Maximum length of Main Bonding

[claret73]

I did find the answer pretty much to this in an old thread & was answered by Chris...

But wonder if I could get a few more suggestions as to being correct.
Installed a Main Water Bond from a DB Board to the Main Incoming water supply which was (in my opinion) well over 25m away. We ran it along the existing SWA supplying the Workshop/Garage. It was run in 10mm.

No Test was carried out to confirm the 0.05 Max reading and from what I can figure am not sure if the cable has a high enough CSA.

In OSG I see an R2 reading on 10mm at 20deg of 0.00183 (even though the cable is run outside for most of its length), again from Chris's answer I can only have 27m before 0.05 resistance is breached.

I'm right in saying anything over 27m needs to step up to 16mm.

If the resistance is above the 0.05 does this have no barring consequences as to the potential difference between exposed & extraneous parts? Can't seem to find the exact clarification on this.
Cheers

 

[acat]

The wording is "it is recommended that the resistance of the bonding conductors does not exceed 0.05ohms. 16mm will give you a 47mtr run


Chris

 

[Deleted member 9648]

Guys I've seen this 0.05 ohms max in various threads on here but I've not seen it in the BRB or onsite guide. Not saying it isnt there but I would be grateful if someone can point me at the reg cos I appear to have missed that one.

 

[acat]

Guidance Note 3 page 35.


Chris

 

[scotsparky]

Calum what about safety circuits that have no RCD protection or Sub Mains or older installations that didn't require RCD protection?? Where would the Earth Fault Loop Path? why would you want it to be under 0.05 ohms?

I know the answers and its not "stupid"

 

[DurhamSparky]

has CBW been in here with his defibrillator and resurrected the thread!!

 

[ezzzekiel]

yeah thats just what i was thinking !!!

 

[ELEKTRIC]

From table 9A on the OSG (page 166) we get the value of resistance per metre of a given conductor cross sectional area (csa), for example:
What is the maximum permissible length of a 10mm2 protective conductor so that it is effective?
From the OSG we see that the value of resistance per metre of 10mm2 protective conductor is 1.83mΩ/metre, so the maximum length will be:

0.05 x 1000 ÷ 1.83 = 27.32 metres​

Or:
L = R (max permissible resistance) x (csa) ÷ ρ (resistivity of copper = 0.0178 μΩmetre) (use 0.0183)
L = 0.05Ω x 10mm2 ÷ 0.0183 = 27.32 metres
This value is the maximum permissible length for a 10mm2 protective conductor

​

Cross sectional area Maximum permissible length

1 mm2​

2.76 metres​

1.5 mm2​

4.13 metres​

2.5 mm2​

6.74 metres ​

4 mm2​

10.84 metres​

6 mm2​

16.23 metres​

10 mm2​

27.32 metres​

16 mm2​

43.47 metres​

25 mm2​

68.77 metres​

35 mm2​

95.41 metres​

This test is to ensure that the main bonding conductors are unbroken, and have a resistance low enough to ensure that, in the event of a fault, all exposed and extraneous parts will be live at the same potential.

To achieve this is recommended that the resistance of the bonding conductor DO NOT exceed 0.05 Ohms.​

The reading has to be less than 0.05 Ohms to be acceptable.​

If the resistance is more than 0.05 Ohms the bonding is unsatisfactory and given a CODE 2

 

[ELEKTRIC]

From table 9A on the OSG (page 166) we get the value of resistance per metre of a given conductor cross sectional area (csa), for example:
What is the maximum permissible length of a 10mm2 protective conductor so that it is effective?
From the OSG we see that the value of resistance per metre of 10mm2 protective conductor is 1.83mΩ/metre, so the maximum length will be:

0.05 x 1000 ÷ 1.83 = 27.32 metres​

Or:
L = R (max permissible resistance) x (csa) ÷ ρ (resistivity of copper = 0.0178 μΩmetre) (use 0.0183)
L = 0.05Ω x 10mm2 ÷ 0.0183 = 27.32 metres
This value is the maximum permissible length for a 10mm2 protective conductor

​

Cross sectional area Maximum permissible length

1 mm2​

2.76 metres​

1.5 mm2​

4.13 metres​

2.5 mm2​

6.74 metres ​

4 mm2​

10.84 metres​

6 mm2​

16.23 metres​

10 mm2​

27.32 metres​

16 mm2​

43.47 metres​

25 mm2​

68.77 metres​

35 mm2​

95.41 metres​

CONTINUITY TEST OF MAIN EQUIPOTENTIAL BONDING CONDUCTORS ​

This test is to ensure that the main bonding conductors are unbroken, and have a resistance low enough to ensure that, in the event of a fault, all exposed and extraneous parts will be live at the same potential.

To achieve this is recommended that the resistance of the bonding conductor DO NOT exceed 0.05 Ohms.​

​

The reading has to be less than 0.05 Ohms to be acceptable.​

If the resistance is more than 0.05 Ohms the bonding is unsatisfactory and given a CODE 2​

​

​

​

 

[SimpleSimon]

Where does it say that an RCD protection supparses that of nainsook bonding?

 

[SimpleSimon]

Oh it's all disappeared like magic!!

 

[Spudnik]

Having a tidy up SS.