What safety devices are there when using 240v via an inverter?

[MisterB]

If I use 240v via the EHU, there are safety devices (RCD's I assume?) to offer protection against faults with the manufacturer installed consumer unit.

But what about when using 240v via a battery supply, when using appliances being fed via an inverter?

I know my inverter automatically switches off if I overload it, but what if a fault developed in the wiring or the appliance itself? Should I actually install a mini consumer unit with RCD's or arrange the wiring via a relay so that it auto switches and both the inverter and EHU feed everything via the consumer unit already installed?

autorouter
Raul
Hoovie

I already have the relay recommended to me on earlier threads and it makes sense to me to make it an auto changing setup, so that all 240v runs via the but I am a little unsure as to feeding all the 240v from just one socket on the inverter will suffice?

It's a generic 2000w/4000w inverter with two UK sockets, does that suggest each socket can supply 1000w or could just one socket provide up to 2000w ?

 

[DavidCh]

There are people here that know far more than me but here is my understanding. Firstly, the two sockets will be in parallel somei would expect you could split the 4kw anyway you like between them, or just use one. You have a choice on protection. Either you plug directly into your inverter with no other connections and it is ‘safe” since there is no connection to ground and no path to give you a shock (this is termed ‘floating’). Or you can bond the earth connction to neutral in the inverte and fit an rcd. This means the rcd is protecting you. The rcd will do nothing without this bond, even though the test button will still work. In this case it is essential that the external ehu earth is not connected when the inverter is in use. I have a relay to achieve this. Safest is to not wire your existing sockets to the inverter but plug directly into the inverter. A real 4kw inverter would be a very big and heavy beast so I would very much doubt you would get that out of it (4kw is 17amp at 230v and 330amp at 12v!). If you are genuinely taking 17amp you would have to share between the two sockets but I am pretty sure that’s not what you have.

 

[Stealaway]

What appliances do you use with the inverter?

I only use mine for the TV ect and only turn it on at such times so I never need to touch it.
Are any of your devices Double Insulated or low voltage transformed?

 

[Littlewheels]

I understood if you switch off your Inverter when on EHU you bypass everything on the MH and are protected via the RCD on the mains supply.

 

[MisterB]

There are people here that know far more than me but here is my understanding. Firstly, the two sockets will be in parallel somei would expect you could split the 4kw anyway you like between them, or just use one. You have a choice on protection. Either you plug directly into your inverter with no other connections and it is ‘safe” since there is no connection to ground and no path to give you a shock (this is termed ‘floating’). Or you can bond the earth connction to neutral in the inverte and fit an rcd. This means the rcd is protecting you. The rcd will do nothing without this bond, even though the test button will still work. In this case it is essential that the external ehu earth is not connected when the inverter is in use. I have a relay to achieve this. Safest is to not wire your existing sockets to the inverter but plug directly into the inverter. A real 4kw inverter would be a very big and heavy beast so I would very much doubt you would get that out of it (4kw is 17amp at 230v and 330amp at 12v!). If you are genuinely taking 17amp you would have to share between the two sockets but I am pretty sure that’s not what you have.

It's a 2000w with 4000w peak power. Thanks for the response I will sit down with a coffee and read it properly, best wishes

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[MisterB]

I've just read through your response and think I understand. A further question then please .... If I was using 240v (off grid) via the inverter to feed an external socket so we could use the induction hob outside (in sort of a BBQ/al fresco mode of cooking) what protections would there be?

 

[MisterB]

What appliances do you use with the inverter?

I only use mine for the TV ect and only turn it on at such times so I never need to touch it.
Are any of your devices Double Insulated or low voltage transformed?

We use a microwave, electric kettle, toaster, induction hob ... although not all at the same time!

 

[Pausim]

It would be unwise to assume there is a positive and negative connection when using an inverter. They often achieve 230V by sending out of phase 115V down both wires, meaning both are live. For this reason any safety devices need to be 2 pole switching not the usual single pole switching used on UK sockets and plug in RCDs.

 

[MisterB]

For this reason any safety devices need to be 2 pole switching not the usual single pole switching used on UK sockets and plug in RCDs.

So how best would this be achieved using my initial post as an example?

 

[MichaelT]

Ours is wired through the normal distribution board so we have the normal RCD's in place plus the inverter has overload protection etc.

