I thought the same, but when contactor engaged with the forward switch, I pushed and pulled the contactors with same said pencil to no avail. I even readjusted the spring tension on all the forward contacts and added shim to the flat contacts thinking that maybe they were not getting good connection...no change. Motor was completely rebuilt, and not many miles on it , I'm sorry to admit. I keep going back to some not yet found protection relay that I am bypassing with the heroic pencil.
Something odd about that.... I understood that the pencil-pressure was only effective UNTIL you ALSO set the motor Switch into FWD. After which it was to no avail.
So I/we have been looking for a 'low power' cause (control circuit. switch or relay..) for a 'high power' fail.
But... once you push that pencil down, none of the control circuits that speak to denizens of the OUTPUT side of the WiaD matter.
There is NOTHING ELSE with contacts heavy enough to manage its output EXCEPT the contactor.
So .. there is power TO the contactor (from the WiaD drive output. Until the MS is set to FWD.
There IS a conduction path FROM the contactor (to the motor), 'coz it also works UNTIL the MS is set to FWD.
Is the WiaD drive being shut-off at the SOURCE?
I have been ass u me ing the Thyratron rig neither knows nor cares whom has the right to do what, with which, and to whom with the power it serves-up. Dasn't internally CARE whether FWD or REV contactor is energized.
Or neither. Nor even BOTH.
Switch prevents asking for it. Final 'save' is left up to a mechanical interlock at the contactors.
But the power is still available , 'upstream'..
As a "contactor-reversing" (only) AKA "1Q" critter, all that control and interlocking is a third-party player's task - not that of the Thyratrons.
EG: the contactors and their control circuitry.
Or a pencil. (BTW .. we gots to get you an 'Orange stick'. Pencil lead can be conductive..)
I had not presumed a WiaD to have fault-detection or alarm circuitry of the sort DC Drives or VFD grew in later epochs.
And yet... if the source has gone dark... it is ACTING as if it did have..
We've been looking only at the Armature circuit(s).
Is there something erratic in the FIELD circuitry?
Field kinkyfudgery relay? Field-loss emulated in error, triggering a shut-down?
Or ACTUAL field-loss, shutdown as-required?
Bill