Steel Bath how to earth.

[Electrifying]

With a Continuity tester on the Ohms setting, test between each metal pipe
that enters the bathroom (Extraneous conductive parts) and the circuit
protective conductor (cpc/earth) of each electrical circuit in the bathroom.
If the reading is less than 1667ohms and all circuits are protected
by 30mA RCD’s then no Supplementary Bonding is required.
If any of the above requirements cannot be met, Supplementary Bonding
must be installed.

A bit of a wild statement - what if he does the test that you suggest and gets a reading of infinity - i.e. no continuity at all........does he supplemetry bond whatever the metalwork is and introduce a hazard that wasn't there in the first place??

Although 701.415.2(v) does, indeed, state that RCD protection is also needed in order to allow supplementary bonding to be omitted,I'm not entirely sure that I really understand the thinking behind that. I'm certainly not denying that RCD protection is a good idea for a bathroom, but I'm not sure why its absence should cause one to have to locally bond e-p-cs which are already (as required by 701.415.2(vi) effectively bonded together. Perhaps I'm missing something.Kind Regards, John

Maybe you're missing the fact that without RCD protection the disconnection time under earth fault conditions will be a lot higher (i.e. within 0.4 sec as opposed to 0.04 sec), so the rise in difference in potential between an 'exposed conductive part' (the 'fault') and other metal parts could be a lot higher due to the prolonged fault condition.
Supplementary bonding will therefore help reduce the difference in potential that may occur.

With an RCD protecting the circuit, and Main Bonding in place, it is not deemed necessary.

That's my take on it, anyway.

 

[JohnW2]

I would say much better informed than some of the electricians that I refer to as "electricians"

Well, that's obviously flattering, for which I thank you - but the fact that you need to make the statement as a whole is obviously a bit sad.

Kind Regards, John.

 

[RF Lighting]

I bet some of the so called electricians don't waffle on as much as JohnW2 though

 

[JohnW2]

Maybe you're missing the fact that without RCD protection the disconnection time under earth fault conditions will be a lot higher (i.e. within 0.4 sec as opposed to 0.04 sec), so the rise in difference in potential between an 'exposed conductive part' (the 'fault') and other metal parts could be a lot higher due to the prolonged fault condition.

I don't really understand that. Even 0.04 seconds is 2 cycles as 50Hz - why should the p.d. become 'a lot higher' subsequent to the first two cycles of a fault?

Kind Regards, John.

 

[sparkticus]

A bit of a wild statement - what if he does the test that you suggest and gets a reading of infinity - i.e. no continuity at all........does he supplemetry bond whatever the metalwork is and introduce a hazard that wasn't there in the first place??

That's a good question but one where we would need more information.
If those two pipes were connected to plastic just under the boards with zero risk of them becoming live then in my opinion they offer no intrinsic risk and I would personally not bond them. In my opinion bonding them (which is essentially connecting them to the MET via other bonds/plumbing etc) increases risk of obtaining a PD between them and something live within arms reach (a faulty shower for example)



If they disappeared under the boards in copper but the resistance reading was infinity between them (unlikely) and infinity between each one and the MET then I would personally see that as too high a risk not to bond. One or both pipes might be in close proximity to a cable or other source of electrical risk. I know I would not feel very secure if I was in that bath hanging on to them in such a case.

 

[sparkticus]

I bet some of the so called electricians don't waffle on as much as JohnW2 though

Not so much waffle as debate to the Nth degree

Though that shows interest and interest is a good thing in my book.

 

[sparkticus]

I would say much better informed than some of the electricians that I refer to as "electricians"

Well, that's obviously flattering, for which I thank you - but the fact that you need to make the statement as a whole is obviously a bit sad.

A bit sad yes and I don't want to sound like a moaning old man (even if I am) I am just a bit irritated almost daily by people who make no effort to understand the underlying principles and have a single solution for all circumstances. I saw an EIC this week that showed Zs values almost 0.35 ohms less than the measured Ze In fact the entire cert was a irresponsibly/badly filled out (I was going to ask if the final circuit had been connected directly to the supply transformer via some jump start leads) Why I let it bother me I do not know. I suppose it is that I care about the reputation of the trade that I practice and make my living from. On the plus side these people are are not in the majority and I do have the good fortune to work with some brilliant people from time to time. So everything in perspective as D Cockburn might say about potential fault current

 

[JohnW2]

I bet some of the so called electricians don't waffle on as much as JohnW2 though

Not so much waffle as debate to the Nth degree Though that shows interest and interest is a good thing in my book.

