Breaker question for sparkies

Hey folks.

I am trying to figure out a problem with the power supply in my shop.

We were working in the shop one evening when we had a power failure. I finally tracked it down to the main breaker for the shop which is a 200 amp which has never tripped since it was installed.

The maximum that we were drawing was 98 amps calculating lighting-1460 watts 12 amps, RPC- has its own 40 amp breaker, radial arm saw-10 amps, bandsaw-12 amps, air compressor-12 amps, water pump- 12 amps.

The day was rainy with some lightning and wind, though no lightning really close.

My question is if the power load was nearly half of the rating of the main breaker could a spike on the line cause the breaker to trip?

The 120 v loads are fairly well balanced and all wiring in the building is in emt. The building has its own service and is grounded properly.

Thanks in advance,

Brad
 
Let me get this straight: you were simultaneously operating two power saws, an air compressor and a water pump? (Sorry, I don't know what an RPC is.) Most of those machines have very high starting loads. Now even if you add up the normal starting loads, you won't come up with 200 amps. But if your service to the main breaker isn't up to the task, you'll get voltage drop. The greater the voltage drop, the greater the starting current a motor will draw. I think it's quite possible you were momentarily drawing over 200 amps.

I suggest you measure your voltage at the main breaker, both with minimum load and again with everything turned on. I think you'll be surprised at how much voltage drop you get.

If you have several 120 volt machines that you run simultaneously, you should make sure they're not all on the same leg; that will significantly reduce voltage drop when two machines are operating at the same time.

If you have 120V machines that can run on 240, you should convert them over.
 
I think Mark has a pretty good idea on your problem. I have also seen a dead short not trip a 30 amp breaker but trip the 200 amp main.
 
QUESTION

"My question is if the power load was nearly half of the rating of the main breaker could a spike on the line cause the breaker to trip?"

ANSWER

If you're setting there and the loads are started up and running and you're only at approximately half the main breakers ampacity rating, I DOUBT ANY SHORT TERM "SPIKE" (Subject to definition, amps and duration of a spike) WOULD CAUSE THE BREAKER TO TRIP.

If the main is a Thermal/Magnetic breaker, the thermal wouldn't kick out at only half the rating and it would take one heck of a "spike" to trip the magnetic. ALTHOUGH A SUDDEN VERY HIGH CURRENT SPIKE IS WHAT COULD TRIP IT, I doubt that happened since your individual loads are small in comparison to a big 200 amp main, i.e. I could envision their own smaller branch breaker tripping on start up, but NOT the 200 amp main.

That being said, something tripped it and if it happens again, Id be tempted to just buy a new breaker, they can go bad you know.

Its true a motor requires more current on start up so if you were already near the mains ampacity (NOT just half like you were) and one of the larger motors started, I could see that as possibly tripping a main breaker, but your motors are relatively small loads in contract to a huge 200 amp main breaker, and since you're only at 100 amps if all were already running, I just don't see any of them starting as the cause to trip the 200 amp main.

Still, lightning and power line surges can do funny things and perhaps that had something to do with your main tripping??????? (Hard to say sitting here) But unless it continues to do it I wouldnt worry for a while, but if so Id try a new main breaker.

Of course, loose connections and/or excess voltage drop can cause problems, so you may want to take some voltage measurements with all your equipment running just in case.

John T Long retired EE so no warranty, see what the good and more current practicing electricians have to say........
 
Might want to pull the cover and check the connections, look for heat discoloration, melted insulation where the incoming lines connect to the main. If it's a bolt in main be sure the out feed connections are tight. If it's a back fed main, pull it and look at the bus bar connections.

If all looks good, with the system normally loaded, using a digital volt meter, check for voltage drop through the breaker (one lead on line 1 lug, the other lead on line 1 load terminal). Do the same with line 2, and line 3 if 3 phase. There will be "some" voltage drop, probably not more than 3 volts. What you're looking for is all lines to be close to equal. If they're different, example line 1 has 1.3v and line 2 has 6.8v, the breaker is going bad.
 
Brad,
read your post and it brought to mind a problem I had about 5 years ago. We have a GE 200 amp service,that I installed when we built the house. About 6 years ago we suffered a power outage,everybody else around us had lights and power. I went to the main breaker on the panel box tripped it and still nothing. Went to the meter base and pulled the meter, back up stairs to the panel box got the allen wrenches pulled the main breaker,disassembled it and found corrosion on the contacts. Buffed the contacts with buffing wheel and jewelers rouge, cleaned them added a thin coat of dielectric, reassembled, reinstalled meter tripped main breaker behold we had lights. Still working to this day with the exception of power outages caused by wind etc,not our problem. We have a generator for power outage.You may have to go into the main breaker to see if there is corrosion.Hope what I entered helps,
Regards,
LOU
 
Hey Lou.

I think that you might have a good idea on the breaker.

I am going to do dome tests to see if this is a problem.

BTW your garden looks great as always.

Brad
 
Thanks for the info John.

I am going to do some testing and if nothing is apparent will probably replace the breaker.

As always I learned a lot from your post.

Brad
 
Hey Mark.

In my post I tried to detail what loads were on the system. The air comp and water pump are automatic and could have been on at any time.

RPC stand for a rotary phase converter. I should have been clearer. It consists of a 10kva step up transformer from 220 to 550 volts, a 5 hp 3 phase motor (idler) and a capacitor bank and relay setup to start the idler and balance the voltages on the 3 phase output.

This unit has its own circuit panel with a 40 amp main and plugs into a welder circuit protected by a 50 amp breaker. This is a temporary setup until it is installed in the mechanical room being built.

I am going to do a full load test and check for voltage drop and it may be time to convert my table and radial arm saw to 220 volt as you say.

Thanks for the post.

Brad
 
Brad, I now remember your very interesting phase converter posts. In the IT world, RPC is "Remote Procedure Call" and I couldn't get head to go any further than that.

Your phase converter might play havoc with power factor even when it's not under load, so it could be a contributor to the problem.
 
I would do a FOP test (Fall Of Potential) on the breaker. Take a Multimeter, set to millivolts, and read across each phase of the breaker....yes L1 to T1, L2 to T2. Typically you wont read any voltage with your meter set to 600V. Set to millivolts though, you might find that your breaker contacts have a high resistance.....meaning you need a new main breaker.
 
Brad,
Didn't you make a 3 phase converter for your bandsaw? If so, how is it working?

If your main tripped only once, it could be the lightning.

If it tripping all the time, different story. A few years ago, a church which used the old fuses for mains, was blowing fuses, $25 each. It wasn't the current blowing fuses, it was the fuse holder made a bad connection to fuse, got hot and caused fuses to blow. So heat will also cause breakers to trip. I used a cheap IR thermometer to measure the heat.

Recently, I had to replace the main breaker on a rental. After pulling the main, you could see it wasn't making a good connection to the buss bar.
Good luck finding your problem.
George
 
If the phase converter is giving you indigestion, you might want to consider replacing it with a VFD, variable frequency drive.

I've seen demonstrations of these and they are so cool I want to buy a 3-phase tool just so I can get one!

What it is if you don't already know, is an electronic device that uses normal single-phase electricity to produce 3-phase for the tool. You can control the frequency, and thus the speed, of the motor as well. Granted, the motor produces very little torque at low frequencies, but you still have quite a bit of useful variability.

They've come way down in price recently.
 

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