anyone recommend an earth leakage clamp meter ?

[petehall347]

just bought another loop tester . another bargain .. this time its a robin KMP-4120 . it should not trip rcd.s .

[stj]

the high current is to detect loose connections or shit crimps etc.

[redwire]

I got confused by the Megger LT6 Loop Tester - it looks like a vanilla ohmmeter but "The test current, up to 25 A, is dependent on the impedance of the phase-earth loop being measured and flows for two half cycles of the supply voltage."
So I think it somehow imposes a signal on a conductor and looks at the resulting voltage blip? Maybe it uses a CT to inject current on a conductor. That would trip a RCD too.

[petehall347]

rcd test is just a resistor - i suppose a good tester could use a variable resistance somehow to ramp it till it trips in order to calculate the trip current.

better ones do have automatic ramp test . trip current can be measured with clamp meter . trip time is displayed on rcd tester .

[stj]

rcd test is just a resistor - i suppose a good tester could use a variable resistance somehow to ramp it till it trips in order to calculate the trip current.

[petehall347]

I thought that RCD tester injects a little 1/2 wave-rectified current pulses into already existing wiring between say N and PE? It's different than the usuals that use a resistor Line to to N or PE to cause a current imbalance.

rcd tester might do . i now have a loop tester to check earthing . but cant just plug into wall and test as rcd trips . quite normal for this model .

[redwire]

I thought that RCD tester injects a little 1/2 wave-rectified current pulses into already existing wiring between say N and PE? It's different than the usuals that use a resistor Line to to N or PE to cause a current imbalance.

[petehall347]

finally got the loop tester and it trips the rcd . only way to use this one is bypass the rcd . or modify to use less testing current like 15ma .

[petehall347]

OK big spender, that LT6 looks interesting - it measures impedance between two nodes i.e. GND and Neutral but having mains power present is not a problem?

I have very carefully used my multimeter on Ohms for that lol. It sorta works - some sites have say 1.0VAC from PE GND to Neutral, usually with plenty of RF so a multimeter can get confused about it, read a silly Ohms value. It's just a quick sanity test to see if Neutral or ground is open (to a water pipe).

it needs power to operate so i guess its just fine .

[redwire]

OK big spender, that LT6 looks interesting - it measures impedance between two nodes i.e. GND and Neutral but having mains power present is not a problem?

I have very carefully used my multimeter on Ohms for that lol. It sorta works - some sites have say 1.0VAC from PE GND to Neutral, usually with plenty of RF so a multimeter can get confused about it, read a silly Ohms value. It's just a quick sanity test to see if Neutral or ground is open (to a water pipe).

[petehall347]

so today i splashed out and bought a megger LT6 loop tester for £7.50 .

[stj]

or the circuits are linked by some grounding in the walls.
old pipe maybe.

[redwire]

A friend owns a very old duplex house (~1912) with non-grounded wiring. So he installed all RCD breakers on each branch circuit to meet Code, a while ago. Each side of the duplex on separate energy meters.
Well, recently it rained and all 6 RCD breakers tripped (and won't reset) for one side of the duplex.

Best guess so far is the front entrance outdoor light fixture(s) are soaked. There are two light fixtures, one for each unit's front door in a common roof overhang.
But why trip all 6 breakers? My guess is there might be a cross-connected neutral to the light fixtures or worse. He says the light fixture junction boxes are way full of wiring when they should not be. On/off switch has a single wire leading to the fixture.
Or maybe a Line is energized all the time (neutral is switched) and water leakage current is somewhere weird.

[petehall347]

the rcd tester i bought off that ebay for £12.50 arrived and the rcd,s tested good . the one i got is the ROBIN RCD KMP 5406DL . rain is coming soon so will maybe find out what was tripping it . or at least which circuit .

[petehall347]

i would rather have a nice box made for the job then i can be satisfied my work is good . like i said they can be had for around £20 . https://docs.rs-online.com/01e2/0900766b800828c1.pdf

[redwire]

Eaton RCD Application Guide
Look past 4.1.1. pg 23 Protection in TN networks has longggg trip times. Also some good info there.

I can't see the trip time being important, changing with age. It's the mechanical parts plus the electronic delay. RCD testers look expensive, I guess if you have the money for that.
A scope on line trigger can show the trip times.

[petehall347]

you could make one with a microcontroller and an opto-triac

yes i know that but its easier to buy a tester ready made , i would need one anyway to check the home made one was working properly .

[stj]

you could make one with a microcontroller and an opto-triac

[petehall347]

What's wrong with using a resistor for an RCD test load? That's what I do.
Inside, RCD's do get old with the capacitors or mechanical failing (old lube). Or mains transients hit them. They don't last forever.
In North America, had to laugh the RCD's can jam due to old age, they try to trip but can't, get stuck BUZZZZZZZZZZZZZZ. So the SCR driving the coil shorts, the coil burns up, melts open circuit - it's a cooked mess, some failure mode nobody considered. The assumption is the solenoid is only ever briefly activated.

resistor wont tell me how quick it works or do various tests . has to be under 40ms for a 30ma rcd . .

[redwire]

What's wrong with using a resistor for an RCD test load? That's what I do.
Inside, RCD's do get old with the capacitors or mechanical failing (old lube). Or mains transients hit them. They don't last forever.
In North America, had to laugh the RCD's can jam due to old age, they try to trip but can't, get stuck BUZZZZZZZZZZZZZZ. So the SCR driving the coil shorts, the coil burns up, melts open circuit - it's a cooked mess, some failure mode nobody considered. The assumption is the solenoid is only ever briefly activated.