The two socket outlets feed a 125A lifeguard unit with multiple RCBOs and a skid set up for the client. Unsure if the 125A skin counts as a big appliance or connectable installation. Also unsure if this makes any difference.
"I've got a question about a stand alone generator set up and would like some constructive feedback.
I have a 125kva genset feeding to externally mounted 125A MCBs from a 250A MCCB. Each 125A MCB then feeds a 5pin plug. The geneset will be stationary and 1 plug will be used to supply a lifegaurd the other with be used for equipment at a later date.
As this is a stand alone power system I believe AS/NZS 4059.1.2009 applies. I believe it will need an earth electrode as stated in 4.4.2.2. In this case I would have to mount a earth bar (250A rated) internally to comply with AS/NZS 3000 and also a neutral bar(not in my awesome drawing) with MEN link and inspection required.
Thoughts?"
For me, I wasn't sure if an isolated output or RCD output would work. Everything seemed to keep pointing to needing to feed a MSB from the generator and then feed the two 125A socket outlets from this. Unsure if this MSB could be mounted on the generator.
While has no legal standing in NZ, the same standards are referenced (i.e. AS/NZS 3000 and AS/NZS 3010) and the same technical principles apply.
The document advises in various places (e.g note 1 on page 20) that an earth stake is optional, but not recommended and uses AS/NZS 3010:2005 section 2.5.6 to substanciate this advice.
The "Lifeguard" unit is not a connectable installation.
Definition in Act limits CIs to vehicles, relocatable buildings, and pleasure vessels.
Nor is it an appliance - it doesn't consume any electricity.
It's basically just a big EPOD.
If the protection and sockets are part of the generator unit;
this is just a bigger version of a standard genset with a couple of sockets.
There's no PEW involved; it's all 'plug-&-play'.
It's just equipment supplied directly from a generator .
Guidance for that is in an Appendix to "3010".
Scaling up doesn't change the fact that it's just a bigger version of the same thing.
So if the mcbs & sockets are constructed as part of the genset assembly;
it's not an installation at all, it's all just a genset.
If the sockets, mcbs, and MCCB are a separate, relocatable, 'plug-&-play' assembly;
then it could be treated as a "transportable structure"
Wired as a connectable installation i.a.w. "3001"; and thereafter subject to WoEF requirements.
Trouble with that is the "final subcircuits" to the 125 A sockets would have to have RCD protection.
The level of leakage on circuits at that current rating is likely to be above the tripping threshold for 30 mA RCDs.
That's if they operate at all; which will depend on the supply to this transportable structure having a correctly polarised supply from the genset.
At 125 kVA; I'd expect this to be a 3-phase genset, with N tied to E.
But if it's isolated output, RCDs won't provide fault protection by automatic disconnection.
On the other hand, if it's isolated output, then you'd have a separated supply;
which provides fault protection by a different method - for first fault .
3001 is really aimed at transportable structures that have people inside.
Eg caravans, site huts, mobile kitchens, workshops, etc
It can be used for other transportable equipment; but often it's better to treat such stuff as portable equipment instead.
"3001" isn't really designed or intended for use at this level of current; so it doesn't provide a very useful pathway.
If the assembly with the mcbs & sockets is fixed in place,
and especially if it's connected to genset by fixed wiring (without being part of the genset as above);
then installing that wiring is PEW and the resulting "installation" may be treated as a standalone power system.
We don't have an definition for the term
If following part 2 of "3000"; the ESR 60(2) requires compliance with"4509-1".
Which requires setting up an earthing system; with an electrode and N-E link, that looks very like an MEN installation.
It's not an MEN installation; because the "M" of "MEN" stands for "multiple".
Meaning the neutral is earthed not only at the installation, but also at source (and at every other installation supplied from that source).
A minimum of two electrodes; whereas following "4509-1" you only get one.
But it looks rather like an MEN installation, and the N-E link provides a correctly-polarised supply.
So fault protection by automatic disconnection (using either overcurrent device or or RCD) works as intended & required.
The earth electrode doesn't do much electrically (it might help stop the wind blowing the structure away?).
If not being installed to Part 2 of "3000"; it doesn't have to comply with "4509-1".
But then it would be under Part 1, so you'd need a Certified design to follow.
But if it isn't any sort of "electrical installation"; there are NO installation requirements at all.
It can all just be electrical equipment supplied from a generating source.
No Standards to comply with; no certification, no inspection. No WoEF. Much simpler.
You can use either a polarised output - in which case the RCDs on the "Lifeguard' will operate as intended.
Or an isolated output, in which case you have first-fault fault protection by separated supply, and (limited) 2nd-fault protection by RCDs in the "lifeguard".
And you won't have any problems trying to avoid nuisance tripping of an RCD at the genset level, from the combined leakage of all the leads to various equipment being used, and also within that equipment.
In this configuration of supply to equipment from generating set; an earth electrode is not required.
