Two trips in two days

[plugwash]

Many items of equipment have a small amount of leakage current in normal use.
That RCD is rated 30mA, and the maximum allowed current in normal use is 9mA, which divided across 7 circuits is only just over 1mA per circuit.
Above 9mA random tripping is possible.

Having the entire installation on a single RCD was never valid.

"valid" or not, in the early days of RCDs I don't think it was uncommon. Later split load boards became a thing and different sparkies wired them up differently, some putting more on the RCD than others. Later still dual RCD splits and RCBO boards became a thing.

There must be a huge number of installations out there with most or all of the installation on one RCD, it's not an optimal setup but I don't think it's the disaster some make it out to be either.

The RCD you have got is obsolete - BS4293 was replaced by BS61008 in 1990, 4293 was eventually withdrawn in 2009.
A replacement consumer unit would have individual RCBOs, so any fault would disconnect a single circuit only.

I would not bet on getting a CU with individual RCBOs unless I specifically specced such a thing.

Replacing the CU for one with all RCBOs may be a sensible source of action if the cause can't be pinned down, but I would certainly want to see insulation tests on the installation and appliances first to rule out anything obvious.

 

[winston1]

It is highly unlikely the appliance switch will be double pole, whereas the Fused Connection Unit, if fitted, will completely isolate the appliance and help with fault-finding.

If fault finding is required the appliance will need pulling out and unplugged. No need for the unnecessary FCU as you surely must know.

 

[SUNRAY]

If fault finding is required the appliance will need pulling out and unplugged. No need for the unnecessary FCU as you surely must know.

that is if it hasn't been hardwired in to save the space, also many machines also open from the front where all the electrics is often situated.

 

[winston1]

Many don’t and it is often not the electrics that fail. The CU is your friend.

 

[ericmark]

I would certainly want to see insulation tests on the installation and appliances first to rule out anything obvious.

Yes although my installation tester uses DC, and a capacitor will not pass DC but it will pass AC, so a filter can allow a small current to earth with AC, also the cables with have some capacitance and inductive linking, so where you can't hold a RCD in then clearly you start with an insulation tester, but where the RCD is holding then you need some other method to see how close to the tripping current you are.

Most 30 mA RCD's trip around the 25 mA mark, they are required to trip between 15 and 30 mA and most RCD testers have a ½ setting, so check it does not trip at 15 mA, if the test is done with all connected then one is reasonable sure the back ground leakage is not on the edge, but for the 30 mA test if there is a leakage of 9 mA it means it may need 39 mA to trip, from bitter experience I know strain from the connecting wires can change the sensitivity of a RCD, so it needs testing with all cables in place and torqued up.

So only real way is to measure the back ground leakage, however in real life RCD's tend to trip before anyone touches anything live, when my roof leaked the RCD feeding the sockets under the roof tripped well before anyone touched them, so in real life it does not really matter that much if they don't trip bang on 30 mA. What is more of a problem is to ensure they don't trip with back ground leakage.

We all do it, we walk into the house, the RCD has tripped, we reset it, and only after resetting do we consider food in the freezer, with my upright freezers it displays the highest temperature it reached before power was restored until you open the door, but not all do this, and how warm a freezer gets depends where it was on the defrost cycle and how much is in the freezer, so if only just finished defrost cycle when power goes off, the time is very short maybe ½ hour, but if just switched off freezing, it may take 12 hours to defrost.

I am no biologist or cook, I don't know the dangers of refreezing food, so all I can do it reduce the risk of power cuts to freezers to as low as I can. The same applies to trip hazards with power cuts, I want to make it so unlikely to loose lights, use of auto lighting rechargeable torches, and the lights do not share a RCD with anything else. Maybe not always best idea as I can loose lights but still have sockets so the torch will not auto light, but chance is slim.

But no one is telling the home owner what to do, he needs to make his own risk assessment, if the risk of having spoilt food is low, he may consider one RCD is enough, I lived in a caravan with one RCD for all without a problem, OK gas fridge, no freezer, and battery backed lights, but it is up to the owner to do the risk assessment. No one is forcing you to have multi RCD's, but if a single RCD trips it you paying the bill.

 

[SUNRAY]

Many don’t and it is often not the electrics that fail. The CU is your friend.

So you'te now advocating turning off the power to the entire house so you can work on a kitchen appliance?
Where will your madness stop?

 

[martygturner]

Run some calgon or a dose of citric acid through both the dishwasher and the washer, nothing like a corroded element to increase a load.

 

[SUNRAY]

Having the entire installation on a single RCD was never valid.
The RCD you have got is obsolete - BS4293 was replaced by BS61008 in 1990, 4293 was eventually withdrawn in 2009.
A replacement consumer unit would have individual RCBOs, so any fault would disconnect a single circuit only.

I don't know what you mean by 'never valid', IME when RCD's first became popular in domestic situations, the common thing to do was insert a 2way enclosure between the meter and the plethora of steel/cast iron/wooden fuse boxes in place of the VOELCB which was habitually taking the whole load of the property. I still ocassionally either still either in place despite a more modern fusebox/CU being fitted.
One bad example from a few years back:

except I don't understand the coil and earth wiring

Of course VOELCB's worked equally well on AC or DC and we seem to be heading back that way

 

[martygturner]

The coil was so you could press the red button and instant isolation...human rcd of its day.

 

[SUNRAY]

The coil was so you could press the red button and instant isolation...human rcd of its day.

the coil is supposed to be wired between earth and circuit earth wiring

 

[Harry Bloomfield]

There must be a huge number of installations out there with most or all of the installation on one RCD, it's not an optimal setup but I don't think it's the disaster some make it out to be either.

It was a big step up from a personal safety point of view, but a single RCD protecting lots of circuits can make it extremely difficult to trace a cause for it tripping, should a fault develop - even more so, when the tripping is irregular.

 

[SUNRAY]

It was a big step up from a personal safety point of view, but a single RCD protecting lots of circuits can make it extremely difficult to trace a cause for it tripping, should a fault develop - even more so, when the tripping is irregular.

And that is when my own CU was changed to RCBO's, and eventually even the kitchen had temporary arrangements to subdevide to trace to the dishwasher.
The problem had cropped up for me so many times I now got to white water goods first for random tripping.

 

[SUNRAY]

Doesn’t solve your problem but there is no need to do that. The dishwasher will have its own switch.

And on this subject the switch it, if there is one, is NEVER before the mains filter where the fault usually occurs.