We have 400A thermal magnetic breaker to feed a 600A MLO panel, this panel feed (4) elevators at 70FLA (didn't know inrush current). We meter the panel and at certain time, the meter reads 850A at phase A and other time, it reads 1,200A at phase B. The 400A breaker never tripped. I am wondering why. Thanks!
Breaker Doesn't Trip?
- Thread starter anbm
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zog
Senior Member
- Location
- Charlotte, NC
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
- Location
- Massachusetts
Along with the great answers you have gotten I would ask how sure are you of your meter and it's settings? Is the meter set correctly for, or even compatible with the probe you are using?
Can you try it against a know load?
Can you look up the trip curves for the breaker you have?
Can you try it against a know load?
Can you look up the trip curves for the breaker you have?
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
According to the trip curve for a 400A Eaton-CH HKD breaker with fixed thermal trip, and adjustable magnetic trip, the lowest setting on the adjustable portion is 5x (5 x 400 = 2000A). The trip curve indicates that the 1200A would need to be present from between 60 secs-140 secs (error band)before the breaker would trip.
Your measurements were most likely catching the inrush from the motors due to elevator operation, and it was not the continuous amount of current.
Your measurements were most likely catching the inrush from the motors due to elevator operation, and it was not the continuous amount of current.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If you had two elevators start at the same time, you would see probably around 840A (70 x 6 x 2); 3 at the same time would read 1260A. Do those values look familiar? 
If you had two elevators start at the same time, you would see probably around 840A (70 x 6 x 2); 3 at the same time would read 1260A. Do those values look familiar?
Excellent deduction Dr. Evil. :grin:
I agree, looks like OP captured the inrush of one or more elevators starting.
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