Disconnect appliances before RCD testing?

[Chappers]

Hi everyone, I was with Chief Big Spark at work doing some periodic inspection and testing on units. Chief was doing the testing, I was giving him emotional support cos were using his meter and he doesn't like others looking at it or tocuhing it. Very possessive, poor thing. He says he has always tested RCDs with appliances in the location still connected, but on that day he did the RCD test and found it wasn't tripping off in <40ms. In fact it was 120ms. Changed the RCD and result was the same. Changed it again, still same. Never happened before, he said, so was confused. While he was planning to strip the place down, I came up with the idea that something plugged in may be altering the reading, and was right - when the fridge compressor was running, the RCD was, according to the meter, knocking off in 120ms. With the fridge disconnected or compressor not running, it was 26ms.

Does anyone else ensure everything is unplugged/disconnected, and does anyone know why it was altering the tripping time of the RCD. Or maybe the RCD was tripping off more quickly, but meter reading was being affected somehow by fridge...

Ta.

 

[WarrenG]

Yep Fridges, computer equipment leak to earth. You should unplug equipment before running tests.

 

[randyrat]

Yup. Take it all out....
It's the only way to get a true set of readings. Fridges especially can be a pain in the **** full stop

 

[bahco]

yeah agree with the others...allways remove everything before testing less hassle

 

[Chappers]

Thanks for that. Looks like he's just been lucky in the past, although he's now wondering how many RCDs he's changed that were fine and only got a good reading after when re-testing because something like a fridge's compressor had stopped running by then. Live and learn...

 

[shagg]

so what do you unplug the fridge before you get a fault then sorry to take the **** guys but aint the RCD supposed to trip in the given time no matter what's plugged in.

 

[WarrenG]

so what do you unplug the fridge before you get a fault then sorry to take the **** guys but aint the RCD supposed to trip in the given time no matter what's plugged in.

The RCD tester presents a leakage current to the RCD to test the devices tripping times, i.e. 50% of the devices rated current no trip, 100% of the devices rated current less than 300ms (BS EN 61009) etc.

If there is equipment plugged into circuits protected by the RCD that has leakages, these will be picked up by the RCD and the test results will show inaccurate readings because the RCD may not trip in the required times due to the excess of leakage current.

The equipment with leakage current may be low enough to not trip the RCD in normal use but when added to the test currents show inaccurate results. This would make the RCD look faulty.

Typical equipment with high leakages include electronic equipment with mains input filters, washing machines, fridges, grills, immersions, ovens etc.

 

[jonny]

I'm with Shagg here. Shouldn't the RCD trip in the required time regardless of where the cumalative earth leakage is coming from? Wouldn't the tester leakage just "top up" the fridge's leakage on the circuit to the point the RCD activates as expected?

There's obvious merit in your explanation because as the man says, it is happening.

Just a further note, are we saying then that whilst this fridge is running one will not protected by the RCD in the required time in the event of a fault?

 

[Plan]

I tend to agree having a fridge etc in circuit just adds to the residual earth leakage making your rcd appear more sensitive ie tripping at 15mA rather than at 30mA. However remove everything from circuit then you have no prob only gonna have to do it anyway to do ir test

 

[Spudnik]

I tend to agree having a fridge etc in circuit just adds to the residual earth leakage making your rcd appear more sensitive ie tripping at 15mA rather than at 30mA. However remove everything from circuit then you have no prob only gonna have to do it anyway to do ir test

I agree and also about the IR test.

First thing i do is unplug everything.

Then once all testing is done plug back in!

 

[Guest123]

Sequence of tests dictates surely that you would carry out "dead" tests firsts anyway, continuity, I/R etc, ergo all appliances should be removed from the circuit to avoid damage and false readings from I/R testing.

IMO.

 

[professional]

It`s a good idea to ramp test an rcd (with all circuits discnnected) before testing at 30mA etc, that way you get an idea of the `background` fault current on the connected circuits - very useful for fault finding. Far, far too many perefectly good rcd`s are returned because people do NOT use common sense whilst testing.

 

[kung]

Thanks for that. Looks like he's just been lucky in the past

Either that or his apprentice flew round before he pushed the test button and unplugged everything and thought what a clown