This is my first posting here - I am not an electrician so please bear with me.
I am trying to establish the best method to provide earthing of a 60A supply to a new build garage / workshop to be taken from a domestic residence. The incoming supply to the house is TN-C-S with a supplementary earth rod. An isolator and Henley blocks have been installed at the head end ready to connect a 60A switched fuse for the garage sub-main cable which is a 14m length of 16mm2 3-core SWA cable laid underground between the buildings. An earth rod and pit has been installed adjacent to the garage in case it is required. Inside the garage is a 10-way RCD consumer unit. The Part P registered electrician who will be responsible for the inspection/testing is of the belief that the garage must have its own separate earthing system i.e. it needs to be TT whereas if compliance allows I would prefer to extend the equi-potential zone of the house and PME it. Hence work on the installation so far allows for either eventuality. There are no water, gas pipes or metal framing in the garage but there is a substantial steel door frame and vehicle lift which could be bonded. From what information I can find, there are instances where 'exporting' the earth is acceptable and others where TT earthing is a requirement. My difficulty is establishing the rules for compliance and where there is room for judgement based on circumstances. My main reason for wanting to extend the EPZ is that extension leads could be run from the house or the garage to anywhere around the buildings possibly at the same time - which with separate earthing seems dangerous to me. If PME of the garage is acceptable, the earth conductor in the sub-main is of adequate csa to serve as CPC and main bonding conductor. I would propose to also connect the new earth rod to the garage earth marshalling terminal as a supplementary earth for added protection. I would welcome the advice and opinions of professionals familiar with this type of installation.
I am trying to establish the best method to provide earthing of a 60A supply to a new build garage / workshop to be taken from a domestic residence. The incoming supply to the house is TN-C-S with a supplementary earth rod. An isolator and Henley blocks have been installed at the head end ready to connect a 60A switched fuse for the garage sub-main cable which is a 14m length of 16mm2 3-core SWA cable laid underground between the buildings. An earth rod and pit has been installed adjacent to the garage in case it is required. Inside the garage is a 10-way RCD consumer unit. The Part P registered electrician who will be responsible for the inspection/testing is of the belief that the garage must have its own separate earthing system i.e. it needs to be TT whereas if compliance allows I would prefer to extend the equi-potential zone of the house and PME it. Hence work on the installation so far allows for either eventuality. There are no water, gas pipes or metal framing in the garage but there is a substantial steel door frame and vehicle lift which could be bonded. From what information I can find, there are instances where 'exporting' the earth is acceptable and others where TT earthing is a requirement. My difficulty is establishing the rules for compliance and where there is room for judgement based on circumstances. My main reason for wanting to extend the EPZ is that extension leads could be run from the house or the garage to anywhere around the buildings possibly at the same time - which with separate earthing seems dangerous to me. If PME of the garage is acceptable, the earth conductor in the sub-main is of adequate csa to serve as CPC and main bonding conductor. I would propose to also connect the new earth rod to the garage earth marshalling terminal as a supplementary earth for added protection. I would welcome the advice and opinions of professionals familiar with this type of installation.