Bathroom supplementary earth bonding - do I need more?

[EFLImpudence]

Indeed, but your (415.2.2-based) argument would seem to apply even if satisfactory Main bonding was not present and/or 701.415.2(vi) was not satisfied (i.e. such that the regs seem to indicate that SB would be required), wouldn't they?

I don't see the argument.
Main bonding should be checked whatever job is being done and should be compliant.
Were it not in place then the 415.2 tests would surely be equally relevant for SB but the situation should not arise.

That makes sense, but there is presumably some reason why they put the RCD Ia into that reg?

As I said, because that is the arbitrary limit for omission of SB, albeit (effectively) impossible to ever be relevant like the 23kΩ limit for MB.

I would imagine that satisfying the '415.2.2 test' when there is no RCD could quite easily be a struggle (particularly for a shower circuit), since it presumably requires a resistance between parts which is nearly 4.6 times lower than the 'maximum Zs' (currently) required of a circuit for ADS.

Yes, of course. That is why it is why SB is dependent upon it (test).

 

[JohnW2]

I don't see the argument.
Main bonding should be checked whatever job is being done and should be compliant.

It should, indeed. However, the authors of the regs presumably must have contemplated some situations in which that is not the case, otherwise they would presumably not have bothered to make it an explicit requirement for omission of SB.

Were it not in place then the 415.2 tests would surely be equally relevant for SB but the situation should not arise.

Well, not really relevant as far as the regs were concerned, since SB would be required regardless of the results of the tests. And, if you had just installed the SB for that reason, you presumably would not have any 'doubt' that it was there (and adequate) - hence,again, not requiring a test.

Kind Regards, John

 

[banjo67xxx]

I hope that no-one has ever suggested that you would have to have SB on your fancy chrome rail - as I'm sure was said early on, it is perfectly acceptable for the SB (attached to the pipe feeding the rail) to be outside the room (e.g. in your airing cupboard).

Thanks for the clarification on that point. I had seen a comment about it being visible, and as such beneath the floor boards was not sufficient. But its good to know that it can be visible in a different room.

BTW, in your discussions about reasons why you would want to measure effectiveness of SB. Could the regs be referring to the possibility of the SB being connected to a corroded pipe, and thus you might want to measure it to ensure that the corrosion was not creating a resistance.

 

[EFLImpudence]

I think I have deciphered your last post. It was confusing.

I have never thought about it before but don't know why the regs. mention the lack of MB when it is compulsory.
Just emphasising the fact, I suppose.

I don't see the argument.
Main bonding should be checked whatever job is being done and should be compliant.

It should, indeed. However, the authors of the regs presumably must have contemplated some situations in which that is not the case, otherwise they would presumably not have bothered to make it an explicit requirement for omission of SB.

It seems strange when talking about when SB is required or not, to ask about something else which, is mandatory regardless. being absent but I see your point.

Were it not in place then the 415.2 tests would surely be equally relevant for SB but the situation should not arise.

Well, not really relevant as far as the regs were concerned, since SB would be required regardless of the results of the tests.

Well, firstly it doesn't really ever apply. does it?
Secondly, the conditions for omission of SB because of RCDs etc. not being met does not mean that SB must be applied when not required in its own right.

And, if you had just installed the SB for that reason,

Ok ???

you presumably would not have any 'doubt' that it was there (and adequate) - hence,again, not requiring a test.

The same tests would apply as when no RCD is present.
The measurements could likely be higher without any MB but it would never arise, would it?

 

[EFLImpudence]

BTW, in your discussions about reasons why you would want to measure effectiveness of SB. Could the regs be referring to the possibility of the SB being connected to a corroded pipe, and thus you might want to measure it to ensure that the corrosion was not creating a resistance.

Good thinking. Yes that could have an effect and may raise suspicion.

All the measurements I/we have been talking about are between the parts themselves but, yes, a test which showed it was likely bonded in the past could deteriorate and become unsatisfactory.

