I have a Sunsynk 8kW inverter and am using the ATS output to power a relay that connects neutral to earth when the inverter is operating in off-grid mode. My understanding is that this is to prevent the neutral from floating away from a "safe" earth reference while the grid supply is off.

Now I have been thinking about this, and am wondering if there is another acceptable way of doing this. I sadly do not know much about laws and electrical code, so perhaps someone can enlighten me on this. But my idea was to use a TVS diode instead of a relay to keep the neutral tethered to an earth reference. Let me explain. If the neutral is connected to earth in a permanent way, the earth leakage trips on my side (which is expected, since there is a slight voltage difference). But what if I use a bidirectional TVS diode between earth and neutral - one that would not conduct at the usual difference, and would clamp the voltage to around 10V or so? That would prevent any tripping when using grid power, and would keep the inverter neutral from going further than 10V from earth.

Would this satisfy the same safety requirement that the relay is doing? Also, for my curiosity, what are the hazards of letting the inverter neutral drift? From what I can tell both neutral and live wires are well insulated and do not come into contact with exposed surfaces.

I like this idea for several reasons:

• It does not have the power usage of keeping a relay turned on.
• It is a solid-state solution which could theoretically last much longer than an electromechanical relay.
• Most importantly, it frees up the one ATS output I have on my inverter so I can use it for other things.

 

Any input and insight from other members would be appreciated.

56 minutes ago, Sir Rodgers said:

I have a Sunsynk 8kW inverter and am using the ATS output to power a relay that connects neutral to earth when the inverter is operating in off-grid mode. My understanding is that this is to prevent the neutral from floating away from a "safe" earth reference while the grid supply is off.

Now I have been thinking about this, and am wondering if there is another acceptable way of doing this. I sadly do not know much about laws and electrical code, so perhaps someone can enlighten me on this. But my idea was to use a TVS diode instead of a relay to keep the neutral tethered to an earth reference. Let me explain. If the neutral is connected to earth in a permanent way, the earth leakage trips on my side (which is expected, since there is a slight voltage difference). But what if I use a bidirectional TVS diode between earth and neutral - one that would not conduct at the usual difference, and would clamp the voltage to around 10V or so? That would prevent any tripping when using grid power, and would keep the inverter neutral from going further than 10V from earth.

Would this satisfy the same safety requirement that the relay is doing? Also, for my curiosity, what are the hazards of letting the inverter neutral drift? From what I can tell both neutral and live wires are well insulated and do not come into contact with exposed surfaces.

I like this idea for several reasons:

• It does not have the power usage of keeping a relay turned on.
• It is a solid-state solution which could theoretically last much longer than an electromechanical relay.
• Most importantly, it frees up the one ATS output I have on my inverter so I can use it for other things.

 

Any input and insight from other members would be appreciated.

Very novel idea. On face value , the diode will remain unbiased  when grid is on and earth to neutral potential at zero zero . Yes it has capacitance and and small leakage current , but will not influence the ELD. 

BUT ...

When grid is off and residential earth bond is not available , yes the TVS will now clamp, but the effective impedance of that 'bond' is not small enough , meaning it will compromise the trigger thresholds of the ELD .  

 

Lastly , the failure modes of TVS includes a failure to open circuit. What makes that worst , is the fault will remain undetected, rendering the ELD as useless. 

The near failsafe mode of electromechanical really is optimal and safe , so my recommendation is stick to the relay.

Oh , and also , in the case of a hard earth fault , the fault current will have one return path only , that is thru the TVS , and will invariably toast the device.

I kept on pushing my installer and electrician on the whole earth bond relay thing (with photos and regulations) and they kept saying it is not necessary. 

11 hours ago, dropkick said:

The near failsafe mode of electromechanical really is optimal and safe , so my recommendation is stick to the relay.

Thanks. I suspected that would be the reason that I did not see many alternatives... 

 

2 hours ago, Scubadude said:

I kept on pushing my installer and electrician on the whole earth bond relay thing (with photos and regulations) and they kept saying it is not necessary. 

Do you know how to get access to the relevant regulations? I would also like to learn what the rules are regarding these installations. I've met too many unreliable electricians to be trusting them without learning things for myself as well.