Any thoughts on below set up would be welcome please I have a dedicated 16 amp ( type B) circuit from consumer unit ( with 30 mA RCD protection) which feeds a 16 amp 3 pin socket in garage. The outlet is not in continuous use . A 3 pin plug is available and connects directly to a single to 3 phase static converter - ultimately feeding small lathe. The direct output from the phase converter is L1 , 2 and 3 and Earth ( N) - this is hard connected into 3 phase 25A , 30 mA 3 phase RCD and then onward to a 6 amp 3 phase type C MCB. The lathe is connected with the 3 phases and the earth ( so earth is effectively via initial plug from 16 amp single phase circuit) There is some ' supplementary' bonding of the 3 phase 'earth' back to the single phase consumer unit via a connection to copper cold water feed ( which does have a bond which checks out) and direct from a single phase 240 v socket ring main in garage. Question - RCD on 3 phase works, 16 amp single phase RCD circuit checks out and Earth leakage on 3 phase checked before each infrequent use Are there any concerns about this installation which all appears to have worked for some time Many thanks
It is down to the inverter. If the inverter isolates then the output is IT. Same as using a shaver socket. If it feeds one item then like with a shaver socket there is no real need for RCD protection but if feeding multi-items then you need to do a risk assessment. The wave form may not be a sine wave and it may need a special RCD as a result. The RCD will likely work using the test button but likely will not work with an earth fault. Without reading the spec for the inverter one does not really know if it isolates or not. If the inverter only drives a single motor I would not be worried only if it powers multi-items is there a real problem.
I dont see any need for an RCD either. When I had a go at repairing and upgrading an old generator for someone I added an RCD into the output and mounted it in the panel, the RCD would not trip with the test meter until I connected one leg of the output to the earth (it was a floating earth before) of the genny. Everything fine after that.
Many thanks, MGW, Lectrician and Peter, During previous testing - when a earth connection was made between either L1 or L2, the 3 phase RCD and the incomer 240 v RCD did trip. On the L1 to ground it also pulled out the 6 amp MCB I assume the 'additional' 3 phase RCD is not hurting anything so will retain in circuit. For info - in case of use in future L1 to L2, L1 to L3 and L1 to Ground are all approx 420 ac L2 to L3 L2 to grd L3 to Grd are all zero / milli volts I appreciate the feedback Regards
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