Floating Neutral

[MikeM3]

I am a long time retired electrician, I have worked on many different
systems, I was High Voltage trained among other things.

I understand what floating means, but I don't understand a floating
neutral.

To amuse myself in my retirement, I decided to build a Solar System,
something that I knew nothing about, except that it is like black magic,
electricity from the sky!

I have 2 inverters, 12v X 3Kw and 12v X 4Kw, I have been advised that
I cannot parallel them, I have also found that they have floating neutrals,
the AC output of 230 volts, goes to a conventional UK socket outlet, but
without an earth, this causes the RCBOs on the lighting circuits to trip, I
tried earthing the unit, to the mains earth, but that didn't work either.

So, you know my next question, can I link this "Floating Neutral", to the
earth socket on the output?

Thank you for taking the time to read this, I hope that somebody with
more knowledge than I have, can advise me.

Mike.

 

[pc1966]

Strictly speaking you can't have a floating neutral as neutral is defined as the conductor that is earth-referenced. However, for many it is simply the conductor with the blue insulation!

It is not uncommon for small generators and inverters to be IT (isolated) supplies as it is simpler and largely avoids all of the issues of earth-referencing a supply where you don't have a direct means of earthing, you are relying on the CPC and it might not be guaranteed to be earth-referenced under fault conditions such as a loss of mains power.

 

[timhoward]

I suspect your current inverters are unfortunately going to be unsuitable for anything other than 'island' off grid installations.
It's crucial that inverters cannot back-feed a grid supply if the grid supply is lost, and grid-connected inverters either shut down or disconnect themselves from the grid in these circumstances to ensure things remain safe.
Other than safety there are bigger questions like how the waveform from your inverter would synchronise.

I think you need to start scouring ebay for inverters that were intended to be grid connected to advance your hobby.

 

[MikeM3]

Thank you both for your replies, why the neutral is called floating, I have no idea,
both the neutral and the positive go to the output sockets, I believe that I should
be able to connect the neutral to the earth without mishap, I only wanted some
advice from anybody who knows.

I think that the RCBOs are built to balance the neutral and earth, and since my
system doesn't have an earth, there is no balance, I could take a chance and just
try connecting to earth, but I don't want to ruin an inverter, they are quite dear to
me, as I am on a fixed income via my pension, I wouldn't want to buy a replacement.

I have no intention of connecting to the grid, the mains are off, before I connect
my version of solar power.

Thank you for taking time to read and reply.

Mike.

 

[newfutile]

Its AC after the inverter so there is no positive, (RCD) Residual Current Device and rcbo dont need an earth to work,these should never be connected to your consumer unit in any way.
As stated before they wont be in phase and there is a chance that in a power cut it will backfeed the grid ,this is a very dangerous situation . You would need a grid tie inverter which has protection to stop all the above problems.
4KW on 12 volts is a lot of power do you have many panels?

 

[timhoward]

Thank you both for your replies, why the neutral is called floating, I have no idea,

The best way I can put it, is that your inverter is ensuring there is a potential difference of 230v between the two lines. The potential difference between either of them and earth is not defined since the system is specifically designed that earth is not referenced for safety reasons. In theory neutral could be 600v to earth and live 830v to earth (silly example to illustrate the point)
Hence the term "floating". A bit confusing indeed.

 

[MikeM3]

Its AC after the inverter so there is no positive, (RCD) Residual Current Device and rcbo dont need an earth to work,these should never be connected to your consumer unit in any way.
As stated before they wont be in phase and there is a chance that in a power cut it will backfeed the grid ,this is a very dangerous situation . You would need a grid tie inverter which has protection to stop all the above problems.
4KW on 12 volts is a lot of power do you have many panels?

I just wrote a long reply, newfutile, but lost it because I was not logged in!

The panels that I have are supposed to be 1Kw each at 12 volts, they seem
to work fine, the problem that I have, is when I feed the flat, the lights trip,
because of the RCBO, in the circuit, I think that it needs a balance between
the Neutral and the Earth.

I tried connecting the circuit to the house earth and nothing happened, the
lights still tripped.

So I want to know, can I earth the floating neutral?

Thank you.

Mike.

 

[MikeM3]

The best way I can put it, is that your inverter is ensuring there is a potential difference of 230v between the two lines. The potential difference between either of them and earth is not defined since the system is specifically designed that earth is not referenced for safety reasons. In theory neutral could be 600v to earth and live 830v to earth (silly example to illustrate the point)
Hence the term "floating". A bit confusing indeed.

Another interesting suggestion Tim, if I cannot earth the floating neutral, I am
looking at Equalising/levelling transformers, that I believe is one way to get it
right, I also believe that transformers, will make paralleling possible.

Thank you for your time and reply.

Mike.