Tt rcd protection

chappy2000 · May 9, 2016

Hi all, hoping someone can help. Have a car park with its own supply, meter box located in the corner of a shared car park, TT system. Small db located inside meter box supplying only two circuits, one for car park lighting and one for electric gates. My question is does this installation require at least a 100ma rcd due to it being a tt system. Only current protection for the circuits are 60898 MCB'S. All electric connections and meter box are only accessible via key / tool and there are no user controls.

Leesparkykent · May 9, 2016

chappy2000 said:
Hi all, hoping someone can help. Have a car park with its own supply, meter box located in the corner of a shared car park, TT system. Small db located inside meter box supplying only two circuits, one for car park lighting and one for electric gates. My question is does this installation require at least a 100ma rcd due to it being a tt system. Only current protection for the circuits are 60898 MCB'S. All electric connections and meter box are only accessible via key / tool and there are no user controls.

whats the Ra you've measured?

chappy2000 · May 9, 2016

Hi, thanks for the quick reply. 18.9 measured ze

Leesparkykent · May 9, 2016

chappy2000 said:
Hi, thanks for the quick reply. 18.9 measured ze

well yes you require an RCD as the protective devices are basically ornamental as they are atm when it comes to fault protection.

chappy2000 · May 9, 2016

Thanks. I understand it requires rcd protection to achieve zs but I didn't know if different rules apply as it's not located or serving a dwelling, I regeneration years ago a reg referring to Street lighting

davesparks · May 10, 2016

chappy2000 said:
Hi, thanks for the quick reply. 18.9 measured ze

What is the Ra?
Presumably pretty low so it might be possible to get it lower and negate the need for an RCD.

GEOFF S · May 10, 2016

davesparks said:
What is the Ra?
Presumably pretty low so it might be possible to get it lower and negate the need for an RCD.

Hi

I wouldn't of thought that strategy would be feasible Dave, several points, its not just Ra, Rb also needs to be considered, also who's going to monitor the earthing system what if seasonal variation increases to the point where devices do not operate effectively?

Cheers