generally when you cascade RCDs you get discrimination of the wrong sort. So the RCD in the shed only sees the imbalance from the devices in the shed. The device protecting the kitchen sees that plus any imbalance resulting from the other devices connected through it. There may be none, but often there will be a little. So if the both trip at 30ma difference between live and neutral current its likely either both will trip, or just the one protecting the kitchen will trip.
Dave
ISTR mine was around 2kW...
It is an induction motor - so high inrush current, and high stall current (often > 5x normal operation).
Even if you can find one that is noticeably faster (normal ones trip in <=40mS), it only helps on that small number of cases where the leakage current falls between the maximum non trip current and the minimum trip current of the two devices. (ignoring tolerances and thresholds)
If you already have a RCD, adding another does not give any real advantage, but does give you two places to check when there is a trip.
If you want proper discrimination from the house circuit, then run a dedicated sub main circuit in such a way that it does not need a RCD, and then feed a CU in the shed, and place the RCD there.
John read my previous post, that is what I did but building control insisted I had RCD protection at both ends of the garage feed.
Richard
Then use a 10mA one at the shed
You are not likely to have that much leakage and if you do you probably want to know about it anyway...
That still does not give discrimination, and could result one either or both tripping.
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