Done a CU change today, brief testing before hand I knew there was a problem on one circuit, believed to be the element in the immersion tank so put the very low IR readings down to this.
Fitted new CU with plumber arranged to look at the immersion, changed it and thought that would be that. House previously had no main rcd protection at CU.
When I did the IR testing today before powering up i got >199 on all circuits accept the immersion heater radial.
L-E 0.9 Mohms N-E 3Mohms L-N 2.3Mohms.
So knew something was a miss. Bit of investigation and tucked behind the water tank was a rcd socket with 2 shower pumps plugged in. so the immersion radial does both the tank and a double socket.
Removed rcd socket and got >199 ohms on all tests
Put Rcd socket back in and found that the 2 shower pumps (Both 3 amp fused plug in sorts) would trip the rcd in the consumer unit but not the rcd socket. It had not tripped previously when the old re-wireable fuses were in use. Customer didn't even know it was there!
The pumps when plugged into a normal socket did not trip the CU rcd. The RCD in the Cu would trip with the pumps plugged in but not even working with both showers off.
Ramp tested the rcd socket and it trips at 24mA, The 2 pumps when plugged into a normal socket do not trip the CU rcd, it only trips if plugged into the rcd socket.
Taken it out to achieve discrimination or come 2019 selectivity, but its baffled me as it ramp tests as okay at 24Ma, I put the rcd socket on the upstairs ring and put the vacuum on it, no tripping. so seems as if the 2 pumps are the cause but as said when on a normal 2 gang socket the Cu rcd doesnt trip.
Could it be leakage across both the rcd socket and the 2 pumps combined? Only other thing on consumer unit rcd is the cooker circuit which at 500v IR got >999 on all tests.
its good to know for future reference as I like to know why things tripped.
rcd socket shown below:
![[ElectriciansForums.net] Trying to figure cause of tripping](https://www.electriciansforums.net/attachments/20180911_185550-jpg.44257/ "[ElectriciansForums.net] Trying to figure cause of tripping")
Fitted new CU with plumber arranged to look at the immersion, changed it and thought that would be that. House previously had no main rcd protection at CU.
When I did the IR testing today before powering up i got >199 on all circuits accept the immersion heater radial.
L-E 0.9 Mohms N-E 3Mohms L-N 2.3Mohms.
So knew something was a miss. Bit of investigation and tucked behind the water tank was a rcd socket with 2 shower pumps plugged in. so the immersion radial does both the tank and a double socket.
Removed rcd socket and got >199 ohms on all tests
Put Rcd socket back in and found that the 2 shower pumps (Both 3 amp fused plug in sorts) would trip the rcd in the consumer unit but not the rcd socket. It had not tripped previously when the old re-wireable fuses were in use. Customer didn't even know it was there!
The pumps when plugged into a normal socket did not trip the CU rcd. The RCD in the Cu would trip with the pumps plugged in but not even working with both showers off.
Ramp tested the rcd socket and it trips at 24mA, The 2 pumps when plugged into a normal socket do not trip the CU rcd, it only trips if plugged into the rcd socket.
Taken it out to achieve discrimination or come 2019 selectivity, but its baffled me as it ramp tests as okay at 24Ma, I put the rcd socket on the upstairs ring and put the vacuum on it, no tripping. so seems as if the 2 pumps are the cause but as said when on a normal 2 gang socket the Cu rcd doesnt trip.
Could it be leakage across both the rcd socket and the 2 pumps combined? Only other thing on consumer unit rcd is the cooker circuit which at 500v IR got >999 on all tests.
its good to know for future reference as I like to know why things tripped.
rcd socket shown below:
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