IG came to be quite the 'cause' when computers entered filthly electrical systems.
To go down the list:
Crossed over polarities -- far, far, more common than they should be -- so many out there tying their best to give us more repair work...
Over loaded circuits -- until digital logic came along sagging voltages passed largely without remark...
&&&&&
I've never encountered an IG installation in commercial service that was not companion to an isolated power system: an SDS. ( Secondarily Derived Service )
They went together like bread and butter.
It was a LOT cheaper to just drop these in rather than re-work and correct a fundamentally screwed up building -- some of which were bona-fide antiques.
Now that decades have gone by -- and ABOVE ALL -- with the rise of laptops in general office use (which have intrinsic isolated power and secondarily derived services -- every last one) the passion for IG and isolated power has evaporated.
It won't be coming back any time soon.
