Thread: Earth to water pipe? IMportant?

Originally Posted by Gav 110

This has not come from the “official” report and is my opinion from factual information I have obtained from my schooling, life as an electrician and personal observations, so take it as you will

Which bar the speculation about the trampoline and contact with the overhead leading to failure of the neutral, is pretty much exactly the way it is described in the report. Funny that thing we call “experience”.

Usually your hang is the culprit and the electricity will flow through your hand to your arm, either down your leg to earth (oh ****, what the **** moment)

I guess that could happen if taking a **** in the dark.

Originally Posted by Homestar

FYI, generators running the mains network like this don’t have a star point, they’re delta connected. The only star point is at the local LV transformer. Earthing back to that wouldn’t be any better in most circumstances due to the length and therefore the resistance of the conductor - you’d end up with the same issue.

My experience working on the Protection of Overhead Lines, Transformers & Switchgear tells me if the star point is not at the generator, it will be found at the 1st transformer in the HV yard before the conductors go onto the overheads otherwise Earth Fault Protection and Neutral Earth Fault relays wouldn't work on all the distribution transformers down the line, only on the last little 11000 to 400 Volts ones. Generator earthing and stator earth fault protection | EEP (electrical-engineering-portal.com)

I'll address the 2nd part of the post at the end of this post as Old Farang seems to believe the same thing as dished up by the regulator largely for cost reasons I suspect.

Originally Posted by Old Farang

The case of the poor girl in Perth is heart breaking. But I have to question some of the stuff in those reports:


I realise that both of those reports are not a copy of the actual report, but written by somebody that thinks they know.

Despite at one time holding an electrical contractors licence in WA, I am stuffed if I have ever heard the expression: "equipotential bonding"!
Just as I have been pulled up on here for referring to the MEN system as "Multiple Earthed Neutral"! (supposedly now called something else!)

WHAT ON EARTH IS EQUIPOTENTIAL BONDING

WHAT ON EARTH IS EQUIPOTENTIAL BONDING - Masterspec

With few exceptions, New Zealand and Australia use the Multiple Earthed Neutral (MEN) system as the basis of electrical distribution and installations. Basically within an electrical installation, the earthing system is separate from the neutral conductor, and is connected to exposed conductive parts of equipment. Internationally this system is considered safe and reliable when it comes to dealing with short circuits, earth faults etc.

AS/NZS 3000 Electrical installations (known as the Australian/New Zealand Wiring Rules.......

From Figure 3 of the report investigation_report_beldon_electrical_accident_re port_-_final_version_25_september_2019.pdf (commerce.wa.gov.au)

Now imagine if you had a earth conductor from the transformer to the consumer's premises which all the bonding and earth terminals at the premises are connected to and it was the same size as the neutral conductor, not very expensive as it could be just a 3rd core in the cable, the touch voltage at the tap would've only been 6 volts as measured in the figure 2 of the report. For the price of an earth conductor this tragedy could've been avoided, instead of relying on a poor earth path back to the transformer via the general mass of earth, that varies under dry and wet conditions.

There can be a big difference in safety between, the regs, rules, standard practice, etc and the best technical solution especially when price comes into it.

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1) It's not usual to have multiple earth bonds, but it can't hurt to reconnect that loose earth wire. Turning the power off is a sensible precaution (don't forget the hot water) In a new installation you can not use the waterpipe as your main earth, but any metallic waterpipe must be bonded to the main earth. The water pipe usually gives a much better connection to the earth mass than a stake anyway, so that's a good thing.

. 2) The girl in Perth - lots of factors involved, and it's tough to say how the accident could have been avoided. If the neutral was broken and the earthing is so poor, the occupants may have noticed dim lights, etc., (hard to do with LEDs), but it's not up to them to monitor the power supply in this way. That jug would definitely have taken a long time to boil. I've dealt with probably a dozen or more broken neutrals in house services during my career, and more often than not the call of "dim lights" came during hot weather when the ground had dried out and there was higher ground resistance. Sandy soil, of course, was the worst.

A normally connected safety switch would not pick up the Perth fault. What would do it would be a core balance circuit breaker (i.e. safety switch) monitoring the consumer's mains between the point of attachment where the wires enter the house, and the switchboard (before the service neutral link).

Safety switches have two wires running through them, and the current in these wires must almost exactly match or the circuit breaker will open and interrupt the electricity supply. Usually an imbalance of .03A is the limit. If the current does not balance it means that some of it is going somewhere that it should not (usually to earth). Bad thing.

Safety switches as described above are not fitted to consumer's mains.

The other option is to install old-fashioned earth leakage circuit breakers, which monitor the current in the main earth conductor. These could be problematic, as there is nearly always SOME current in the main earth, and sometimes quite a bit, even under normal circumstances. The question is, how much is too much?

DISCLAIMER Internet advice ranges from Wise to Dangerously Misguided (and for that matter Misguidedly Dangerous). Are you going to believe that? Make your own mistakes.

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One point to add to the Perth story - the combination of low rainfall for much of the year and high permeability (sandy) soil in much of the area means that any earth stake in many parts of the city will be pretty ineffective.

Originally Posted by edddo

Thanks

I have reclamped it back to the pipe.
Will get the leccy to come and do a safety check.
The buildings here are circa 85 - must have been the norm around then?

In reference to turning off the mains before reconnecting the earth...I sure did......thanks.
Certainly has spurred some conversation..... and thinking on my part. It has also confirmed my ignorance on the topic.
Will be getting the leccy here quick smart to check the house and the shack.

Off topic slightly,

On equipment one can never have too many earths.

I undid a metal panel on an AC once, holding it, no earth attached,the metal run capacitor,clipped to the panel, had a dead short to earth.

I still cant work out why metal cased capacitors dont have an earth pin.

Originally Posted by JDNSW

One point to add to the Perth story - the combination of low rainfall for much of the year and high permeability (sandy) soil in much of the area means that any earth stake in many parts of the city will be pretty ineffective.

Yep in the middle of summer of one of the things where I work does when we keep getting random lockups of remote location PLCs is dumping 20l of water down around the earth spike. Funnily enough it generally means that location doesn't fail till after the next hot week.