it is not effectively connected in the first place.

Wouldn't that require MAIN bonding if all the radiators in the premises were at 6kΩ wrt the MET?

Also, R≤50V/Ia does apply between exposed conductive parts as well as extraneous conductive parts.

Between the parts, yes - but not from exposed parts to the MET before bonding.

 

[D Skelton]

Ahhh, two educated beings with slightly differing opinions reaching common ground is a beautiful thing. I thought the debate would never end!

I don't want to go on for ever but will just say that I think the confusion arose because I was looking at the subject from a position of the conditions for applying supplementary bonding from scratch and you were from a position of testing a completed installation for an EICR.

Therefore the 0.05Ω is used to verify the bonding is satisfactory but has nothing to do with whether it is required or not in the first place.

Totally agree.

I will admit I don't really know what to say to this. I have never come across the situation.
The fact is a radiator (not fixed to the ground) cannot be extraneous nor can plastic pipes so you are saying the water requires bonding.

The very meaning of the word extraneous means 'liable to introduce potential' namely earth potential. It doesn't really matter what something is, what is made of (within reason) or how it gets from 'A' to 'B', if it can introduce earth potential then it is extraneous. Now obviously, plastic is non conductive so cannot in itself introduce a potential but it transports a conductive liquid. In the case of a PVC join in a copper pipe the water is simply bridging the gap in the copper, albeit not very well, but the gap is bridged non the less. If a radiator forming an integral part of the heating system within a property is connected to extraneous pipework then it is also extraneous, what some of that pipework may be made up of is immaterial.

This would lead to the situation of (with plastic pipes) bonding being applied to the radiators themselves rather than the pipes.
If the water leads to this situation then perhaps plastic pipes should not be allowed unless the actual supply pipe is plastic.

You will never find a radiator connected directly to a copper pipe. Firstly because it looks atrocious but more importantly because the rad valve requires a compression fit with olive, something that is never recommended with PVC pipe. Still, should a crime against common sense be committed and a radiator connected directly to plastic pipework be found to be extraneous then there are specifically made radiator bonding clamps available from any reputable wholesaler for this very situation! lol.

With regards to plastic pipes not being allowed, I agree! Unless... people using them are educated about using supplementary bonding to ensure continuity across PVC joins and PVC lengths of pipe! There are products on the market that make this literally a five second job, but plumbers being plumbers (never the sharpest tools in the box are they?) have never and will never give a cr@p about anything related to electrical safety.

Wouldn't that require MAIN bonding if all the radiators in the premises were at 6kΩ wrt the MET?

In a bathroom, no, it would require supplementary bonding as regardless to its cause, one of the three conditions is not met. The absence or inadequacy of main bonding is another matter that needs addressing, that when addressed, if addressed first could potentially change the need for supplementary bonding within the bathroom thereafter.

Between the parts, yes - but not from exposed parts to the MET before bonding.

Obviously yes, I agree.


Well Geoff, I can certainly say I have enjoyed this! We got there in the end and I think it's fair to say that we now understand where some of our opinions differ slightly. You're now in my book of 'Guys who can hold their own in a decent debate' and you're up there on the first page with Eng and his love for debates on the relationship between TT systems and RCD protection! Like I said, excercising the grey matter surely makes a difference to answering threads such as: "How do I wire a two way light switch?" and the age old favourite "I've done a Electrical Trainee course, does that make me fully qualified?".

 

[Geoffsd]

Ah, I wasn't thinking of just one (or two) plastic joint. That would allow normal bonding out of sight.
I was thinking of long lengths and couldn't see how the water could do that.

Thank you for the compliments - reciprocated.




PM me if you really want to know how to wire two-way lights. :smile5:



:seeya:

 

[Guitarist]

Thanks for the debate guys. Thoroughly enjoyable and enough to make plumbers realise how easy they have it, for double the money we earn...

 

[telectrix]

Thanks for the debate guys. Thoroughly enjoyable and enough to make plumbers realise how easy they have it, for double the money we earn...

but plumbers have a far greater responsibility. they could cause a water stain on the bedroom shagpile, which disaster would be, as we all know, of far greater importance to mrs. jones than keeping her family safe from minor irritations like electrocution and house fires.

