Safe T Cut, Drop Out

[slapout]

House on 3 phase (15 Year old house) with safety t cut wired in between meter and Square D load center ( breaker box ). If memory serves me both are 50 amp. rated. The safe t cut is set at 10 ma (on possible 20, 30, or direct choice of settings). Last night the Safe T Cut main breaker dropped out twice (loose of electric to house) over a 4 hour period, 2300 and 0300.

This happens occasionally, normally during hot season. Will voltage surge or low power, cause this drop out? Any ideas as to cause, all seems okay at present.

[Crossy]

Determining why an RCD drops out can be a right royal pain, particularly when it doesn't do it consistently The classic 'unplug things until the problem goes away' technique just won't work.

If it's set to 10mA and you have a number of items with switching PSUs (PC, LCD TV etc etc) then you may get random tripping. You can quite safely set your unit to 30mA and see if it fixes the issue, do not however set to 'direct' as that removes all leakage protection.

Surges are unlikely to cause trips although a voltage imbalance between phases could. If you have the kit check the phase voltages during the period when trips occur most.

If we were in the UK, I'd suggest you hire a PAT (Portable Appliance Tester) and check all your kit, something is leaking just a little too much.

Moving to DIY.

[david96]

A high standing leakage currents could be causing the nusiance tripping, the RCD is just doing what is it supposed to do. Standing leakage current should not exceed 30% of the rated trip value and RCDs must trip between 50 and 100% of rated trip current in mA.

Any electronic equipment with capacitors connected to earth will cause leakage currents.

[slapout]

Thanks crossy; I set at 30 and no repeat. I have noticed during some low voltage periods that some circuits work and others do not in our house and the neighbors are without electric (we are only one with 3 phase) but safety t cut never kicked off during this.