 

[JohnW2]

It seems strange when talking about when SB is required or not, to ask about something else which, is mandatory regardless. being absent but I see your point.

Quite - that was my very point. Mind you, on reflection, I suppose the requirement for all circuits to satisfy the ADS requirements is at least as strange. Again, (assuming that they accept that ADS may be satisfied by an RCD in a TT installation), it is something that is mandatory, regardless of the issue od SB. In fact, one might regard it as even stranger than the mention of Main Bonding given that, since one of the other requirements is RCD protection, in the context of SB, the adequacy of ADS is not really all that important (not as important as Main Bonding).

... the conditions for omission of SB because of RCDs etc. not being met does not mean that SB must be applied when not required in its own right.

If one applies common sense and/or invokes your interpretation of 415.2.2 then that is true.

And, if you had just installed the SB for that reason, you presumably would not have any 'doubt' that it was there (and adequate) - hence,again, not requiring a test.

The same tests would apply as when no RCD is present.

... but it was you who reminded me that 415.2.2 says that the test only needs to be done "Where doubt exists about the effectiveness of the SB" (even suggsting that such doubt might exist because of non-visibility of the SB). So, as I said, if you had just installed the SB, I would not expect you to have any doubt about its 'effectiveness' (or existence!), would you? If you did not feel that doubt existed, then 415.2.2 does not require any tests.

Kind Regards, John

 

[JohnW2]

Thanks for the clarification on that point. I had seen a comment about it being visible, and as such beneath the floor boards was not sufficient. But its good to know that it can be visible in a different room.

You're welcome. At the worst of times it's only the connections of the SB (to pipes etc.) that need to be 'accessible', but the regs explicitly say that the SB can be outside of the room.

BTW, in your discussions about reasons why you would want to measure effectiveness of SB. Could the regs be referring to the possibility of the SB being connected to a corroded pipe, and thus you might want to measure it to ensure that the corrosion was not creating a resistance.

Sure. As we've been discussing, the regs say that the tests should be done "Where doubt exists regarding the effectiveness of the SB", and seeing corrosion in the vicinity of the bonding (which, as above, must be accessible for inspection) would certainly be one thing which would/could raise such doubts.

However, if you've managed to follow the exchanges between EFLI and myself, his view/interpretation of the regs goes a lot further than that. He feels that if one undertakes the prescribed test (in a room with no visible SB) and gets a satisfactory result, then it is not necessary to install SB even if one cannot see any SB (which perhaps doesn't even exist). I agree totally with him that such is 'perfectly satisfactory electrical common sense', but (as you've probably seen!) I do not personally interpret the regs as actually saying that one may omit installing SB in that situation. As you may be aware, the regulations and 'electrical common sense' are not necessarily always quite the same thing!

Kind Regards, John

 

[EFLImpudence]

And, if you had just installed the SB for that reason, you presumably would not have any 'doubt' that it was there (and adequate) - hence,again, not requiring a test.

The same tests would apply as when no RCD is present.

... but it was you who reminded me that 415.2.2 says that the test only needs to be done "Where doubt exists about the effectiveness of the SB"

No . I don't think I said that - certainly didn't mean to.

The tests are to determine whether SB is required.

The problem arises in other threads elsewhere when no SB is seen by an inexperienced EICRer who asks "Which code applies?" without testing to see if it it required or hidden.

(even suggsting that such doubt might exist because of non-visibility of the SB). So, as I said, if you had just installed the SB, I would not expect you to have any doubt about its 'effectiveness' (or existence!), would you?

No, obviously not.

If you did not feel that doubt existed, then 415.2.2 does not require any tests.

No, but the tests would have been done to determine if I had needed to install the SB.

 

[JohnW2]

... but it was you who reminded me that 415.2.2 says that the test only needs to be done "Where doubt exists about the effectiveness of the SB"

No . I don't think I said that - certainly didn't mean to.

Hmmm ...

.... that [415.2.2] appears to be stating the resistance requirements for assessing "the effectiveness of supplementary bonding" (which presumably implies that supplementary bonding is already in place), rather than for deciding whether supplementary bonding may be omitted.

