High RCD trip time.

[ricardo123]

Have been doing a CU change today.

Anyone come across high RCD readings before?

I had a 310ms trip time on the 1x 0~ of my RCD trip times. All other readings RCD at 1x 180~ and 5x, ZS, Ze, R1+R2 spot on and good readings.

There are two known extras with this circuit that I might add, firstly I had to crimp the earth in the CU as it wasn't long enough. Secondly it supplies one socket, one end of the earth is strandard, the other a solid core, so suggests to me its been connected together in JB in the floor space.

Any idea's would be much appreciated, I know it's only 10 ms out which is fairly negligible, just going to make a note of it in the comments that reason unknown!!

 

[gamblor6]

was all appliances out the circuit. fridge or freezer still plugged in will affect the reading, rcd may just need changing.

 

[ricardo123]

RCD protects 3 circuits.

1. Ring main fine.
2. Radial with 3 sockets fine.

Below is the problem one.

3. Radial Cooker circuit (powering the single socket as its a gas cooker) is where I get the problem, sure I had both other circuits off when testing it, maybe I didn't!?, can't say for sure.

 

[gamblor6]

the rcd only really needs tested once if its used like that, not on every circuit, even tho on most test sheets each circuit has a space for trip times this is for rcbo times per circuit.

 

[Deleted member 9648]

Make sure all loads are disconnected and the readings will almost always come down......if necessary test the RCD with all final circuits disconnected then you can be sure there is no load to affect the reading.
Anything with a capacitor is particularly likely to cause a high trip time ,as when the power is suddenly interupted the capacitor holds a charge and fools the tester into giving a higher trip time.

 

[IQ Electrical]

I agree with the above 2 posts, if the rcd protects multiple circuits then you test it once, ideally at the outgoing terminals with no load connected.

 

[the pict]

This is something I have always had doubts about if an RCD is there to give protection on associated circuits should it not be tested at its point of use, in circuit, other wise you would be as well pushing the button and saying it's working fine But I may have it wrong I would welcome points of veiw
Pict

 

[telectrix]

i agree with pict on this one. in the event that the rcd should operate due to a fault, it will operate with all circuits connected and energised. IMO that is how it should be tested.

 

[IQ Electrical]

Often capacitive discharge 'fools' the meter into displaying a higher disconnection time, that is the reason for the 'no load' test regime.

 

[the pict]

Point taken IQ although if the history of the ubiquitous RCD is taken into account it's first incarnation was to be plugged into a socket when using mains powered stuff outside, then it was required to be installed at the point of origin on any circuit that may be reasonably expected to be used to power equipment that may be used outdoors That is why I believe it should be tested in circuit and apart from a capacitor start/run fridge, freezer, or maybe a washer on rotation change I cant see any other "hidden" capacitors but to be sure I usually whip out plugs, not always easy but it needs done for IR any way
Pict

 

[gamblor6]

gn3 rather generously states that an rcd should be tested at a convinient point in the circuit.

 

[telectrix]

i can just imagine the scene, DIY'er changing a socket, gets hold of a "live" conductor , and his wife shouts out " hang on dear while i unplug the fridge and the telly so the RCD will trip and save you"

 

[MarkieSparkie]

I think the answer is more simple folks. The long trip time was on the first tripping test, if the RCD has not been regularly tripped on the test button (how many householders quarterly test their RCDs?), the RCD mechanical mechanism can be sluggish, when operated several times it loosens up and the trip times get quicker. I always like to trip RCDs on the button a couple of times before testing for this very reason. I learnt the hard way with the old Wylex BS4293 RCDs these were notoriously sticky, Wylex made a packet out of replacements, condemned needlessly by testers.

 

[domestic spark]

Make sure all loads are disconnected and the readings will almost always come down......if necessary test the RCD with all final circuits disconnected then you can be sure there is no load to affect the reading.
Anything with a capacitor is particularly likely to cause a high trip time ,as when the power is suddenly interupted the capacitor holds a charge and fools the tester into giving a higher trip time.

you mean like, kitchen flourecents, ip rated 28w type bathroom fittings? is this still the case even if you swich these off at the light swiches i mean?

 

[IQ Electrical]

you mean like, kitchen flourecents, ip rated 28w type bathroom fittings? is this still the case even if you swich these off at the light swiches i mean?

You can switch off locally but you can't always be certain that every load is isolated, that's why the recommended procedure is on the outgoing terminals of the device with loads disconnected.

The capacitors etc. don't actually make the RCD/RCBO trip any later but as wirepuller says, they 'trick' the rcd tester into displaying a higher trip time.