Earth Leakage Unit Question

[Slow Blow]

And did they not charge for eTolls

I know you in CT

That's what they are now doing in Jhb as part of their call out fee

It's fair enough if you are paying the eToll to get to the client.

[Houses4Rent]

Thanks guys, 2 hours I shall allow and that was mean for on site time only, pure labour, not driving time, not sourcing time. First hour labour includes call out in the their model.

Building extra costs like etoll would also be fair, but we do not have those - yet.

[david2677]

A ELU serves as a protective device where if there is a leakage current from neutral to earth that is deemed a potential hazard (30ma) it should isolate the functions. 30ma is a current that will shock and maim or kill but again this depends on the strength of the heart if it is able to withstand a current of that magnitude- frankly most humans survive that current but again it is better safe than sorry. What I don't understand is why stoves and geyser are permissible to dedicate yet they carry a greater hazard than plugs

[AndyD]

Something else: I was quoted 5 hours labour (excl materials) to replace a main breaker and put a surge arrestor next to it. Am I right in saying that its a matter of making a few cable connections at the board which - lets be generous - should not take more than an hour maybe?

Before I would submit a quotation for installing an RCD/earth leakage breaker I would insulation test every circuit, I'd take a global leakage reading using a clamp meter and I'd test all the circuits for crossed or borrowed neutrals. All of these problems could go unnoticed if there was no RCD but would cause tripping if one was installed. My quote would include the repair of any of these faults as well as the RCD installation.

A ELU serves as a protective device where if there is a leakage current from neutral to earth

It will also detect leakage current from live to earth or even from live or neutral to the neutral of another non-earth leakage circuit.

All I know is that Earth Leakage is only on sockets, not on light circuits. But I have no idea why and would like to know.

What I don't understand is why stoves and geyser are permissible to dedicate yet they carry a greater hazard than plugs

I think the original idea was that portable appliances are far more prone to damage because they are constantly moved around and the trailing lead is prone to damage, statistically they were far more likely to cause fatal shocks. Fixed appliances suce as geysers and even light fittings aren't constantly manhandled and moved around so it shouldn't deteriorate in the same way and become hazardous. For this reason as well PAT testing (Portable Appliance Testing) is a mandatory requirement in many EU countries although it hasn't caught on here yet.

Why would one not want a Earth Leakage?

Some appliances, especially IT equipment or anything with a switch mode power supply can have a small amount of standing leakage. This leakage is usually due to the components on input side of the power supply and built-in surge arrestors. It is acceptable because the CPC (earth wire) is considered a functional part of the circuit as well as the safety. My house for example at present has around 9 PC's, several laptops, servers and various routers and switches and all these items will have a small amount of leakage but the RCD or earth leakage breaker sees the cumulative result so if each of these devices had 2mA leakage for example the RCD will see >24mA before anything else is plugged in. Most RCD's will trip at around 25-28mA so the high amount of acceptable standing leakage can cause nuisance tripping.

[Justloadit]

I think the original idea was that portable appliances are far more prone to damage because they are constantly moved around and the trailing lead is prone to damage, statistically they were far more likely to cause fatal shocks. Fixed appliances suce as geysers and even light fittings aren't constantly manhandled and moved around so it shouldn't deteriorate in the same way and become hazardous. For this reason as well PAT testing (Portable Appliance Testing) is a mandatory requirement in many EU countries although it hasn't caught on here yet.

What I have experienced with stoves, especially the old plate type, was that with time, the element eventually burns through the metal sleeving and makes contact to earth. Under this situation, provided the earth is sound, the user is still safe, and depending on where the failure took place, the electricity bill goes up when using this plate, as part of the mains flows to earth. In other situations, the circuit breaker simply trips.

Some appliances, especially IT equipment or anything with a switch mode power supply can have a small amount of standing leakage. This leakage is usually due to the components on input side of the power supply and built-in surge arrestors. It is acceptable because the CPC (earth wire) is considered a functional part of the circuit as well as the safety. My house for example at present has around 9 PC's, several laptops, servers and various routers and switches and all these items will have a small amount of leakage but the RCD or earth leakage breaker sees the cumulative result so if each of these devices had 2mA leakage for example the RCD will see >24mA before anything else is plugged in. Most RCD's will trip at around 25-28mA so the high amount of acceptable standing leakage can cause nuisance tripping.

The leakage in these switch mode circuits arises from 2 paths. One is the high frequency used to create the magnetic fields in the power supplies, so that effectively the mutual inductance of the transformer makes a connection between the supply and any metal in the vicinity of the transformer, and to counter act this, manufacturers usually place a small value capacitor between the Neutral supply, and the common of the secondary supply circuit creating a very high impedance path for electricity to flow.

This can be experienced, when one connects 2 computers via a serial cable, if you are touching the metal parts of each side of each computer, you usually feel the current flowing, or if you touch the metal parts together, you usually see a tiny arc as you connect and disconnect.

[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.