Operator proofing a motor test panel

[EricMc]

The product we build uses hydraulic motors. They can range from 110VAC, 220VAC single and 3 phase, 480VAC, and 575VAC, depending on the customer.
We test these motors on a test panel with a selector switch for the different voltages. They are all 1HP motors. Each voltage has a motor starter and overload. They also have fuses for each starter.
The problem is we go through a lot of fuses. The operators either wire the motors incorrectly, have the wrong voltage for the motor they are testing, or the motors come to us bad.
Is there anyway around the fuse problem? I've seen thermal overcurrennt circuit breakers for 250VAC and less, but not sure if they are a substitute.

 

[aolalde]

I suggest you replace the fuses with an inverse time circuit breaker with current rating matching the fuses. See NEC 430-1

 

[EricMc]

Thanks aolalde.
Do you know where I can find a good cheap breaker for a 1HP motor?
I can get a Square D one for $400. I know it can pay for itself in 6 months, but I might have a problem justifying five of them for one panel to my boss.

 

[PUMPDESIGNER]

I would always use a circuit breaker in your application.
But make sure you use a circuit breaker with "instantaneous magnetic trip". That feature is excellent for motors or any load capable of generating high fault currents.

The problem with magnetic trip is that it must be adjusted or purchased to account for the highest current you expect to see. But it sounds as if you have very definite motors which would allow for that.

PUMPDESIGNER

 

[jbartos]

Suggestion: Set up a circuit test arrangement that would diagnose an incorrect motor - power supply setting. A little bit of mechanization in this time and age would not hurt anything.

 

[EricMc]

How would I set up a circuit diagnostic? The operators wire the motors (i.e. 1-line, 2-line, 3-line, 4-7, 5-8, 6-9).
The operators aren't smart enough to do this. Let alone any other wiring. Time is also a restriction. We build dock levelers. We operate the levelers before they ship. What could I set up to prevent the operators from energizing an incorrectly wired motor?
Thanks for the replies.

 

[aolalde]

Your best bet is the “NO LOAD TEST” of each motor. Get the insulation resistance with a Megger (250 to 500 VDC) before any attempt to energize the motor. I do not know were to buy cheap circuit breakers, instantaneous magnetic trip as PUMPDESIGNER suggested could be cheaper ( I am not sure) but will protect your motor windings from damage.

Try one prototype for the most used voltage, monitor the results and decide after a trial period if that solution helps your operations.

 

[bklauba]

At the risk of changing the focus of this discussion from what gear to use for circuit and motor protection, to an IE approach towards, who should be doing the testing: Have you considered making testing these devices a specific job? It sounds like each builder / assembler tests what they build, but they have often shown poor learning or testing skills, making this problem worse.

Without some resolution to the problem, it is hard to see how you can address the issue of "the motors come to us bad." Some accurate data as to what the reject rate of as-delivered product truly is, would allow you to give feedback to the supplier, or find another.

While working at an EASA motor shop in NW Indiana, at a time when we were drowning in work (due to a fire at a local steel mill; we had every electric motor in their operation undergoing rebuild or rewind), two employees whose skills were mechanical, not electrical, were asked to test a 240 pri / 12 sec, 15 kVA transformer. They managed to hook it up to our 12 - 575 / 300A test panel, injecting 240 volts INTO THE SECONDARY!! Took out the mains in the shop, plus at least one of the transformers on the pole outside. It took more than a couple fuses to put us back in operation. (It did provide an endless source of humor, heaped in abundance on those two sorry guys.)

Think about making testing a separate job, recruiting those who have shown some aptitude testing, perhaps with a modest pay incentive. ID all the items tested, so that the builders / assemblers that have high reject rates can get some feedback/guidance/training, or whatever.


BK

 

[EricMc]

Thanks for the comment.
A couple of operators prewire the motors. They wire 2' long SO cords to the motor and strip back the other end. When the motor is installed into the leveler by a different operator, that operator hooks up a power cord from the test panel via insulated alligator clips and test runs the leveler.
Sometimes the initial wiring is done wrong, sometimes the operator runs the wrong voltage through the motor and sometimes the rubber boots on the clips get pulled back and short to each other. I'm guessing 99% of the time its human error and not the motor.
Most of the operators are temps. They have poor supervisors also. I can say that, because I'm in maintenance.
I'm trying to minimize costs from fuses and delays without expecting much from the operators.

 

[busbar]

Consider the likelihood that replacement of fuses will probably lead to greater abuse/lack of care because it’s easier to reset and bang again.

