one for dingbat

[maguire]

Hi
Having read a good number of your posts I wonder if you could tell me which additional reference/text books you advise your students, You made a comment in one post that the vast majority of practising electricians have an insuffient grasp of earthing and bonding, my understanding is based on what is required where and when, however I do admit I am weak on concept. I have a copy of snags and solution for reference, but without being to maths orintated I would welcome some advise on any publication you think would help
Mac

 

[Doodley]

A good starter would be IEE BS7671:2008 wiring regulations and the on-site guide! Then there are guidance notes - seperate publications that are specific to certain areas, i.e. guidance note 3: inspection and testing. There is a seperate IEE publication for earthing and bonding.

 

[Doodley]

•Guidance Note 1: Selection and Erection of Equipment, 5th Edition
•Guidance Note 2: Isolation and Switching, 5th Edition
•Guidance Note 3: Inspection & Testing, 5th Edition
•Guidance Note 4: Protection Against Fire, 5th Edition
•Guidance Note 5: Protection Against Electric Shock, 5th Edition
•Guidance Note 6: Protection Against Overcurrent, 5th Edition
•Guidance Note 7: Special Locations, 3rd Edition
•Guidance Note 8: Earthing and Bonding

All can be found/purchased at http://www.theiet.org/publishing/books/wir-reg/index.cfm

 

[maguire]

Hi and Ta I'v got the regs and the osg and a whole lot more, however the concept of Bonding still eludes me, For example if a fault occurs on a immersion heater and the breaker for what ever reason does not operate and a potemtial exists in the tank and associated pipe work why export that fault all round the house I know is a worst case situation but I am trying to illustrate a point, also, on page 145 of the NICEIC tool box guide an example is given for supp bonding where required if the requirement of reg 411 cannot be met so if none of the extraneous conductive parts were bonded then the would not be part of the fault loop, So if you can put me right on where I am unclear on the principle please by all means do
Mac

 

[dingbat]

...the concept of Bonding still eludes me...

A quick explanation:

Earthing is to create an earth fault loop of low enough impedance to generate sufficient levels of fault current to quickly disconnect protective devices.

During the period that a fault exists, all exposed conductive parts become live to at-or-near the fault potential. This is dangerous if you are in simultaneous contact with something at earth potential - extraneous conductive parts.

So, we bond those parts to the main earthing terminal, meaning that they also become live in the event of a fault. The potential difference is reduced and so the shock risk is reduced.

Look at page 32 of the regs, diagram 2.1

We earth exposed conductive parts (conductors 1 & 3).
We bond extraneous conductive parts (conductor 2 and, if necessary 4).

Hope that helps. Otherwise Guidance Note 8 tells you the same in 168 pages.

 

[maguire]

Cheers for that Dingbat your third paragraph has completely resolved my misconception,
Mac