Online assistance for electrical trade people in New Zealand and Australia Login  |  Register  |   Forgot Password
Assistance for electrical trade people
 

 

 

 


Click here to send Forum Admin a pdf document for publication on this Topic

Documents must be less than 200k in pdf format

Posted By Topic: WA(Aust) Mar2018 girl electrocuted. Report release

DougP
Sep 28 2019 23:05

As per the link


https://www.commerce.wa.gov.au/publications/beldon-electrical-accident-report
   

August
Sep 29 2019 21:15

Interesting read,
What could have been done to prevent this in regards to earthing system?

   

medistat
Sep 29 2019 23:37

Very interesting. Does anyone know to what extent NZ's 'smart' meters are logging voltage/current rises outside of the average and/or indicative issues that would allow this to not happen here?
   

texynz
Sep 30 2019 11:25

Very interesting read. Having experienced this myself (in my case the neutral was in a ground level pillar), and trying to convince the line company needed to send out someone to sort this ASAP as the tenants in the flat was getting random zaps off random taps.
   

Phazor
Oct 02 2019 08:05

I was wondering why as there was a couple of earth loop impedence tests done previously during routine maintenance how come they didn't show up a high impedance that needed further investigation.

I must say there was good record keeping done at that property NZ would have nothing like that to reference to.
   

DougP
Oct 02 2019 08:55

Yes Phazor. That was my thoughts as well. Other aspects of the investigation were reported in detail, but there's no actual test results from multiple visits and tests carried out less than 12 months before the incident. The most recent tests were only about 5 weeks before the incident.
   

pluto
Oct 02 2019 14:47

One has to look at the root cause of this incident, and then think how could a re-occurance be prevented.

1. The mains entry box, the need to cater for a secure termination of a 6 mm2 hard drawn cable in and 16mm2 cable soft drawn cable out.

2. The mains entry box again, the twisting of the conductor before inserting into the connection block and tighting of the two screws.

3. The mains entry box again,increasing the diameter of the screw to 80% of the terminal hols size would be another good improvment to make.

4. The main earth electrode in AU is only 1.2 metres long and when high current tested as part of the investigation was found to be 300 + ohms.

In NZ the main earth electrode is 1.8 metrea so it likely to be better (lower resistance) to the mass of earth.

There are many in the AU electric supply ndustry that say that AU should using the same lenght of earth electrode as NZ to get lower resistances to the mass of the earth.
   

DougP
Oct 02 2019 17:26

I agree that the additional 600mm of the stake does make a difference. I've tested stakes not fully driven (hit rock), and then tested another stake a couple of meters away (fully driven). The difference was something like 100 ohm down to maybe 30 ohms (from memory). But in Australia the soil might possibly be drier? That's where the additional depth might help.

But the testing I was referring to above was the A to N loop tests at previous service visits to the property - "the line and earth fault loop impedance was measured" (page 24), carried out 5 times in the previous 12 months while investigating problems at the property.

But no details of those tests were given in the report.
   

pluto
Oct 02 2019 17:46

The A to N loop test would if a EFLI meter was used only puts about 23 amps load for about 1.5 cycles, so the high resistance joint in the mains entry box terminal would or could go un-noticed.

Hence my thinking of making the mains entry box terminals better.

The A to N loop test would in normal operation not be done unlees new or extensions work is being carried out and this could be many years apart.
   

DougP
Oct 02 2019 18:38

That's exactly what a loop impedance tester is for. Testing loop impedance down to the 100th's of an ohm. The only way it could go un-noticed is if the operator is incompetent, or the test was never performed but only written on the report.

An ELFI tester is one of the best pieces of test equipment available to any electrician. Unfortunately, so many either just don't own one, or don't know how to use it correctly.
   

August
Oct 02 2019 19:59

Interestingly enough I have had a high resistance joint in a open service main test OK under no load conditions with main switch OFF testing at line side of main switch.
But with switch ON and small amount of extra load ontop of tester, tests resulted in a HIGH impedence.
   

AlecK
Oct 03 2019 08:59

remember an EFLI tester is only imposing typically 23 A.
   

Someone
Oct 03 2019 18:51

23A is still enough to get useful readings; remember that the load at the time of the incident seems to have been a kettle (and maybe other appliances) - not a flat out house.

