To bond or not to bond, that is the question.

[TwistLock]

Called out for a quote to replace a stove in a residential high rise built in ’60’s.
( Zinsco sub-panel in unit. They don’t want it changed just yet and I can clearly see someone replaced both buss’s already with plated copper along with most breakers ).
Existing FMC from sub-panel hardwired to existing 1960 stove in kitchen (50a / 6awg cu). 3 wires: 2 ungrounded conductors, 1 grounded conductor, no EGC.
Because there is FMC existing I will pull a #10 ground so I can use a nema 14-50 cord / receptacle.

That’s the lay of the land. My actual question is other than all this:

Regardless if I change the sub-panel or not I noticed as they used to do that the sub-panel’s neutral buss is strapped to the can (bonded). There are no EGC’s. Lifting the dropped ceiling tile I see 1-½” emt feeding the panel. Looking at the other end of the run in the main breaker center (photo) down the shared hallway I see FMC originating.

Question: Which is the lesser of evils - leaving the sub-panel bonded to neutral buss (whether I update it or not) because that’s what was passed back in the day. Or disconnecting / separating the ground strap from neutral buss in the sub-panel ?

https://imgur.com/a/2L0Rihq

 

[augie47]

Obviously the correct way would be to pull an EGC back to the service panel.
If that's not possible, to me, the lesser evil would be to leave the neutral bonded.
The flex in the feeder is less likely to handle a significant short than the bonded neutral.
(Obviously just an opinion)

 

[TwistLock]

Definitely. Ran this by the homeowner as part of panel upgrade, but the electrical room being at least 100' away, listening to the homeowner describe stories of getting board approval let alone working with building management, possibly wanting to pull all new wire if the snake won't push through left me with the strong impression they don't want to pay for it.
As for the stove, pulling a ground to sub 15ft away, with every other units sub possibly still being strapped and all those mingling conduits in contact with the steel studs & concrete, had me wondering what was the best I could do with limited scope, ( if there were any benefits to lifting the bond at sub, under these particular circumstances, that I was unaware of ).
Your 'opinion' sobered me to leave it as I found it.