Switches
Designing reliable power switching at the operator interface
By Rolf Horn, applications engineer at DigiKey A
power switch looks like one of the simplest components on an industrial control panel. But it is often subjected to high electrical stress and
extreme environmental conditions. When the switch is carrying high current rather than sending a low-voltage signal to a controller, failure can expose the equipment to downtime, unsafe operation, or loss of system availability.
For example, a power switch in an industrial, transportation, or telecom application may be exposed to dust, moisture, vibration, shock, frequent actuation, and high startup currents. In these environments, engineers need a front-panel switch that can remain mechanically secure, electrically stable, and environmentally sealed while still providing an operator interface.
NKK Switches offers its JWLW Series 16 A rocker switches, designed for rugged operator interface equipment. They combine high-current AC switching capability, IP67-rated panel sealing, high inrush- current handling, and sealed mechanical construction in a snap-in rocker format. This allows engineers to address the design problem of reliable load switching and environmental hardening at the human- machine interface. The first requirement is electrical where the switch must be rated for the system voltage and current profile of the load it is expected to carry.
Electrical rating for load current The JWLW Series 16 A rocker switches (Figure 1) can control both AC and DC loads. They are nominally rated for a resistive load of 16 A at either the standard North American (125 VAC
) or international 32 October 2026
between contacts and the case. This high dielectric strength shows a robust internal construction with significant creepage and clearance distances, providing a wide safety margin against line voltage transients.
Managing high inrush current and contact stress
The capacity to switch high currents is a primary function of a rocker switch. The capability of the JWLW series with a TV-8 rating is a critical performance metric that separates industrial-grade components from standard commercial switches.
Figure 1. An NKK JWLW Series 16 A snap-in mount switch with an IP67 rating. (Image source: NKK)
(250 VAC
) mains voltage. This high current capacity allows the switches to serve as a main control across a wide range of resistive loads, including industrial machines and high-power appliances, without the need for an intermediate relay or contactor.
The rocker switches have a 5 A, 72 VDC rating for telecommunication applications. Switching DC loads is more challenging than switching AC due to the absence of a natural current zero-crossing to aid in arc extinction. A sustained DC arc can cause contact erosion and failure.
Because DC switching does not benefit from the natural current zero-crossing of AC, engineers should verify the applicable DC rating and part number suffix for the exact JWLW configuration being specified. For an engineer designing power distribution units, this rating provides a high degree of confidence and simplifies regulatory compliance.
Components in Electronics Another meaningful electrical
characteristic is the contact resistance of 20 milliohms. At the full 16 A AC rating, a 20 milliohm resistance dissipates 5.12 watts of heat within the switch contacts. This low value is critical for preventing overheating and ensuring thermal stability over the component’s lifetime.
The reliability of the insulation system is defined by its insulation resistance and dielectric strength. The JWLW Series 16 A rocker switches guarantee a minimum insulation resistance of 1,000 megaohms at 500 VDC
A transient surge can severely affect the switch contacts. As the mechanical contacts of a switch close, they can physically bounce several times in microseconds before settling. If a high inrush current flows during this bounce period, an electrical arc forms across the small contact gap each time the contact separates. Repeated arcing can accelerate contact erosion, and in severe cases, contribute to contact welding.
The JWLW Series 16 A rocker switch’s TV-8 rating indicates that they have been tested under defined high-inrush conditions. TV-8 involves two tests performed at 120 VAC
.
. This extremely high resistance ensures that leakage current between electrically isolated parts of the switch is negligible.
The dielectric strength measures the insulation’s ability to withstand a high voltage without breaking down. The JWLW switch is rated for a minimum of 2,000 VAC
for one minute between contacts, and an even higher 4,000 VAC
for one minute
First is the overload test, in which the switches must withstand 50 operations while switching a steady-state current of 12 A, with a minimum peak inrush current of 163 A. After this, the switches undergo an endurance test, where they must complete 25,000 operations, switching a steady-state current of 8 A with a minimum peak inrush current of 117 A.
A switch that passes these tests demonstrates that its contact systems and mechanical construction are designed to
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