A Voltimum user is facing a dilemma on whether to pass an installation. The tech team at SELECT are here to help!
This Q & A is one of the thousands posted in our Technical Expertise area and answered on a daily basis by our Voltimum Experts.
Question:
On testing a domestic property the is ZE 4.45ohms and the PFC is 45A (not KA) it's a tnc.s system and Scottish Power has accepted responsibility for the fault and is renewing the mains cable in four weeks. I have installed an earth spike which reduced the ZE by 2 ohms but the PFC stayed the same. All the circuits are protected by RCBO's. I carried out a full EICR and all the RCBO's tripped at around 17.9ms x 1 and 18 ms x 5 but the average ZS on the circuits is 4.34oms and the PFC is higher than the 6KA rated RCBO's and the highest rated KA RCBO's available are still too low The question is, can I pass this installation as safe to use until the mains cable is replaced
Answer:
Obviously, the high level of Ze measured at the incoming supply is the cause of high Zs measurements at the end of final circuits and also responsible for the low fault current!
You state that you have installed an earth electrode in addition to the distributors existing earthing arrangement (as a temporary measure we would assume) and all final circuits are protected by RCBO's (30mA ?) and you state that work for rectifying the fault on the incoming supply TN-C-S earth has been organised.
Given this, it would appear from the information you have provided that the installation is in a safe condition for use however on the EICR if there are any C1 or C2 observations it is recommended that the installation should be reported as 'unsatisfactory'.
Remember the EICR is a record of the condition of the inspection and test found at the time carried out and would include observations and recommendations that the client should act upon to ensure the safety of the installation i.e they are then responsible for organising any necessary remedial work.
If reporting on the TN-C-S earthing system the absence of a reliable and effective means of earthing would be recommended to be reported as a C2 Observation so would result in an overall unsatisfactory report.
After SP have completed the repair I would be recommending that a further test of the installation both at the origin of supply on all final circuits is carried out to ensure the reliability and effectiveness of the earthing - a new EICR does not need to be issued for this as a record of the remedial work is all that is necessary - probably a new schedule of test results is all that is required together with any record of the distributors upgrade work.