Hi Peter

We fitted some VFD's in the summer and I was reading through the documentation for these Siemens Inverter drives. I thought you might find this of interest. Read section 6 for EMC & EMI definitions. http://cache.automation.siemens.com/...ications_e.pdf

There is what's called a DC Link between the incoming supply and the output circuits (page 8) and it seems that high frequency interferance on the output side can feed back to the incoming supply, as you are experiencing, if you don't have the correct filters on the supply.

One thing I noticed from reading the document was the need for good earthing and separation of cables (page 43). Does the mobile fish van put down an earthing rod when in use?

From your latest posts it appears that you have found a solution but it's always nice to read up on the fundamentals.