Bonding gas/water yellow and blue

[Houndogg10]

Hi I am recently qualified and still have a lot of learning/reading to do but Blue plastic waterpipe incoming, seems to always be a grey area with electricians I work with, me personally wouldn’t bond it..... Although we have to prove that in the plumbers install their is no copper going to earth?? Can someone enlighten me on this please

Many thanks..... and go easy on me lol

 

[Pete999]

Carrying out a 500 v IR test from the MET to the piece of metal if you get 0.02 Mohms or higher then it’s believed not to be extraneous that is it won’t induce an earth potential if you follow the formula 230/ 0.01 amps= 23000 ohms.

Don't forget to factor in the average hunmanbody resistance of 1000 ohms deduct this from your calculated 23000 ohms gives 23000 minus 10000 = 22Kohms

 

[Ian1981]

Don't forget to factor in the average hunmanbody resistance of 1000 ohms deduct this from your calculated 23000 ohms gives 23000 minus 10000 = 22Kohms

Yep your right pete.

 

[Midwest]

So, we've (or I've learnt) two different tests or equations.

One for extraneous-conductive-parts as defined by reg 411.3.1.2 (equation suggested in GN8 6.1), and one for supplementary bonding, as defined by reg 415.2.2.

Sorted.

 

[Richard Burns]

I’m interested into what Midwest has previously said about that change to the existing guidance on it.
Tho I suspect upgrading the bonding is more to do with New works carried out.
I’m aware that there’s no statutory law that requires that an electrical installation needs upgrading to the current regulations if you like but that new work must be designed and installed to the current edition of bs 7671.

What I was trying to say was that the certificate declaration says that you have not made the installation worse in terms of safety. If your work was compliant but the installation as a whole had problems then you would not have made things worse and so could complete the work without upgrading the bonding (for instance).

However this is countered by the requirement to ensure earthing and bonding is adequate for the protective measure employed.
Which takes precedence? Hmm open to interpretation.
Obviously the best thing to do would be to upgrade, but, as you say, it can be ridiculous to do so in some cases.

 

[Deleted member 26818]

22 Mohms is the value which indicates a conductive -part is isolated from Earth (22Mohms if we take account of the resistance of the human body).
0.02 Mohms (20 Ohms) is the value which indicates a conductive-part is reliably connected to Earth and is the minimum resistance in the range which requires bonding.
7.67 kohms is the maximum resistance in the range which requires bonding (6.67 kohms if we take account of the resistance of the human body).
0.05 ohms is the maximum resistance for the connection of a bonding conductor to an extraneous conductive-part.

 

[Ian1981]

Yep your right pete.

22 Mohms is the value which indicates a conductive -part is isolated from Earth (22Mohms if we take account of the resistance of the human body).
0.02 Mohms (20 Ohms) is the value which indicates a conductive-part is reliably connected to Earth and is the minimum resistance in the range which requires bonding.
7.67 kohms is the maximum resistance in the range which requires bonding (6.67 kohms if we take account of the resistance of the human body).
0.05 ohms is the maximum resistance for the connection of a bonding conductor to an extraneous conductive-part.

7.67 would be if your using a 30mA rcd as your threshold if you like.
But 0.02 Mohms is not 20 ohms perhaps you misquoted?
0.05 ohms for a bonding conductor is only guidance at best as only GN3 references this value and not bs 7671 that is it’s not set in stone.

 

[Deleted member 26818]

Yes 30mA, not necessarily RCD protected.
Sorry yes should kohms not Mohms.

 

[Risteard]

Alsways took it as applying to al Earth conductors.
Main earths, bonding, CPCs, etc.

Bonding conductors are not earth conductors though although they are protective conductors.

 

[Midwest]

In reading GN8 6.1 again, it mentions the BS PD 6519, IEC 60479 Guide to effects of current on human beings & livestock, which apparently provides data for ZTL & IB.
For hand to hand contact, it gives a resistance of the human body of 1000ohms, and 0.5mA as the threshold of perception and 10mA as the let-go threshold.

Using those figures (specifically 10mA), gives a figure of 22kohms, suggesting the designer elects to accept the let-go threshold as a safe level. It also says the designer might need to consider variations in resistance & whether a lower limit on the current flowing threw the human body or livestock is necessary.

From that, can I deduce using 30mA as IB, resulting in a figure of 6.67kohms for RCP, is not recommended?

I do have a copy of a 'Connections Technical' that also gives a figure of 6.67kohms, from a calculation using a 30mA RCD. Makes you wonder who to believe!

 

[Richard Burns]

It is up to the designer to decide what level of safety is required for the installation and so then specify the required level of resistance that is acceptable to determine the identification of extraneous conductive parts.
Generally 10mA is used because it is a catch all situation, not too bad not perfect.
If you have lots of large animals then less than 2mA may be the best approach, if there is minimal chance of any accidental contact and everyone in the area is adult then 30mA may be suitable.

 

[Deleted member 26818]

It’s not based on a 30mA RCD, it’s just based on 30mA.

 

[Midwest]

It’s not based on a 30mA RCD, it’s just based on 30mA.

The Connection Magazine example is, if you are referring to my post 114?

 

[Deleted member 26818]

The Connection Magazine example is, if you are referring to my post 114?

Well that’s just nonsensical.
A 30mA RCD can let through much more current than 30mA.

 

[Ian1981]

Yes but for additional protection it must disconnect in at least 0.04 of a second

 

[Midwest]

Well that’s just nonsensical.
A 30mA RCD can let through much more current than 30mA.

Page 48. Quite a good piece, forgot I had it (and read it!), till this thread started.
Connections Magazine Autumn 2014 - https://issuu.com/redactive/docs/con_aut14