Do you mean some regs. but not others?
I wouldn't say it is extremely common.
It depends on the requirements.
Not 'very rarely'.
What else is there?
No. 701.415 starts with '..in accordance with 415.2...'
Bathroom supplementary earth bonding - do I need more?
- Thread starter banjo67xxx
- Start date
It depends on the requirements.
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Some regs. One only has to be non-compliant with one reg to be non-compliant!
I was talking about the actual 'situation' i.e. all resistances between pipe and pipe and between pipe and circuit CPs being very low. How common do you regard that (in copper-plumbed premises)?
In the absence of RCD protection etc, the regs require supplementary bonding, as described. If I understand you correctly, you may well decide that such bonding does not need to be installed on the basis of your measurements - is that correct?
Is that perhaps a veiled reference to 415.2.2? If so, that 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.
Kind REgards, John
With which would it not be compliant?
I thought you meant because there was not actually a separate SB connected to the terminal.
Not particularly common.
Should there be a 45A shower in a large house then the requirements may be difficult to meet with CPCs and pipes.
In some of the flats I look after where all services are on the other side of the bathroom wall it is quite easy.
Yes. That is how it is done.
Not veiled.
Same difference, It says "Where doubt exists", presumably not visible.
So, you test "the effectiveness" and the results are satisfactory - what then?
If those requirements are met without (as above flats) bonding then the conditions are satisfied.
Assessing "the effectiveness" does not tell you whether there is bonding in place or the runs are short the same results are achieved.
Well, even that one is a good start for discussion. As 415.2 effectively says, in the case of a bathroom, one has to comply with 701.415.2 as well as 415.2 itself, and 701.415.2 appears to explicity require connection of SB to "the terminal of the CPC".
Fair enouigh. I would have said that left an awful lot of premises where the situation I described was true, but life is too short to spend time discussing 'how common' that makes it!
It certainly makes electrical sense to do it like that, but I'm still far from convinced that this is what the regs intended. If you are relying on 415.2.2 to make this (sensible) approach compliant, then please see below.
Hmmmm. It actually says "Where doubt exists about the effectiveness of supplementary equipotential bonding...", rather than "Where doubt exists about how well electrically connected e-c-ps are...". As I said, I would have thought that one can only "assess the effectiveness" of something which exists, and I really don't find it easy to interpret those above words as meaning that 415.2.2 can be used to decide whether SB may be omitted (in a location that does not yet have SB).
I'm not sure I've ever thought about this before, but I'm having some difficulty in actually understanding the logic of the 'tests' described in 415.2.2, which relate specifically to the resistance between simultaneously touchable extraneous-c-ps and exposed-c-ps. I need to think about this, and may have more to say after I've thunk!
Kind Regards, John
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It's not really that specific.
It says "Local SB shall be established connecting together the terminals..." and, as has been agreed, 543 states what may be used for this purpose.
Apart from that, there are plenty of regs. which state something must be done in such a way but obviously do not apply when that thing is not required at all.
Main Bonding, for example, has very specific instructions about its connection but is not required if the part is not extraneous.
It is often the case that SB is not immediately visible as it does not have to be in the room.
Therefore a test is carried out to determine R≤50/Ia. It does not then matter what is achieving this desired result.
You are missing the main point that SB is to ensure touch voltage is below 50V so if it already is all is well.
I am surprised.
As above, it is to limit touch voltage to what is considered 'safe' i.e. 50V.
Therefore, if the installation (in the location) only has a touch voltage of, say, 25V then there is no need for supplementary (i.e. additional) bonding.
In the case of the OP there is only a lighting circuit and radiator pipe.
So R≤50/Ia = R≤50/30 = R≤1.66Ω
His measured resistance is 0.2Ω. 30x0.2 = 6V.
Whether this is because of the bonding he has seen in the airing cupboard or just the situation in the premises does not really matter.
[Just in case there is a 5A fuse and not 6A MCB (used in the example) I would point out that the conditions are similar; indeed, less onerous.]
I think all I can do is acknowledge that I understand that to be your view and interpretation. FWIW, to me, mentioning 'terminals' when they could just have said 'connecting to CPC' seems to imply they were thinking fairly specifically.
Yet again, that makes total electrical sense. However, in all that is written in the regs about SB, I don't see anything which actually says, or (I know you disagree) even implies, that one can omit explicit SB if tests show that resistances are (for whatever reason) already lower than would be required of 'effective' SB.
Not at all - see below.