So essentially all that really needs to be considered is I have 2 socket outlets that are part of the genset and the only real consideration is do I set the genset up as an isolated output or an RCD protected output
I did look at the guidance on feeding single loads but was unsure if that still applied with the 2 socket outlets etcetc
Does 7.3.6 Earthing prohibit the use of isolated supply above 25kVA? Based on the exception? or is this just in relation to connections to an installation?
Generator sets shall be bonded at the neutral or star point of a 3 phase winding "where appropriate"
Units under 25KVA can be used as a separated supply like eg on mobile irrigators
If you don't have a earthen star point on a stand alone generator your RCDs will not work. Yes the "test" button works but if you do a red test they will not trip.
So
All generators must have an earthen star point unless
1. They are connected to an installation with an MEN point
Or
2 they are under 25kva and supply one or two outlets or pieces of electrical equipment.
This link can be removable depending on the requirements of the genset
Really it depends on each individual application
Eg. You have a life guard mounted on a generator 4 non rcd outs 2 that are. Need's an MEN
You connect to a building via a plug and lead don't need a MEN point because the building has one.
It really trul depends on your application
Gen sets don't need an earth electrode for standalone
They do need a MEN point to keep earth and neutral ant the same potential.
It's a confusing standard but I would look at these and use best practice
Assuming that's 7.3.6 of "3000";
then yes 7.3 applies to generating systems (not just motor-driven; but any sort) that are being installed as part of an installation.
.
Similarly; 2.5.6.2.1 of '3010" does not apply unless installing the generator into an electrical installation.
And there's no similar requirement in App B.
However most gensets of this size will have a N-E link.
Note it's not an "MEN", and it isn't there to keep the neutral close to earth potential .
That's the function of an earth electrode, connected to N via an MEC and MEN link.
Which is one of two functions of the installation's earthing system for an MEN distribution system.
The other function is to provide a fault current path for fault protection by automatic disconnection.
And that's the only real function of a N-E link in a genset providing supply direct to equipment.
So calling it an MEN, when it has nothing to do with MEN, is not just technically wrong but leads to musunderstanding.
Note that "3010" is now very careful on this point.
For direct supply to equipment; go to App B of "3010" 2017
Just be sure to get the version including Amendment 1.
There were a number or errors in the Standard as published (somehow SA published an earlier draft than the one the Committee had voted on);
and several of these errors are in App B, including in the Figs.
As with any separated supply, hazards can arise when supplying multiple items of equipment. The system provides good fault protection for a first fault to earth, but not for a second fault. And RCDs won't deal with it (unless one of the faults is upstream of the RCD).
That would mean the "Lifeguard" unit isn't providing the "additional protection" (against shock) that RCDs are normally used for.
To be clear, the RCDs will still detect any imbalance in current between live conductors (that's why the test button still works).
It's just that in an IT system, for any first "earth" fault there will be NO current imbalance.
Current can't flow anywhere other than the live conductors; because while the fault connects to earth (eg through a person) at one end, there's no connection at the source end - no circuit.
Which means there can be no current through a person touching an enlivened part;
so there's nothing for the RCD to do anyway.
And that's why testing the RCD with an external tester doesn't work; such testers rely on there being a circuit back to source via PEC and N-E link (usually an MEN).
We have fault protection by electrical separation; and that's actually far safer than automatic disconnection for a first-fault scenario.
Which is as far as we are required to provide protection.
You cant get a shock unless there's a second "earth" fault (the faults will generally be to the equipotential bonding system, not to actual earth).
And that's why it's recommended to limit how much equipment is supplied by a separated supply.
If we get a second fault downstream of same RCD, it still won't trip; because while current will flow through the faults to, and through, the equipotential bonding system; there won't be any current imbalance where the RCD's toroid is sensing.
But one fault downstream of one RCD, and another fault downstream of another RCD (or anywhere on the supply side of the RCDs), will cause at least one RCD to trip.
RCDs on an IT system will work for most scenarios that can cause shock from fault current through a person.
So the do provide some additional protection over and above protection by electrical separation.
So not a good idea to ditch the "Lifeguard" ; even of you choose IT supply.
Remember also the requirement for fault protection by automatic disconnection is that it must operate when the fault occurs;
and not wait until a person touches the fault-livened conductive parts and becomes part of a circuit.
To get this type of protection to work ( using either RCD or overcurrent device to do the disconnecting),
there has to be a circuit , via an earthing system, back to source.
A problem with small gensets (and inverters, and transformers) is that they can only provide a limited amount of current;
making it hard to achieve fault protection by automatic disconnection using an overcurrent device
Same for short circuit protection .
However genset of this size (125 kVA) can probably deliver enough current to provide standard fault protection by operation of an overcurrent device; where a small portable genset simply can't.
There's also the fact that when setting up a separated supply; switches and protective devices must operate in all live conductors.
Not in only the Actives.
True that's a rule of "3000" so not mandated when not in an installation; but why would you knowingly go against long-established fundamental principles?
Personally; I'd opt for a polarised output by ensuring that genset N & R are linked;
and get fault protection by automatic disconnection using the circuit breakers , with "additional protection" by the "lifeguard" RCDs.
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