We had an issue, which turns out to be rather perplexing for the customer who had thought we had sent out a faulty inverter. So as you can imagine we sent a replacement out as we were not sure and the customer had bombarded us with emails, pictures and videos.

From what was sent they were getting readings and no output which they showed. however.....

I noticed the wires were backwards and they were using a cheap hobby multi meter which had not shown the correct polarity (when the voltage is -)  Yes you are probably getting it already right?
Well yes that had wired the  positive and negative backwards.
Fortunately the protection devices we supplied had not caused any issues, which I think caused more confusion as they could not believe there mistake.

I should note that we gave them a link to the installation video, the wiring ports are clearly marked and there was also a video and a email as well as a manual.

In the email I had to explain that the wiring diagram shows the input side not the output of the plug connector. So its backwards if you read the manual and follow it, it does make sense and the plug is clearly marked ( abate small).

It got to the point where the customer was claiming its all wired in correctly and that they had a qualified electrician confirm that it was wired correctly and had installed it. =
You could tell this was a outright lie, as it wasn't to code and the wire colours were wrong. This is a BIG issue. 

So rather than taking any notice of us, as in their eyes we were wrong and it was broken, they could have saved themselves money by actually starting again and double checking the connections were correct. (told them)...

SO There you go, we had no faulty item, is was simply a case of not looking at what youre doing and taking care and following the 5 ways of instructions.

IMPORTANT LESSION

In defense I have wired in inverters the wrong way. but  when we do the install we have to "prove" and "test" and also check, while most will do a double test, I do three before we even power up and then a follow test has to take place.

The plugs have tiny marks as to what wire they take and it can be easy to miss them or lose your place when wiring them.

And to make this even more of a chore, I once was trying to find a fault with the wrong polarity.. I spent about 2 hours trying to find the problem. - Meter wires were in the wrong ports.