"Open Circuit Neutral" - do we have this problem here in NZ?

Forums › Home Workshop DIY › "Open Circuit Neutral" - do we have this problem here in NZ?

Batman

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#230771 12-Mar-2018 15:58

people have died when their neutral return wire gets disconnected from the power pole ... I was wondering, if there's a way to stop this in anyone's house?

http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=12007573

MichaelNZ

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#1973389 12-Mar-2018 16:11

We are off the grid. Solves many problems, except a period of dark and cloudy days.

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kryptonjohn

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#1973395 12-Mar-2018 16:28

I would have thought the house would also have an earth wire pegged into the ground - doesn't that provide the same protection?

However, our bach power went off recently and we could see that the earth wire to the power pole had broken off in a storm. The lines guy came out and repaired it, and commented that houses in the area tend to have poor earthing because the dry sandy soil is a poor conductor, and that therefore the house was in a risky state as it could have accumulated a dangerous charge.

wellygary

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#1973397 12-Mar-2018 16:30

it appears to be a result of no separate earth electrode and the pipework has been used as an earth substitute.

I suspect the water pipe feed into the house was replaced with plastic at some point, and bingo the pipework becomes live when this fault occurs...

https://www.ecdonline.com.au/content/business-and-management/article/standards-australia-issues-caution-on-earthing-practices-49127735

"Standards Australia has issued a notice to alert tradespersons of a safety hazard involving the previous practice of using continuous, metallic water reticulation systems as an earthing medium rather than using the currently required method of earthing using an earth electrode."

gregmcc

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#1973399 12-Mar-2018 16:31

it happens a lot more than you expect. and it may not even be your broken neutral causing the problem, it may be one of your neighbours with the broken neutral causing the problem

richms

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#1973467 12-Mar-2018 18:59

We had a stuffed neutral up a pole here for ages. I was always on low voltage here, with massive dimming of lights when starting up the circ saw etc. No shock problems that I know about unless the neighbours had problems with that.

They found it when changing the powerpole and power got much better afterwards. Since there was never a total outage nothing got reported.

Richard rich.ms

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#1973503 12-Mar-2018 19:33

I just had to get my fly in lead replaced due to a broken neutral. $1700 later :-(

Test showed impedance of 2.6 Ohms, when the legal limit was 0.4.

Pretty sure my return was going via my earth cable. Very dangerous....

Aredwood

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#1973516 12-Mar-2018 20:01

This reminds me of another project that I need to do. A current monitor for the cable going to the earth stake. So I will get alerted to any neutral faults.

Most of my lights are non dimmable LED. Meaning they will keep working at normal brightness, even if the available voltage dropped to around 100V. So I would be unlikely to notice a problem due to the lights dimming. And there has already been a neutral failure in the street cables. Thankfully it was further down the street. Worst case scenario, I could get 400V being fed to my house.

Edited to add

My street has underground power cables. Which were installed mid to late 60s. They are single core cables which have been direct buried. (have seen them being dug up for repairs) With only a single layer of insulation between the live conductors and surrounding clay, it is only a matter of time before more problems happen. I think they should all be replaced, but Vector dont seem to be interested in doing so.

When Chorus discovered these power cables. They approved extra spending to dig up the footpaths for installing UFB. And they ignored the grass verges, As they didn't want to dig anywhere near those cables.

hio77

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#1973542 12-Mar-2018 20:39

Aredwood: This reminds me of another project that I need to do. A current monitor for the cable going to the earth stake. So I will get alerted to any neutral faults.

i'd be interested in the results of this project.

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Aredwood

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#1973670 12-Mar-2018 23:58

@hio77 It will actually be a pretty easy project to make. Split core current transformer around the main earth cable (can be installed without needing to disconnect the earth cable). output into a amplifier/buffer, then peak detector/ latch circuit. And you would want to add a circuit that checks for under voltage and over voltage as well.

The fun part will be deciding what that circuit should then do once excessive current or incorrect voltage has been detected. Easiest would be to get it to switch off sensitive devices.

Another option is assuming you have a new switchboard, Get a sparkie to add a shunt trip device you your main switch, or a circuit breaker that feeds important circuits. So you can get your monitoring circuit to disconnect the power to the whole house, or the protected circuit.