Ok. Never before had this problem.
Connect supply live and neutral to earth leakage.
Press test button and it trips. Cool.
Connect load live to bottom of unit. Press test button and it trips. Cool.
Connect load neutral to bottom of unit and press test button. Does not trip. Not so cool.
When I connect the load neutral to the unit, it does not trip.
Come now, my brothers, I need some more brains here.
Should have said, when I connect the load neutral AND THEN PRESS THE TEST BUTTON, it does not trip. It also does not trip with the plug tester. Tried 3 new earth leakages, same problem.
Take it that it is single phase unit and that voltages appear correct including neutral to earth been almost nothing.
Is your earthing test out OK on Earth Loop impedance
Definitely strange one - It should pick up the imbalance as all it does is check what goes down live comes back on the neutral in simple terms.
I seem to recall a similar problem on an ABB ELU a couple of years back and the niggle in the back of my head recalls an earthing problem, in that the return from the fault went back on the neutral not down to earth to create the imbalance - I need to ask the guys in the morning.
I would take amp reading on live and neutral and see if they are balanced and if you have milliamp scale see if the imbalance appears with ELU tester , next turn off all live circuit breakers and try the test button
Other plan would be to connect a constant load directly to the unit , 150w lamp or stove plate , and short neutral to earth or place a plug tester in parallel directly under the unit
The way that the ELU works, is that the Live and Neutral wire go through an iron core. The core then has a secondary winding connected to a trigger mechanism. When the amps going through the Live is returned through the Neutral, the current difference is zero. When there is an Earth leakage on either the live and Neutral, then the current in the Live and the Neutral is not the same and does not cancel out, and the difference then if greater than 20mA for a 20mA ELU, triggers the mechanism, and it trips.
This only works if the Earth connection to Neutral is done before the ELU and has good mechanical connection. However if the Earth to Neutral connection is lost/broken, then the ELU will not detect a leakage to Earth, as there is none being the missing link from Neutral to Earth. This is the same scenario when connecting a Genset to the ELU with out a Neutral/Earth bridge, and the reason that the SANAS states that alternative supplies require their own Earth/Neutral bond, else the ELU does not pick up an Earth leakage fault..
Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za
The test button on the earth leakage relay should work irrespective of whether the neutral is earthed or not.
There is an internal resister that is in series with the test button and when the button is pressed, a current will flow through the core to the resister but the return current bypasses the core to the neutral thus creating the imbalance that trips the unit. The test button operation thus does not rely on an earth for the unit to trip.
I'll be back at site tomorrow to attempt to find the fault. At the moment, the downstairs plugs do not have earth leakage protection, but the building is not yet occupied.
I need to let what little brains I have, rest for the night and persevere tomorrow.
I'm still puzzled. Usually one has nuicance tripping but in this case, the unit does not trip when it should.
This following diagram shows how the test button is internally connected in the earth leakage relay.
Now, something on the installation is preventing the test button from tripping the unit.
I have to find out what it is.
Last edited by Derlyn; 18-Apr-24 at 05:34 PM.
Clutching at straws here, but -
Earth and neutral is bridged on the load side?
An earth neutral fault to the point where the neutral loop impedance on the load side is a tiny fraction of the neutral loop impedance on the supply side.
Participation is voluntary.
Alcocks Electrical Services | Alcocks Pest Control & Entomological Services | Alcocks Hygiene Services
Good morning Dave.
On my way back to site now.
Some more testing to do.
Theoretically, a bridged neutral and earth on the load side should cause the ELR to trip if there's a load present, not prevent it from tripping, which is the case here.. That's the confusing part.
Hopefully, later today, I can give some feedback.
Like I said, it's a first for me, so it's one of those occurances which I am sure doesn't rear it's head too often.
On reflection I am possibly wrong on the relative neutral loop impedance readings. But I am mindful of your typical earthing arrangement in East London and that the unit is vacant - i.e. possibly no load on the load side to produce a current to leak to earth on the load side.
Participation is voluntary.
Alcocks Electrical Services | Alcocks Pest Control & Entomological Services | Alcocks Hygiene Services
Ok. Was a neutral earth fault on a 1mm FTE going to an outside bulkhead light.
The live was not yet connected in the db because the light switches were wired but not yet mounted due to the painters still doing their thing.
What is puzzling is that this fault caused the elr not to trip, instead of tripping when there's a fault.
Granted, there's no load being drawn there, but this is the first time ever that I've come across a neurral fault rendering the elr useless.
Maybe someone can explain this to me one day.
Lekker weekend all. ✌️
Was the light on ELU ?
Posting Permissions
Reply With Quote
Did you like this article? Share it with your favourite social network.