Aboutcleggsan Expertise All technical areas of Electronics Engineering.
Experience BSEE, MBA, Design, R&D, University Research.
Senior Life Member of IEEE. Life Fellow of AES.
Organizations IEEE, Consumer Electronics Society, Audio Engineering Society.
Broad teaching experience; work experience mostly in consumer electronics and conversion from analog to digital technologies. Pioneer in digital audio at all levels.
Question My name is Luke Robson, I recently completed 2nd year (of 4 years) of the engineering program at the UBC-Okanagan (Kelowna, BC, Canada). I am going into electrical engineering and am currently doing an 8 month co-op work term with a sawmill in BC.
I was wondering if you would be able to provide some help with the one problem/situation they have asked me to look at. There are two saw trimmer lines, both on separate circuit lines, and they both are wired to the MCC room connected to a PLC and are on separate breakers. The only connection between the two lines is a common ground connection. Now the problem is, that when a 4 ft man-heater is plugged into line 2, it blows both breakers, not just the one. I was asked to try and figure out why it blows both breakers not just the one.
My thoughts on this so far is that since there is a common ground, that when it trips the one breaker, it sends a surge through to ground, but the ground connection may have some resistance in there, and sends some of that surge into the other breaker and causes that to blow as well. It is only my fourth day working, so I have not been able to go out with an electrician to measure anything yet, only to think of possible problems/solutions. I was wondering if you had any ideas or comments on this situation.
Thanks,
Luke Robson
Answer I would need to know more about the wiring of the lines and their layout. But, to give you some generic guidance let me suggest this:
ONE: I do not know what the man-heater is, but I am assuming it draws a fair amount of current. So, try, instead of the heater, something much smaller in consumption - say a kitchen toaster or some appliance that pulls a much smaller amount of current. If you are running more than 120v then you could throw a line dropper transformer in to allow you to use the smaller load.
TWO: Is there current in the common ground line that runs between the two circuits? If so this would indicate an imbalance. You can check current with a clamp over ammeter. Should not have any current in the ground line.
THREE: Keep the clamp on ammeter in and watch it when you throw on the man-heater, watching the current surge so you can get an idea of the magnitude of the thing. If it blows instantly you know there is a big jolt somewhere. If it takes a few seconds then it is a marginal thing. And, what amp rating are the circuit breakers? Way above the rating of the heater?
FOUR: Try it when the opposite breaker is manually lifted open before you load on the man-heater is placed on line.
FIVE: Check the wiring between the two lines to make sure they really are isolated from each other. I would go through the MCC and just check for crossover wiring or something strange. And, are the two circuit breakers nearby each other? Could they be co-wired somehow that is causing the problem?
So, you have a few things to check out. Hopefully the above trials will lead you to something. Then let me know the next wave of troubleshooting, but give me some quantitative data such as voltage of the services, amp ratings of the breakers, current or power ratings of the heaters and trimmers, etc.
