EPS Setup for Whole House Supply

[garypcook]

Our EPS supplies the whole house via a manual changeover switch, we manage the loads to ensure we stay below the 5kW rating of the inverter. See attached sketch - should also say we have a TT earth so don't need a separate earth rod (not shown in the diagram) .

The EPS has worked brilliantly during 2 power cuts in the last couple of weeks, however RCD in the consumer unit supplying the inverter has tripped on both occasions at some point during the power cut - I think when we flick the changeover switch to EPS. Not a problem as the EPS still works and provides power to the house but we need to remember to reset the RCD when grid power is back on otherwise we're then on pure grid power with no input from the inverter. The installer is going to look at this but any ideas why this may be the case? See sketch in EPS mode.

We also have a small neon light fitted to the changeover switch (not shown on the diagrams) to indicate when grid power is available so we don't have to constantly flick the changeover switch to check if power is back on.

[Will]

great write up, thanks for this.

[Cr125mxer]

Hi

I may be completely wrong and only now learning about these things.

As I understand it, when the inverter switches over to EPS supply it disconnects the main supply and then links the N-PE in the inverter. As you’re feeding back into the “beginning” of your main supply with the EPS supply it may be seeing some sort of small current flow Imbalance through the RCD that trips.

Like I say, I may be completely wrong but I’m very interested in the EPS setup as we can experience quite a few short duration power cuts in bad weather.

[cutlea01]

This is the setup I've wired for EPS operation in the event I want to run in Island Mode or during a grid outage:

When the changeover switch is operated, the RCD for the grid mains supply to the inverter will trip. Your above explanation seems fitting.

[SolarJunkie]

I will post a pic when I get the opportunity, but my EPS has been wired to avoid the RCD tripping that occurs.
I have a feeling that I used an MCB instead of an RCD for the PV system.
There are articles on this very topic on the web, as it is a known phenomena.

[cutlea01]

I have an RCBO in the dedicated CU for the grid supply to the inverter, which trips when the changeover switch is operated. My diagram is in post 6. I incorrectly stated I have an RCD. I'm wondering why I should need an RCBO, or any RCD type device on this circuit, as no resident at the property will be exposed to any of this wiring, and anyone touching the inverter and associated wiring should be knowledgeable. So I'm thinking to just change the RCBO to a MCB and so no more tripping? Anyone see any issues with this?

[captaincaveman]

I have an RCBO in the dedicated CU for the grid supply to the inverter, which trips when the changeover switch is operated. My diagram is in post 6. I incorrectly stated I have an RCD. I'm wondering why I should need an RCBO, or any RCD type device on this circuit, as no resident at the property will be exposed to any of this wiring, and anyone touching the inverter and associated wiring should be knowledgeable. So I'm thinking to just change the RCBO to a MCB and so no more tripping? Anyone see any issues with this?

RCD /RCBO are not just for protection of someone touching the wiring and equipment but also in the event of a fault developing with the installation and creating a hazzard which would then trip the protection instantly or trip when a person touches something made live by the fault.