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Discuss Supplementary Bonding in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

M

mgumbrell

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Supplementary Bonding:-
· Regarding Regulation 415.2.2
o What would be regarding as having satisfied the effectiveness of supplementary equipotential bonding?
§ I understand that the Resistance between simultaneously accessible exposed-conductive-parts on a 230v system (50v being the agreed safe “touch Voltage”) should be calculated at the highest rating of the protection device serving that area; typically 32A. However a fault to earth could happen at any location in an installation. Therefore what (I[SUB]a[/SUB]) should be used to calculate the effectiveness as this may be a sub-main cable causing a fault to earth protected by a MCCB. In short apart from special locations (Part 7) that may define Supplementary Bonding requirements what (I[SUB]a[/SUB]) should be used in the calculation of resistance in formula (R ≤ 50 V/I[SUB]a[/SUB]) Based on:-
· 32A Circuit Breaker the Resistance between simultaneously accessible exposed-conductive-parts should be less than or equal to – 1.563 Ω (Is this correct?)
· 32A 30ma RCBO the Resistance between simultaneously accessible exposed-conductive-parts should be less than or equal to – 1666.667 Ω (Is this correct?)
o However, where there is a mixture of circuits protected by various protective devices; again I am unsure on what protective device rating should be used.

Is anyone able to advise?

Regards
Matt
 
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M

MKS

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  • #2
Second part looks ok, you need to re evaluate the first :)
 
D

Deleted member 9648

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  • #3
Your terminology is incorrect......supplementary bonding is between conductive parts and extraneous conductive parts. The measurement is made between simultaneous exposed conductive parts and extraneous conductive parts.............not between simultaneous exposed conductive parts.
 
Mgumbrel, the current component for that equation is not the rating of the protective device but the effective operating current of the particular device.
So for a type b 32 amp circuit breaker, for a disconnection time of 0.1 to 5 seconds, it is 160amps ( from brb).
therefore r=50/160 which is 0.31 ohms. 0.31 ohms is the maximum reading taken between exposed conductive parts and extraineous conductive parts in that bathroom. If there are a mixture of circuits in the bathroom then use the largest protective device for the largest circuit.
The example above would have a different outcome for a different protective device.
Hope this helps
 
M

mgumbrell

  • Thread Starter Thread Starter
  • #5
Thank you guys.

Wirepuller:- I took the annotation from 415.2.2 wich does state "....simultaneously accessible exposed-conductive-parts...."

dagrat:- So there is no diference if a RCBO (32A) is being used, it still remains that the reading must be below 0.31 ohms. However this only works for overcurrent and not earth fault at 30mA

Regards
Matt
 
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