I didn't expect much debate, let alone argument. I can read, and assimilate a set of regulations as well as anyone else, but I realised that there were (probably necessarily) many aspects of the Wiring Regs which were not exhaustive or particularly (if at all!!) clear, and which therefore require interpretation. There are also many practical issues which people learn to deal with by experience, not education or regulations.

I therefore came to this forum a few months ago with the aim of discovering how practising electricians thought, how they interpreted and applied the regs and how they tackled practical situations. Perhaps naively, I thought I was going to find something approaching a consensus about the issues which were not clearly answered by the word of the regs, and I certainly didn't expect to find myself debating, let alone arguing, with electricians about these issues. I suppose I shouldn't really have been surprised to discover that, in practice, even electrical wiring is often no more precise a science than are most other disciplines with which I've been involved.

I'm sure that I won’t always be here. Whatever may appear to be the case, the wiring of electrical installations is not a significant part of my life, and at some point I will undoubtedly decide that the time has come for me to get on with the rest of my life proper. I suppose the only reason I’ve stayed for as long as I have is because it has proved to be a far more interesting and challenging intellectual exercise than I would ever have expected!

Enough of this waffle

Kind Regards, John.

 

[sparkticus]

I therefore came to this forum a few months ago with the aim of discovering how practising electricians thought,

Steady now, electricians "thinking" is an extremely radical concept

 

[RF Lighting]

I'm sure that I won’t always be here

Oh you will

I joined to pass a bit of time while I was off work for 5 weeks with a broken ankle. That was heading on for 6 years and 13 thousand posts ago

I love it here how much it makes you actually think about why you are doing things and personally I think being a contributer to this forum has made me a better electrician, and I certainly have a better understanding of the science of electricity, it's distribution and BS7671 too.

I'm only teasing by the way. I'm sure you know you can rattle on a bit but your posts make for interesting reading.

 

[EFLImpudence]

I'm sure that I won’t always be here.

Untitled

• EFLImpudence
• 3 Aug 2011
• 1

Only joking

 

[sparkticus]

I love it here how much it makes you actually think about why you are doing things and personally I think being a contributer to this forum has made me a better electrician, and I certainly have a better understanding of the science of electricity, it's distribution and BS7671 too.

Absolutely, I only joined a matter of weeks ago and wish I had joined much earlier. It has been a significant learning experience for me too. I am also inspired by the fact that there are electricians/electrical engineers, DIYers and interested professionals from other professions with so much knowledge of electrical science, electrical regulations and full of challenging questions.

 

[sparkticus]

at some point I will undoubtedly decide that the time has come for me to get on with the rest of my life proper.

Oh dear, I guess you didn't read the small print when you signed up


DIYNOT rules

- Pressing accept indicates you agree to making lifelong contributions to the forum. Forum members may only leave after producing a signed copy of their enlistment into the foreign legion.

 

[sparkticus]

Maybe you're missing the fact that without RCD protection the disconnection time under earth fault conditions will be a lot higher (i.e. within 0.4 sec as opposed to 0.04 sec), so the rise in difference in potential between an 'exposed conductive part' (the 'fault') and other metal parts could be a lot higher due to the prolonged fault condition.

I don't really understand that. Even 0.04 seconds is 2 cycles as 50Hz - why should the p.d. become 'a lot higher' subsequent to the first two cycles of a fault?

Yes two cycles and plenty of time for the fault current to rise to an almost quiescent state. It is the act of rapid disconnection that attempts to provide the protection. An RCD does little to limit the amplitude of the fault current. EDIT- Sorry I also meant to respond to the rise in potential.
2 cycles of AC will result in full voltage amplitude. There will be attenuating factors along the fault path but full voltage is still applied.

 

[Electrifying]

I don't really understand that. Even 0.04 seconds is 2 cycles as 50Hz - why should the p.d. become 'a lot higher' subsequent to the first two cycles of a fault?

Kind Regards, John.

You're thinking too much into it - it's simpler than you think.

We know from the touch-voltage equation that if your 'Earth Loop Impedance' (the 'earthing' bit), is less than 1667 ohms, then a 30mA RCD will disconnect before the voltage reaches 50 Volts, (what they deem as safe).

Without an RCD, you cannot guarantee disconnection before a dangerous potential difference is reached, so you have to supplementary bond, in order to 'additionally' reduce this 'difference' - that's why, like a 30mA RCD, supplementary bonding is called 'additional protection'
It's applied to a bathroom because of the obvious additional danger.