TNC-S house and 3KVA generator

Trapeze · 30-10-2022 9:42pm #1

I have the above setup. My changeover switch breaks the live and neutral. Therefore should my neutral and earth on the generator be bonded?

Would pressing the test button on my CU RCD, when using the genny confirm if I needed to bond the E+N at the genny.

kirk. · 31-10-2022 11:37pm

I think its done alright depending on the supply coming from the Genny

You'd be making a tns supply same as the bigger Genny's and probably a RCD on supply to house, forget exact details

Problem with the the RCD test button is it's using the live conductors L N to prove the RCD works but doesn't tell you whether it works in an earth fault situation , an RCD tester uses the earth fault path to test

Trapeze · 01-11-2022 10:23am

Thanks for the reply. It's a difficult one to answer.

I've drawn out the circuit without bonded neutral and I can't find a return path. However neither can I find a path if I touched a live appliance casing.

I think on the whole it's (in my case) best to have it bonded at the generator. At least a fault should trip the rcd in the consumer unit.

I'm thinking of keeping a prepared plug top beside the changeover switch and pluging this into an in-circuit socket before changeover.

kirk. · 01-11-2022 1:45pm

Ya that's the way u would do it anyway a separate lead with the link so the link is removed then when generator is used somewhere else

kirk. · 01-11-2022 1:59pm

https://electrical-engineering-portal.com/neutral-earthing-systems-generator-sets

I think section 3 explains it there

The linking and the RCD recommended before the installation .

There's a caution on the sizing of the generator and "indirect contact" , that's one of the issues with smaller generators is tripping in a fault situation , afaik that's why the RCD is recommended?

01-11-2022 5:16pm

I would not break the ESB neutral, I would only switch the phase.

There was a very good publication from the ETCI on this back in the day. This generally recommended not breaking the ESB neutral. I still have a copy.

I believe there should only be one neutralizing point in the installation. Not one main one and one for the generator. multiple neutralization points lead to unpredictable fault paths.

Also if you switch out the ESB neutralization point then you rely on all future generators being neutralized, how can you be confident of this?

Apologies for poor quality reply, I am abroad and using my mobile.

When back at work I can post an image of the ETCI recommended approach if permitted.

kirk. · 01-11-2022 5:23pm

Yes I have that I think a blue cover on it be a good few years old now

01-11-2022 5:36pm

https://www.boards.ie/discussion/comment/119820040#Comment_119820040

I think you are correct. It’s a pity it was not continued. Although dated the laws of physics remain the same.

I know that at work the last time I was involved in installing a generator we did it as I described above. This one was 150 kVA.

Trapeze · 02-11-2022 1:04pm

Thanks guys. I think I'll go with the temporary bonding until I've need of an electrician, I'll then ask about having him leave the neutral in the changeover sw intact.

02-11-2022 2:23pm

https://www.boards.ie/discussion/comment/119823326#Comment_119823326

What are you going to temporarily bond? Do you mean neutralize at the generator?

kirk. · 02-11-2022 2:46pm

I would only leave a 2- pole changeover for portable generator hookup

Could have a centre tapped generator connected and you've a N-E short

Apart from the earthing arrangement other issue is generators in a fault will they supply enough current to trip an MCB in a earth fault , afaik that's the reason for recommending an RCD on the supply as a supplementary measure

02-11-2022 2:52pm

“I would only leave a 2- pole changeover for portable generator hookup”

Can you explain why?

kirk. · 02-11-2022 3:12pm

I did above

02-11-2022 3:22pm

https://www.boards.ie/discussion/comment/119824082#Comment_119824082

I don’t see any explanation for breaking the neutral there.

I did consider this approach in the past. It was only when I looked into it that I discovered that it was not the norm. The panel builder that we have used at work (albeit for very large industrial installations) recommended that I do not do this (he build the change over switch for me for a 3 phase farm yard).

I accept fully your point about the RCD.

kirk. · 02-11-2022 3:26pm

A portable generator may have a voltage between N-E , you're connecting it to a short circuit at the neutralising link at the cabinet

Different ball game proper standby generators , for unknown portable generators I would use DP changeover

02-11-2022 3:32pm

“you're connecting it to a short circuit at the neutralising link at the cabinet”

You are right. The generator RCD may not work as the neutralizing link is downstream. I had not considered the issue of the generator RCD.

When I did this the generator did not require an RCD as it was a large 3 phase unit driven by a tractor.

kirk. · 02-11-2022 3:47pm

You don't know what someone will connect up to those inlet plugs

Could be a reverse polarity or anything backfeeding.onto the grid

02-11-2022 3:56pm

https://www.boards.ie/discussion/comment/119824447#Comment_119824447

If reverse polarity the phase would be connected to earth

Trapeze · 02-11-2022 4:47pm

https://www.boards.ie/discussion/comment/119823703#Comment_119823703

Yes, but as in a previous post. I leave a prepared plugtop beside the changeover switch. I'll plug this in after operating the changeover and remove it when power comes back.

10-11-2022 5:34pm

https://www.boards.ie/discussion/comment/119824809#Comment_119824809

Why do it this way? It is quite unconventional.

If you want to neutralize a generator because you switch out the neutralizing point then just connect neutral to earth at the generator. Alternatively neutralize at the generator switch at the point that the generator connects in.

Trapeze · 10-11-2022 6:10pm

My reason is (and I might be wrong) is that I think that it's not desirable to have a neutralized generator when using it as a stand alone power supply (ie power tools) ?

japprentice · 17-11-2022 5:04pm

https://www.boards.ie/discussion/comment/119819998#Comment_119819998

Can you upload that etci document interesting to see.

TNC-S house and 3KVA generator

Comments