HI, first post so treat me gently please! (Also posted this in the Sticky Threads by mistake).
At work we have a moveable electric hoist unit that travels round and gets plugged in via a fly lead on a spring loaded cable extension drum to one of various sockets. The sockets are fed as a radial and are 3P+N+E, all fed from the same 4-pole 30ma RCD. The oddity to me is that the hoist itself has a 500ma RCD i.e. after the 30mA RCD. We KNOW we have a fault somewhere on the hoist itself and are looking into that. What I can't figure though is why the RCD's are this way round, it goes against the principles of discrimination to my mind. Neither RCD is anything special that I know i.e. time delayed etc. Not suprisingly when it faults the 30mA trip at the dis. board is generally the one to go (I'm not personally there to investigate). The install is probably nearly 20 years old so I can only guess regs then were less stringent. To my mind there is a pretty high risk of the hoist electrical cables being crushed etc and posing a risk to the operator. I've looked at my regs and OSG and appreciate all the bits about it being commercial premises and under the supervision of skilled / instructed workers etc so possibly allowing for omission of RCD's. Rough plan is to check out that the 500mA RCD is working correctly (with an RCD tester), find the fault causing the 30mA to trip and then we're back to having it working but again with the 500mA RCD. As an aside the socket outlets would have been done by the builder and the hoist supplied by A N Other contractor. Hope this makes sense. Any thoughts please on why the RCD's could be this way round? Main issue is, is it considered "safe" with the 500mA jobbie in place. Thanks.
At work we have a moveable electric hoist unit that travels round and gets plugged in via a fly lead on a spring loaded cable extension drum to one of various sockets. The sockets are fed as a radial and are 3P+N+E, all fed from the same 4-pole 30ma RCD. The oddity to me is that the hoist itself has a 500ma RCD i.e. after the 30mA RCD. We KNOW we have a fault somewhere on the hoist itself and are looking into that. What I can't figure though is why the RCD's are this way round, it goes against the principles of discrimination to my mind. Neither RCD is anything special that I know i.e. time delayed etc. Not suprisingly when it faults the 30mA trip at the dis. board is generally the one to go (I'm not personally there to investigate). The install is probably nearly 20 years old so I can only guess regs then were less stringent. To my mind there is a pretty high risk of the hoist electrical cables being crushed etc and posing a risk to the operator. I've looked at my regs and OSG and appreciate all the bits about it being commercial premises and under the supervision of skilled / instructed workers etc so possibly allowing for omission of RCD's. Rough plan is to check out that the 500mA RCD is working correctly (with an RCD tester), find the fault causing the 30mA to trip and then we're back to having it working but again with the 500mA RCD. As an aside the socket outlets would have been done by the builder and the hoist supplied by A N Other contractor. Hope this makes sense. Any thoughts please on why the RCD's could be this way round? Main issue is, is it considered "safe" with the 500mA jobbie in place. Thanks.
