Safety Precautions for Basic Switches

For the individual precautions for each Switch, refer to the Precautions section of each Switch.

Do not wire the Switch or touch any terminal of the Switch while power is being supplied to the Switch. Doing so may result in electric shock.

Electrical Conditions

Load

The switching capacity of the Switch significantly differs depending on whether the Switch is used to break an alternating current or a direct current. Be sure to check both the AC and DC ratings of the Switch by referring to its datasheet. The control capacity will drop drastically if it is a DC load. This is because a DC load, unlike an AC load, has no current zero cross point. Therefore, if an arc is generated, it may continue for a comparatively long time. Furthermore, the current direction is always the same, which results in contact relocation phenomena, and the contacts hold each other with ease and will
not separate if the surfaces of the contacts are uneven.

Some types of load have a large difference between usual current and inrush current. Make sure that the inrush current is within the permissible value. The higher the inrush current in the closed circuit is, the more the contact abrasion or shift will be. Consequently, contact weld, contact separation failures, or insulation failures may result. Furthermore, the Switch may break or become damaged.

If the load is inductive, counter-electromotive voltage will be generated.
The higher the voltage is, the higher the generated energy is, which will increase the abrasion of the contacts and contact relocation phenomena. Make sure to use the Switch within the rated conditions.

Inrush Current

The switching capacity of each Switch appearing on a datasheet is the rated capacity. When applying the Switch to a circuit with a special load with unusual inrush and switching current and voltage waveforms, be sure to test the Switch under the actual conditions before use.

If the load is a micro voltage or current load, use a dedicated Switch for micro loads. The reliability of silver-plated contacts, which are used by standard Switch models, is insufficient in such a case.

If the Switch is used for switching both micro and high-capacity loads, be sure to connect relays suitable to the loads.

Types of Load vs. Inrush Current

The rated loads of the Switch are as follows:

Inductive Load:

Lamp Load:

Motor Load:

Note:It is important to know the time constant (L/R) of an inductive load in a DC circuit.

Load Connections

Example of Power Source Connection (Different Polarity)

The power source may short-circuit in failure mode if the loads are connected in the same way as the "incorrect" circuit below.

Even in a "correct" circuit, note that the insulation performance of the switch may deteriorate and the switch life may be shortened because one load is connected to one contact.

Example of Incorrect Connection of Power Source (Different Current Type)

The DC and AC power may be mixed.

Do not configure a circuit that may place a voltage between the contacts of the Switch; otherwise metal deposition will occur between the contacts.

Contact Protective Circuit

Apply a contact protective circuit to extend contact life, prevent noise, and suppress the generation of carbide or nitric acid. Be sure to apply the contact protective circuit properly, otherwise an adverse effect may result. The use of the contact protective circuit may delay the response time of the load.

Life Expectancy

The life of the Switch greatly varies with switching conditions. Before using the Switch, be sure to test the Switch under actual conditions.
Make sure that the number of switching operations is within the permissible range. If a deteriorated Switch is used continuously, insulation failures, contact weld, contact failures, Switch damage, or Switch burnout may result.

Mounting

Before mounting, dismounting, wiring, or inspecting the Switch, be sure to turn OFF the power supply to the Switch, otherwise an electric shock may be received or the Switch may burn.

Wiring

When mounting the Switch to the mounting panel, keep a sufficient insulation distance between the mounting panel and the Switch. If the insulation distance is insufficient, add an appropriate insulation guard or separator. This is especially important if the Switch is mounted to a metal object.

The Basic Switch does not incorporate a ground terminal. Do not mount the Basic Switch while power is being supplied.

The following provides typical examples of contact protective circuits.
If the Switch is used in an excessively humid place for switching a load that generates arcs with ease, such as an inductive load, the arcs may generate NOx, which will change into HNO₃ (nitric acid) if it
reacts with moisture. Consequently, the internal metal part may be corroded and result in an operating failure of the Switch. Be sure to select the best contact preventive circuit from the following in order to prevent this.

Typical Examples of Contact Protective Circuit

Circuit example		Applicablecurrent		Feature		Element selection
		AC	DC
CR circuit		See note.	Yes	Note:	When AC is switched, the load impedance must be lower than the CR impedance.	C: 0.5 to 1 μF per switching current (1 A) R: 0.5 to 1 Ω per switching voltage (1 V) The values may change according to the characteristics of the load. The capacitor suppresses the spark discharge of current when the contacts are open. The resistor limits the inrush current when the contacts are closed again. Consider these roles of the capacitor and resistor and determine the ideal capacitance and resistance values from experimentation. Use a capacitor with a dielectric strength between 200 and 300 V. When AC is switched, make sure that the capacitor has no polarity.
		Yes	Yes	The operating time will increase if the load is a relay or solenoid. It is effective to connect the CR circuit in parallel to the load when the power supply voltage is 24 or 48 V and in parallel to the contacts when the power supply voltage is 100 to 200 V.
Diode method		No	Yes	Energy stored in the coil is changed into current by the diode connected in parallel to the load. Then the current flowing to the coil is consumed and Joule heat is generated by the resistance of the inductive load. The reset time delay in this method is longer than that of the CR method.		The diode must withstand a peak inverse voltage 10 times higher than the circuit voltage and a forward current as high as or higher than the load current.
Diode and Zener diode method		No	Yes	This method will be effective if the reset time delay caused by the diode method is too long.		Zener voltage for a Zener diode must be about 1.2 times higher than the power source since the load may not work under some circumstances.
Varistor method		Yes	Yes	This method makes use of constant-voltage characteristic of the varistor so that no high-voltage is imposed on the contacts. This method causes a reset time delay more or less. It is effective to connect varistor in parallel to the load when the supply voltage is 24 to 48 V and in parallel to the contacts when the supply voltage is 100 to 200 V.		---

Do not apply contact protective circuits as shown below.

Incorrect		Incorrect
	This circuit effectively suppresses arcs when the contacts are OFF. The capacitance will be charged, however, when the contacts are OFF. Consequently, when the contacts are ON again, short-circuited current from the capacitance may cause contact weld.		This circuit effectively suppresses arcs when the contacts are OFF. When the contacts are ON again, however, charge current flows to the capacitor, which may result in contact weld.

Terminal Connections

Be sure to connect appropriate wires to the Switch by considering the voltage and current applied to the Switch.

Solder Terminals

When soldering lead wires to the Switch, make sure that the capacity of the soldering iron is 60 W maximum and that the temperature of the iron tip is 300°C maximum unless otherwise specified in the datasheet of the Switch. Improper soldering may cause abnormal heat radiation from the Switch and the Switch may burn.

The characteristics of the Switch will deteriorate if a soldering iron with a capacity of more than 60 W is applied to any part of the Switch for 6 s or more. For Switches with special soldering specifications, however (provided in Terminal Connections under Cautions where appropriate), be sure to perform soldering according to the specifications.

Be sure to apply only the minimum required amount of flux. The Switch may have contact failures if flux intrudes into the interior of the Switch.

Quick-connect Terminals

Wire the quick-connect terminals with the specified receptacles and insert the terminals straight into the receptacles. Do not impose excessive external force on the terminals in the horizontal or vertical directions, otherwise the terminals may deform or the housing may become damaged.