henmill
Member
- Location
- Little Rock, AR, US
Hello all,
I have been dealing with a problem child system involving roadway and highmast lighting. There is a particular service point powering 9 high masts, 16 wall packs, and 7 roadway lights, for a total load current of about 140 amps. The service cabinet has a 200 amp main breaker by Siemens (FXD6 ...) and most of the lights run on 480V single phase, Line-to-Line.
To make a long story short, things were working fine for a while last summer until we started running into issues where the main breaker would trip whilst none of the branch circuits would trip. We even had one or two of the 200 amp fast acting fuses from the cold sequence disconnect blow. Then, there was a small fire...
The service cabinet has since been replaced including all new internals, and we have gone through and meg tested (500 Vdc) each segment of cable and replaced any that tested below 50 Megohms. Hooked everything up and have had a couple instances of tripping the main breaker again...
This past Friday we let it run pretty much all day with no faults. I measured the overall current draw several times throughout the day as well as each branch circuit, with nothing being above what we expect to see. The lights ran that night but Saturday evening the main tripped.
SO, my question to you folks is if you have heard of, or experienced yourself, a thermal-magnetic circuit breaker such as ours tripping at a lower-than-rated continuous current due to high ambient temperatures caused by the nearby equipment in the cabinet? Particularly, the contactor. I noted that the thing was really quite hot on Friday when I went to turn the circuit back to Auto mode. BTW the whole circuit is controlled by a single photocell and contactor in the service cabinet. Contactor is of course rated for 200 A.
Here is a link to a Siemens document. Page 116 describes de-rating of the circuit breaker's nominal rating based on higher than 40 C ambient temps.
http://www.enm.com/Products/Content/Siemens/Controls/IndustrialControls2015/IC14_Sect17_010115.pdf
Thanks for any input or comments!
Henry
I have been dealing with a problem child system involving roadway and highmast lighting. There is a particular service point powering 9 high masts, 16 wall packs, and 7 roadway lights, for a total load current of about 140 amps. The service cabinet has a 200 amp main breaker by Siemens (FXD6 ...) and most of the lights run on 480V single phase, Line-to-Line.
To make a long story short, things were working fine for a while last summer until we started running into issues where the main breaker would trip whilst none of the branch circuits would trip. We even had one or two of the 200 amp fast acting fuses from the cold sequence disconnect blow. Then, there was a small fire...
The service cabinet has since been replaced including all new internals, and we have gone through and meg tested (500 Vdc) each segment of cable and replaced any that tested below 50 Megohms. Hooked everything up and have had a couple instances of tripping the main breaker again...
This past Friday we let it run pretty much all day with no faults. I measured the overall current draw several times throughout the day as well as each branch circuit, with nothing being above what we expect to see. The lights ran that night but Saturday evening the main tripped.
SO, my question to you folks is if you have heard of, or experienced yourself, a thermal-magnetic circuit breaker such as ours tripping at a lower-than-rated continuous current due to high ambient temperatures caused by the nearby equipment in the cabinet? Particularly, the contactor. I noted that the thing was really quite hot on Friday when I went to turn the circuit back to Auto mode. BTW the whole circuit is controlled by a single photocell and contactor in the service cabinet. Contactor is of course rated for 200 A.
Here is a link to a Siemens document. Page 116 describes de-rating of the circuit breaker's nominal rating based on higher than 40 C ambient temps.
http://www.enm.com/Products/Content/Siemens/Controls/IndustrialControls2015/IC14_Sect17_010115.pdf
Thanks for any input or comments!
Henry
