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Neutral Sensor on a Siemens 555 trip unit

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M

Mumbaigirl

Member
Location
USA
Occupation
Electrical Engineer
I have a 480V Siemens P5 Panelboard with 1200A 3P-LNX Main Breaker with a 555 ETU-LSIG, GF Trip with a neutral sensor (CT).

This panel is currently fed from a from a 13.2 - 480V Xfmr. We are now eliminating the transformer and bringing in a direct 480V feed to this panel from one of the MCCs. I want to know if not wiring the neutral thereby not using the neutral CT in the panelboard will be okay. Will there be something that I need to change in the 555-trip unit to disable the GF trip? The panelboard has three 3P-LMX breakers that feeds rental units.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Mumbaigirl said:
I have a 480V Siemens P5 Panelboard with 1200A 3P-LNX Main Breaker with a 555 ETU-LSIG, GF Trip with a neutral sensor (CT).

This panel is currently fed from a from a 13.2 - 480V Xfmr. We are now eliminating the transformer and bringing in a direct 480V feed to this panel from one of the MCCs. I want to know if not wiring the neutral thereby not using the neutral CT in the panelboard will be okay. Will there be something that I need to change in the 555-trip unit to disable the GF trip? The panelboard has three 3P-LMX breakers that feeds rental units.
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You could leave the sensor wired, even though there are no conductors through it. Then adjust the settings on this breaker to be higher than its upstream feeder.

You may not be able to completely disable the GF function however, most breakers can be set up for 3-wire or 4-wire systems. Do you have L-N loads fed through this breaker?
 
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