I have a hydro turbine that generates 3 phase ac, I then rectifier it to run a grid tie inverter, I'm wondering if I should earth the negative output of the rectifier?

 

If the eventual service is grounded, then unless you have galvanic isolation, I would think NOT.

 

One way to check would be to measure the resistance between the inverter -ve input and its case. If there is a 0 ohm connection, it is already earthed by the inverter. Otherwise, as @MaxHeadRoom says, no.

 

I'll go and check between negative and inverter case, I did check between the 3 phase rectifier heatsink and inverter and I was was getting some volts and as the heatsink is exposed I thought it should be earthed but I'm a bit unclear as to what the reciter case is connected to?

 

So I checked and I have full voltage between the dc negative and the inverter case that is earthed so I cause a short if I earthed the negative?

 

The reading can occur due to leakage, especially using a sensitive high impedance meter for the reading, you would need to provide a resistance to ground and see if the voltage remains or collapses. if the latter, then it usually indicates the reading is just leakage.

 

The reading can occur due to leakage, especially using a sensitive high impedance meter for the reading, you would need to provide a resistance to ground and see if the voltage remains or collapses. if the latter, then it usually indicates the reading is just leakage.

Good point, what resistance would you suggest? I'm a bit concerned about about damaging the inverter?

 

Usually 1K to 5K is enough.