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Posted By Topic: House with back up portable generator wiring

fungus
Mar 20 2020 18:57

Hi all, I lived in a lifestyle block and decided to have a 7.5kw petrol back up generator to power my house in case of mains failure. I have done the installation with a Clipsal 1pole 4PS63CAM manual changeover switch. Generator goes through a 32A lead into the appliance inlet and then wired straight into a MEN switchboard.

I have just come across ASNZS3010:2017 Electrical Install - Generating sets.

My setup is pretty close to one of the pictures shown (see attached).

My only question is, I don't have a switch for my neutral between the generator to the neutral bar as indicated in 2). Is this okay without the switching? or is it illegal?

I have an extra main switch for the feed 1) but I will just leave it as where it is.

Prefer not to add the switching for the neutral if its not illegal as I don't have any more room in the switchboard.

What are your thoughts?

   

fungus
Mar 20 2020 18:59

See link below for picture

https://ibb.co/nBt94Dr
https://ibb.co/nBt94Dr
   

OctaneOutlaw
Mar 20 2020 19:18

I haven't dealt much with generators so can't offer to much guidance but the currently cited version of 3010 is AS/NZS3010:2005 so that's the version you should be using for information I believe
   

Sarmajor
Mar 20 2020 19:40

The issue with single pole switching is that the neural of the appliance inlet (assuming you use one) is that the neutral pin is a live conductor..
But even if it is hard wired you still have isolation of live conductor issues with single pole switching.
   

Cookies
Mar 20 2020 19:46

Hi there without going too much into it you need to isolate the neutral at incoming mains failure via way of a changeover switch I.e. not feed ing anything back into the grid when essentially linesmen/faultsmen may be working on it.
You need to achieve complete isolation from from the incoming mains while the generator is in use, temporarily supplying the house.

You can also split load the house from the generator to control load but it gets confusing.
   

Cookies
Mar 20 2020 20:10

Those changeovers take a fair amount of room so no chance in the switchboard you have by the sound of it
   

Sarmajor
Mar 21 2020 07:20

I think some people need to have a read of the AS/NZS3000:2007 and check a few things out.

2.3.2.1.1 Alternating current systems
Says “ No switch or circuit-breaker shall be inserted in the neutral
conductor—
(A) of consumers mains”

Additionally not one of the diagrams in as/nzs3010 shows a switch in the main supply neutral conductor..

Given that the incoming supply neutral is connected via MEN link to earth any generator connected to a correctly wired system will never be able to get the neutral to rise above earth potential.. and further the incoming supply neutral is connected tio earth at many other points including at the Star point of the Distribution Transformer.

Installations wired with a switch in the consumer mains have been the subject of complaints to the EWRB and have resulted in fines for offending electricians and Inspectors.

The neutral conductor that must be switched is the one that does to the appliance inlet socket.
   

pluto
Mar 21 2020 08:08

The use of a generating set with an RCD in the output will never be able to supply the electrical installation due to the MEN link in the main switchboard.

Remove the RCD from the generating set and ensure that the output winding is fully isolated from the generating set frame if the output overload is NOT a double pole MCB for this in lieu of the RCD.

You need to correct in every respect follow fig 7.4 of as/nzs 3000:2007 but use a 32 amp plug and socket to be able to use the full 7.5 kVA output. You could use a 15 amp plug and socket to allow extra output power for motor starting energy.

In fig 7.4 the overcurrent device to protect the inlet plug is not shown and should be provided and should not exceed the rating of the inlet plug. AS/NZS 3010 shows the correct arrangement required.
   

DougP
Mar 21 2020 08:17

As Sarmajor said, the neutral to the generator inlet must be switched as shown in the diagram. The diagram is basically the same in the 2017 version or the 2005 version.

Additionally, as he also said, the incoming neutral must remain intact and not be switched. I'm not sure if Cookies just didn't word their reply very well, or if they actually think that the incoming neutral must be switched?

Lastly, you can not use a generator that has an RCD fitted to supply an installation. The generator must be an "Isolated type" which means it can not be an RCD protected type, because they must have a N-E link in place before the RCD in order for it to work.
   

Cookies
Mar 21 2020 11:31

No not meaning a switch in the consumer mains, a changeover switch (either normal mains or generator output) sorry maybe bad wording!


