phil d
Well-known member
Well they do say it happens to the best of us, and this tale proves it, despite many years in the industry I found myself dealing with a schoolboy error on a job yesterday, the annoying thing was I had created the problem!
On the farm we have large fans in the end of the building to provide ventilation, we had a problem and it was found we needed more airflow, the solution was more fans. Not a problem said I, when I designed the system I installed bigger cables than needed for the fans, partly in case there were any changes, and partly, because of cost. I was using vast amounts of the larger cable and was getting it very cheaply, so it made sense to run the fans in the larger cable, anyway here's the story.
2 more fans were being installed, I checked my calcs and could indeed run 2 fans off one feed, the problem was the overload in the main panel, it was designed for 1 fan, with a loading of 3.5 Amps, so I came up with a plan, make a small enclosure containing 4 overloads, remove the one in the main panel, take the 2 fan feeds into this box, and split them across 4 overload units, each cable feeding 2 overloads, each overload feeding 1 fan, simple.
I got the parts and set to work, built the unit in a nice enclosure with a clear front panel, so as to enable easy viewing of the trips, installed it all on Sunday and away we went, it worked fine, then one of the motors tripped, I reset it and after about 30 minutes, it tripped again.
Now previous to this I had never had an issue with this motor, it had run fine for 4 years, I reset it and it ran for about 8 hours, then tripped again!
I rang technical to see if they could shed any light on this, they asked what my overloads were set at, 3.5 Amps, rated full load current, they said they recommend setting at 115% of FLC.
I went back yesterday to make the adjustments, then realised something else, I had made a really neat job of the panel, 4 overload units, side by side, and a bank of Weidmuller connectors next to them to connect the cables to, it looked lovely, really neat, then it hit me, all the overloads were butted up next to each other, no airgap between them, well that wouldn't help.
I then realised why the unit hadn't tripped for 7 hours, it had gone cold in the late afternoon!
To think that only a couple of months ago, there was I advising someone who was doing an install using large breakers to not place all the high loads next to each other to avoid nuisance tripping caused by heat build up.
What a silly beggar I am. lol :facepalm:
On the farm we have large fans in the end of the building to provide ventilation, we had a problem and it was found we needed more airflow, the solution was more fans. Not a problem said I, when I designed the system I installed bigger cables than needed for the fans, partly in case there were any changes, and partly, because of cost. I was using vast amounts of the larger cable and was getting it very cheaply, so it made sense to run the fans in the larger cable, anyway here's the story.
2 more fans were being installed, I checked my calcs and could indeed run 2 fans off one feed, the problem was the overload in the main panel, it was designed for 1 fan, with a loading of 3.5 Amps, so I came up with a plan, make a small enclosure containing 4 overloads, remove the one in the main panel, take the 2 fan feeds into this box, and split them across 4 overload units, each cable feeding 2 overloads, each overload feeding 1 fan, simple.
I got the parts and set to work, built the unit in a nice enclosure with a clear front panel, so as to enable easy viewing of the trips, installed it all on Sunday and away we went, it worked fine, then one of the motors tripped, I reset it and after about 30 minutes, it tripped again.
Now previous to this I had never had an issue with this motor, it had run fine for 4 years, I reset it and it ran for about 8 hours, then tripped again!
I rang technical to see if they could shed any light on this, they asked what my overloads were set at, 3.5 Amps, rated full load current, they said they recommend setting at 115% of FLC.
I went back yesterday to make the adjustments, then realised something else, I had made a really neat job of the panel, 4 overload units, side by side, and a bank of Weidmuller connectors next to them to connect the cables to, it looked lovely, really neat, then it hit me, all the overloads were butted up next to each other, no airgap between them, well that wouldn't help.
I then realised why the unit hadn't tripped for 7 hours, it had gone cold in the late afternoon!
To think that only a couple of months ago, there was I advising someone who was doing an install using large breakers to not place all the high loads next to each other to avoid nuisance tripping caused by heat build up.
What a silly beggar I am. lol :facepalm: