Connect heatsink to mains earth or isolated ground (transformer)

[Spikee]

I'm currently building a constant current load an i use a big fan assisted tunnel heatsink.
My power resistor (100w TO247) and my mosfet (TO220) are both isolated from the heatsink. ( mica plates and plastic washers).

I use an transformer to power my project so it is isolated. My case is aluminum and is grounded to mains earth.
Now i'm not sure if i need to connect the heatsink to mains earth or the ground plane on my PCB.

Any advice ?

Thanks
Spikee

[SeanB]

If the heatsink is touchable from the outside then ground it to the case. Grounding it to the load side will increase capacitance to ground, so ground it to the case anyway, then the only capacitance is the power device tabs.

[Spikee]

the heatsink is not touchable from the outside. Thanks for the information!