I am not aware of any official figures for the fraction of RCDs that get tested as frequently as they should, anecdotally, in many cases they often do not, but it does not seem to be a problem. There are figures from surveys for fire alarm tests, which are probably similar, and they too show a general apathy. Govt safety campaigns to encourage users to press "test" when the clocks change to summer time seem to have had some success.  page 18 shows 25% of housholds have never tested their fire/smoke alarms


For situations where RCD failure is a more serious risk, such as caravans and shore supplies to moored up boats, then the usual recommendation is that two RCDs are cascaded - so there is one at the source end, the caravan pitch or the mooring post,  and another in the load - i.e. within the caravan or boat. If the failure rate of any one is say 1%, then the chance of 2 independent RCD failures, and an un-noticed dangerous fault condition, is considered rare enough to be safe.

On the same lines one or more 100mA delay RCD(s) at the head of an installation, and 30mA instant devices (RCBO or RCD )for final circuits are a 'belt and braces' solution, and is the common agricultural configuration (or a 300mA delay type covering  big sites with many out buildings)

Domestic users in built up areas in the UK are probably mostly not  TT - new housing tends to be PME, and older housing stock is often TN-S (more than a third of  the 15 million or so houses in the UK predate the second world war, (and so does their hemp wrapped lead sheathed supply wiring!) UK housing stock data  Note that PME only came in in earnest from about 1970 onwards, before that TT and TN-S were the only normal options.

Where TT is common is in rural areas where there are few buildings per transformer, and especially farms with livestock, but at the same time there is more land with each curtilage in such locations. For private earth electrodes, rods are common, though the regs permit more or less any shape of metal. rods are often 4ft (1.2m long) and we'd normally also bond to barns an so on with steel foundations, and this is often a significant bonus electrode.

The supplier electrodes are supposed to be not more than 20 ohms, even for the lone pole-pig transformer in a field, and these are more likely to be bare wires or tapes buried at the foot of the supply poles, as unlike the typical home owner with a hammer or SDS drill,  the installers have access to a digger.

Others with more experience will doubtless chip in shortly.


regards

Mike.

I am not aware of any official figures for the fraction of RCDs that get tested as frequently as they should, anecdotally, in many cases they often do not, but it does not seem to be a problem. There are figures from surveys for fire alarm tests, which are probably similar, and they too show a general apathy. Govt safety campaigns to encourage users to press "test" when the clocks change to summer time seem to have had some success.  page 18 shows 25% of housholds have never tested their fire/smoke alarms


For situations where RCD failure is a more serious risk, such as caravans and shore supplies to moored up boats, then the usual recommendation is that two RCDs are cascaded - so there is one at the source end, the caravan pitch or the mooring post,  and another in the load - i.e. within the caravan or boat. If the failure rate of any one is say 1%, then the chance of 2 independent RCD failures, and an un-noticed dangerous fault condition, is considered rare enough to be safe.

On the same lines one or more 100mA delay RCD(s) at the head of an installation, and 30mA instant devices (RCBO or RCD )for final circuits are a 'belt and braces' solution, and is the common agricultural configuration (or a 300mA delay type covering  big sites with many out buildings)

Domestic users in built up areas in the UK are probably mostly not  TT - new housing tends to be PME, and older housing stock is often TN-S (more than a third of  the 15 million or so houses in the UK predate the second world war, (and so does their hemp wrapped lead sheathed supply wiring!) UK housing stock data  Note that PME only came in in earnest from about 1970 onwards, before that TT and TN-S were the only normal options.

Where TT is common is in rural areas where there are few buildings per transformer, and especially farms with livestock, but at the same time there is more land with each curtilage in such locations. For private earth electrodes, rods are common, though the regs permit more or less any shape of metal. rods are often 4ft (1.2m long) and we'd normally also bond to barns an so on with steel foundations, and this is often a significant bonus electrode.

The supplier electrodes are supposed to be not more than 20 ohms, even for the lone pole-pig transformer in a field, and these are more likely to be bare wires or tapes buried at the foot of the supply poles, as unlike the typical home owner with a hammer or SDS drill,  the installers have access to a digger.

Others with more experience will doubtless chip in shortly.


regards

Mike.