Cutting neutral and 220ing shared circuit

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Hi I was hoping someone could explain to me how when you are sharing a neutral on a branch circuit and you cut that neutral without deenergizing the shared circuit why are you susseptable to backfeeding on the other ungrounded conducter. I understand that it happens I just don't understand the technical reason why.
 

infinity

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Location
New Jersey
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Journeyman Electrician
It's because the two loads are now in series and each load will see a different voltage drop across it based on it's resistance. The current will be the same through both loads. Two equal loads will share the total voltage equally. For a 208 volt system two identical loads will have 104 volts across them. For a 240 volt system the two loads will have 120 volts across them.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Hi I was hoping someone could explain to me how when you are sharing a neutral on a branch circuit and you cut that neutral without deenergizing the shared circuit why are you susseptable to backfeeding on the other ungrounded conducter. I understand that it happens I just don't understand the technical reason why.
Power is going into the shared circuit. It will travel through a load and look for a return path to the source. Hence, energized grounded conductor.
 

nakulak

Senior Member
draw it out on a piece of paper

plug on left is fed from left with a phase

in middle is juction box with neutrals

plug on right is fed from right with b phase

cut neutral going to panel, and you have a phase on left plug, former neutrals connecting the two plugs are now just a jumper, and b phase on right, so now you have the two plugs fed with 220. make sense ?
 
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