GFCI breakers vs. receptacles on early 1900s 2 wire knob n tube

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V02maxed

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Location
Plymouth, WI
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Industrial Journeyman Electrician
I have a question regarding GFCI breakers vs. receptacles.
I am an industrial journeyman and don't do residential much but I have a early 1900s two story home that still has much of the upstairs lighting/receptacles on 2 wire knob & tube wiring. Outlets added on the outside walls are now 3 wire grounded dropped down from the attic, but interior wall receps. and lighting are still 2 wire. The downstairs has been updated to 3 wire grounded, but I wanted to add some safety to the upstairs with GFCI at least so I can get away from 2 prong outlets. With the lighting being intermixed with the receptacle breakers, it seems to make more sense to just use 2 - 15amp GFCI breakers at the panel than to replace the 10 or so receptacles on those two circuits which would still leave the lighting un grounded.
Is this acceptable, or would each outlet need a GFCI to be able to switch to 3 prong receptacles with the "no ground" label on the outlet?
The attic is a walk up attic with a floor so simply dropping down 3 wire into the walls and lighting isn't really possible without removing an attic floor.
I'm just trying to figure out how to add some safety within the code. Thank you for any suggestions or help.
 
Because K&T is often wired in a star configuration and with no fixed association of one neutral with one hot, you cannot expect to use the load side of a GFCI receptacle to feed downstream outlets. Nor is a GFCI breaker guaranteed to work without rewiring! You might get lucky though.
So yes, you may need to use a GFCI receptacle at each receptacle outlet.

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I have found most K&T circuitry to be installed pretty well(until DIYers got to it). I would try to identify Hot or hots and there neutral, lift them off the lugs and put a meter on them. If they are not tied in somewhere down stream they will read open, and you can add the GFCI breaker. I have had success in the past with both branch and multi-wire branch circuits. If the held upon install I have never had a call back.
 
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