They can be too sensitive in two ways... one being a faulty unit that trips below its anticipated tripping current, or one that trips when it should do, but your appliance / circuit has more than expected leakage.
"duplex" is what we would call a "double socket" I take it?
Yup, here RCDs have been mandated for any circuit which is likely to be used to power equipment outside for some time. Recent changes to the regulations require their use on additional circuit types as well - such that RCD protection will become common for almost all circuits)
Yup - the same as our RCDs
Indeed - that is one of the occasions we use RCDs. They are also used where it is necessary to protect a circuit and the earth fault loop impedance (i.e. the round trip resistance from supply line to earth) is too large to reliably trip the circuit protective device. This scenario is commonly seen where there is no earth/ground provided by the power company, and a local earth spike is used instead.
You can get sockets like this here - although they usually don't have the capacity to protect additional sockets (they would obviously be incompatible with ring circuits). These can be retrofitted to older installs to provide a safe socket to power garden equipment etc. More commonly, the RCD is fitted at the consumer unit (fuse board/box) on modern installs.
Our regs have not allowed sockets in bathrooms at all until recently. They still preclude them in small rooms since there are minimum distances between baths etc and a socket if fitted.
Motors are not usually cited as typically causing problems with RCDs here - although when a RCD is already loaded very closely to its tripping current, any power surge (as may be caused by motors starting) can push them over the edge.
With regard to Fridges/Freezers (and anything else you don't want tripping like the central heating, or your tropical fish tank etc)), it advisable to place these on dedicated circuits without RCD protection (or with their own dedicated RCDs). (we have devices called RCBOs which are circuit breakers and RCDs combined into a single unit - quite handy for fitting to circuits like this)
Indeed, you should not reverse the L/N connections for the reason you highlight. The common RCD trip mechanisms in washers tends to be either internal leaks that are allowing the electrics to become damp, or a heating element that is close to its end of life - the mineral insulation can become damp and conductive and hence result in enough leakage to cause a problem. Regular usage however can mask the fault by keeping it dry enough to not trip.
What trip rating are your GFIs usually specified at? (30mA is typical for our RCDs that are intended to protect against shock).
I also have a feeling that the standards to which RCDs are designed also requires a certain amount of harmonic noise interference rejection to mitigate problems caused by switch on/off surges.
And to you also! (only six hours to christmas this side of the globe!) ;-)
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