 

[Jay Sparks]

Not really connected to this thread and probably a bit of useless info but I did a continuity test on a cup of water the other day using my megger mft. It started out at around 18 kohms and gradually rose until I got bored of holding the probes in the cup (around 50 kohms). But I believe it would of continued to get higher.

Dont really know why I did it, just after reading this exciting thread/debate, I wanted to know what kind of reading I would get. Not that it matters one little bit.lol

 

[Geordie Spark]

Not really connected to this thread and probably a bit of useless info but I did a continuity test on a cup of water the other day using my megger mft. It started out at around 18 kohms and gradually rose until I got bored of holding the probes in the cup (around 50 kohms). But I believe it would of continued to get higher.

Dont really know why I did it, just after reading this exciting thread/debate, I wanted to know what kind of reading I would get. Not that it matters one little bit.lol

Maybe if you'd kept it going long enough you could have made yourself a cup of tea?

It's a useful little tip to remember for the day the kettle breaks. ;-

 

[Jay Sparks]

The strange thing was that when I took out the probes and dried them, then put them back in again, the reading continued from when I took them out.....I would of thought that it would of started from the 18 kohms again.

I might try it on my pee next time but holding the probes and trying to pee will be hard.lol

 

[Silly Sausage]

Jay...
Just guessing here, I wonder if that's got to do with electrolysis?
The longer you do it, the less ions there will be in water, so conductivity falls.
You've probably slightly plated your negative probe!


edit: obvious mistake rectified!!!

 

[telectrix]

the water itself is non-conductive, it's the impurities in it that cause conductivity.

 

[davethsparky]

Can't remember which course I was doing but on one of them we were told that if a plastic 22mm pipe is over 600mm long then the water inside will be of high enough resistance to not require bonding.
Seemed a bit fishy to me as water in different areas will have different resistivity.

 

[Guitarist]

the water itself is non-conductive, it's the impurities in it that cause conductivity.

And if the property has a water softener, then the conductivity will be relatively high, due to the salt content in the water.

 

[hoppy]

Thanks for a great educating post, I have learned a thing or two.

Can I confirm I have got my head around this subject correctly.

To test if something is extraneous, IR test @ 500V between main earth and the part in question, if below 45k ohms then considered extraneous (why 45k ohms)?
Then continuity check between part and MET value must be below 50v / Ia or the part in question will require supp bonding regardless of RCD protected or not as it is considered to not be effectively connected to earth?

Also, you should continuity test between all extraneous and exposed conductive parts in a bathroom and the resistances between these parts should again be below 50V / Ia? Again if not then sup bonding is required regardless of RCD Protection?

The lack of sup bonding if calculated and measured to be required is therefore always a code 2 regardless of rcd protection?

Thanks

Craig

 

[D Skelton]

Up to 5mA across the body, although perceivable, will not cause any ill effects ie. pain or involuntary convulsion of the muscle. Anything above 5mA and there is a chance of damage caused directly or indirectly as a result of the shock. Many people will accept anything over 10mA to be the dangerous level of current where involuntary muscle contractions will definitely happen. I and many others consider good practice to be preventing the chance of anything higher than 5mA to flow through the body in the event of a fault. GN3 I believe (although I could be wrong here) also uses 45kohms as the figure to determine whether or not something is extraneous or not. It's all about safe leves of current at the end of the day, in all honesty it's a point we could all argue until the cows come home as we will each have our own views as to what 'safe' current levels are as there isn't really anything written down in statute. The reason for 45kohms is simple; 230/5mA = 46kohms. 1000ohms is accepted to be the lowest possible value of bodily resistance, so this is then taken away from the 46kohms leaving 45kohms. In other words, if you were isolated from earth and connected to 230V nothing would happen, if you were to then touch something measuring 45kohms to true earth then adding your 1000ohms to the equation would mean that no more than 5mA would flow through your body. It would be a perceivable amount of current but under normal circumstances you would be under no danger.

In answer to your other questions; yes, although some points could be debatable (see previous posts)

 

[Guitarist]

10mA is considered the "let-go" threshold, and as such GN8 uses 22k as the figure (the reason hospital RCD's were always 10mA). That said, it does acknowledge that in certain circumstances the designer may consider 10mA too high.