Supplementary Bonding - How was it wired?

[telectrix]

where a RCD is fitted, R<= 1667. the 0.05 is considered to be a negligible resistance between different extraneous metal parts and MET. in other words, the OCPD is guaranteed to trip within the required time.

 

[Geoffsd]

I was going to do my continuity tests, and was quite confident that using the formulae from reg. 415.2.2; R< 50/Ia ,where in the case of a 6amp BS EN 60898 MCB Ia = 30amp. Therefore R=50/30 < (less than) 1.666ohms. However, talking to another electrician, he said the reading should be below 0.05ohms. Can anyone advise?

You are correct.

 

[Midwest]

where a RCD is fitted, R<= 1667. the 0.05 is considered to be a negligible resistance between different extraneous metal parts and MET. in other words, the OCPD is guaranteed to trip within the required time.

So what is 'reg. 415.2.2; R< 50/Ia' for?

 

[Geoffsd]

So what is 'reg. 415.2.2; R< 50/Ia' for?

If the protective device is an RCD then R ≤ 50/Ia of RCD = 50/0.03 = 1666

If an MCB then R ≤ 50/Ia of MCB (30,50,80,100,125.160,200,225,250 or 315)

 

[Midwest]

I was going to do my continuity tests, and was quite confident that using the formulae from reg. 415.2.2; R< 50/Ia ,where in the case of a 6amp BS EN 60898 MCB Ia = 30amp. Therefore R=50/30 < (less than) 1.666ohms. However, talking to another electrician, he said the reading should be below 0.05ohms. Can anyone advise?

Did my tests. Pipes in heater cupboard, all 0.00-0.05ohms. Same pipes to MET, 0.00-0.05ohms. Extraneous conductive parts in bathroom (i.e. cold & hot supply to basin & rads & connecting pipework) > 99.9kohms. Same result to cpc of circuits in bathroom. On inspection of cupboard under kitchen sink, plastic water main to plastic pipe, to short peice of copper to sink. I suspect the house is plumbed predominantly in plastic pipe, with the last visible peice in copper, which I believe does not require bonding.

 

[Geoffsd]

Pipes in heater cupboard, all 0.00-0.05ohms. Same pipes to MET, 0.00-0.05ohms.

It would seem they are already bonded and satisfactory.
0.05 is just an accepted value of negligible impedance and does not relate to any test as such, other than a satisfactory connection.

Extraneous conductive parts in bathroom (i.e. cold & hot supply to basin & rads & connecting pipework) > 99.9kohms. Same result to cpc of circuits in bathroom.

Then they do not require bonding and should not be bonded.
If that is the maximum range reading it could be a lot higher. You could test with IR.

On inspection of cupboard under kitchen sink, plastic water main to plastic pipe, to short peice of copper to sink. I suspect the house is plumbed predominantly in plastic pipe, with the last visible peice in copper, which I believe does not require bonding.

Correct.

 

[Midwest]

Thanks All

 

[Midwest]

Out of interest; I was reading somewhere on this forum that if the R < 1667ohms, the extra' cond' should be bonded R> 22kohms it does not, I know that's noy quite right, but I can't find that thread now. What formulea are used for such figures, and where does that appear in the regs?

 

[SPARTYKUS]

I believe all would be revealed in GN8 (guidance note 8) - the earthing and bonding one. Pretty sure its in that one. If not then its GN3, the testing and inspection one.

 

[Midwest]

I believe all would be revealed in GN8 (guidance note 8) - the earthing and bonding one. Pretty sure its in that one. If not then its GN3, the testing and inspection one.

Reading G8 now, what page? :clap:

 

[SPARTYKUS]

Reading G8 now, what page? :clap:

Er, ah..... I'll take the zero out of ten on that one!!

not near my copy, sorry. You'll just have to read through the whole book )

 

[Midwest]

Dooooh, just trying to cheat.

 

[Richard Burns]

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