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: Seperate earth electrode as bonding

codaxx
May 24 2018 13:20

Hey guys.
So, i have been asked to refit a traffic sign. A buried 1C Neutral screen cable has been run to the sign, no PEC (existing cable).
Due to having no PEC for the earthing of the metal sign, they have put in an earth electrode and have got there earth off that.

Now, because it is not a switchboard, i am confused whether i link the earth the neutral or not.
The men link is in place at the board.

personally i would have run a 2C neutral screen with neutral screen as the earth.
   

pluto
May 24 2018 14:20

Was the original supply arrangement from a street light supply? If so it amy ahve been a TN-C supply and the earthing comes from the neutral (PEN) conductor .

If it was always from a TN-C-S (MEN) supply from a switchboard the use of an remote earth at the sign position would have never been correct.

An option would be to provide a simple switchboard at the sign and then use the outbuilding provisions of AS/NZS clause 5.5.3.1.
   

AlecK
May 24 2018 14:26

The set-up described is non-compliant.

If the sign is part of an installation, it should have either been earthed using a PEC, or set up as an outbuilding c/w MEN link (as Pluto suggests) - which would require at least one circuit protection device as well, in order to be classified as a switchboard.

If not an installation but works; earthing to the N might be acceptable - but being at ground level rather than up a pole, other precautions would also be necessary to ensure keeping within touch voltage limits.
   

codaxx
May 24 2018 16:51

Ok, I missed out some crucial details here.

So, the sign has a RCBO inside it (sign is enclosed with electronics/RCBO inside)

There is no PEC, so i assume they got (or there idea) was to have a seperate electrode for the sign to act as an earth.

To be compliant, would i add a small switchboard with busbars and then add a MEN link? if so, this would be classed as high risk and would also need an inspector?


   

codaxx
May 24 2018 16:53

also, it is a pole sign but within arms reach (only 2 meters off ground)
   

Sarmajor
May 24 2018 17:52

Where does the supply come from?

Under the current rules you have to treat it as an outbuilding for the purpose of earthing etc.

As for the high risk aspect that is where the origin of the supply is important. If it is fed from works then the new men system and earthing is high risk and requires inspection. If it is fed from an existing men switchboard then it becomes a sub main and under the current rules is not high risk.
   

codaxx
May 24 2018 18:18

ah ok.
The supply is from an existing MEN SWB, the sign is about 200m away from the main SWB

I will treat it as an sub-board with earth electrode. sounds like low risk, but needs that MEN link for its separate electrode

cheers guys for the clear up. Just confused on how the original installers looked at it and how they had configured it. looks like there was no MEN link so therefore, was probably never compliant.

There is seperate circuit protection in the sign, the sign is secured closed and needs a tool to open. I think i will look at the sign as a form of a switchboard, and will add the MEN link to satisfy sub board requirements with seperate earth electrode.

Thanks for the help, I always overthink instead of \'just think\'
   

Satobsat
May 24 2018 20:34

Would the original lighting inside the sign have been double insulated? Or extra low voltage even? Might not have needed an earth originally?
   

codaxx
May 24 2018 21:12

that would have been a better idea, but the electronics that turn the 230v into ELV are in the sign itself.
Definitely not double insulated, so earth definitely needed.

Would have made sense for the original run to be 2C Neutral screen but first time ive seen this kind of setup so a little confusing but the other guys have made sense of it
   

AlecK
May 25 2018 12:09

Have to disagree with Sarmajor on the \"high risk\" issue.

If set up as a switchboard under the \'outbuilding\' configuration (PEN supply with MEN link & electrode), then we need to go through ALL of that clause [5.5.3.1(b)].
including the bits that say
(ii) the DB in the outbuilding shall be regarded as a main switchboard for the purposes of effecting the MEN connection;
and
(iii) the earthing conductor between the DB in the outbuilding and the earth electrode shall be regarded as a main earthing conductor for the purposes of earthing the electrical installation in the outbuilding.

So now we have (among other things) 3 items in poarticular:
- an earth electrode
- an MEN link
- an MEC.
Now look at the definition of \"main earthing system\" in ESR 4 - and those 3 things are the very definition of a main earthing system.
Now the definition of \"mains work\"; and it includes work on any \"main earthing system>

And mains work that is not maintenance / replacement is high risk as per ESR 6A.

