max zs on a tt system

[marksparky]

hi folks was wonderin if u have a tt system with a ze of say 113ohms, and a circuit say lights with a r1+r2 of 1.33ohms, in the section on test results were it asks max zs allowed by bs7671.... the answer for a type b 6amp mcb would be 6.13. So if my zs is ze..113+ (r1+r2)1.33 =114.33
which is clearly much more than 6.13ohms. My question is as the circuit is protected by a 30ma rcd does the max zs permitted by bs7671 now become 1667ohms as opposed to 6.13? cheers.

 

[telectrix]

yes.....

 

[Octopus]

yes.....

But it doesn't mean that when testing a value of 1666 is OK though!

 

[truckster]

and another yes......Simon what do you think?

 

[marksparky]

cheers telectrix for the prompt reply, i thought as much but always good to seek clarification from the more knowledgable members for the forum

 

[marksparky]

lol yes alarm bells wud be ringing with a value of such, followed by tester being turned off and on a few times

 

[petlac]

Just had my NICEIC assessment and my assessor stated that Table 41.5 should be used for TT systems. Thus for a 30mA it is 1667.

 

[sparks1973]

what it is is 50V (max touch voltage)/30mA=166.6666667...so 1667....

 

[petlac]

Check out regulation 411.5 Ra x IΔn <or= 50V..... thus 50V/0.03 (30mA) = 1666.66666 etc.