Does this system look ok?

[HappyHippyDad]

I have just finished designing the solar layout for my shed. It's a little different from standard 230V domestic electrics so I was hoping you guys would cast an eye over it and give me some opinions.

I have done all the maths and am happy with the size of the solar panel, battery, inverter and charge controller so it is more the following points I was hoping for some thoughts on:

1. Size and position of the protective devices (fuses and breakers)?
2. Earthing?
3. Types of fuses (blade or inline fuses or something else? Perhaps DC breakers?)
4. Anything else?

Cheers.

 

[Risteard]

Because no current would flow through you as the system has no Earth reference.

And in terms of "the line" mentioned both conductors are line (phase) conductor. There is no neutral conductor as no pole of the supply is Earthed.

 

[HappyHippyDad]

Because no current would flow through you as the system has no Earth reference.

And in terms of "the line" mentioned both conductors are line (phase) conductor. There is no neutral conductor as no pole of the supply is Earthed.

My mistake, both are line conductors. So if I did make contact with one of the conductors which are at 240V (with regards each other), would there be no flow of current through me? Is there no potential difference between the conductor and the physical earth?

 

[davesparks]

My mistake, both are line conductors. So if I did make contact with one of the conductors which are at 240V (with regards each other), would there be no flow of current through me? Is there no potential difference between the conductor and the physical earth?

For current to flow there must be a complete circuit, without one side of the supply connected to earth then there would not be a complete circuit.

 

[HappyHippyDad]

For current to flow there must be a complete circuit, without one side of the supply connected to earth then there would not be a complete circuit.

So if there was a neutral-Earth link in the inverter and I used an earth rod as in the diagram with an earthing conductor between the inverter and CU, then the RCD would trip as one side of the supply is connected to earth and hence has a reference point?

 

[Richard Burns]

You are earthing the supply neutral rather than providing a neutral earth link. At the present they are both line conductors, earthing one of them causes it to becomes the neutral as it now has an earth reference and can be considered to have (close to) zero potential at all times.

The situation is like this diagram if you touch one pole of the battery (one conductor from the inverter) then the other terminal has no connection with earth and so current will not flow through you to earth.
In the second diagram the other pole is connected to earth and so there is a connection (albeit of high resistance) to you via earth and current can flow.

 

[Lucien Nunes]

Edit: Oops I missed some posts.

With IT:

If for instance I touched the line on the load side of the RCD and >30mA (probably >22mA) flowed through me to the ground

But it wouldnt flow to ground in an IT system as there's no way for it to get back to the inverter output to complete the circuit. Ground does not magically gobble up current - it's just another 'wire' leading back to the earthed neutral at the star point. So with IT, nothing is earthed, no current flows, you don't get a shock, the RCD doesn't trip, but the fault remains because you don't find out about it. Suppose another fault occurs to a different point in the circuit. Now you have two faults via earth but they're both downstream of the RCD. You get a shock but the return path doesn't bypass the RCD, so it still doesn't trip, i.e. it offers no protection.

This is why IT is ideal for a single piece of equipment that is very unlikely to have two faults in different places - no earth to install and test just for a temporary setup - so a lot of inverters and generators float their output. Use it to power an 'installation' and you start to need the security of knowing that any fault will be detected and cleared.

With TN-S:

So if there was a neutral-Earth link in the inverter and I used an earth rod as in the diagram with an earthing conductor between the inverter and CU, then the RCD would trip as one side of the supply is connected to earth and hence has a reference point?

Yes.

 

[davesparks]

So if there was a neutral-Earth link in the inverter and I used an earth rod as in the diagram with an earthing conductor between the inverter and CU, then the RCD would trip as one side of the supply is connected to earth and hence has a reference point?

Yes, but only if your earth rod has a suitably low Ra.

 

[HappyHippyDad]

I really do appreciate all the reply's.

This all makes perfect sense now, thankyou.

 

[LeeH]

This is a great thread as I'm doing something similar and have little PV knowledge.

I have an island in the middle of my pond and would like some sort of supply to power lights under the bridge and other items.

I'll draw up the plans.

 

[HappyHippyDad]

I'm not really planning on doing this as the IT system seems fine, but I would be interested in whether this system is acceptable (assuming Ra is low enough) and whether the RCD would trip?

 

[Lucien Nunes]

What is the thinking behind earthing the ELV DC circuit? Why have you not earthed the AC side? I am not sure what you are getting at here.

E2A the problem with showing things as boxes instead of circuit symbols is that they don't reveal important information. What, if anything, is connected to the earth contact in the inverter socket, for example?

 

[HappyHippyDad]

What is the thinking behind earthing the ELV DC circuit? Why have you not earthed the AC side? I am not sure what you are getting at here.

E2A the problem with showing things as boxes instead of circuit symbols is that they don't reveal important information. What, if anything, is connected to the earth contact in the inverter socket, for example?

I'm sorry Lucien, this basically shows up my lack of understanding of earthing systems and must be frustrating for you to read.

I guess I'm still 'toying' with the idea of having an RCD as I plan to have 2 or 3 sockets coming off of the inverter (i.e more than one appliance).

Where would the earth be connected to the inverter and where would it go to? Is this actually possible with the type of inverter I have (the only information I have on the inverter is from the chinese gentleman intimating that it doesn't need to be earthed)?

What is the difference between an internally floating earth in an inverter (which I'm guessing mine is) and one with an N-E link? If the earth is internally floating does this mean that there is no option to utilise an earthing system in order to accomadate the use of an RCD?

 

[davesparks]

Why are you so dead set on trying to fit an RCD into this system? Electrical separation as a method of shock protection is, if done correctly, much better than relying on an RCD


Sent from my iPad using Tapatalk

 

[Richard Burns]

Electrical separation is fairly hard to implement safely with respect to multiple points of use, especially in a small area.

 

[Lucien Nunes]

What is the difference between an internally floating earth in an inverter (which I'm guessing mine is) and one with an N-E link?

The floating one doesn't have an N-E link
But you could perhaps provide one at the DB.
Generally the ELV side will be electrically separate from the AC output but might be connected to the case, so the result of independently earthing the LV connection would be unpredictable.