My house had a new consumer unit fitted in 2005 it's partly fitted with RCBOs and partly with MCBs it was installed by the DNO who are SSE in this area bearing in mind the year it was installed are the rcd fitted likely to be electronic type or plain electromechanical ones I'm asking out of curiosity because if ever there's a fault in my workshop ( for this read that I make a mistake or an error when experimenting) usually the house RCD trips despite me having an electronic plug in one on my test bench supply which I think should fire first ide really appreciate your wise words on this thanks x Kelly
Do you have a make and model no for the RCD ? In 2005 most in common use would be mechanical. However, it may trip first, as it is already seeing some current imbalance from the rest of the house.
If you have 2 RCDs in series unless you have time delay on one then you will not get selectivity (the new name for discrimination). I am assuming you effectively have 2 30mA RCDs in series so you will not have any time delay?
Whilst you may have different sensitivities when you ramp test them your experiment gone wrong may have been a lot more than 30mA fault current. If so it is a complete toss up which one goes first. Unless the have different levels of DC immunity say a Type AC and a Type A and there is a DC component to your fault current. A low level of DC may lock up a Type AC but not a Type A. A lot of manufacturers have stopped shipping Type ACs in favour of Type As as these are the minimum standard in some countries.
I managed to trip my BS 4293 RCD in my workshop when trying to get my AFDD on test by pulling the neutral out of a terminal block to create an arc with a fan heater as a load. Lots of sparking which did not trip the AFDD but my ancient 30mA RCD did not like it!
Installing a 10 mA RCD downstream of the 30 mA RCD won’t guarantee discrimination, but will make it safer.
If you are testing RCDs in your workshop or tripping a RCD or using a checkbox such as my Seaward box to test your RCD tester then you can make yourself a dedicated plug in adapter that will allow you to do your testing without tripping the RCD in the main consumer unit, obviously you will need to ensure that it is only used for its intended purpose.
The make of the trips looks like it says E N there are some symbols between the letters that I can't describe although one of them looks like the castle shaped chess piece if you know what I mean the RCD and non RCD trips are all of the same make the RCD ones are rated 30 mA the consumer unit they are in is made by MEM. Also the trip that supplies my workshop also feeds a double socket which the microwave oven is plugged into there is no other load on the circuit it's rated 30mA and 16A. Curiously I noticed that the shower is on a non RCD trip is this something the DNO should of been more careful of?
Other than that solutions depend on if you have a dedicated circuit to the work shop or can install one that can have RCD protection omitted from it or provided by a higher rated RCD with time delay, which will depend on the cable type and its installation method.
Hi Andy I will order one of those sockets it seems like a good idea the extra protection will be useful and if it saves me a trip down to the house that's got to be good. What I do in my workshop is mostly playing about with old test gear and radio equipment although my main station is all modern gear I do enjoy playing with older equipment. Just to set your mind at rest I don't trip it thatoften it's just that when I do its a real nuisance. RCDs are not good when you've got bad arthritese in both knees!
Sounds like time for a review and update of the devices installed in the consumer unit with at least RCD protection being added to shower circuit.
If the work shop circuit supplies the microwave socket, which is presumably in the kitchen, running a new separate circuit to the workshop could be a consideration as you cannot alter the RCD protection to the existing one.
Thanks for the info Chris il be able( hopefully) to look up the details of my breakers on the inter web now I know what breed they are! Also Sparkingchip I've just ordered one of the 10mA RCD sockets should be here in a day or 3 OMG I've just spent £50 what am I doing!!!!
if ever there's a fault in my workshop ( for this read that I make a mistake or an error when experimenting)
Ever thought of using an isolating transformer when playing around with the more "interesting" kit? - that what TV repair engineers used to use before the days of RCDs and has some advantages (mostly stops you getting a shock, rather than just cutting off the power if you do).
