Earth Leakage Unit Question

[Mark_Spark]

And what would you do about this nuisance tripping?

[AndyD]

Every installation would be different. If the nuisance tripping was mainly due to cumulative functional leakage from electronic devices alongside a couple of other traditional appliances with acceptable earth leakage faults I'd make a decision whether to rearrange the distribution of the final circuits across two RCD's instead of one or repair the items with earth leakage faults even though they're within limits. Also you could consider installing a non-RCD dedicated circuit with red sockets for PC's and other IT/classII equipment or even fit an RCBO instead of the MCB for certain circuits then remove them from the main RCD.

[Slow Blow]

Just to come back to this thread, I have had a very interesting ELU tripping fault, 2 ELU's om separate phases kept tripping intermittently, I tested the whole installation and found no faults but the units would still trip (usually at night or early morning), as no-one was staying in the house at the time, I disconnected all outgoing circuits from the ELU's including all neutral wires and just left the incoming power connected to the top of the ELU's, they still tripped intermittently, has anyone ever come across this type of situation and what did they manage to do to rectify it?

[Justloadit]

Sounds like you have 2 dud units.

The way an ELU works is based on the differential of the current flowing in the live wires and Neutral.
This differential is easily measure, by using a sensitive current toroid, in which the live and neutrals are passed through the centre. When a load is connected to the ELU, the current phase going to the load through the live, is cancelled by the current coming back through the neutral, irrespective of the type of load, resistive or inductive. There may be small leakages that are introduced into the electrical system due to wires and switch mode power supplies, so the detection circuit is made with an off set, which is marked on the front of the ELU, 20mA for domestic and 30mA for industrial applications to reduce nuisance tripping.

When there is an earth fault, the current flows from the live connection to earth, and does not come back through the neutral connection. The current going through the live and returning on the neutral are now of unequal values, and the tripping circuit is triggered above the offset for the particular ELU.

If there are no loads connected to the ELU, and it intermittently trips, means that the detection part of the ELU is faulty and needs to be replaced.

[AndyD]

As Justloadit stated, if an RCD trips with absolutely nothing connected to the load side of it then it's faulty and needs replacing.