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[Raul]

There’s many ways to skin a Kat. If you have a look at victron wiring unlimited, it will give you ideas how to protect your inverter output. Every inverter output HAS to have protection. The level of that protection depends on your needs, application and practicalities. At a minimum you should have a over current ( fuse/rcb) protection. If rcd is needed, then the advise above applies. Don’t mix ehu with inverter, if both sources are for the same outlets. Fit your changeover switch, and make sure you have over curent before the change over switch. Each source has to come to change over with its own protection. Then it branches out to the circuits.

 

[Pausim]

So how best would this be achieved using my initial post as an example?

I am not qualified to say but don’t rely on a single pole RCD of the plug in type. Raul above suggests following the Victron advice.

I use something similar to the £90 unit on the right which has DP switching, the cheap SP one on the left could leave one wire live and dangerous if the inverter is using out of phase down both wires.

 

[Raul]

If the neutral bonding is done right, many will fail to achieve that, you will find 0v between neutral and earth.
Bonding is done at source, and PE back to source path has to have a low resistance path. You will end up with PEN split to PE N and instead of ground electrode, you use the chassis of inverter.
I’m not advising or telling how to, as this can be interpreted wrong, and potentially have a dangerous life chassis.

Victron gear, runs on this principle, with a ground relay active bond, when on stand alone mode. It switches to ehu system when plugged in, by opening the ground relay. They are two diferent systems when operating in stand alone compared to ehu plugged in. You can’t mix them, is one or the other.

 

[DavidCh]

To be clear. If you use the inverter on its own, with the induction hob plugged into the sockets on the inverter then the inverter is ‘floating’ and there is no path to earth so you cannot get a shock unless you hold the neutral and the live wire (and no rcd can protect you from that anyway!). The complexity comes the moment you start wiring in sockets, especially if they are used for EHU as well. Remember, to get a shock there must be a path from the inverter, through you, back to the inverter. When the inverter is ‘floating’ and there is no path back to it. The fact that when it is ‘floating’ 115v may be present on both live and neutral is academic, there is no where for it to go. However, I am not a qualified electrician and this information may not be correct so do not take it as authorities, it is simply my understanding. And I would not hold a wire from the inverter to prove it!

 

[MisterB]

Rough and ready sketch of my initial plan. Comments please .... I'm just trying to keep it simple but obviously safety is the main concern

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[DavidCh]

Yes you can do that providing you

a) know what you are doing and why.
b) bond neutral and earth at the inverter
c) use a three gang changeover that switches live neutral AND earth

The EHU earth MUST be isolated when the inverter is in use.

 

[MisterB]

Yes you can do that providing you

a) know what you are doing and why.
b) bond neutral and earth at the inverter
c) use a three gang changeover that switches live neutral AND earth

The EHU earth MUST be isolated when the inverter is in use.

I have this auto change over relay ..

https://r.search.yahoo.com/_ylt=AwrLA5YCuE9kY_gzsMxB4iA5;_ylu=Y29sbwNpcjIEcG9zAzEEdnRpZAMEc2VjA3Ny/RV=2/RE=1682974850/RO=10/RU=https%3a%2f%2fuk.farnell.com%2ffinder%2f62-82-8-230-0300%2frelay-dpst-no-250vac-16a%2fdp%2f1169280/RK=2/RS=Gd44EacLd1Z.CIHfhoB61mJlOQ0-

or i could just forget the autochangeover stuff until i treat myself to a renogy inverter, where its all built in apparently?

 

[Googlebot]

There is a thread in my signature about how I did this.

Working great still.

 

[JockandRita]

or i could just forget the autochangeover stuff until i treat myself to a renogy inverter, where its all built in apparently?

If our inverter connection to the mains sockets wasn't already built in to the MH Dave, including that autochangeover relay you linked to above, I think I'd be going down the Renogy route.

Good luck with it all.

Jock.

 

[DBK]

I fitted the change-over relay for my inverter downstream of the consumer unit, this avoids the inverter feeding the battery charger and potentially the 'fridge if it was still turned to 240 volts.

I have fitted an RCD (which should be of the latching sort to avoid having to reset it every time you use the inverter) but I now realise it doesn't work as I haven't bonded one side of the output to the chassis but as its only ever used for double insulated devices like hairdryers this isn't a concern.