And the main reason we do earth-loop measurements is to extrapolate out to short circuits with far higher current flows.

I guess there could be thermal effects from the current persisting for seconds/minutes that wouldn't be picked up by an earth loop tester, though.
   

Phazor
Oct 03 2019 19:04

Trouble is now all the young fullas are putting in RCDs no ELFI test required bro just push the test button OK walk away.
   

Someone
Oct 03 2019 20:29

Was ELFI testing mandatory before RCDs on every (domestic) socket were? I thought it was a reasonably recent requirement, but I wasn't around then.

It's still an alternative to measure Rph+Re, which tells you nothing about the supply stability.

Arguably it's the preferred option given the whole "test everything you can before you liven" thing.
   

AlecK
Oct 04 2019 08:47

ALWAYS had to measure continuity of PEC for EVERY circuit to EVERY point; and PEC impedance is directly related to / part of EFLI.
And still required to do those PEC tests, regardless of whether RCD-protected or not
   

bakinthegame
Oct 04 2019 18:45

Scary stuff, what a horrible situation....

Interesting from an electrical perspective though.

Reminds me of a job I came across in Titirangi - previous sparky had done a re-Wire.

I found the main incoming Neutral only just hanging on (only 1 core of 8 was still present at the POE)
Then upon further investigation found an earth rod driven into the ground with a 6mm earth lying unattached next to it on the ground!

Was pure luck I came by at the right time and remedied everything before the installation became live & caused a death or serious injury.

   

Someone
Oct 04 2019 18:54

AlecK's Quote:
ALWAYS had to measure continuity of PEC for EVERY circuit to EVERY point; and PEC impedance is directly related to / part of EFLI.
And still required to do those PEC tests, regardless of whether RCD-protected or not

My comment:
Yes, but that's only as far as the supplying switchboard. It doesn't tell you anything about the performance of the upstream supply, like the bad neutral in this case.
   

daniel2
Oct 05 2019 14:26

Quite an eye opener.

I skimmed through most of the report. Was it a bad earth?

A brief summary, as follows:

- The main neutral snaps off at the incoming mains entry point above the roof.
- The main earth acts as the return path for the neutral.
- The mother is washing her car with a hose and the outside metal water tap is wet.
- She yells out to one of her kids to turn on the jug for a cup of coffee or tea.
- The daughter turns off the tap at the side of the house and gets an electric shock. She can’t release the tap as her hand is locked to the tap with at lest 100mA of current going through her.
- The mother tries to pull her off but gets a shock.
- Both mother and children go to the main switchboard to turn off the mains but get a shock off the metal surround.
- The rings the Housing agency which owns the house, with no response.
- She rings the emergency line.
- The daughter can’t be resuscitated and dies.
   

Someone
Oct 05 2019 23:55

Even with a 10 Ohm earth stake (which is unusually good), you can still get 100-150V easily. They can't be expected to carry bulk current like that. The MEN system really relies on an intact supply neutral for safe operation.

The girl didn't die, but has 'severe brain injuries'. https://www.abc.net.au/news/2019-01-02/denishar-woods-family-receive-$1-million-payment/10679436
   

AlecK
Oct 06 2019 08:27

True earth continuity testing doesn't tell us about the integrity of the supply.
Nor does the A+E resistance test for EFLI of a final subcircuit.
Which is OK, because Section 8 is about testing our own work to prove compliance, and not about testing the integrity of supply, nor any kind of fault-finding.

The direct answer to your question about whether EFLI testing was required before RCDs were made mandatory is "no". And that's all I was saying; that even before EFLI testing was mandated for non-RCD sockets, we always had to test the PEC half of the EF loop. And we still have to; not only for those sockets, but for EVERY circuit and EVERY point on the circuit. Any problems in the Active part of the loop that are such as would impair operation of overcurrent devices under earth fault conditions are going to show up in use, typically as volt drop

As for which EFLI test is preferred, clearly the live test is preferred by Section 8; because if there is a supply we have to use it. We are only allowed to use the A+E method if there is no supply available.

   

SaintAlan
Oct 06 2019 19:36

Most unfortunate.
But this is the real hazard of the MEN system; most of us have seen lost-neutral faults and it has been discussed here before.
If the main neutral is lost the appliances can continue working for a while on the earth return until the earth rod gets cooked, then everything connected to the earth bar becomes live.