Greetings,

I've read many places on this forum that an RCD is always installed after the inverter, not before. Why is this the case?

Secondly, I'm planning a SunSynk installation at a site with a type AC 300mA sensitivity RCD installed at the service entrance/incomer DB. 

Should I expect a lot of nuisance tripping after inverter installation?

NOTE: There is no other RCD in panel boards / consumer units further down.

I have an RCD before and after my inverter.

The reason why one puts an RCD on the inverter output is to protect all circuits against earth faults. Just remember that a normal breaker will only trip on its rating which may be 10 or 20 Amp. RCD will trip on leakage of 30mAmp.

3 hours ago, Kilowatt Power said:

I've read many places on this forum that an RCD is always installed after the inverter, not before. Why is this the case?

If input feed drops, the inverter goes into islanding mode, where the load is isolated from the grid side.  If the RCD is only on the grid side, then the load no longer has any RCD protection (dangerous and illegal).

If you have a second RCD on the load side, the load side neutrals must be completely separated from grid side (which is often amazingly difficult in old houses).

4 hours ago, Jacques Ester said:

I have an RCD before and after my inverter.

Good to know that it is possible to have an RCD on the grid side of a solar inverter. The notion that a secondary power source (solar/battery) would create imbalances that would cause the input RCD to trip is therefore false.

1 hour ago, JustinSchoeman said:

If input feed drops, the inverter goes into islanding mode, where the load is isolated from the grid side.  If the RCD is only on the grid side, then the load no longer has any RCD protection (dangerous and illegal)

I get it. I reckon this pretty much explains why it is better to have the RCD on the load side rather than on the grid side. Cheers mate!

I have my Solar Inverter connected after my Main RCD, and get a lot of nuisance tripping when the grid power drops and comes back, so now I want to install a 63 Amp Breaker Before the Main RCD, and then connect my Solar Inverter before the Main RCD. Hopefully this will resolve my Main RCD nuisance tripping. 

Edited February 28, 20224 yr by Colin B

9 hours ago, Kilowatt Power said:

I've read many places on this forum that an RCD is always installed after the inverter, not before. Why is this the case?

The reason is that all inverters have smallish capacitors to earth from both neutral and live. These are to mitigate EMI/RFI from the switching transients. These capacitors cause current in the earth conductors: transient currents, plus some milliamps of 50 Hz current. Both of these make a Residual Current Device before the inverter more likely to nuisance trip. You can still have them, but not the usual 30 mA ones. But then of course, there is less protection for those squishy, sensitive humans.

9 hours ago, Kilowatt Power said:

NOTE: There is no other RCD in panel boards / consumer units further down.

It's not hard to add these. They usually take up two standard 17.5 mm positions in a switchbox / distribution board, and you can even get ones with flying leads that take up just one position. They should cost of the order of R1000, though I haven't priced one recently, and certainly not in South Africa.

On 2022/02/28 at 4:54 PM, Coulomb said:

It's not hard to add these

Space in the 8-12 ways consumer unit (distribution board) is fully taken up by a 2 pole isolator switch (main switch) and MCBs. Thinking of replacing the 2P isolator switch with a 2P RCD/RCCB that will also act as the main switch.

On 2022/02/28 at 4:54 PM, Coulomb said:

certainly not in South Africa.

I happen to come from the land of long distance runners (right smack on the equator) where use of RCDs is not mandatory *sigh* 

On 2022/02/28 at 4:54 PM, Coulomb said:

Both of these make a Residual Current Device before the inverter more likely to nuisance trip. You can still have them, but not the usual 30 mA ones.

The 4P RCCB inside the incomer DB / service entrance has a residual current sensitivity of 300mA. I guess earth current from the inverter input EMI/RFI filter caps is well below 300mA.

9 hours ago, Kilowatt Power said:

guess earth current from the inverter input EMI/RFI filter caps is well below 300mA.

Yes, that won't be a problem. But obviously it won't protect the squishies from 100-300 mA shocks, which can be fatal. 

On 2022/02/28 at 7:57 AM, Jacques Ester said:

I have an RCD before and after my inverter.

Is your inverter purely off-grid with no capability for grid feed-in or a true hybrid like the SunSynk?

I suspect a true hybrid even with zero export enabled will trip an RCCB on the grid side due to the miniscule power that finds its way back to the utility meter.

Off grid type. Kodak King

Can u please help me do u get dedicated rcd or elcb or any other type of earth leakage protection just for inverters and a test device to test the milliamp ma trip of this devices suitable for inverters. 2) my rcd or elcb is connected after the inverter on the output side with the neutral connect to neutral bar on the db box and the earth on the earth bar on the db box .  If i go to inverter power my normal elcb tester register that my live and neutral wires are reverse and no ma trip is possible 

On 2022/02/28 at 10:00 AM, JustinSchoeman said:

If input feed drops, the inverter goes into islanding mode, where the load is isolated from the grid side.  If the RCD is only on the grid side, then the load no longer has any RCD protection (dangerous and illegal).

If you have a second RCD on the load side, the load side neutrals must be completely separated from grid side (which is often amazingly difficult in old houses).

 

There is no 'special' earth leakage device for inverters.  If your tester is complaining, then you probably have your Earth-Neutral bonding set up wrong.