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Mike G.
Mike G., Master Electrician
Category: Electrical
Satisfied Customers: 7527
Experience:  Proven Professional 48 years Experience
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We have 208 3 phase power in our shop and the breakers to

Customer Question

We have 208 3 phase power in our shop and the breakers to the compressor and three 20 amp breakers are popping. The three are all popping at the same time and at the top of the breaker box as well as the triple pole for the air compressor which is on the top on the left side. The breaker for the air compressor has been getting really hot but the other side are what I would say is in the normal range. One last note we recently had to replace a breaker for one of the two poles 60 amp breaker.
This is Brad Rush from Granite South thx
Submitted: 1 year ago.
Category: Electrical
Expert:  Mike G. replied 1 year ago.

Hi Brad, I'm Mike G and I'll be assisting you. Do you have a 2 wire voltage tester?

Customer: replied 1 year ago.
I do somewhere or I will get one.
Expert:  Mike G. replied 1 year ago.

You'll need to test lug to lug for voltage. I suspect a voltage drop causing an increase in amperage on the circuits. It will be on one leg common to all the breakers that trip. Test as follows and let me know the readings.

1 to 2

2 to 3

3 to 1

Then test each to ground.

Customer: replied 1 year ago.
I tested all three and then all three to ground. I on 1 to 2 -- 206 to 208, 1 to 3 206 to 208, 2 to 3 I would get an initial number of 160 to 175 then would go to 206 to 208. In testing all the legs to ground I got 119 to 120 ish
Expert:  Mike G. replied 1 year ago.

Turn off all the breaker and retest. The low voltage reading is as expected. Either L2 or L3 has a bad connection ahead of it. The low voltage is definately your problem. Might want to check the main for the panel feeder. It may be just a loose connection.

Customer: replied 1 year ago.
When you say "ahead of it" means there is a bad connection between the box and the meter? Why would the top left air compressor get so hot and trip so much and definitely more now during the summer?
Expert:  Mike G. replied 1 year ago.

You have a main lug panel. There has to be a main breaker ahead of it. Need to check terminations and the breaker.

Customer: replied 1 year ago.
I checked all the connections and they appear to be very tight with nothing loose.I checked the unloaded panel with everything off and it was 207,208,206 and 119.8, 120.2, 122 to ground
Expert:  Mike G. replied 1 year ago.

Test the connections at the main breaker with everything on. Need to find the cause of the low voltage reading.

Customer: replied 1 year ago.
tested at the main coming in 204, 203, 206 while the compressor was note our compressor is on a transformer from 208 to 480 I believe.
Expert:  Mike G. replied 1 year ago.

The low reading a d the comment about Summer being more of a problem, makes a bad connection most likely. Now it may make and break depending on load and tempature. Low voltage = high amperage. That's what trips a breaker.