S
SpannerSpark
Hello all,
I have just installed new circuit for a friend from an existing install. The new circuit is fed via underground SWA (from an old building) to a new building. In the new building I have fitted a 2way CU with combined main switch/30mA RCD (new type RCD BS61009) and two MCBs (lights & sockets). The only CU in the old building (the feed to my new circuit) is an old wylex metal clad with a old style single main switch/30mA RCD (WSES80/2F BS4293?) covering all circuits. Therefore i told my friend that I would need to add a new small CU in the old building or in some other way provide some discrimination between the old and new 30mA RCDs. He said he would really like the install to work sooner rather than later and so i agreed to test my new install and then temporarily fit the new circuit to the old CU. I explained that any RCD trip type fault would most probably take out both RCDs and all circuits. The new circuit tested out exactly as expected, all good. The system worked for a couple of days and then the old RCD tripped, was reset and then a couple of days later tripped again. Is was then than i was in a position to install the new CU in the old building, protected my new circuit on the new CU (main switch and 32A MCB only as the earthing system is TNCS and the distribution circuit Zs was low enough to not need a 100mA type. Since then all circuits have behaved 100% ok (another two days). I have checked and rechecked my measurements, all spot on (e.g insulation res >500M all circuits inc distribution SWA). i was wondering if the old style RCDs worked differently and could in some way have a problem being connected to a circuit with a new style RCD in it.
I know that now my distribution circuit has no RCD then any latent fault before the new CU RCD wont show up, thats why i have remeasured my circuit and its spot on.
I have just installed new circuit for a friend from an existing install. The new circuit is fed via underground SWA (from an old building) to a new building. In the new building I have fitted a 2way CU with combined main switch/30mA RCD (new type RCD BS61009) and two MCBs (lights & sockets). The only CU in the old building (the feed to my new circuit) is an old wylex metal clad with a old style single main switch/30mA RCD (WSES80/2F BS4293?) covering all circuits. Therefore i told my friend that I would need to add a new small CU in the old building or in some other way provide some discrimination between the old and new 30mA RCDs. He said he would really like the install to work sooner rather than later and so i agreed to test my new install and then temporarily fit the new circuit to the old CU. I explained that any RCD trip type fault would most probably take out both RCDs and all circuits. The new circuit tested out exactly as expected, all good. The system worked for a couple of days and then the old RCD tripped, was reset and then a couple of days later tripped again. Is was then than i was in a position to install the new CU in the old building, protected my new circuit on the new CU (main switch and 32A MCB only as the earthing system is TNCS and the distribution circuit Zs was low enough to not need a 100mA type. Since then all circuits have behaved 100% ok (another two days). I have checked and rechecked my measurements, all spot on (e.g insulation res >500M all circuits inc distribution SWA). i was wondering if the old style RCDs worked differently and could in some way have a problem being connected to a circuit with a new style RCD in it.
I know that now my distribution circuit has no RCD then any latent fault before the new CU RCD wont show up, thats why i have remeasured my circuit and its spot on.
