What is this for?

[Russ Knight]

MEP803A dual genset with transfer switch. This is mounted on the transfer switch housing.

 

[DaneGer21]

This is 100% a guess; but maybe a diagnostic port?

 

[DieselAddict]

That is a power output plug.

 

[Daybreak]

3 phase power outlet plug.

 

[robertsears1]

Here is the male end of a FDECU-5 cord (5 ton heat pump, 60 amps per phase, 208V). The other picture is a male and female connector on my 804b. If you are lucky, you may find a used one for around $50.

Robert