Sunsynk inverter - no N -E bond

**Gene** · 19-Aug-23, 07:56 PM

I got a client that had a 14kW Sunsynk inverter installed with batt , solar the lot, he requested a COC for the house wiring as it trips when eskom power comes back on everytime, and that he got a COC from the installer for the solar so no worries here.
Now a quick test and i found that when eskom is down the live and earth measures 78 Volt and neutral and earth measures 97 volt...!!! . as i know that the sunsynk has a automatic neutral earth switch when in operation ,this one does not work or is not set?, or i have to install a neutral earth relay - i requested that he contact the installer, but he asked me to get this system in operation , so here is a case where the fly by night made his money and is gone, this is the second time i had to fix others problems on inverters that was installed by FBN... and also supplying a COC...

**Dylboy** · 19-Aug-23, 08:11 PM

Yes ya the internal relay is just to operate an external relay which makes the neutral and earth bond : )

The size cable for the Neutral and Earth bond is yet to be determined as it's a link to reference.

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**Isetech** · 19-Aug-23, 08:30 PM

Some sunsynk inverters have the relay built into the unit and some have a contact which will open or close to activate a relay. For example the new combined battery/inverters have a built in relay, so no neutral/earth bonding is required, it is done insde the unit.

You need to check the manual to verify the method to use.

I have been hearing chatter that a permanent bond is going to become the SANS requirement. Had a few calls asking about the 10 amp flowing in the neutral /earth, still waitng for feedabck from the manufactuer about this high current, but it seems nobody is concerned about it. They say it could have something to do with the electronics in the inverter.

**Dylboy** · 20-Aug-23, 01:30 PM

With regards to the perm bridge, I have had a 15Amp fuse blow which means more than 10Amps flows...

I think it's due to network and having that permanent bridge makes a better N and E bond than municipality thus the current flow.

It's much like a PEN failure where the neutral on the network becomes open or high resistance thus the current choosing earth to flow and when it find a less restrictive path such as your Neutral then the current flows there from the street...

Not a fan of Perm bond, look it is much easier to do. We also need to know what CSA of cable to use...

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**Derlyn** · 20-Aug-23, 04:28 PM

6mm and you're safe.

**Isetech** · 20-Aug-23, 05:45 PM

Like the bypass/change over switch, 5 kw you use can use a 25 amp changeover and an 8 kw you can use a 40 amp.

The same with the bridge wire, it must be rated to the application, 5 kw inverter would be a 4 mm wire, 8 kw a 6 mm wire.

You see some people use a 10 amp relay for the bridge, next thing they ranting on social media about relays failing.

**Derlyn** · 20-Aug-23, 06:58 PM

Originally Posted by Isetech

Like the bypass/change over switch, 5 kw you use can use a 25 amp changeover and an 8 kw you can use a 40 amp.

Unless your DB is not split into essentials and non essentials then the change over must be rated the same as your DB main switch ie. domestic installation 60A. I've seen a couple such installations with an 8Kw and a DB that's not split and the installers ( telephone technicians ) think that a 40A change over is ok. They think it's one size fits all.

**Isetech** · 20-Aug-23, 10:07 PM

Its a tricky one because we install a 50 amp breaker on the supply to the inverter , and a 32 amp double pole on the UPS side of the inverter. It is something to take note of when designing the system, you could have up to 50 amps flowing through the bypass switch when in grid and not inverter mode. If would be a good idea to use a 40 amp double pole on the load side of the bypass switch if you wanted to save space or money on the bypass switch.

Originally Posted by Derlyn

Unless your DB is not split into essentials and non essentials then the change over must be rated the same as your DB main switch ie. domestic installation 60A. I've seen a couple such installations with an 8Kw and a DB that's not split and the installers ( telephone technicians ) think that a 40A change over is ok. They think it's one size fits all.