600V circuit breakers are not cheap anywhere. Thermal-magnetic breakers have limited life if used for switching duty and no so rated. Breakers will typically allow greater damage of starter/contactor/switch internals from overcurrents.

Employees working with low-voltage equipment are not exempt from 29CFR1910.331-335 OSHA training, whether considered ‘temporary’ or ‘permanent’—‘qualified’ or ‘unqualified.’

 

[jbartos]

Suggestion to EricMc (Electrical) Mar 2, 2004 marked ///\\How would I set up a circuit diagnostic? The operators wire the motors (i.e. 1-line, 2-line, 3-line, 4-7, 5-8, 6-9).
The operators aren't smart enough to do this.
///It does not have to be anything complicated.\\ Let alone any other wiring. Time is also a restriction.
///There may be developed something fitting the time constraints. How much does it take to replace fuse and search for any errors?\\ We build dock levelers. We operate the levelers before they ship. What could I set up to prevent the operators from energizing an incorrectly wired motor?
///Simple in line resistors could be used to test if the motor and power supply is properly aligned. There may also be ammeters in each line to read the line currents. The resistors should be rated such that any higher voltage would not damage the resistors or motors. It may need a little ingenuity to develop it; however, it is a feasible project.\\

 

[busbar]

It’s not realistic to expect that products miswired or mispowered by a customer, regardless of his best intentions, would be replaced or repaired without the customer incurring some additional cost.

If a motor is powered at half or double voltage {or more} during production/test, causing a fuse or breaker operation, isn’t it probable that the gear’s reliability has been reduced?

Some baseline training and a rudimentary quality-control program may be a good investment, if only to keep workmen’s comp expenses in check.

 

[EricMc]

It would be great if there was more accountability and training for production workers and their supervisors. I think they still look at it as if a fuse blows there must have been something wrong with the fuse. No matter how many times I tell them different.
Another problem I have is, I'm the maintenance department. Troublehooting a blown fuse wasn't my problem. The problem is I don't like putting in double shifts. If second shift blows a fuse or I'm busy fixing other equipment, a lot of downtime occurs. I fixed most of the down time by moving all of the fuses for the motor controllers to a separate enclosure and started using safe fuse holders with integral indicating lights. I then put extra fuses in the cabinet and showed them how to change the fuses. This reduces downtime, but raises fuse expenses. That's why I was looking for a fuse replacement.
Jbartos said something about installing resistors and ammeters to test alignment. Would that be a small test voltage running down the leads before the main power is applied to the motor?
Busbar has a good point about possible damage to the motors.
Maybe I should be working more on Jbartos idea then a fuse substitute.

 

[SteveKW]

The resister idea is nice but just applying the lowest voltage FIRST will have the same effect!

That's what we do in our shop...apply low voltage first and work our way up!

I would tell you that we have very oversized breakers on my panels and rarely have to reset them even on bad motors.
But I take the time train my men to have an "ear" as to what the motor is doing. This its seems, is a luxury you do not have!

With a good "ear" its very hard to damage a motor with twice the voltage applied to it for a few seconds. I have not had the luxury to see what 575 volts will do to a 110 volt motor though!

A single (solid insulated) wire brought out from the test panel in the form of an eye loop is handy to hang a clamp on ammeter.


I like your fuse panel solution. Sounds like the best solution for your situation due to the lack of trained personnel!

 

[EricMc]

I haven't seen 575V applied to a 110V motor either. I'll give the workers a little credit. We use two power cords for testing. Three wire SO cord for single phase and a 4 wire for 3 phase. Usually the wiring might have two of nine motor wires swapped. They get confused sometimes with the 230V wiring. On a single phase motor its the high voltage and a 3 phase motor it's the low voltage.

 

[OperaHouse]

The solution might be a smart build sheet. Unfortunantly, most solutions aren't cheap. A bar code on the build sheet could be read and the test panel would automatically switch to the right voltage. A varient of this would be at the build stage a test cord would be installed of the appropriate voltage. This would have a seperate multi pin connector that would plug into the test panel that would tell it the appropriate test condition. I am a fan of using old PC's for testing. Plug in cards for these are available for under $200. Add a couple current transformers and you have a semi auto testing station that can give you a test print out. Turn on current, max current in cycle, motor inbalance. Preset values, as indicated by the test plug" would shut the system down if currents were exceded. If a motor start relay didn't have to be turned on, a very low test voltage could be turned on to see if the currents were in balance and expected value prior to selection of normal voltage. This whole procedure would still require someone who knew what they were doing when the test cable was first selected.