anyone recommend an earth leakage clamp meter ?

[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 .

[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.

[stj]

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

[petehall347]

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

[redwire]

It says the same thing - "25A test current (20Ω range) ... for 2 half cycles of AC (20msec)."
Have to do a teardown of one to see how they are pumping so much current through for the impedance test, yet it can take a mains surprise.
It looks really good. Don't use them in North America and we should.

The impedance test pulse might be fast enough to not trip a RCD, not sure what the response time of them is.
D-Lok for RCD's rated 10mA or less, might trip.

[petehall347]

i cant remember ever seeing a 10ma rcd so cant see it being a problem .

[stj]

you wont see a 10mA rcd on 240v - too easy to false-trip one.

[redwire]

North American GFCI mainly for shock protection and GFCI duplex outlets are 4-6mA here. I have one powering my workbench.
I see British duplex outlet 10mA but you're kinda dead?
Whole house RCD I guess is 30mA.

I did read cable capacitance can also cause false tripping, long runs >50m.

[stj]

30mA is the common value for 240v

[petehall347]

30mA is the common value for 240v

along with 100ma .

[petehall347]

loop tester turned up today . seems to work ok but i suspect it needs calibrating . when i get chance i will check it against the first one i bought .
back to the rcd tripping issue it's fixed now and no more nuisance tripping even during heavy rain .

[petehall347]

plot thickens 2 times tripping different days .. but getting close to the tripping issue ,, narrowed it down to one circuit when it rains . this is going to be fun . 10mm armoured cable approx 100 to 120 metres long . hoping its simply at one end or the other as pulling it up for visual inspection isnt going to be easy . if the ends appear good it will have to be cut somewhere near the middle to see which half is bad . or maybe use the megger and try and calculate where it might be . and of course i dont work in the rain so it might fix itself before i start . suppose i could connect a car battery to it and look for smoke coming out of the ground .

[stj]

you need a time domain reflectometer
BT used to have crude ones with crt's in a compact case, maybe you can find one on ebay.
or something more modern even.
https://www.youtube.com/watch?v=gw_JAc7l8CA

[petehall347]

you need a time domain reflectometer
BT used to have crude ones with crt's in a compact case, maybe you can find one on ebay.
or something more modern even.
https://www.youtube.com/watch?v=gw_JAc7l8CA

i have a seaward oscar 250 but think its no use for this problem . had it for years and not found a use for it yet . think its more fore for it shit .

[redwire]

Where does this cable run?
Outdoor armoured cable (TECK cable) is plastic coated over the armour, then you have the plastic-jacketed conductors.
So you need at least the inner conductor's insulation being breached to have a ground fault or leakage.
Or there is a splice, and that's what is getting wet.

One site, we injected compressed air to see if it could make it to the other side.

[petehall347]

Where does this cable run?
Outdoor armoured cable (TECK cable) is plastic coated over the armour, then you have the plastic-jacketed conductors.
So you need at least the inner conductor's insulation being breached to have a ground fault or leakage.
Or there is a splice, and that's what is getting wet.

One site, we injected compressed air to see if it could make it to the other side.

we call it swa . plastic coat outside the steel wire armoured . there is one splice that was done years ago that's underground .i did that with a proper potted connector .
https://www.tlc-direct.co.uk/Main_In...SWA/index.html

[petehall347]

today's findings with the swa cable .. disconnect both ends and checked resistance and getting 60k ohms between live and earth .this is same at both ends . disconnected the earth at supply end so now the earth wire is disconnected both ends .its ok because there is local earth rod as i made it terra terra anyway . funny thing is there is 9 volts showing between the disconnected earth and the ground rod . whether this is because of cable capacitance or leakage i do not know .. the trip hasn't tripped yet but its not raining .

[stj]

if you know where the splice is, try watering the ground and see if it trips!

[petehall347]

if you know where the splice is, try watering the ground and see if it trips!

thought about this but if the wet problem is underground surely it will stay wet for lots longer .. this problem goes away not long after the rain stops . its the 60k ohms between live and earth that is a clue here but find it odd its same reading no matter which end of the long cable i measure from unless its bad right near the middle . am hoping the issue is now fixed for now by disconnecting the earth wire . maybe not though thinking about it .

[petehall347]

on another note it only has a 2 pole switch at supply end so going to swap that for a 40 amp mcb so the cable wont completely burn out if it hard shorts ..