Same difference, It says "Where doubt exists", presumably not visible. So, you test "the effectiveness" ...

The tests are to determine whether SB is required.

I think we have 'agreed to disagree' about your interpretation of the regs. The reg I'm reading says that the tests should be undertaken "Where doubt exists regarding the effectiveness of the supplementary protective bonding" (not "Where doubt exists regarding how low a resistance path exists between extraneous-c-ps and exposed-c-ps", or "Where doubt exists regarding whether SB is required")

If you did not feel that doubt existed, then 415.2.2 does not require any tests.

No, but the tests would have been done to determine if I had needed to install the SB.

Perhaps, but would you really bother if, for example, there were no RCD and a 50A shower circuit?

Kind Regards, John

 

[EFLImpudence]

... but it was you who reminded me that 415.2.2 says that the test only needs to be done "Where doubt exists about the effectiveness of the SB"

No . I don't think I said that - certainly didn't mean to.

Hmmm ...

.... that [415.2.2] appears to be stating the resistance requirements for assessing "the effectiveness of supplementary bonding" (which presumably implies that supplementary bonding is already in place), rather than for deciding whether supplementary bonding may be omitted.

Same difference, It says "Where doubt exists", presumably not visible. So, you test "the effectiveness" ...

Yes, but that was in answer to your point.
I also said "Same difference".
I didn't mean that was the only reason.

Why is it unacceptable to you that, given SB is applied to achieve a certain resistance value, it is therefore not necessary if that value is already achieved without it?

I think we have 'agreed to disagree' about your interpretation of the regs. The reg I'm reading says that the tests should be undertaken "Where doubt exists regarding the effectiveness of the supplementary protective bonding" (not "Where doubt exists regarding how low a resistance path exists between extraneous-c-ps and exposed-c-ps", or "Where doubt exists regarding whether SB is required")

Ok.

Why then do the regs. only demand R≤50/Ia
If SB shall be applied in any case why would not the required value be a figure of 0.1Ω or such like?

Perhaps, but would you really bother if, for example, there were no RCD and a 50A shower circuit?

Well, why would you not?

You are implying that SB shall be applied regardless.

This is not so.

 

[JohnW2]

Why is it unacceptable to you that, given SB is applied to achieve a certain resistance value, it is therefore not necessary if that value is already achieved without it?

I thought I'd made it very clear that it is far from 'unacceptable' to me, personally. As I have said (probably several times), it makes complete sense (both electrical and 'common') to me. I do, however, have difficulty in interpreting the words of the regs as sharing that electrical/common sense view.

Although I am personally very comfortable with your approach, if I reach for my Devil's Advocate hat, I can see how people (perhaps including those who wrote the regs) could be unhappy. If, as you have acknowledged could be the case, one does not know what is resulting in a low resistance one measures when does a "415.2.2 test", some may say that one cannot guarantee that it is always going to be that low - it could be due to some 'temporary plumbing' or all sorts of other possible things. As you know, there is precedence for regs which are similarly unhappy about reliance on things which one can't guarantee won't change.

I think we have 'agreed to disagree' about your interpretation of the regs. The reg I'm reading says that the tests should be undertaken "Where doubt exists regarding the effectiveness of the supplementary protective bonding" (not "Where doubt exists regarding how low a resistance path exists between extraneous-c-ps and exposed-c-ps", or "Where doubt exists regarding whether SB is required")

Ok. Why then do the regs. only demand R≤50/Ia. If SB shall be applied in any case why would not the required value be a figure of 0.1Ω or such like?

We know why they specify R≤50/Ia, but in some senses your question is a good one. If the resistance is anything other than 'very low', I think one might want to investigate, even if the resistance measured 'passes the test'. In the case of RCD protection, I would personally be very concerned, and would want to investigate, if the resistance were anything other than 'very low', even though the regs would accept a value up to 1,666Ω, wouldn't you?

Kind Regards, John