I've got a surface at 6000 V that electrostatically attracts material, and I want to add some 120VAC cartridge heaters to it. The metal outer housing of a cartridge heater is insulated from both of the 120VAC leads coming from it. I was going to install several of these 120VAC heaters into a metal block and put it on the surface at 6000 V, as I want the metal block's exterior to be at 6000 V. The 6000 V is at very low current and originates from a high-voltage power supply also powered by 120VAC. What safety or other (e.g. ground fault?) issues do I need to consider or address? Thanks!

 

Can you send drawings. Hand drawn is OK. A picture of "cartridge heater" will help.
picture=1k words.

 

Here, this has pictures and specifications:
cartridge heaters | McMaster-Carr
Here's a diagram:

 

Looks like you need a 120 to 120vac isolator.

 

Probably the insulation of the heater is not suitable for adequate performance at 6000 volts. So the reasonable plan will be transformer isolation, which is much more common.
But a much better plan will be to keep the heaters mains powered and use radiant heating to transfer the heat.
To put it bluntly, some ideas are just not well advised.