Worksafe have published a "technical bulletin" (guidance document) for short-term connection of a genset to an installation in emergency.
Available here:
https://www.worksafe.govt.nz/about-us/n ... emergency/
and can be downloaded as a PDF.
The problem is that most small gensets available are intended to direct supply to equipment; and are NOT suitable for connection to an MEN installation. here & now is not the time or place to get into why not
So, in order to get a short-term supply, either the genset needs to be altered, or the installation does.
Worksafe have opted for altering the installation.
The guidance gets around this by allowing for use of
a) an RCD-protected genset, or
b) a centre-tapped genset in conjunction with an RCD.
In all cases:
- the incoming mains - A(s) & N - must be disconnected at main switch / N-bar, & terminated safely;
- the genset is connected to the main switch (line side);
- if the genset is centre-tapped; an RCD must be installed upstream of the installation main switch
- load must be reduced so that the max demand does not exceed the rated capacity of the genset
- the installation's MEN link must be removed (any others, eg at DBs, must also be removed; but that's not stated);
- the fact that these alterations have been made must be clearly labelled at the MSB; and
- The work must be certified, including stating that the work was done in accordance with the Worksafe guidance
- no inspection required, even though it's 'mains work", because they've declared this work to be classified as "general PEW.
The guidance forbids using a genset with isolated output for this altered arrangement.
However because this type is suitable for connection to an MEN installation (in fact the only type that is);
we can instead follow "4509.1" to set the installation up as a stand-alone installation.
Or we can give it a polarised output by making a connection between the output N and the earth / frame.
The Guidance applies only to gensets with rated output 15 A or above;
and forbids use of small gensets that have 10 A sockets as the only output(s).
And for 'larger three phase" gensets; the set-up must be designed by an Engineer or Inspector;
though it's not clear what they mean by "larger".
When time comes to restore normal supply from the grid; all these alterations must be reversed
and of course that work also must be certified;
plus the installation must be assessed in accordance with section 5 of "3019"
(which includes all the checks & tests in Sections 3 & 4 )
Please DON'T just follow this summary; 'cos I may have missed something.
Get the official document
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looking at the issue of max demand; the simplest way to ensure that it doesn't exceed the rating of the genset is to use a current-limiting mcb in the generator output . With luck the genset will already have this.
But has to be far easier to install an mcb to provide max demand by limitation;
than to disconnect / lock out a bunch of circuits, then have to re-instate them later.
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How to we know we have a centre-tap genset, and so have to fit an RCD?
Pretty much every older unit will have the middle of its winding connected to earth / frame, giving a 2-phase (180 deg) 115 V output.
It'll have 230 V A - "N" 115 A - E, and 115 V "N" - E.
In fact there is no "N", it's actually A2
You won't be able to test the RCD using any normal RCD tester, because all external testers use the A- E voltage ;
Because there's only half the voltage; a standard "30 mA" test will only cause 15 mA to flow and of course it won't trip.
The RCD's integral test button will still work, because that uses A - N voltage (in this case A1 A2)
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Obviously the best option is to set up provision for "alternative supply", in accordance with clause 7.3 of "3000" and relevant sections of "3010".
That way the installation is 'future-proofed" for the next outage.
But in an emergency you probably won't have time; and your customer probably has other priorities for spending his money.
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One other thing to watch is if the installation has an inverter.
Mostly these are grid-connect units for "mains parallel" operation; and as such are required to have "anti-islanding" to prevent back-feed onto the grid when it goes down. DON"T alter this set-up.
A multi-mode inverter is capable is also operating in "island' mode; but to take advantage we have to take this output through a changeover device same as any other 'alternative supply", and use an extra pole of the device to change the mode of the inverter.
And regardless of what type of inverter; don't set up an inverter and a genset to run in parallel.
It may seem logical to disconnect the mains, and use a genset to simulate mains supply so the inverter will operate;
but the two forms of source don't work together.
generator supply in an emergency
Re: generator supply in an emergency
Yes, I had some of the same questions
We have a couple of big Tractor PTO Generators for cowshed supply when the power is out.
The generator came with an RCD.
Many years ago I removed the RCD because the cowshed leaks power like a sieve. It's the 30mA that is the problem.
30mA a whole installation is very small? (especially 1970's cowsheds)
But as they say, regulation/guidance around this area is very light..............
We have a couple of big Tractor PTO Generators for cowshed supply when the power is out.
The generator came with an RCD.
Many years ago I removed the RCD because the cowshed leaks power like a sieve. It's the 30mA that is the problem.
30mA a whole installation is very small? (especially 1970's cowsheds)
But as they say, regulation/guidance around this area is very light..............
Re: generator supply in an emergency
So if I find an inspector......If the generator is for larger three phase connections, an electrical engineer or inspector must be used to provide a design for this supply configuration.
What will be in this design?
Does somebody have a template?
Re: generator supply in an emergency
All the generating devices I have used have a built-in protection device to stop overload.The maximum demand of the electrical installation must not exceed the maximum rating of the generator.
The cowshed maximum demand was bigger than the generater but it was managed via a selection of required circuits