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.

 

[Octopus]

Do you not want any power at night? lol

 

[PEG]

Is that charge controller 20A max,rated or current limited?

 

[HappyHippyDad]

Do you not want any power at night? lol

I assumed the 12V load side was still taking its supply from the battery, not the solar panel?

 

[HappyHippyDad]

Is that charge controller 20A max,rated or current limited?

20A Max rated.

 

[davesparks]

What does that earth rod connect to?

I'd want something in there to prevent over-discharge of the battery by the inverter, otherwise you run the risk of accidentally damaging the battery.


Sent from my iPad using Tapatalk

 

[HappyHippyDad]

What does that earth rod connect to?

I'd want something in there to prevent over-discharge of the battery by the inverter, otherwise you run the risk of accidentally damaging the battery.


Sent from my iPad using Tapatalk

The earth rod is connected to the earth bar in the CU.

The description of the inverter states that it has 'low battery alarm/shut off'

 

[davesparks]

The earth rod is connected to the earth bar in the CU.

The description of the inverter states that it has 'low battery alarm/shut off'

Ok, but are you going to connect it to anything else? What I'm interested in is what the earth rod will actually be doing? And for that matter what the RCD will be doing?

At the moment it looks like the earth rod is connected to the CU earth bar but not to either pole of the inverter output, so it will not do anything electrically.

It's hard to tell but is that mcb single or double pole?

 

[HappyHippyDad]

Ok, but are you going to connect it to anything else? What I'm interested in is what the earth rod will actually be doing? And for that matter what the RCD will be doing?

At the moment it looks like the earth rod is connected to the CU earth bar but not to either pole of the inverter output, so it will not do anything electrically.

It's hard to tell but is that mcb single or double pole?

The description that came with the inverter was very poor and did not say anything about earthing the inverter and there is no earthing point on the inverter, although I don't think that is what you are getting at.

The MCB would be a type B single pole, not sure why it would have to be DP? In a household 230V CU the MCB would be single pole. The RCD would act act as a main switch offering DP isolation to the sockets. The RCD is offering 30mA protection to the sockets just the same as a TT, well it is TT! I get the feeling you know all this so I must be missing something, unless it wasn't clear from the drawing which is quite possible.

Perhaps should mention that the supply to the CU from the inverter will simply be where it is plugged into the inverter in a standard plug (13A), so there isn't really any point in having the 16Amcb.

 

[davesparks]

The description that came with the inverter was very poor and did not say anything about earthing the inverter and there is no earthing point on the inverter, although I don't think that is what you are getting at.

The MCB would be a type B single pole, not sure why it would have to be DP? In a household 230V CU the MCB would be single pole. The RCD would act act as a main switch offering DP isolation to the sockets. The RCD is offering 30mA protection to the sockets just the same as a TT, well it is TT! I get the feeling you know all this so I must be missing something, unless it wasn't clear from the drawing which is quite possible.

Perhaps should mention that the supply to the CU from the inverter will simply be where it is plugged into the inverter in a standard plug (13A), so there isn't really any point in having the 16Amcb.

Yes you are missing quite a big something! I am genuinely interested in anything of this nature as I make a living setting up generators and non-grid supplies for events. What I think you have missed is that you are effectively installing the whole supply system rather than just connecting a consumers installation to an external supply system.

It is not a TT system, the inverter will be an isolated source or IT system. If you want to introduce an earth reference then you would be creating a TNS system. This is exactly the same as installing a generator.
The first letter T indicates that the source is solidly connected to earth, in the case of a single phase supply this is one of the poles which becomes a neutral once it is connected to earth, the letter I is used to indicate that the source is isolated from earth (or earthed through a deliberate impedance)

Why might you want a DP mcb? With neither pole connected to earth on a single phase supply then you do not have a neutral, just two lives. Depending on how your inverter is connected internally this could somehow be referenced to the case or it may be completely isolated from it (most likely). If the system is completely isolated from earth then I see no advantage to using a DP mcb in such a small setup, but if you are going to introduce an earth via a rod and then connect it to the 'earth' terminal of the inverter then you could end up with the two poles at different voltages relative to the earth and then need DP protection.

