Calling B-A-S Re:'Equipotential bonding ......' comment

[Careful_Bodger]

Hi B-A-S,

You said 'Equipotential bonding doesn't have to go back to the CU.' (17/12/04)

Can you expand on this a bit? I thought that this was the whole point about (Mains) Equipotential Bonding? (as opposed to Supp Bonding)

...and why shouldn't it be 'under the floor'? Is there a Reg?

Thanks!

 

[securespark]

In Ban's absence, I shall say this:

Both phrases "Main Bonding" and "Supplementary Bonding" have been legitimately shortened. The full phrase should have the word

"Equipotential"

inserted before the word "Bonding".

Main Equipotential Bonding reduces electric shock risk by connecting together any exposed conductive parts (like the earthed casing of a faulty appliance) to any extraneous conductive parts (like water pipes/taps). It bonds items like pipework, ducting, exposed girders etc directly to the MET.

Supplementary Equipotential Bonding involves connecting together the conductive parts of electrical AND non-electrical items such as pipes, wastes, metal baths and sinks and cpc's to prevent a dangerous voltage between them appearing under earth fault conditions.

In both cases, as stated, the aim by both types of bonding is to reduce any voltage that may appear in metalwork under earth fault conditions.

PD (potential difference) is the difference in voltage between one conductor and another. If the tap you are holding with one hand is bonded to earth like the faulty appliance you are touching with the other, then the PD likely to flow is very little (or hopefully zero), and no shock risk is present.

The under floor bit I do not understand as I cannot remember what Ban wrote originally. Can you dig it out?


Ban.

Which size fuse do you want? I have mailed you, but guess you are out of the office now...

 

[andy]

it can go to the MET instead of the CU. not sure why not under floorboards tho

 

[Careful_Bodger]

Thanks for your comment on BAS's behalf, SSpark, but if my understanding is correct then your definitions dont agree with those in the Guide to the Regs.

At the risk embarrasing myself these state (extracted & summarised from http://www.tlc-direct.co.uk/Book/5.4.3.htm )......

Two types of equipotential bonding conductor are specified.

1. - Main equipotential bonding conductors
These conductors connect together the installation earthing system and the metalwork of other services such as gas and water. <etc>

2. - Supplementary bonding conductors
These conductors connect together extraneous conductive parts - that is, metalwork which is not associated with the electrical installation but which may provide a conducting path giving rise to shock. <etc>

I am only trying to learn here - so any clarification is really appreciated.

 

[andy]

Thanks for your comment on BAS's behalf, SSpark, but if my understanding is correct then your definitions dont agree with those in the Guide to the Regs.

At the risk embarrasing myself these state (extracted & summarised from http://www.tlc-direct.co.uk/Book/5.4.3.htm )......

Two types of equipotential bonding conductor are specified.

1. - Main equipotential bonding conductors
These conductors connect together the installation earthing system and the metalwork of other services such as gas and water. <etc>

2. - Supplementary bonding conductors
These conductors connect together extraneous conductive parts - that is, metalwork which is not associated with the electrical installation but which may provide a conducting path giving rise to shock. <etc>

I am only trying to learn here - so any clarification is really appreciated.

what dont you understand? i dont see anything wrong with what SS said or the above?

 

[plugwash]

main bonding is about making your whole house an equipotential zone (so you bond the main incoming mains to incoming pipes)

however such a large equipotential zone is never going to be a brilliant one so the same is done on an individual room level in high risk areas. (bathrooms and swimming pools mainly)

 

[Careful_Bodger]

Andrew,

SS stated that Main Equpotential Bonding included 'extraneous conductive parts (like water pipes/taps)'.

The IEE's definition puts this into the Supplementary Bonding category. The IEE also use the term Main Equipotential Bonding only for services such as water and gas.

I was also confused since SS uses 'Supplementary Equipotential Bonding', whereas the IEE shorten it to 'Supplementary Bonding'. This might be just a matter of terminology, but the IEE is (presumably) gospel in this matter???

If you can help my pre-christmas addled brain, I'd be most greatful

 

[kai]

ermm.

 

[securespark]

I was also confused since SS uses 'Supplementary Equipotential Bonding', whereas the IEE shorten it to 'Supplementary Bonding'.

Careful, one of the first things I said was that the phrases "Main Bonding" and "Supplementary Bonding" should have the word "Equipotential" inserted in the middle.

Therefore, the phrase 'Supplementary Bonding' is a legitimate replacement for 'Supplementary Equipotential Bonding'.

Both the IEE and the NIC recognise this.


The IEE's definition of extraneous conductive part is: A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.

So, taps and pipes come under this description.

Where have you found the definitions?

You also say that "The IEE's definition puts this into the Supplementary Bonding category."

So why do I see in the regs, a diagram showing a main equipotential bonding conductor feeding a main water pipe and an extraneous conductive part?
Furthermore, regulation 413-02-02 states that main equipotential bonding conductors shall connect to the MET extraneous conductive parts including:

water service pipes, gas installation pipes, other service pipes and ducting, central heating and air-con systems, exposed metallic structural parts of the building, and the lightning protective system.

NOT just "services such as water and gas".

Have a look at a copy of the OSG (On-site Guide). This should help.

 

[Careful_Bodger]

Wow - thanks for the excellent reply SS.

I got all my info from my copy of the Regs (7th ed), particularly the definitions used therein and figures 5.13 & 5.14 (also at http://www.tlc-direct.co.uk/Book/5.4.3.htm - for anyone following this thread without a copy)

I shall recheck my copy of OSG as you suggest.

Cheers

 

[securespark]

But Careful, the 7th Edition was issued in 1916! We've come a long way since then......

 

[Careful_Bodger]

bottom right hand corner '7th Ed' - but I take your point

 

[pipme]

C_B I think this is similar to SS's 'On site Guide', it is published by the Institute of Electrical Engineers - IEE

You refer to John Whitfield's 7th edition of 'The Electricians Guide'.

P

 

[Careful_Bodger]

Okay, I I should have said 'Guide to the Regs'

........and there was I trying to be specific about choice of bonding terminology

Good sparring tho' - and it all helps with understanding, which is the point of being here.............. isn't it????

 

[pipme]

Both publications are very good for the interested reader.
P