Earth Only Through Earth Leakage Relay Toroid?

The arrangement will only work if the leak current flows through the earth conductor passing through the toroid. If it flows through stuctural steelwork instead, then the unit will not detect it and will not trip on this fault. If a human is part of the circuit between the live terminal and the structural steelwork, then electrocution of that individual is a possible outcome. So the answer rather depends upon what the unit has been installed to do.

To illustrate, in UK domestic wiring to BS7671 latest edition, the live and neutral conductors are asked to balance. If there is no imbalance, the unit does not trip; if there is imbalance beyond the trip setting, it does. There is no connection with the earth conductor. 30mA is the standard trip setting for the protection of humans in this case, and a trip usually happens part-way through the first cycle of the leak current being there. 100mA is the usual trip setting to protect the wiring from live-to-earth faults inside it. Heritage installations to earlier editions of BS7671 may have 500mA trips to protect the wiring, or none at all.

Hmm, I will have to look further tomorrow. All I remember at the moment is that the earth runs from "somewhere" (being a place I did not check), to the MEN, which is also bonded to the the genset frame.

Good stuff. Observation and enquiry is everything. Sadly, the installation cannot be seen from here.

Please allow me 24hours and I should be able to get the drawings... thankyou, i think i'm closer to understanding why it was done the way it was.

Aren't some changes made when events in Nature like Droughts cause problems with Grounding in the Earth ?

What - on a TN-C-S supply?

Contact Merlin Gerin

I wouldn't be scared, but I would definitely get to the bottom of the matter if it were my job.

Now that the genset has run 5x current for how many times...how is the insulation holding up?

It may be something simple like paint under the ground lug at the frame, or electrical isolation of the generator and prime mover, wrong ground attachment point, i.e., a complete circuit for the intended fault path.

Toroids on all leads is normal in my book. Do they not provide a monitor and control point for the genset?

Here is the genset manufacturer's drawing. It certainly shows the toroid on the earth. Merlin Gerin docs all show actives and neutral going through the toroid. Could this be for non-MEN earthing system perhaps? In the above scenario, will a fault to the ground upon which one is standing (through a person) 35metres away from the genset result in current being detected at/by the toroid, resulting in the earth relay activating?

Cuba Pete, the 5x fault current is 5x RCD fault current (150mA, even at 500mA) so I think the insulation will still be intact.

Pictures of the genset wiring cabinet will follow in approximately 4 hours...

The drawing is not readable at this scale, even at 400% zoom on this internet browser. Please describe the function of the rectangle middle bottom to which the wires from the toroid are connected.

I've tried to zoom the part of the diagram... the toroid goes to contacts on the earth eakage relay.

The drawing is not clear. Why don't you send it and the manufacturer's literature as a "link"?.

because i don't know how :(

Pictures of the way the earth leakage relay toroid was - one of the original wiring with earth through the toroid which would not trip when tested, and one with the actives and neutral through the toroid which would trip when tested. the drawing in the above post shows the toroid on the earth...

please help me to unnderstand?

Is that really an earth leak trip or is it a current transformer instead? Where is the contactor that opens to disconnect the supply in the event of a fault? What are those thin grey wires and to what are they connected?

The blue and yellow boxy looking thing is the toroid.

The box to the right of the toroid trips when the earth leakage relay trips, and will not close again unless the relay has been reset. It opens to disconnect the supply.

The grey wires go to the merlin gerin rh68m earth leakage relay.

Just readable on the drawing - why was the panel modified away from the drawing to the condition in the second photograph? When? Who did it and why?

It seems that this mod is to protect from an earth fault either in the earth conductor or in the steelwork; were it so then this is a worthwhile improvement.

Using an RCD test device I could not get the earth leakage relay to trip. Another electrician had changed the relay and the toroid and could not get it to work. I arrived and saw the earth running through the toroid - something I have never seen before. The new earth leakage relay drawings showed the actives and neutral should run through the toroid so I changed from the first pic to the second pic and all test ok.

Then do not worry. The improvement was worthwhile. Result!

I am still trying to work out why it was wired the way it was. This could be limited earthing knowledge, but I am thinking that the earth running through the toroid would only protect life if the fault occured on/at the genset frame, thereby inducing current to/through the earth stake. If, 30metres away from the genset, current runs from an active phase through a person to the ground upon which they stand, would the relay trip? I'm thinking not... your thoughts?

The only use for an earth connection is to operate a circuit protective device in the event of a fault. The as-modified installation is better than the original as the wiring is protected against phase-to-steelwork faults in addition to phase-to-earth conductor faults.

A 150mA trip point will not protect life; a 75mA fault has the capacity to kill though not to trip. If personal protection is required, then fitting additional 30mA trips en route to appliances would be the way to go, and only local information can determine whether this is needed.

Thankyou PWSlack. I had to go back to Learning101 and remember that when someone doesn't give the answer I want then there is a good chance they are trying to direct me somewhere. Not to mention the answer in your first response does the job. Sigh, I'm not the brightest spark in the fire, but not yet ash either :)

I'm now thinking that the best way for things to work by monitoring the earth conductor would be to run the MEN link through the toroid.

The original setup took the genset drawing literally and ran the conductor from the earth stake through the toroid and then to the earth bar.

Thankyou once again, I've enjoyed the learning

A 150mA trip point will not protect life. It will largely protect wiring and prevent fire.

If anyone is interested, AS/NZS 3000:2007 Clause 2.6.2.1 states, "No earthing or protective conductor shall pass through the magnetic circuit of an RCD".