High Resistance Ground

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Jim1959

Senior Member
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Longmont, CO
I realized my question may not be complete enough. I am referring to an HRG section of an MCC like I have seen used in the gas and oil field.
 

Ingenieur

Senior Member
Location
Earth
Short version
an impedance (usually resistance sometimes inductance) is inserted into the X0 path (wye) or a neut/grounded conductor derived by a zig-zag xfmr (delta)

it limits gnd fault current
480/277
18.4 Ohm ngr neut grounding resistor
i gf = 277/18.4 = 15 A

gives equipment protection due to lower fault i
can give a warning rather than trip so process can maintain operation while fault is located/rectified

'post glover' has tons of info
they make ngr's
 
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Ingenieur

Senior Member
Location
Earth
Another advantage
limits frame potential when faulted
we monitor the egc loop ~2 ohm
if it > 2 trip ckt (broken wire, loose connection, corrosion, etc)
if ngr i = 15 A
frame under fault ~ 2 x 15 = 30 v (balance across ngr)
assume 1000 ohm body R the victim sees 30 mA until trip (4-6 cycles)
high probabilty of survival
 
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