[Amps] Possible issue with B- run in wire with less than HV rating? (Separate HV PSU and RF decks)

[Marius Hauki]

Hi. I have been following the interesting safety discussion.

Let us consider this scenario: we have a separate amp and HV deck. The
anode has a potential of 3650 volts on it. The cap bank in the HV deck
is fully charged.

We have these wires between the HV supply and the RF deck:

B+ lead: SHV plugs and receptacles in both ends and RG59 between.
Chassis ground is connected to the plug shell on both sides.
B- lead: The B- is a normal relatively heavy gage cable and it is
connected with a normal plug and receptacle with isolation rated to
1kV . The amp is grounded grid, so we run a  separate B- lead as
mentioned. The B- lead is rated to 1kV in terms of insulation.

Fault:
We now for some reason have a short between the anode and the grid or
the anode and the chassis.

B- becomes minus 3650V compared to the chassis

Since B- has only a 1kV insulation, and now sits at -3650V there is a
danger of arcs between B- and chassis (now at at zero potential). The
chassis to B- resistor has failed, for some reason and is open
circuit.

The operator happens to hold the B- cable for some "cable rearranging"
behind the rack. It is not unplugged so it should be safe (he is
nowhere near the B+ cable). He also leans on the the chassis where the
amp subrack is grounded with a copper strap.
Now there is a sudden arc from the B- to the operator. The current
runts from chassis ground thru the operator to the B- connector.

Doesn this mean that we should also  use HV insulated wire on the B- ?

73
LB3HC