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matt11111

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I am trying to do a electrical analysis on a machine shop. The lathes in the shop have multiple motors (spindle, oil pump, etc) Each motor has an individual nameplate but I need to know the overall electrical spec's of the machine as a whole( ei total current draw) Can I just simple add all the individual nameplate ratings together of the individual motors or does it depend on how the machines are wired?

PaliBob

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If all you need to know is the total rated current draw on each motor, then you can add the nameplate numbers. That number though will not be the total draw any more than adding up the numbers in your circuit breaker panel will give you a total draw for your panel.
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matt11111

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So the rated numbers on the motor are just the absolute maximums? Is there a way to determine exactly how much current is being draw from a machine during general use?

matt11111

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If all you need to know is the total rated current draw on each motor, then you can add the nameplate numbers. That number though will not be the total draw any more than adding up the numbers in your circuit breaker panel will give you a total draw for your panel.
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So the rated numbers on the motor are just the absolute maximums? Is there a way to determine exactly how much current is being draw from a machine during general use?

Gigs

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Nameplate on a motor isn't really absolute maximum, it's closer to a full load maximum. A motor can draw many times nameplate if it's stalled, yet still not enough to trip a breaker before things catch on fire... which is why there are overload protection devices on the motor.

matt11111

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Nameplate on a motor isn't really absolute maximum, it's closer to a full load maximum. A motor can draw many times nameplate if it's stalled, yet still not enough to trip a breaker before things catch on fire... which is why there are overload protection devices on the motor.

Is it correct to say, the RLA specifies what the current draw should be on a motor when operating in optimal conditions? and in reality does a machine actually draw close to the RLA or does it often consume more?

Gigs

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A motor consuming more than its nameplate amps is generally considered overloaded, and probably can't do that in continuous service. There are additional ratings for motors that determine how long they can sustained an overloaded condition in terms of duty cycle (that's called service factor).

If you have to size a circuit based on nameplate amps I think the formula is 125% per NEC.

InPhase277

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I am trying to do a electrical analysis on a machine shop. The lathes in the shop have multiple motors (spindle, oil pump, etc) Each motor has an individual nameplate but I need to know the overall electrical spec's of the machine as a whole( ei total current draw) Can I just simple add all the individual nameplate ratings together of the individual motors or does it depend on how the machines are wired?
I'm curious. Why are doing "an electrical analysis" on this machine shop?

matt11111

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I'm curious. Why are doing "an electrical analysis" on this machine shop?

J. V.

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Take a good look at the lathes themselves. Every lathe I have ever worked on (plenty) had a nameplate for the lathe itself. This nameplate is used to determine wire size and breaker size. You CANNOT use individual motor nameplates. Motor nameplate designations are usually the maximum. You need the average.

matt11111

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Take a good look at the lathes themselves. Every lathe I have ever worked on (plenty) had a nameplate for the lathe itself. This nameplate is used to determine wire size and breaker size. You CANNOT use individual motor nameplates. Motor nameplate designations are usually the maximum. You need the average.

I have looked at the lathes in the shop many times and only a few have what looks like an overall nameplate. Most of them though only have individual nameplates on each motor.
What I'm looking for is some sort of measurment of the daily power consumption by the machine. For example if it is energized for X period of time how much power/current will be consumed. From what I've read online the nameplate information states the current draw at rated load. So it would be the current draw if the rated voltage,freq,and PF were present. Is this correct?

mattman

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Name plates are worthless for you.

Breaker sizes are worthless.

motor sizes are worthless.

OK, here is the answer, I've done this.

Buy a set of data loggers....like the hobo units.....couple hundred bucks.

Hook them up to the incoming power feed

Let the collect data for a few hours, days or weeks. Then download the data to a pc.

they will give the amp draw (max, min average whatever you want) then you can calculate the power usage.

If you are too poor or cheap to buy the data loggers then get an amp clamp and test the incoming power while the lathe is running, not as good as a datalogger but better than totally making stuff up (or believing nameplates).

And...tell the company if they are looking for energy savings (as almost all do) they need to worry more about the lighting and compressors not the value added work.

Gigs

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People do underestimate how inefficient compressed air is.

Replacing all the compressed air tools with electrical tools might double your electrical efficiency in some cases.

mattman

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An air motor is 8 times less effeicient than an electric motor.

People have just come think of compressed air as free.

matt11111

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Name plates are worthless for you.

Breaker sizes are worthless.

motor sizes are worthless.

OK, here is the answer, I've done this.

Buy a set of data loggers....like the hobo units.....couple hundred bucks.

Hook them up to the incoming power feed

Let the collect data for a few hours, days or weeks. Then download the data to a pc.

they will give the amp draw (max, min average whatever you want) then you can calculate the power usage.

If you are too poor or cheap to buy the data loggers then get an amp clamp and test the incoming power while the lathe is running, not as good as a datalogger but better than totally making stuff up (or believing nameplates).

And...tell the company if they are looking for energy savings (as almost all do) they need to worry more about the lighting and compressors not the value added work.

Can amp clamps measure the current on a 3 phase system and can they tell me the phase angle of the current?

mattman

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An amp clamp can get the current draw on on leg at time, if the sytems is balanced, one leg is probably close enough.

Going to have get a bit more sophisticated for phase angle....I used a Fluke 43B for such sillyness, but they are pricey. I think some lower priced models have O scope features.

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