As an extra thought I set my change-over relay so it was activated by detecting the EHU voltage. In retrospect I think it's better to wire so it reacts to the inverter output. This means if you are on say a 3A EHU in Italy and want to run a high current device like a hairdryer you don't have to disconnect the EHU. You can just turn on the inverter and it will disconnect automatically.

There's a link in my signature to an account of my stuttering attempts to fit an inverter. It may help if only as a warning of the pitfalls.

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[MisterB]

If our inverter connection to the mains sockets wasn't already built in to the MH Dave, including that autochangeover relay you linked to above, I think I'd be going down the Renogy route.

Good luck with it all.

Jock.

its a bloody minefield, but hey there are quite a few people offering advice which is great as far as i am concerned - i am certainly not offended or upset even if it appears i may have bitten off more than i can chew .... if i go down the renogy route it will be for the 3000w inverter so not cheap, around £300 just so i dont have to flick a switch, seems a bit OTT if you look at it from afar ...

ps - want a spare relay if i do LOL???

 

[JockandRita]

ps - want a spare relay if i do LOL???

Thanks Dave, but no thanks as I bought a replacement when I thought the original had gone faulty on me. It turned out there was nowt wrong with it.................................so I've now got a spare of my own.

Cheers,
Jock.

 

[MisterB]

There is a thread in my signature about how I did this.

Working great still.

thanks, i read it several times and will probably read it again a few more times! one thing i hadnt considered (but you have) is that by using my proposed plan of routing everything through the existing consumer unit, it means that the mains battery charger would operate and potentially the fridge and water/heating circuit would also become live, water/heating wouldnt be an issue as could just turn it off (or even on if battery is full and the sun is shining), i could again turn the fridge off or even on but having the battery charger on and being charged by the battery via the inverter seems a little absurd - or is it just me?


i may just revert back to how i have been using everything, with the inverter just feeding three totally separate sockets which are independent of the EHU supply and never the twain shall meet !!

 

[pappajohn]

the two sockets will be in parallel somei would expect you could split the 4kw anyway

It isn't 4kw.
It's 2kw with a momentary 4kw peak 'start up' load.

 

[Googlebot]

thanks, i read it several times and will probably read it again a few more times! one thing i hadnt considered (but you have) is that by using my proposed plan of routing everything through the existing consumer unit, it means that the mains battery charger would operate and potentially the fridge and water/heating circuit would also become live, water/heating wouldnt be an issue as could just turn it off (or even on if battery is full and the sun is shining), i could again turn the fridge off or even on but having the battery charger on and being charged by the battery via the inverter seems a little absurd - or is it just me?


i may just revert back to how i have been using everything, with the inverter just feeding three totally separate sockets which are independent of the EHU supply and never the twain shall meet !!

Yes, you must separate the battery charger.

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[DavidCh]

It isn't 4kw.
It's 2kw with a momentary 4kw peak 'start up' load.

So same applies, just each socket would have a max current of 13amp and one is less than the peak 18 amp so be careful.

 

[DavidCh]

Yes, you must separate the battery charger.

I only switch the sockets

 

[JockandRita]

MisterB. Even with our autochangeover setup Dave, I still have to ensure that the F/F is switched manually over to gas.

Cheers,

Jock.

 

[EuroTrotters]

MisterB. Even with our autochangeover setup Dave, I still have to ensure that the F/F is switched manually over to gas.

Cheers,

Jock.

I have done a few auto changeovers.

Each one always isolates the fridge and battery charger when power is via inverter

 

[MisterB]

Thanks for all your responses (especially those who pointed out the downside/pitfalls/dangers of my plan!)

It's made me take a deep breath and to consider why I am trying to overcomplicate matters when what I already have works and at a cost that doesn't actually give me any more than having to flick a switch myself! If I do go down the Renogy inverter path then it will resolve that conflict aswell as being able to use the kettle and microwave at the same time ( which is a 'nice to have' as opposed to a 'must have')

My original post was about protective devices when using the inverter, which I now understand (I think) are provided by the way the inverter works. That need for protection was based on also wanting to use a 240v induction hob outside whilst off grid (via the inverter) aswell.

My solution, having been guided by everyones comments is that I will use a camping lead with rcd protection when cooking outdoors!

Amazon product ASIN B09RQTR5KL
I can also use lead when on EHU aswell

So my final question, which was the basis of my first post, is should I have/do I need safety devices from the 240v power out side of the inverter before feeding any sockets?

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