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TT system for garage, RCD question

Hello, not used this forum in a while and have had to re-register. I hope someone can help. I have an upcoming job to replace an existing small consumer unit in a garage about 30m from the house. The supply at  the house is PME, and the current set up is a 4mm SWA fed from an MCB in the house CU,  I recommended a switch fuse but the customer does not want this as it means destroying the wooden cabinet the existing CU is in. So the feed to the garage will be from a 32A mcb..Ive specified an earth rod at the garage as its concrete floor.is damp and dont want to export the PME. I will earth the outer armoured wire via the gland at the house end only, not at the garage end, and provide a TT earth system to the new garage CU.


My question is regarding rcd's ? The 2 way garage CU will have x2 30mA  rcbo's for the outgoing circuits so then is there really a need for a 100ma main switch ? as it would serve no purpose. So to reiterate, the supply is SWA, protected by mcb at the house..If I use a 63A/100A mainswitch at the garage CU, will this be okay as it provides manual dp isolation., I want to reuse to existing garage CU and its metal.


The last time I installed an earth rod was over 20 years ago so want to
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  • There is no room at the house to fit an upstream time delayed RCD,or anything else for that matter. DP rcbo's,are a good option thanks for recommendation, the garage needs 20A for power, and a 6A for lighting.

    Recommendations for dp rcbo's and a 100ma mainswitch in the garage board to protect against rcbo failure sounds like the ideal option.


    However Im most interested about the dp protection on a TT install, is it a requirement that TT installs have DP protection ? Would a mainswitch provide this if single pole rcbo's were ever used? , as a mainswitch is not  a "protective device", its a manually operated isolator..





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  • There is no room at the house to fit an upstream time delayed RCD,or anything else for that matter. DP rcbo's,are a good option thanks for recommendation, the garage needs 20A for power, and a 6A for lighting.

    Recommendations for dp rcbo's and a 100ma mainswitch in the garage board to protect against rcbo failure sounds like the ideal option.


    However Im most interested about the dp protection on a TT install, is it a requirement that TT installs have DP protection ? Would a mainswitch provide this if single pole rcbo's were ever used? , as a mainswitch is not  a "protective device", its a manually operated isolator..





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