Without an earth reference connected to the inverter output then your earth rod and RCD will do absolutely nothing. Without an earth reference at the source then a current cannot flow to earth and so an RCD achieves nothing.


Personally I think you are over thinking a simple system and would be best just plugging in to the inverter with TRS and 4ways rather than over complicating it with rods and RCDs and suchlike as they could introduce more problems than they solve. Keep it as a simple inverter output which is isolated from earth.

 

[Lucien Nunes]

epending on how your inverter is connected internally this could somehow be referenced to the case or it may be completely isolated from it (most likely).

As Davesparks says it could be either, I have inverters on the shelf supplied with both configurations. If it is internally floating, and you are only likely to be powering one piece of kit at a time, probably keep it IT. If it contains an N-E link then you can make it TN-S by earthing it. TT would be a nonsense as that would mean putting in one earth rod to earth the inverter neutral, then another rod to pick up the earth for your circuit - when you could just connect the two with a piece of wire!

The 150A fuse might get stressed by the starting current of the saw!

 

[Deleted member 26818]

No isolator for the panel.

 

[jackhammerJIM]

why the 35mm tails from inverter to battery ?

 

[Lucien Nunes]

Seems a good size to me. Inverter rated load 2kW, efficiency approx 90%, minimum voltage 10.5V
Peak load current 2000/0.9/10.5=211A, running current with the saw HHD intends to power more like 120A

For 10% voltage drop max permissible resistance 10.5*0.1/211=5mΩ
Allow 0.5-1mΩ at each connection (very rough figure, varies greatly) so allow max cable resistance around 2mΩ. 35mm² approx 1.1mΩ per metre at 20°C, max circuit length around 2m, well in at 0.4m.

 

[HappyHippyDad]

Yes you are missing quite a big something! I am genuinely interested in anything of this nature as I make a living setting up generators and non-grid supplies for events. What I think you have missed is that you are effectively installing the whole supply system rather than just connecting a consumers installation to an external supply system.

It is not a TT system, the inverter will be an isolated source or IT system. If you want to introduce an earth reference then you would be creating a TNS system. This is exactly the same as installing a generator.
The first letter T indicates that the source is solidly connected to earth, in the case of a single phase supply this is one of the poles which becomes a neutral once it is connected to earth, the letter I is used to indicate that the source is isolated from earth (or earthed through a deliberate impedance)

Why might you want a DP mcb? With neither pole connected to earth on a single phase supply then you do not have a neutral, just two lives. Depending on how your inverter is connected internally this could somehow be referenced to the case or it may be completely isolated from it (most likely). If the system is completely isolated from earth then I see no advantage to using a DP mcb in such a small setup, but if you are going to introduce an earth via a rod and then connect it to the 'earth' terminal of the inverter then you could end up with the two poles at different voltages relative to the earth and then need DP protection.

Without an earth reference connected to the inverter output then your earth rod and RCD will do absolutely nothing. Without an earth reference at the source then a current cannot flow to earth and so an RCD achieves nothing.


Personally I think you are over thinking a simple system and would be best just plugging in to the inverter with TRS and 4ways rather than over complicating it with rods and RCDs and suchlike as they could introduce more problems than they solve. Keep it as a simple inverter output which is isolated from earth.

As Davesparks says it could be either, I have inverters on the shelf supplied with both configurations. If it is internally floating, and you are only likely to be powering one piece of kit at a time, probably keep it IT. If it contains an N-E link then you can make it TN-S by earthing it. TT would be a nonsense as that would mean putting in one earth rod to earth the inverter neutral, then another rod to pick up the earth for your circuit - when you could just connect the two with a piece of wire!

The 150A fuse might get stressed by the starting current of the saw!

I'm sorry for dredging this up again, however I can't quite get my head around why the RCD would not trip? I realise it must be ineffective as both of you say it is, but I don't understand why. I can see now how it is clearly not a TT and would be IT, however..

The current would flow through the RCD. If for instance I touched the line on the load side of the RCD and >30mA (probably >22mA) flowed through me to the ground, why would the RCD not trip as there would be an inbalance?