The DUT is a relatively high-power LED driver driven by a SELV high-power +24VDC supply. It'll drive LED voltages up to 55V by specification. So everything is considered safe as far voltages are concerned but the power levels are moderate, about 620W actual, 1.2kW design limitation.
Normally I don't thankfully have to deal with UL. But on this project it's a requirement. UL reps told me I need 13mm clearance on mounting points to a non-insulated "track" for ignition hazard reasons. Apparently surface copper in the earth potential is exempt but that further raises the question whether you then have to have 13mm clearance from earth to any other parts on your PCB.
I haven't previously seen this as a reason for clearance/creepage. Could anyone point out to me where is it actually defined? In the eye-wateringly expensive UL 60950-1? IEC 60950 (or 62368) is a bargain by comparison.
Mounting holes are bolted in this case into sheet metal plate that is in contact with device chassis/earth. A device like this certainly can go up in flames albeit the external PSU and on-board fuses should kick in on a catastrophic failure.
Yes, it'd be nice to question UL guys directly but getting answers from them is a long game.