A/C Tripping Main

D

dheaston

Member
Location
Westminister, CA
Occupation
Maintenance Electrician
A/C unit is tripping the 1600 amp main. A/C unit is feed with 480 volt, on a 35 amp 3 phase breaker, subpanel feed with 250 amp 3 phase breaker, in a distribution panel protected by an 800 amp main, distribution panel is feed with a 400 amp 3 phase breaker at the main 1600 amp switchgear. Fault makes all the back to the 1600 amp main and trips.
Would you say?
Thank you
 
dkidd

dkidd

Senior Member
Location
here
Occupation
PE
dheaston said:
A/C unit is tripping the 1600 amp main. A/C unit is feed with 480 volt, on a 35 amp 3 phase breaker, subpanel feed with 250 amp 3 phase breaker, in a distribution panel protected by an 800 amp main, distribution panel is feed with a 400 amp 3 phase breaker at the main 1600 amp switchgear. Fault makes all the back to the 1600 amp main and trips.
Would you say?
Thank you
Click to expand...
Check for a ground fault setting on the main.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Pretty common occurrence with the ground fault settings. Usually it is a bad second stage compressor during the summer, or a faulted heating element in the winter.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It's a fair bet that if a single A/C unit is causing a 1600A Main breaker to trip, it's the result of there not having being a "coordination study" performed. Unfortunately unless there is one specified and performed, 90%+ of people never change the factory default settings on breakers. The factory default settings for GF are often ridiculously low, probably as a "CYA" for the breaker mfr.
 
ATSman

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Jraef said:
It's a fair bet that if a single A/C unit is causing a 1600A Main breaker to trip, it's the result of there not having being a "coordination study" performed. Unfortunately unless there is one specified and performed, 90%+ of people never change the factory default settings on breakers. The factory default settings for GF are often ridiculously low, probably as a "CYA" for the breaker mfr.
Click to expand...
Or, what we find a lot is if Acceptance/ Commissioning tests are performed by a testing company, they often turn the current setting down to minimum to limit the size of the test set they need for current pickup. Then forget to turn it up before they leave. This is also the case with breaker OC and instantaneous trip unit settings.
 
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