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Joined: Jul 2002
Posts: 8,443
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This is one thing that really gets me going,
we opened the N-E links on a whole street fed with 230/400V MEN and got a Fault Current of 23,000A, tested at the "Consumers Terminals" (The Line-side of the Main Switch).
With the links closed, we had a Fault Current of 36,000A, at the same point.
This was undertaken during an Undergrounding Operation,that I was involved with, a new 11kV transformer being installed mid-street. [Linked Image]

Joined: Jan 2004
Posts: 7
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Junior Member
Hiya Guys,

Nothing like....MEN....urrrgggghhhh I used to hate talking about this, but I'll see how I go..........maybe another beer would be in order first... [Linked Image]
Please also be aware that as this is only my second post here......all corrections will be appreciated.

Yes, open circuit neutrals kill plenty of people, every year all contractors in Victoria ( used to be my home state ) would get sent the *death list*.It never made pleasant reading either. Plumbers usually bore the brunt of undetected neutral faults, I think one year a landscape gardener even died whilst carrying out some unlicensed plumbing work.
Other more common problems would be house fires from earth conductor overload, more often than not it would be the house down the road rather than the house that had the O/C neutral.

The warning signs nearly always being *that* call from a customer "I'm getting shocks when I touch my taps".
As voltage rise on the earthing system is load dependant some faults would go undetected for ages. The design/nature of the MEN system also used to make it real hard to pinpoint the fault location as more often than not it would be on someone elses installation.In one case I do remember the supply authority ended up checking every house in the street...and then found the fault was at their own tranny two streets away.

As for the neutral / earth connection...well from what I can remember ( excuse the rusty brain ) the key word is *integrity*.

The disconnection of the main earth from the neutral bar or link has to be able to be carried out in a manner that does not destroy the integrity of the installations earthing system.
In an older style board ( neutral bar only ) this was pretty easy to achieve. All the circuit earths were soldered on to the main earth, the main earth could then be taken on and off the neutral bar as many times as you liked and earthing system integrity was maintained.

Things got complicated when earth bars were introduced into domestic switchboards... [Linked Image]

Only kidding about that.....but the number of guys that used to get confused about this was pretty amazing. It never mattered which bar you went to first with the main earth as long as earthing system integrity was maintained. A lot of guys would get caught out (defected) because they would twist terminate into the neutral bar first then jump to the earth bar. The twisted up earth in the nuetral bar (unless soldered) could never be considered as having integrity once it was removed.

With regard to the "missing MEN link" what has be considered is the type of fault or overload condition.
Straight phase to neutral overload it doesn't really matter if the links there or not.
For a phase to earth fault you really have to consider the fault current path.......
Now this is were I might stuff up, ( another beer maybe.....) strictly from memory we used to be taught that under an earth fault condition approx 90 - 95 % of the fault current would use the main neutral conductor from the MSB onwards, the balance finding it's way back via the installations main earth generally through some one elses switchboard or sometimes directly to the sub or tranny depending on its proximity.
With the MEN link removed the fault current usually has no other choice than to go to ground and usually still looks for a neutral to get back on ( electricity is so lazy it never wants to work hard and always looks for the easiest path... [Linked Image])
What pauluk has said with with regard to lack of fault current to operate protective devices is correct in theory and can possibly happen ( particularly in areas with high ground resistance and isolated installations) but in an MEN system generally in practice fault current always seems to catch a free ride on someone elses neutral.
A single installation could have it's link out for years and even with faults nobody would be non the wiser.
No MEN link also of course means the neutral has potential for voltage rise and is floating around all over the place...which can also be interesting...... [Linked Image]

The voltage operated ELCB's used to be mandatory in rural installation areas that were suplied on the older style 11Kv SWER ( Single Wire Earth Return ) systems. Not quite sure about nowadays though.

ciao

Joined: Dec 2002
Posts: 1,253
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djk Offline
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I've noticed ESB can go to really extraordinary lengths when it comes to grounding

Is it normal run loops of grounding cable right around a building (burried in concrete) and use multiple earth electrodes?

Or is this an extreme scenario?

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pauluk Offline OP
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The possibility of neutral current returning through the grounding system is one of the reasons why British IEE Regs. specify stricter bonding requirements where PME is in use (e.g. larger bonding cables in case they end up carrying current).

Whwre PME is now being employed even in areas with good soil conductivity, there's certainly a good chance of a substantital portion of current flowing via pipework and the earth, although solid metal-to-metal connections between houses are becoming less common as metallic water services are being replaced with plastic.

By the way, in the Australian/N.Z. version of PME/MEN, do you still require a ground rod as well as the bond to the neutral?

