Poor man's EPS (grid failure) design

[puntloos]

New here - hi!

So most new inverters are able to do EPS, and to my understanding this "effectively" has the inverter pretending just to be a full off-grid generator. (usually a diesel motor strapped to a dynamo).

But when looking in the manual of my current frontrunner inverter (SolaX G4 Hybrid 12kW), there's a whole bunch of complexity - in particular identifying "EPS devices/rings" - items you want to be able to run when there's an outage, such as your fridge, network cabinet, some lights, maybe a microwave. It seems sensible however it requires a ton of extra wires, clever switching stuff.. and the major downside is that any device you didn't predict would be needed (hey can I charge my laptop from this socket, or watch a bit of TV..) can't be powered easily without running some cables.

Why can't I just have power-from-grid normally (and perhaps some fancy-ish setup to give stuff back to grid but I care somewhat less about this)
And if the grid goes away:

1/ Bighuge 3 phase switch. CLICK


2/ EPS out from my inverter now connected to the main house distribution board input. Maybe need an extra earth stake or something?
3/ <run around the house manually switching off my victorian electric kettle collection>
4/ Happiness?

This is the 1-phase version of this:


What am I missing? Assuming the changeover works, I see no way for my grid to anger (or electrocute) people from the outside grid, and once we're back to normal I change back? I can imagine a few edge cases where eg I 'change back' but the inverter is still in EPS mode and... I can't quite imagine this is a problem (it's not like we are connecting the EPS port to the grid or something..)

As for power needs, well, clearly if you switch on eeeeeverything in the entire house you can reach many amps (I calculated 50amp max for my house) but that is in the 'fast-charging my car whilst oven, microwave, hob, vacuum, kettle..' - not a situation you would do if you know you're on battery.. I don't think I'm too worried about accidentally tripping the fuse (?) on the inverter EPS out - I think the 12kW solax can handle 6000W on a single phase max, which should be fine for 90% of my cases.. maybe I should get the 14kW so even my 7000W hob would be fine running off a single phase..

Thoughts?

 

[puntloos]

No thoughts? :/

 

[timselectric]

If you are asking if you can use a changeover switch as a transfer switch. Then the answer is yes.
What your drawing shows is a typical setup.

 

[puntloos]

The thing I'm missing from the drawing I guess is the earth stake? Do we need an extra one? Where does it go? I am worried that if grid is offline it might not provide earthing anymore?

 

[timselectric]

Earth connection is supplemental to the grounding system. It appears that you are in the UK. So the grounding is provided by your utility provider. If you disconnect from the utility neutral, you are also removing your grounding.
You will have to create your own grounding system. Which is only in use when disconnected from the grid.
When your power source is switched between grid and local. Your grounding must also be switched.
You can't have both, at the same time.

 

[hwy17]

You could look at generator transfer switches. In the US they leave the utility neutral connected while on generator power. They might do the same there.

 

[puntloos]

Earth connection is supplemental to the grounding system. It appears that you are in the UK. So the grounding is provided by your utility provider. If you disconnect from the utility neutral, you are also removing your grounding.
You will have to create your own grounding system. Which is only in use when disconnected from the grid.
When your power source is switched between grid and local. Your grounding must also be switched.
You can't have both, at the same time.

Interesting, why is it so bad to connect grounds? (that's what I saw some random dude on the internet (...) claim their electrician did)
But yes, I think switching grounding isn't too hard anyway, if you already have a multipole switch in place so no reason to wire them together

 

[timselectric]

Interesting, why is it so bad to connect grounds? (that's what I saw some random dude on the internet (...) claim their electrician did)
But yes, I think switching grounding isn't too hard anyway, if you already have a multipole switch in place so no reason to wire them together

Your not switching grounds.
You are switching between creating a new grounding system, and using the existing grounding system.
The changeover switch should disconnect the house neutral from the grid. And simultaneously connect it to the grounding system.
At the same time as it switches the line side over.

 

[Bluedog225]

Two grounds creates issues. I forget what it’s called. Ground loop?

 

[timselectric]

It puts neutral current on the ground conductor.
(Between the two bonds)

 

[puntloos]

Dumb question, but is it hard to install a new earth stake to handle the 'stand alone' solution?
Or can I just tie it to a metal radiator (so to speak, obviously) and done?

 

[timselectric]

Dumb question, but is it hard to install a new earth stake to handle the 'stand alone' solution?
Or can I just tie it to a metal radiator (so to speak, obviously) and done?

If you already have a grounding system. You should connect to it.
There should only be one grounding system.
If you are using it as an alternate source for existing loads. It's not a stand alone system.