116 amp draw at startup

rockyridgefarm

Well-known Member
Hey all,

I did a cleaning job yesterday and had a heck of a time with power. The farmer had the oldest breaker box I’ve ever seen. The breakers were about 3” by 6” and we kept having to got to bigger and bigger breakers. Finally he got his amp tester out and we found that we were drawing 116 amps at startup and running almost 60 amps whil running. I’m running a newer 7.5 hp Baldor motor on the cleaner, 3 - 1 hp motors on the augers to load it, and 2- 1 hp motors to unload it. All the smaller motors are on 12 gauge wire and the big motor is on 8 gauge I think. I’m surprised by the amp draw. I guess the first thing to do is change the cleaner motor to a 5 hp. My generator is still in the shop. They said they had time to do it, but now it’s been 5 months.

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With electric, the motor only draws the Amps it needs to run the load. Going to a smaller motor won't help.

Just a quick down-n-dirty calculation, 60 Amps at 240 Volts is 19HP (I know there some factors for AC, bit its still way more than 7.5HP), so clearly something is binding up or something is wrong with the motor itself. It should only be taking ~36 Amps to run the motor at full load.
 
(quoted from post at 04:28:19 07/17/18) With electric, the motor only draws the Amps it needs to run the load. Going to a smaller motor won't help.

Just a quick down-n-dirty calculation, 60 Amps at 240 Volts is 19HP (I know there some factors for AC, bit its still way more than 7.5HP), so clearly something is binding up or something is wrong with the motor itself. It should only be taking ~36 Amps to run the motor at full load.

It's definitely not under full load. I misread the cleaner requirements when I went to buy a motor. The next bigger machine calls for 7.5 hp. This one calls for 5 hp. I also have 5 other ~1 hp motors running at the same time with this 7.5.

Really sorry about the pics. I keep forgetting which way is "up" when taking pics with my phone, and I can't seem to figure out how to orient the pictures right manually for this site.
 
Starting current is always many times the running amps.

I have a 4 hp electric chainsaw. It draws over 70 amps on start. 15 amps on run.

You may want to stage the start of motors.

My dad used to check the power factor when farmers used many motors. He would add capacitors.

Neighbor recently installed 3 phase rotor to run 3 irrigation pumps. I asked why they were using
old school rotors. He didn't know. Said that's what he was told to install.
Farmer could only use 2 until electric company installed a larger transformer.

Farmers needing a lot of motors would convert to 3 phase. My dad would make them converters.
 
Each motor has a tag with a FLA (full load amps) tag. If the tag is missing, and you know the HP, you can use a FLA chart to find the amp rating. Be sure to read the right FLA for the voltage, I assume you are running 208/240 volt. That will be the higher of the 2 numbers on the tag. The lower number will be for 480 volt.

Once the machine is up and running, check the amp draw of each motor by clamping the amprobe around each lead, one at a time. The amp draw must not exceed the rating on the tag. That is the max amps that motor can draw without overheating.

Also check the voltage across the lines at each motor. It should be close to equal. If any pair read lower by about 10 volts or so, there is a bad connection, an imbalance in the panel or incoming voltage. Low voltage or imbalanced voltage will cause higher amp draw. Remember, check it under running load.

If the voltages are good, and the motor is drawing equally high amps on all 3 lines, the motor is overloaded. Either there is something binding or the motor is too small. Continued running that way will overheat and damage the motor.

If voltages are good and the amp draw is dramatically different across the lines, there is a problem with the motor windings.

Be sure each motor is wired for the proper voltage.
 
Did you check his voltage? If he has low line voltage it takes more amps to make the same hp.

Like someone else said, the motor will only draw what it needs, so a 7-1/5 hp motor will run on the same amps as a 5 hp if they are put on the same load. Maybe a little difference because of efficiency, but not much.

Are you starting the motors one at a time?
 
I agree, changing motor HP does nothing.

You will draw 3-6 times FLA during startup, but that is usually a fraction of a second, stage your motor starting to reduce the total draw.

Putting in bigger breakers than design is a BAD idea, you should find the root cause of the issue.

Add up all the motor FLA's, which should be on the nameplates, size up the breaker by 1.5 and make sure that works. I do not know how you did the wiring, but there should be an overload starter for each motor with a main breaker. Put a switch on the panel that energizes each contractor, that way you can turn on one motor at a time. There does not need to be a disconnect at each motor if the main disconnect is within sight of the motor, or if you have a lockable main disconnect and a lockout tagout policy.
 
(quoted from post at 05:52:05 07/17/18) I agree, changing motor HP does nothing.

You will draw 3-6 times FLA during startup, but that is usually a fraction of a second, stage your motor starting to reduce the total draw.

Putting in bigger breakers than design is a BAD idea, you should find the root cause of the issue.

Add up all the motor FLA's, which should be on the nameplates, size up the breaker by 1.5 and make sure that works. I do not know how you did the wiring, but there should be an overload starter for each motor with a main breaker. Put a switch on the panel that energizes each contractor, that way you can turn on one motor at a time. There does not need to be a disconnect at each motor if the main disconnect is within sight of the motor, or if you have a lockable main disconnect and a lockout tagout policy.

I have a breaker box on the trailer as well as a fused main switche on the breaker box and a fused switch for the cleaner only.. This is the first job I’ve had trouble, which is why this is the first time I’ve checked amp load. I always start the cleaner, then the load augers, then the unload augers.
 
I bet you'll find he has low voltage, maybe even with no load. Almost low enough to be 120 instead of 240 with the numbers you're getting.
 
You need to check the voltage at startup and while running. I'll bet it's way too low.

As everybody else said, installing a smaller motor will just make matters worse. The motor has to provide the required torque at the required rpm; doesn't matter if it's RATED at 5 hp or 105 hp; it will be expected to provide whatever horsepower is demanded. (HP = torque x rpm)
 
Then check voltage at customer panel, then at your box, voltage will be low somewhere.

KW = volts * amps, and motors need KW to run.
 
The thing to remember it that circuit breakers are NOT motor protection, they are there to protect the wiring, so UNLESS the motors have internal overloads you must provide that overload protection. Just because you are building them that way and have not had problems does not make it right. You need to follow NEC guidelines if you are going to produce things for other people. This is just part of having a business.
 
With 6 motors all running at once....

7.5HP FLA = 36A
1HP FLA = 6.4A x 5 = 32A

Total 68A, but that's only if all the motors are running at full rated load, which they probably aren't.

Doesn't sound quite so unreasonable, though.

Most likely, like others have said, the voltage is a little low. Probably a long run from the meter, right? How many panel boxes does it go through? How far from the last panel box?

I'm guessing you're running it from an old upright silo unloader feed, which depending on the size of the old silo, is probably barely adequate for a 5HP motor, let alone 12.5HP worth.

Just don't burn the place down and put the screws to them to get your generator fixed ASAP.
 
Hello rockridgefarm,

Mine I turn right from 12 to 3 o'clock. There is a test site here.Try it there
after you take a pictures,

Guido.
 
I am not an electrician, and I don’t play one on tv. Here’s my wiring job. Feel free to come after me with both barrels. I did a five hour job today, with zero electrical issues. I used the boxes I had acquired through flea markets and auctions. Main power comes in through the grey panel, and it is the Main shutoff. Power splits and goes directly to the cleaner, and to the breaker box. The big “bump” switch only runs the cleaner and the shaker underneath. It’s basically just a huge fused light switch.


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