Frequently Asked Questions About
MEG-alert "Motor Guard" and "GEN Guard"
1. Can MEG-alert Motor Guard be used on AC and DC motors?
Yes, Motor Guard is designed to test the insulation of either AC or DC motors. On shunt wound DC motors, it would be necessary to install TWO Motor Guards - one on the armature and one on the fields. Both can be housed in the MCC (motor control center) or an optional MEG-alert "Multi Guard" unit.
2. Can MEG-alert Motor Guard be used on synchronous motors?
Yes, brushless synchronous motors would use one Motor Guard. Brush-type synchronous motors would use two Motor Guards, one on the stator and the second on the field.
3. Does MEG-alert test the motor or generator while it is operating?
No, both Motor Guard and GEN Guard test the insulation resistance of the windings when the motor or generator are NOT operating, that is when they are offline. This test determines if the motor or generator are safe TO START - which is when most experience electrical failures. If the motor or generator is in operation, the green "Test On" LED will not be lit, and the MEG-alert will standby until the motor or generator is shut down. Immediately upon shut down and continuously until the next startup the MEG-alert will test the windings.
4. How do maintenance personnel know if the equipment is being automatically tested?
Warning labels are provided for application to the door of the control cabinet, switchgear, or the equipment. "Test On" LED's are located on the MEG-alert, and remote flashing LED's can be located on the motor starter bucket and/or the control cabinet.
5. How does MEG-alert prevent failure at startup?
Both Motor Guard and GEN Guard are designed to be connected into the starter circuitry. If the insulation resistance is measured to be dangerously low, Motor Guard and GEN Guard will interrupt the starter - locking out the motor and preventing a burnout. No matter how bad the condition of the motor or generator (whether from deterioration of the windings or external factors like moisture) if they are prevented from starting a catastrophic failure will be prevented.
With either Motor Guard or GEN Guard the ground fault must be removed before the motor or generator will be allowed to start. The MEG-alert can be manually reset at that time, or an automatic reset can be designed into the system.
Note: starter lockout is NOT employed on fire pump motor controls. Alarm ONLY circuits are used instead.
6. What other safeguards are designed into the MEG-alert?
Both Motor Guard and GEN Guard are available in several models with different features. The base model is a simple "Go/No Go" switch that lockouts the starter. Other models add a "Pre-alarm" flashing LED light as well as an optional meg-ohm meter that gives the exact measurement. The "Pre-alarm" level means that the insulation resistance is dangerously low, but the MEG-alert will still allow the motor or generator to start. This level (depicted by the yellow range onthe meter) indicates that preventive maintenance is required to prevent damage to the motor or generator.
7. Is remote monitoring of the test levels possible with MEG-alert?
Yes, both Motor Guard and GEN Guard are designed with terminals that can be connected to a transformer, and which will allow for meg-ohm readings and warnings to be transmitted to any location - across the plant or across the country!
8. Can we test more than one motor or generator per MEG-alert?
No, each motor or generator is assigned one MEG-alert. However, multiple motors (up to nine) or multiple generators (up to six) can be connected to a MEG-alert "Multi Guard" which houses the corresponding number of MEG-alerts.
9. How does the "Multi Guard" operation differ from the standard Motor Guard or GEN Guard?
Multi Guard is a single Motor Guard or GEN Guard testing unit that cycles the testing process between each motor or generator on a 30-second interval. The Multi Guard uses just one meg-ohm meter to display test results. Multi Guard bypasses any of the motors are in operation and resume testing the next unit that is offline. Should any of the test results indicate a failure, only that motor or generator will be locked out.
The Multi Guard unit pictured above shows the meg-ohm meter that would record the actual resistance measurement as it cycles between motors or generators. The small rectangle in the lower right of the panel is a digital number display of which motor (number 1 through 9) is being tested. The unit has a switch that allows the automatic cycling of tests, or a manual bypass to test just one motor. The row of LED's to the left indicate the motor that is being tested.
10. Where is the MEG-alert normally located in a typical circuit?
The MEG-alert is connected to the "B" phase, at the motor contactor or generator breaker and to the equipment ground. It is typically mounted in or next to the motor control center or switchgear.
11. Can MEG-alert automatically test the insulation resistance of submersible pumps?
Yes, MEG-alert Motor Guard will test both the submersible pump and the cables from the starter to the motor - regardless of the distance* (see next.)
12. What is the maximum distance the MEG-alert can be separated from the motor or generator?
MEG-alert can be installed up to 1,000 feet from the equipment being tested, as long as the test lead is wired with a minimum of 18 AWG wire.
