High loop impedance reading

[ians]

What is the correct procedure to follow when a high loop impedance reading is measured at the meter box.

In the past I have contacted the faults number and notified the council ... however nothing was done and still nothing has been done.

I have another site which is recording a high loop impedance reading with the earth disconnected from the electrical installation ... it has a lead cable supply from the road.

I have considered knocking a spike into the ground as an additional safety measure until it is sorted out.

How do you tackle high loop impedance readings on a site?

What range would you classify the risk low - medium or high ?

[GCE]

The problem with high loop impedance can be that the neutral star point on the transformer is not earth sufficiently
In PE most of the prepaid meters are actually bridged across earth and neutral in the meter to sort out any potential star point problem. Becomes a fire risk if the neutral earth point is vandalized as the earth wire, on your property, ends up trying to take the street imbalance to earth. It is the reason for 4 pole change over switches.

By improving the earth reading through a spike could solve the problem if the earth from municipal side is bad. If the neutral star point in the sub has a bad connection or a bad earth mat ,it will not improve.
You tend to find that you have elevated voltage on neutral to earth when you have a bad loop impedance.

I have tested, found terrible readings , and when municipal guys came out we found that the transformer earth to the neutral had been stolen.

[Dave A]

We harass the municipality until it gets sorted out by them. It's delegated to one of our admin ladies to chase so it doesn't hold up service staff.

[Dylboy]

Hello

For the high loop test, I read a section of 8.6.5.4 in Ed.3 where it speaks of if the loop is high then an earth fault detection device and an overload device may be used.

So my understanding is if the house Earth from the meter to the DB is low resistance then a circuit breaker and and ELU (or an ELU wjth overlaod protection) can be used. As long as it trips with in 5 seconds and touch voltage not exceed 25V and then the ELU will protect against earth fault.

I may be way off the mark and completely misunderstand that section and if so does anyone know exactly what that little section means or entails ?

Sent from my SM-N960F using Tapatalk

[ians]

Funny you should mention that ... the DB I replaced last week is the first DB I have ever installed 2 earth leakage units ... one for plugs and the other lights and the geyser ... you may ask why the geyser on the light circuit and not with the plug circuits ... because I also fitted a double pole isolator in the DB for the geyser ... so if starts causing the e/l unit to trip you can isolate it then continue using the lights.

[Derlyn]

How do you tackle high loop impedance readings on a site?

What range would you classify the risk low - medium or high ?

Hi Ians

Acceptable earth loop impedance depends on the amperage of the main breaker.
The impedance should be low enough to let a current of at least twice the breaker rating flow in the event of a short.

A domestic installation with a 60Amp main breaker therefore requires a loop impedance of 2 Ohms or less. ( 240V / 120A = 2 Ohms )
If the main breaker is 80 Amp then the loop impedance needs to be 1,5 Ohms or less. ( 240V / 160A = 1,5 Ohms )

Peace out .. Derek

[ians]

The reading is 14.5 ohms.

The reason I asked about the risk ... at what point does it become dangerous to a point that you should isolate the power ... or knock a spike in the ground or link the neutral to the earth ... to reduce the risk of someone getting hurt.

[ians]

There should be a contact number for important stuff like high neutral to earth readings

or high loop impedance readings

or like when we had the fire department on site because the meter box caught on fire due to a bad connection on the council breaker ... I couldnt believe the fire department has to phone the electricity fault number that everyone calls to get them to come to site to removed the fuse on the pole.

[Derlyn]

The reading is 14.5 ohms.

The reason I asked about the risk ... at what point does it become dangerous to a point that you should isolate the power ... or knock a spike in the ground or link the neutral to the earth ... to reduce the risk of someone getting hurt.

Eish ! With a reading like that even with a dead short to earth, not even a 20A breaker will trip.

Like GCE said, an earth spike will not help if the transformer star point is not earthed.
2 options. Bridge earth and neutral on incomer at meter box.
Get Munic to sort out transformer earthing problem.

Here in East London the neutral and earth is bridged at the meter, however, they are now installing smart meters and I noticed that the installers
are not doing this anymore. Don't know if this is deliberate or not. They also not replacing the MOV's that were across the supply in the old meters.

You not gonna believe this, but the Munic here are quite sharp to sort out faults when phoned. I also have a cordial relationship with the guys at Revenue, so when,
on the odd occasion, I need to pull a meter, it's no problem. They are very accomodating and helpful.

Peace out ... Derek

[ians]

Unfortunately I dont live in the Cape ... we call the council for a low voltage 171 volts .. .they send a electrician with a 10 ton truck and duspol tester ... When I tell him the voltage is low he tells me the power is on ... I tell him again slowly ... "THE VOLTAGE IS LOW" with a slightly raised voice ... his response the power is working ... imagine trying to explain loop impedance is high.

Its like trying to tell Growth point property group that there is a power problem in a building ... same response ... the power is on ... but it wasnt for 3 hours yesterday and a week ago and 2 weeks before that etc etc ... oh well it must be a council issue ...