Joined: Mar 2003
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Member
Paul,
Yes we must still use and stake/rod at the switchboard with the men link in Australia.

If any one is interested below is a link to the MEN learning resource package used by electricians when they last renewed their licenses in Qld Australia.

The introduction has a very poignant example of the importance of the MEN system http://eso.qld.gov.au/publicat/men/index.htm

[This message has been edited by Dapo (edited 01-18-2004).]

Joined: Jul 2002
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Hey Norwester, Dapo,
Thanks for the Posts guys. [Linked Image]
Always good to have a Down-under conversation every once in a while!. [Linked Image]

Joined: Jul 2002
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Oh BTW Nor',
I've heard it said:
From the Chat room:
Quote
Watch out for that crazy Kiwi, Trumpy!.
Oh, they weren't kidding!?. [Linked Image]

[This message has been edited by Trumpy (edited 01-19-2004).]

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Posts: 7,520
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pauluk Offline OP
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Dapo,
Thanks for the link. That looks interesting -- I've downloaded the PDF files and will have a proper read later.

Quote
Watch out for that crazy Kiwi, Trumpy!
Well, I can't imagine who could have said that! [Linked Image]

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pauluk Offline OP
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Re the Queensland paper, it makes for some interesting reading.

A few points:
  • Outbuilding supplies. I see you have the option of running a separate earth conductor or of creating a new MEN bond at an outbuilding. Under the British PME arrangements, the latter isn't an option, as the bonding point just ahead of the meter is the last point at which such a connection is allowed.
  • Second outbuilding with daisy-chained sub-main, pg. 46-47. Interesting that you require a soldered neutral where the sub-main neutral is looped through to a second outbuilding. I see the necessity for maintaining the neutral's integrity, of course, but I can't help wondering why soldered joints would be required at the loop-through on the first outbuilding when the diagrams appear to indicate that a normal termination at the busbar in the main panel is acceptable. If screw-terminals are deemed unsuitable for the loop through, why allow them at the point at which the sub-main neutral originates?
  • Bonded service bracket, fig. 3.2, pg. 60. There are still a lot of similar service arrangements on older installations here, but generally without any such bond.
  • Reporting of shocks, pg. 53-56. Am I misinterpreting something here, or as an electrician are you required to notify the power company if somebody calls yout out saying that they have been receiving shocks?



[This message has been edited by pauluk (edited 01-21-2004).]

Joined: Jan 2004
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Pauluk,

Some of those requirements may be Supply Authority ones.

I'm not sure what the UK is like, but over here we run off the SAA and local Supply Authority rules ( sometimes known as "Service and Installation" rules).

The bonding of service brackets or raisers may possibly be a requirement in Queensland, but is not required in Victoria or Western Australia to my knowledge. Unless of course double insulation cannot be maintained at the point of attachment, in which case they must be earthed. Exposed metal....earth or double insulate.

Similarly when I came over to Western Australia I noticed that over here that all metal sinks, troughs and basins must be earthed, yet in Victoria that is not considered necessary.

With regard to outbuildings, the rule of thumb is either take the earth with you or make one. I still see this botched up a lot (as little as two weeks ago......."you want me to do what with that earth".......gggggrrrrr). I'm not sure about soldering up the neutrals as I have never had to do that for the multiple type installations .....but that may be a requirement in Queensland.

The reporting of electrical shocks is mandatory in WA & Victoria and I would assume the same for other States.

In your earlier post you were talking about the size of the main earth. Our main earth size is determined by the size of the installations largest active conductor ( generally the consumer mains ). This is taken from a table directly out of our SAA Wiring Rules. ie a 16mm mains ( typically 80A service ) would require a 6mm main earth. The equipotential bond I think is still set at 4mm, regardless of the main earth size.

What I am interested in knowing is does anybody have a minimum earth stake to ground resistance that has to be met by regulation? Typically all earthing runs have to comply with meeting low resistance/impedance requirements but I have never come across a ground resistance spec other than for HV installations. I have just spent the better part of the last two years installing / upgrading our signaling system earths ( <5 ohms ) and was just wondering about this. I have been told that a typical 1200mm stake should be somewhere between 30 and 70 ohms...seems a little high to me, but I suppose that as we really rely on the supply authority earth at the nearest sub or tranny that it possibly doesn't matter???

Dapo, I downloaded that document at work yesterday...I intend to show it around a bit as we have quite a lot of very young and inexperienced sparkies here ( only because they never seem to get the exposure to the work ). Thanks for posting that, it really is quite informative. You mentioned that it was part of a licence renewal package. Do the guys in the *sunshine state* have to retest on licence renewal?

ciao

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