13. Can MEG-alert GEN Guard test the insulation resistance on grounded generators?
Yes, however a "ground interrupter" will need to be installed with the GEN Guard. The ground interrupter will prevent a false reading. In addition, the GEN Guard is designed with two safety circuits to insure that the ground is re-established before the generator can produce voltage. (Ground interrupters are available as an extra cost component from MEG-alert or local electrical suppliers.)
14. Our motors (or generators) run 24 hours a day. What is the benefit of MEG-alert in this operation?
Even equipment that is intended to run continuously still has downtime. This downtime may be planned or unplanned:
Planned downtime is built in through redundant design, where multiple motors or generators are cycled. Absolutely critical systems are designed with backups. If a MEG-alert is installed, whenever the motor or generator is shut down - for even the briefest of intervals - it is going to be automatically tested. NO electrician will need to be scheduled, no matter if it is in the middle of the night or on a weekend.
Unplanned downtime may occur because of a problem with another part of the production line (another motor, or a belt, chain, bearing, or gear failure.) Whatever the cause, whenever the motor is shut down the MEG-alert will perform continuous insulation tests right up to the moment before it is restarted - in the case of MEG-alert, 100% safely!
15. Can you use MEG-alert for manual testing?
Yes, single MEG-alert units can be equipped with a "Test" button instead of the automatic mode. This permanent installation would still eliminate the need for repertitive manual testing, including access to the high voltage MCC. A permanent MEG-alert Motor Guard or GEN Guard even costs LESS than manual meggering equipment! Plus, you eliminate all the expensive safety equipment.
Multi Guard units can be switched from the auto mode and left in the manual position, and simply switched to the motor in question.
16. Can the MEG-alert be configured with multiple set points?
Yes, most MEG-alert models have two set points: a "pre-alarm" and a fault alarm. The first set point, or pre-alarm is typically set at 10 meg-ohms and indicates early insulation breakdown. The fault alarm is typically set at 1.5 meg-ohms and indicates impending motor failure if not corrected. The fault point is usually connected to the starter lockout function.
Both set points coincide with industry standards (IEEE), but can be adjusted for custom applications. The exception is that MEG-alert Multi Guard models require that all motors or generators connected share the same set points.
17. Can MEG-alert be used on motors or generators with internal low-current winding heaters?
Yes, although in some cases an isolation transformer must be installed on the heater input circuit. Alternatively, the MEG-alert and the heater can be set to alternate operations.
18. What voltage is used to conduct the meg-ohm tests with MEG-alert? Can the continuous testing cause damage to the insulation?
All models use a non-destructive DC current limited to a maximum of 350 microamps. All MEG-alert models use a patented voltage/current safety circuitry that absolutely protects dead grounded equipment. MEG-alert can NOT cause insulation breakdown!
19. What about the effect of MEG-alert testing on solid state control equipment (voltage regulators, variable frequency drives, etc.) in the motor, generator, or control panel?
MEG-alert tests between the B-phase and the ground. There is NO potential for high test voltages on control equipment. However, some generators must be protected by isolating transformers (call MEG-alert engineers for details.)
20. We have a 4160 volt application. How are workers protected from high voltages at or coming from the MEG-alert?
The GP2500 and GP5000 MEG-alert systems are fused and current-limit protected, BOTH on the output from the MEG-alert and from the motor operating voltages. These MEG-alert systems have "Power On" LED's at the unit and on the remote panel, plus a latching On/Off switch to indicate and remove power from the systems.
21. What happens to the MEG-alert if the "motor run" control signal fails and the unit stays in the circuit with operating voltage present?
MEG-alert is designed with high internal impedance to protect the system and trip out the system on a fault alarm after the service ground is detected.
22. Does the MEG-alert test all three phases?
Yes, the MEG-alert test lead is connected to the B-phase and tests all three phases through the neutral (star) of the windings to the ground. If even one of the three phases is faulty, the Motor Guard will detect the problem.
23. Can MEG-alert be used on motors with soft starters?
Yes, in fact MEG-alert is used as standard equipment on some OEM motor controls. It may be necessary to install an accessory terminal - if an open terminal is not already provided - to connect the MEG-alert before the starter to avoid a false fault reading. In addition, an accessory contactor and timing circuit is REQUIRED to allow proper stater function and prevent false readings. Please consult the MEG-alert engineers for details regarding your application (motor horsepower and deceleration time needed.)
24. Can MEG-alert be customized for our unique application?
Yes, although the standard installation can be adapted for nearly any application. With over 20 years of installations worldwide we have seen almost every possible application. But, if you have a unique application our engineers can customize a MEG-alert to match your requirements.
Still have questions? Call MEG-alert Corporation for a
NO Obligation consultation: 866-768-1817
Or email MEG-alert at: info@meg-alert.com