So yes, it DOES require an inspection.

And so it should, because it\'s doing exactly the same job as the main earthing system for the main installation - and getting it wrong can have exactly the same horrible consequences.

   

DougP
May 25 2018 12:37

I saw a similar question recently with regard to a supply to a pump shed (or just an electrical box on a pole with pump(s) connected). It didn\'t have a correctly sized PEC, so the question was asked, if it could have a PEN, MEN link and earth stake.

I even wondered if the box would actually be a switchboard? It may have some controls for the pumps which were away from the box, so I guess they are on \"final subcircuits\".

And I guess if there is a circuit breaker for each pump, then technically it is probably a switchboard.
Then also would an electrical box on a pole be an \"outbuilding\"?

I was trying to see if there was another discussion on here about the difference between a control panel, and a switchboard. But I could\'t see anything definitive.

Although Alec\'s comment above: \"which would require at least one circuit protection device as well, in order to be classified as a switchboard.\" seemed to be definitive.
   

codaxx
May 25 2018 12:39

Cheers Aleck.

So if i was to add an MEN link, that would need an inspection, due to it being part of main earthing system and therefore high risk?

The original sign was knocked down and broken by a car hitting it.

The earth electrode and MEC is existing, but i am not sure of the original setup and whether there was an MEN link or not as original sign needed replacement.

I will have to hunt down original COC to see what the description says if anything about MEN link and sub board
   

Sarmajor
May 25 2018 12:43

Aleck,
I disagree with myself from time to time and this topic is one where the rule makers have failed to make their intentions very clear.

It should be clearly stated that a sub main without a PEC is in fact Mains and then everyone would get the message that the associated earthing system is a main earthing system.

I agree with your interpretation of the relevant clauses. It is somewhat annoying that it takes tying so many things together to get to a conclusion that should be clearly stated.

I see that you clarified this very point back in Dec 2016.



   

codaxx
May 25 2018 12:46

DougP

I will read the wiring rules over the weekend and try nail some definitions and get back to you.

AlecK is an inspector(not saying you are not) and knows his things (not saying you dont) so going from what he says, if circuit protection exist with final subcircuits connected, it can be classed as a switchboard. Whether there are other requirements i am not too sure (of course properly rated for its environment etc is commense sense stuff)
   

pluto
May 25 2018 16:17

An advanced warning the next edition of AS/NZS 3000 to be cited in NZ, will on present intentions of Energy Safety will be providing for other systems of supply, IT and TT being likely.

This will result in the withdrawal of the out-building provision currently provided by AS/NZS 3000 Clause 5.5.3.1 so called the out-building provision. So the use of this system will only be possible in the short term only.

The reason for this warning, while the use of an PEN conductor and remote electrode with an MEN link in the remote switchboard is OK for now, the use of other systems of supply will give a solution but in a different manner.
   

AlecK
May 25 2018 16:45

The expectation - set by ES - is that 3000: 2018 will be cited late 2019.
At present, it does not include any such provisions.
And there\'s absolutely no way that the Amendment 1 project, which won\'t really get under way before August, will be finished by end 2019. A1 is already huge and is likely to take several years to prepare.

So unless a NZ-only \"Amendment A\" is done just for this, the provisions for TT etc won\'t be cited for a long time.
Methinks this \"warning\" is a bit premature.
   

DougP
May 25 2018 17:05

Codaxx..
There\'s not too much to read... the definition of a switchboard is reasonably straightforward.
=======
An assembly of circuit protective devices, with or without switchgear, instruments or connecting devices, suitably arranged and mounted for distribution to, and protection of, one or more submains or final subcircuits or a combination of both.
=======

My query was more about something that looks like a control panel, maybe mounted on or near a machine, connected to motors or whatever of a machine, fed by a circuit from a switchboard, and maybe contains circuit protection for different parts of the machine.

Is that a switchboard, or is it an part of an appliance or equipment?
   

AlecK
May 25 2018 20:09

A good question
To which there is probably more than one correct answer