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General Purpose Relays

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Failure Examples

Note: You may perform troubleshooting, but do not open the case.

Failures and Assessing Causes

Various problems can occur with relays in devices that use relays.
An analysis, such as s fault tree analysis (FTA), is useful for assessing the cause of the problem.
The following table lists relay failure modes and suggests possible causes.

Problems Visible from Outside the Relay

FailureItem to checkPossible cause
Relay does not operate.1. Is the input voltage reaching the relay?・ The breaker or fuse may have been activated.
・ The wiring may be incorrect or there may be a leakage.
・ The screw terminals have not been tightened sufficiently.
2. Is a relay with specifications suitable for the input voltage being used?・ Use 200 VAC relays for 100 VAC voltage lines.
3. Is there voltage drop in the input voltage?・ The supply power has insufficient capacity.
・ The wiring covers a long distance.
4. Is the relay damaged?・ The coil is disconnected.
・ There is mechanical damage from being dropped or exposed to shock.
5. Is there an error in the output circuit?・ Output side power supply
・ Load failure
・ Incorrect wiring
・ Faulty connection
6. Is there a faulty contact?・ Contact error
・ Contact deterioration due to end of service life
・ Mechanical damage
The relay does not release.1. Is the applied voltage completely cut off?・ Leakage current in the protective circuit (surge absorber)
・ Voltage applied by bypass circuit
・ Semiconductor control circuit with residual voltage
2. Relay error・ Contact weld
・ Insulation deterioration
・ Mechanical damage
・ Inductive voltage (long-distance wiring)
The relay malfunctions.
The indicator lights
1. Is incorrect voltage being applied to the relay input terminals?・ Inductive voltage (long-distance wiring)
・ Bypass circuit from inductive voltage (A latching relay not holding.)
2. Is excessive vibration or shock being applied?・ Unsuitable operating conditions
Burnout1. Is there burnout from the coil?・ Incorrect coil specifications selected.
・ Applied voltage exceeds rating.
・ Imperfect operation of electromagnet with AC specifications (insufficient armature connection)
2. Is there burning from the contact?・ Current exceeds rating for contacts.
・ Allowable inrush current exceeded.
・ Short-circuit current ・ Imperfect external connection (heat generated by imperfect contact with socket)

Problems Visible from Inside the Relay

FailureItem to checkPossible cause
Contact welding1. Was there a large current flow?・ A rush current, e.g., from a lamp load
・ Load short-circuited current
2. Has there been abnormal vibration in the contacting section?・ External vibration or shock
AC relay humming
・ Contact chattering from imperfect operation caused by voltage drop (Voltage drop sometimes occurs instantaneously when the motor is operated.)
3. Is switching occurring too frequently?--
4. Has the relay reached the end of its service life?
Faulty contacts1. Is there foreign matter on the contact surfaces?・ Silicone, carbon, or other foreign matter
2. Is the contact surface corroded?・ Contact sulphurization from SO2 and H2S
3. Is there a mechanical cause?・ Terminal displacement, contact displacement, or contact follow
4. Have the contacts deteriorated?・ End of relay service life
Humming1. Is the applied voltage sufficient?・ Incorrect relay coil specifications
・ Applied voltage ripple
・ Slow rise in input voltage
2. Has the correct relay type been chosen?・ DC specifications used for AC lines
3. Is the electromagnet operating correctly?・ Foreign matter between the moving armature and core
Abnormal deterioration of contacts1. Has the correct relay been selected?・ Incorrect selection of voltage, current, or inrush current ratings
2. Has enough consideration been given to the connected load?・ Inrush current from a motor load, solenoid load, lamp load, etc.

Approach to Maintenance

There are two main types of maintenance: corrective maintenance,
i.e., inspections and replacements that take place after a failure has occurred, and preventative maintenance,
i.e., inspections and maintenance that is undertaken before failure occurs.

One of the important issues with preventative maintenance is when to perform inspections and replacements, how to know when that is required, and how to determine the timing.

The factors that must be considered when determining maintenance schedules for relays is the target device and its level of importance and the required reliability level, when looking at maintenance from the device or system perspective. There are also different types of failure for the different characteristics and items based on the type of relay.

Relay failure types can be broadly classified into failures from wear, typified by worn out contacts, and deterioration failures, such as layer shorts in coil windings.

In general, once the conditions of use for the relay being used have been determined, it is possible to predict maintenance requirements because types of wear, such as contact wear, and the timing of wearrelated failures is aligned to the number of operations. On the other hand, deterioration failures, such as layer shorts in coil windings, are greatly affected by the inherent reliability of the relay being used. The maintenance requirements are affected by use reliability, e.g., operating conditions and on-site environment. This means that the failures are often different for each case, which makes it difficult to determine a maintenance schedule beforehand.

In actual operation, wear and deterioration progress at the same time and it is important to know which type of failure is going to occur first when determining maintenance schedules.

The following items are useful for reference when determining maintenance timing.

Maintenance TimingDetermined
by No. of
by time
WearContact wearThe maintenance timing can be determined from the electrical
durability curve drawn from load voltage, current, and load type. If there is no applicable electrical durability curve, the maintenance
timing can be determined from test values from the device.
-If the number of
switching operation per unit time can be determined, the number of operations can be replaced by the time.
Wear in operating mechanismsThe maintenance timing can be determined from number of operations in the mechanical durability of the relay. If the mechanical durability listed in the performance specifications is a value determined under standard test conditions and the actual operating conditions differ from these standard test conditions, the maintenance timing should be determined based on test values from actual operating conditions.-
DeteriorationInsulation Deterioration of Coils and Coil WindingsThe life of a coil can be predicted if the temperature in the conditions that the coil is operated under is known. A total of 40,000 hours at 120°C is used as a reference point for most polyurethane copper wire coils.--
Contacting Stability of ContactsInherent reliability is changed dramatically by operating conditions and the environment. Maintenance timing can be determined by understanding the operating conditions and environment and performing sampling.-It is important to understand toxic gas concentrations that adversely affect the on-site environment and contact material.
Deterioration of performance of metallic material
Deterioration of performance of resin material

Maintenance Guidelines

Mechanical Durability

The external appearance and change in performance are monitored with a rated voltage (or rated frequency for AC operation) applied to a coil when the contact is under no load and is switched at the rated frequency.

Electrical Durability

The external appearance and change in performance are monitored with a rated load connected to the contact and the rated voltage (or rated frequency for AC operation) applied to the coil.
Whether or not the electrical durability has been reached depends on the type of usage.

Guide to Determining the Durability

Evaluated itemSpecified value
External appearanceNo looseness, deformation, or damage
Insulation resistance1 MΩ min. if not specified
Dielectric strength75% min. of initial specified value
Coil resistance95% of initial specified lower limit to 105% of initial specified upper limit
Must-operate voltage1.2 times max. of initial specified value
Must-release voltage0.5 times max. of initial specified value
Operating time1.2 times max. of initial specified value
Release time2 times max. of initial specified value
Contact resistanceContact rated current
or switching current (A)
Measured current (A)Resistance after contact
resistance test (Ω)
Less than 0.010.001100
0.01 min. to less than 0.10.0120
0.1 min. to less than 10.15
1 min.12

Based on the NECA C5442. (NECA: Nippon Electric Control Equipment Industries Association)