   

Cookies
Mar 21 2020 13:07

Just seen your link which stops me looking at a blurry picture!!,
I see what you are meaning more, if you connect the generator “permanently” it appears, and this makes sense that this neutral connection is not required so a single pole changeover would suffice (2.7.10.2 (a))
   

Cookies
Mar 21 2020 13:42

If making it “Permanently connected” is not desirable I am now struggling to actually find a referenced reason (other than drawings) for the neutral on a portable gen set to be switched other than to meet 2.6.1.3 with regarding it as a “live conductor” and physically working on the gen set

Although it would be much better practice and make a lot more sense to isolate the neutral at the changeover switch.
Also under normal mains operation to prevent a potential permanent neutral connection to the gen set or connection point but would a double pole switch at the gen set connection point be enough to satisfy requirements or is there another stated ruling?? (Just out of interest)
(Assuming changeovers are manual for instance)
   

pluto
Mar 21 2020 14:20

If the generating set is permanently the generating set isolator and overload protection needs to switch the neutral connection to the generating set alternator for isolation purposes to work on the alternator.

I would suggest you all carefully read AS/NZS 3010 and 3000 to get all the requirements.

It needs to be done correctly to prevent back-feeding of the generating set output into the local lines company network.

Second-guessing the actual requirements is not an "electrically safe" action.
   

Cookies
Mar 21 2020 15:17

Totally agree just curious Pluto, every time I read your last post though I still can’t make sense of it!!

But good to stick to the drawings regardless then you cant go wrong!!
   

fungus
Mar 22 2020 12:55

Thanks for all the comments/replies -as usual very helpful.

My generator won't be connected permanently. It will only be plugged in during mains failure.

The generator I got is a Powerbuilt Inverter details as below:

https://www.powerbuilttools.co.nz/product/7500w-9-4kva-inverter-open-frame-generator/

Do I just bypass the RCD or replace the RCD with a MCB in order to make it work with my MEN board? or do I need to remove/modify something else as well?

I haven't done anything like this before, just learning as I go......
   

Cookies
Mar 22 2020 13:11

I guess you would have to change for an mcb but then you’ve obviously lost that safety feature when you use the generator elsewhere
   

Cookies
Mar 22 2020 13:17

Does that unit have the 2 outlets fungus? (just wondered how they are separately fused)
   

fungus
Mar 22 2020 13:55

Yes 2x outlets.

1 for 15amp and 1 for 32amp.

I have bought this generator purely to provide back up for the house. Is too bulky to take it anywhere else or camping, I guess if I want to use it for something else, I can always use a PRCD with it?

I thought there was something about removing a link or modify the winding within the generator to make it work (if I removed the rcd)?
   

DougP
Mar 22 2020 14:00

The generator must be an "Isolated output" type. If this generator can't be modified to safely be used as an "isolated type", then it might not be suitable.

You will have to work out the wiring of the RCD on the generator, to find out how they have created the N-E link. Once you have worked that out, you will need to carry out tests to confirm that the generator output is isolated, and that the frame bonding is still in place as required.

   

pluto
Mar 22 2020 14:14

as/nzs 3010:2018 has all the info required look in Appendix B for the earth reference on the RCD. The cited as/nzs 3010;2005 should be the same, but the requirements are more clearly stated in the 2018 version
   

Cookies
Mar 22 2020 15:31

Once you have looked at the internal wiring and made modifications to the system fungus I would imagine that would effectively deem the gen set unsafe for general portable use anyway as your main earthing system of the house would effectively be earthing the casing etc when connected
   

Cookies
Mar 22 2020 15:40

Obviously while doing any modifications you need to link the earths your two outlets and bond to the casing etc
   

pluto
Mar 22 2020 16:46

Cookies Mar 22 2020 15:31

Your comment 1
Once you have looked at the internal wiring and made modifications to the system fungus I would imagine that would effectively deem the gen set unsafe for general portable use anyway as your main earthing system of the house would effectively be earthing the casing etc when connected

My comment 1

Since when is an isolated supply safer than an RCD protected supply?

If you check AS/NZS 3000:2007 Section 1.5 an isolated supply is deemed to a safe method of supply. There is NO such statement when using an RCD, it is only supplementary protection and it gets NO better than that. NOT
   

pluto
Mar 22 2020 16:58

An unintended typo in my comment 1

It should read
Since when is an RCD protected supply safer than an isolated protected supply?

If you check AS/NZS 3000:2007 Section 1.5 an isolated supply is deemed to a safe method of supply. There is NO such statement when using an RCD, it is only supplementary protection and it gets NO better than that.
   

Cookies
Mar 22 2020 22:35

No just saying when construction of this gen set was originally constructed it probably had the option of essentially a totally isolated supply and class 2 construction versus class 1 with exposed conductive parts and altering the original construction for what it was intended may affect the integrity and therefore caution should be taken
   

Cookies
Mar 22 2020 22:40

Sorry I am still struggling to understand some of your comments Pluto