RCD seems to trip without physically tripping???

[rwkshaw]

Hi, I seem to have an RCD that keeps cutting the power at random times without actually tripping, if I reset it, the power comes on and will stay on for anything from a few hours to a few weeks. I've been through all the obvious things, unplugging everything, plug in one at a time etc, nothing causes the power to fail when used. It's a farm and there's lots of 16amp sockets / connections outside, but again, no one thing causes it to trip, nothing is wet or damaged.. Can the RCD "trip" without actually tripping?

 

[littlespark]

what do you mean?

Is it tripping internally, but the switch on the outside isnt going down?

Being a farm, there could be any number of reasons.... corrosion... contamination.... "helpful" farm workers using fencewire instead of a fuse.....

 

[rwkshaw]

what do you mean?

Is it tripping internally, but the switch on the outside isnt going down?

Being a farm, there could be any number of reasons.... corrosion... contamination.... "helpful" farm workers using fencewire instead of a fuse.....

Nothing is tripping at all, it just goes off, that's the issue, but when I reset the RCD, it all comes back on, hence wondering if an RCD can do this when it is failing. There's only 2 of us here, no impact driver bits for fuses, corrosion, damp etc, everything is 2 years old or less

 

[brianmoooore]

All MCBs, rcds, etc can turn off without the operating lever moving. The lever is disconnected from the internal mechanism when they trip to prevent them being wedged on and stopped from doing their job.
I've been working on farm electrics for 50 years. If it's a farm, there is damp.

 

[rwkshaw]

All MCBs, rcds, etc can turn off without the operating lever moving. The lever is disconnected from the internal mechanism when they trip to prevent them being wedged on and stopped from doing their job.
I've been working on farm electrics for 50 years. If it's a farm, there is damp.

I appreciate the advice Brian, and although true 99% of the time, we're a very new farm (2 years) and everything new, modern and dry. I know from working with generators and on stage rigging that if you have the slightest bit of moisture the RCD will trip instantly (unless adjusted accordingly and will keep tripping instantly until that damp is out of the system, this isn't mimicking that at all, if it goes off, I can trip it manually and reset it and everything comes back on, and stays on like I said sometimes for minutes, hours or even days, weeks... Is there a possibility that the RCD may be faulty? Can they throw a wobbler out of the blue? As a side question, in your farm experience, is there a better, more suited RCD/system that can be implemented that has a bit more tolerance to damp etc, like the adjustable ones you have in the 100kva gennys?? Any advice greatly appreciated Rich

 

[littlespark]

Yes, there’s always the chance that an rcd is faulty, especially if it’s tripped a huge number of times. The fact that it’s tripping internally but not throwing the switch suggests it needs properly looked at by a pro with the test equipment.

How much does this one rcd feed? There could be a culmunative earth leakage across several circuits, which individually all test ok, but added together can be at the threshold of tripping.
(Might say 30mA, but could be as low as 20)

 

[brianmoooore]

Faulty RCDs are far from unheard of, and if this one is tripping without the lever moving, then there is something wrong with it, but that doesn't necessarily mean it is tripping when it shouldn't. They can be tested with a MFT that times how long it takes to trip (or not) at half its rated current, its rated current and five times its rated current, and/or a ramp test, where the differential current is increased from zero until the RCD trips, and the current at that point is displayed.
The ones in big gennys are for different purposes that the ones protecting final circuits, where the limit for the safety of humans is 30mA fast trip. Even this is on the high side for horses or cattle.
Note that a 30mA RCD is designed to trip somewhere between 15mA and 30mA, with a typical one tripping around 23 -24mA, and if one RCD supplies more than one final circuit, it can be tripped by the combined leakage from all those circuits, so the best way to avoid nuisance tripping is one RCD to one circuit.

 

[rwkshaw]

Yes, there’s always the chance that an rcd is faulty, especially if it’s tripped a huge number of times. The fact that it’s tripping internally but not throwing the switch suggests it needs properly looked at by a pro with the test equipment.

How much does this one rcd feed? There could be a culmunative earth leakage across several circuits, which individually all test ok, but added together can be at the threshold of tripping.
(Might say 30mA, but could be as low as 20)

I e got a guy coming out tomorrow to do some proper testing, it's just driving me insane At the moment it's probably got no more than 2kw running through it via 6 circuit breakers, I'm wondering whether like you say it could be accumulated problems?? My guy, who's a good mate and 100% trusted mentioned something about installing an mcbo rather than individual breakers? I'm not planning on touching it, I know my limits, I'm just curious really, thanks for the reply