Bonding water and gas

[keniff]

Hi, could someone point me in the right direction, iv read somewhere that if an extraneous conductive part reading is above a certain resistance it should be bonded, where can I find info on this? Thanks in advance

 

[Richard Burns]

http://www.electriciansforums.net/e...xtraneous-yes-no.html?highlight=bonding+22000
Try this sticky thread, for resistance readings below a certain level

 

[MarkieSparkie]

Hi Keith, Safely isolate the installation. Temporary disconnect any main bonding cables (gas, water e.t.c.) from the MET for the duration of the test to remove their parallel earth paths if it's considered necessary. With a Insulation Resistance Ohmmeter set on M Ohms @500V, connect one lead to the MET and the other lead to the "extraneous conductive part". If the meter reading is 0.022M Ohms (22K Ohms) or greater, NO supplementary bonding is required. This is based on a 10mA let-go threshold that I use. The NICEIC alternatively quote =>7K Ohms (6667 Ohms calculated) based on a 30mA let-go threshold. See link below for further details:

http://www.electriciansforums.net/e...ical-regulations/16558-extraneous-yes-no.html

 

[malcolmsanford]

Hi Keith, Safely isolate the installation. Temporary disconnect any main bonding cables (gas, water e.t.c.) from the MET for the duration of the test to remove their parallel earth paths if it's considered necessary. With a high resistance ohmmeter set on M Ohms @500V, connect one lead to the MET and the other lead to the "extraneous conductive part". If the meter reading is 0.022M Ohms (22K Ohms) or greater, NO supplementary bonding is required. This is based on a 10mA let-go threshold that I use. The NICEIC alternatively quote =>7K Ohms (6667 Ohms calculated) based on a 30mA let-go threshold. See link below for further details:

http://www.electriciansforums.net/e...ical-regulations/16558-extraneous-yes-no.html

Hi Mark top answer as usual mate, but I noticed you used the term High Resitance Ohm meter in connection with an Insulation Resistance tester.

We had a thread on here a while back where a lad came on and was told by his tutor to use your term for it, and I think, me included shot the tutor down in flames as we all regarded it as a wrong term.

When someone like you mate uses it, makes me think , has the term now been put into the GN books?

 

[keniff]

Thanks very much for the replies, so is there a formula for this then? You say calculation would I find this in the regs book? Thanks again

 

[malcolmsanford]

415.2.2

 

[MarkieSparkie]

Hi Mark top answer as usual mate, but I noticed you used the term High Resitance Ohm meter in connection with an Insulation Resistance tester.

We had a thread on here a while back where a lad came on and was told by his tutor to use your term for it, and I think, me included shot the tutor down in flames as we all regarded it as a wrong term.

When someone like you mate uses it, makes me think , has the term now been put into the GN books?

Hi Malcolm, Whoops! thanks for pointing that lapse out, C&G used to like High Resistance Ohmmeter back in the early days when I did 2391, currently Insulation Resistance Test Instrument seems to be the favourite of C&G, but the bible GN3 still refers to Insulation Resistance Ohmmeter and is what I should have said as this maybe read by students, however Insulation Resistance Tester is the more widely used industry and manufacturers monika. Pay your money and take your choice?

 

[MarkieSparkie]

Thanks very much for the replies, so is there a formula for this then? You say calculation would I find this in the regs book? Thanks again

The metallic part can be assumed NOT to be an extraneous-conductive-part if the following condition is met:
Rcp=> (Uo/Ib) - Ztl
where,
Rcp is the resistance between the conductive part and the MET in ohms
Uo is the nominal voltage to Earth in volts
Ib is the value of current through the body in amperes that should not be exceeded. (The value may be taken as 0.03A (30mA) for a disconnection time of up to 0.4 s, as given in DD IEC/TS 60479)
Ztl is the impedance of the human body in ohms. The value suggested in DD IEC/TS 60479 is 1000 Ohms where Uo is 230 V (50 Hz) under dry or wet conditions.

Taking Ib as 30 mA and Ztl as 1000 Ohms (as suggested above where the disconnection times in the installation are 0.4 s or less and Uo is 230 V), the limiting value of Rcp is given by:


Rcp => (230V/0.03A) - 1000 Ohms

Rcp => 6667 Ohms

Note: NICEIC round up to =>7K Ohms

Thus, if Rcp exceeds 6667 Ohms, the pipe may be considered not to be an extraneous-conductive-part, such that main bonding of the pipe is not required


Traditionally electricians prefer to use 0.01A (10mA) as the value of current through the body in amperes that should not be exceeded, the let-go threshold, which would change the outcome of the formula to 22K Ohms

The other point to remember is that although we're talking about not needing to bond if over 22K Ohms, in theory there's also the lower limit of 1667 Ohms, due to the 50v touch voltage limit, where the protective device is an RCD (50V/0.03A = 1667 Ohms). 415