Having never thought about it very deeply, that's what I have always assumed (indeed, it's often popped up in discussions here). However, although it's probably just because I'm not thinking clearly enough, I'm now wondering whether 'passing' their test (based on measuring resistance between extraneous-c-p and exposed-c-p), alone, is necessarily guaranteed to achieve that. Certainly in the case of RCD protection, I can think of at least one situation (admittedly pretty far-fetched/unlikely!) in which the resistance between parts could be low enough to satisfy the test, yet the RCD would not operate with touch voltages (between the parts) greater than 50V, although I don't think the same could happen with OPD protection. However, I'm still thinking about all this!
Kind Regards, John
It's not an interpretation. That is how it's done.
Whilst saying "that's how it's done" I acknowledge that most, when applying SB would just connect together everything regardless and connect together the same two pipes several times and/or run a cable along a pipe which has a resistance is nine times lower.
The requirements of supplementary bonding are not, as would be the case with a direct connection between two parts, to reduce the resistance to negligible but enough to ensure the resistance limits touch voltage to 50V.
That is implicit in 415.2 and the note at the bottom of 701.415.2; namely that R≤50/Ia.
So, if it already is, supplementary (additional) measures are not required.
I hesitate to say pointless because touch voltage would be reduced to negligible but that is not required.
What else is there?
Not sure what you have in mind but...
the purpose of supplementary bonding is not to ensure the RCD (or OPD) operates if/when the parts are touched but to limit the touch voltage between them while the RCD (or OPD) is disconnecting the supply because of a fault.
50/30mA = 1666Ω is the reason for allowing omission of SB when RCDs, with the other conditions, are installed - because R≤50/Ia which in this case is IΔn.
Although hardly possible, should the resistance be greater than 1666Ω then SB would still be required even with RCDs present.
Yes, I obviously understand that. Indeed, in the case of OPD protection (even a 5A/6A OPD), one would have a pretty fried victim before the device operated as a result of the parts being touched
Indeed. The question I am still pondering is whether having a current ≥IΔn flowing through the resistance (which you have admitted, we may not know the source/path of) between extraneous-c-p and exposed-c-p necessarily guarantees that there will be an L-N imbalance equal to that current experienced by the RCD (hence resulting in its operation). It probably does, but I need to convince myself that this is necessarily always the case
Kind Regards, John
I dont fully understand what CPC terminals are, but I can tell you that the wiring in the airing cupboard connects the earth from an electrical junction box (part of the central heating circuit) to all 4 water pipes (mains, HW, CH out, CH return). Does this define it as SB rather than "plumber's cross bonding" ?
I dont want to see SB on my fancy chrome towel rail, so if the above is not SB, then I'll use EFLImpudence's argument to convince anyone that the SB already exists somewhere else in the building.
I dont want to see SB on my fancy chrome towel rail, so if the above is not SB, then I'll use EFLImpudence's argument to convince anyone that the SB already exists somewhere else in the building.
Circuit Protective Conductor - Earth wire.
It would appear to be SB.
Plumbers don't normally connect it to the CPCs.
Either or both.
EFLI, in starting to do some more pondering, I have realised that I probably need to first question you! ...[... It probably does, but I need to convince myself that this is necessarily always the case
Do I take it that you are assuming that the electrical circuit is 'satisfactory' (compliant)? If it is, then ADS requirements dictate that R1+R2 cannot be more than a few ohms at the very most, let's say about 10Ω to be generous. That means that the appearance on an exposed-c-p of any voltage more than about 0.3V would cause a 30mA RCD protecting the circuit to operate. If the RCD operates when the potential of exposed-c-ps is >0.3V, there is clearly no way that a touch voltage (between it and extraneous-c-ps) >50V could ever persist, regardless of the resistance between exposed-c-ps and extraneous-c-ps.
That being the case, if one takes your view that SB is only required if there is not already adequate provision for protective devices to prevent touch voltages >50V persisting, then presumably the presence of 30mA RCD protection (of a compliant and fault-free circuit) would always mean that SB was not required, so there would be no point in even measuring the resistance between extraneous-c-p and exposed-c-p (i.e. 'the 415.2.2 test') - is that your view?
Kind Regards, John
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). Despite all the technical distractions, the only real question has been about how that SB should be connected to the CPCs (i.e. 'the mains', as you have described it).
Kind REgards, John
mistake
Well, I suppose so but the discussion only applies when there is a fault so is the answer not really?
If you mean where all the circuits have RCD protection, then that is why no SB is required (that being the same, presumably, as 'may be omitted') as long as ADS and Main Bonding are satisfactory as well.
The 415.2 test is only required when not RCD protected.
The 1666Ω limit is just a number derived from the same calculation (much like 23kΩ for Main Bonding) but not really relevant as it will never be applicable.
Back later.
You know full well what I meant - satisfactory and compliant until a fault arose which cause the 'touch voltage' to appear!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?
That makes sense, but there is presumably some reason why they put the RCD Ia into that reg? 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.
Kind Regards, John
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