Loop Test #'s Help Please

[r136dg]

I'm using a Martindale EZ2500 loop tester & may have been misinterpreting the #'s. I can't find anything that actually defines the abbreviations, gives a good target # area for the system you're running on and the why's. Can anyone help with this by using the photo as an example for defining? If so, please go heavy on the details. Laymen details;-)

I'm on single phase,  a 15/45 meter and MEN connection.

Thanks in advance!

 

[Crossy]

The manual manMAREZ2500.pdf the flow chart of page 6 give some clues.

 

PE -- Phase to Earth loop impedance (Ohms)

PN - Phase to Neutral loop impedance (Ohms)

PFC - Prospective Fault Current (Phase-Earth) Amps

PSC - Prospective Short-circuit Current (Phase-Neutral) Amps

 

Was that test run with thew MEN link in place? I would expect the PE and PN figures to be more similar although 3 Ohms would be a pretty good rod if it were alone.

 

The PFC of 77A means a P-E short would open any breaker up to about 20A even without an RCD 

 

The PSC of only 429A is very low, are you on a long feed, do you suffer volt drop problems?

 

As to reasonable values:-

 

PE - Anything lower than 1000 Ohms will easily trip an RCD on a P-E short. What you have is excellent (but see my note above).

 

PN - A high value (0.5 Ohms is pretty high) shows the possibility of volt drop issues. Plug that number in to your prospective load to see just how much drop you can expect.

 

PFC and PSC are the above impedances converted to Amps to save yo doing it.

 

[r136dg]

Thanks Crossy!

PE & PN #'s are never remotely close on any circuit in our home. Even at the parents in laws home with no MEN which is what spurred my confusion/curiosity. I'll be installing a water heater in their bathroom & tested a circuit i'd like to power the heater from.

 

Voltage fluctuations are common here, seen @ 220V-250. 246V now & the rare extreme drops.

I have digital voltage meters in the DB's that read about 5 volts higher than the loop tester reads on circuits.

Yes, MEN in place at our house, always. There's a run of about 15 meters from meter to pole box with a main breaker. Than aprox 26 meters to distribution boxes, all with aluminum 25mm2. Ground bars at DB's & pole box are linked with the same sized cable.

DB's are grounded at 2 points: Rod earthed in a damp a area & an extra columns rebar that's not attached to trusses.

I do consistently get a High Mains Noise Please Wait message from every test.

 

Does any of this help explain the large PE-PN difference? Should I be concerned about correcting anything? 

Also, if a PFC of 77A is good, what's the happy happy (hi/low) parameters? 

 

Thanks again!

 

[Crossy]

OK let's try a laymans solution.

 

PSC should never exceed the breaking capacity of the protective device on the circuit, usually 4-6 kA for a branch MCB. Test as close to the board as possible.

 

PSC must be big enough to open the MCB "instantaneously", meaning in general around 6 times the breaker rating. So 60A for a 10A breaker. Test at the furthest point on the circuit.

 

PFC must be large enough to open whatever earth leakage device is present within 30ms or so, say 100mA for a 30mA RCD device, this would mean a PE of around 2,200 Ohms. In reality anything over about 1,500 Ohms needs looking at. With no RCD you need to be looking at a PFC that will open the MCB reasonably quickly.

[r136dg]

Outstanding Crossy! Now I can use this thing to it's full potential;-)

Also cleared up what needs doing to make the in-laws water heater safe.

Thanks once again for your time!