Keysight U1272a DMM: Which PTCs in LOW Z Mode?

[ElektronikLabor]

Hello,
today I noticed, that when I measure 1kV with the U1272a DMM in Low Z mode, the DMM gets a bit warm on a certain area of the surface (42°C / 108°F).

This Area is exactly where the PTCs are mounted on the PCB. What is the P/N of that PTCs which are used for that function?
There are four PTCs; I presume they are connected in series?

I hope I don't overdrive them with 1kV?

You can see the PTCs on daves Video (Dave is pointing at them); unfortunately they are heatshrinked.

BTW: The PTCs are drawing 1mA when 1kV is applied

[electr_peter]

Checked U1272A connected to 230V AC mains on Low Z mode. After 20 seconds, surface temperature at the right of rotary switch reached 35-38 C and continued to climb at very slow rate.

Not an issue in my opinion, temp increase is minimal. Heat from low resistance mode has to go somewhere.