RCD disconnection times on a TT system

That figure does seem very high.

Longest time I`ve ever witnessed on an RCD (TN system) was about 90mS (at x1 on a 30mA) and was alarmed at that. For practical reasons the circuit could not be powered down for more than a few seconds but a very quick swap of two RCD circuits revealled the long time stayed with the circuit not the RCD and there were many fridges and freezers on that circuit. I asked my night school 2380 tutor that evening if he agreed with me that the fridges/freezers total was causing this extra time and he that quite likely. A few days later I was able to disconnect all appliances from these circuits and the readings were as I expected . At that time we were taught that circuit itself should be left connected and all appliances disconnect in order that the circuit wiring comes into that test (if a ring then at near midpoint too) . The bloke who was testing was on the 2391 course at the time and his tutor agreed likely too.

I do not do many TT installs.

I`d suggest trying another RCD if possible and also a different test meter.

Although BS (EN) allows 300ms and the old BS allowed 200ms I never saw any RCD that was not far faster than both allowed on a non delayed RCD.

I think your reading obtained would cause me concern.

Having said that I have tested only a limited range of makes and it`s possible that some other makes do tend to have slower times

That figure does seem very high.

Longest time I`ve ever witnessed on an RCD (TN system) was about 90mS (at x1 on a 30mA) and was alarmed at that. For practical reasons the circuit could not be powered down for more than a few seconds but a very quick swap of two RCD circuits revealled the long time stayed with the circuit not the RCD and there were many fridges and freezers on that circuit. I asked my night school 2380 tutor that evening if he agreed with me that the fridges/freezers total was causing this extra time and he that quite likely. A few days later I was able to disconnect all appliances from these circuits and the readings were as I expected . At that time we were taught that circuit itself should be left connected and all appliances disconnect in order that the circuit wiring comes into that test (if a ring then at near midpoint too) . The bloke who was testing was on the 2391 course at the time and his tutor agreed likely too.

I do not do many TT installs.

I`d suggest trying another RCD if possible and also a different test meter.

Although BS (EN) allows 300ms and the old BS allowed 200ms I never saw any RCD that was not far faster than both allowed on a non delayed RCD.

I think your reading obtained would cause me concern.

Having said that I have tested only a limited range of makes and it`s possible that some other makes do tend to have slower times