Open Frame series  

Contact Materials and Definitions

To provide economical switches without sacrificing reliability, Electroswitch has developed contact materials with precious metal inlays and overlays. These are being used in many applications, replacing solid precious metals which were the industry standard. In keeping with our philosophy, new contact materials must meet or exceed all existing standards and must not adversely affect switch performance.

Contact materials that are not gold plated have a protective anti-tarnish coating applied after plating to inhibit oxidation during assembly, shipping, and storage.

The contact materials described provide for a full range of switching applications, from dry circuitry to 1 amp at 110 VAC. Current and voltage ratings on resistive loads at room ambient operating temperatures should not exceed those shown.

Electroswitch developed double wiping contacts for their rotary switches which are self-cleaning and require no maintenance during life under normal operating conditions. The self-cleaning action assures a clean, positive contact capable of wiping through accumulated particles or dust, oxides, and other contaminants.

Non Shorting Type Switch - also called "break before make." When switching from one position to the next, the first contact fully breaks before the second contact is made.

Shorting Type Switch - also called "make before break." When switching from one position to the next, the second contact is closed before the first is opened.

Cycle is defined as a rotation from one stop to the other and return or 330 rotation for a 12 position switch. An operation is normally defined as the making and breaking of an electrical contact.

Contact Materials

Contact Material
Typical Life
(No load,
room ambient)
Brass, silver plated with protective anti-tarnish coating (OMS106, CMS237, CMS80) +100C 10,000 cycles Commercial
Special spring base material with silver alloy rolled on contact surface (CMS333) +100C 100,000 cycles
Silver-to-silver contact
& QPL List
100,000 cycles
Silver-to-silver contact
Spring silver alloy +100C 200,000 cycles
Silver-to-silver contact
Commercial & Military
Increased life

Insulation Materials
Insulation Material MIL Specification Temperature Range
Phenolic L-P-513
Type PBE-P
-65C to +100C
Glass Silicone MIL-P-997
Type GSG
-65C to +85C
Ceramic MIL-1-10
Grade L-422
-65C to +150C
Diallyl Phthalate MIL-M-14 65C to +85C
Glass Epoxy MIL-P-18177
Grade GEE
65C to +85C

Lubrication of Contacts

All switch sections are lubricated using a process which deposits a very thin film on the rotor blades. This film is of sufficient thickness to provide lubrication for the life of a normally hand-operated switch. The film of lubricant will not readily collect dust and dirt, which could lead to reduced switch life.

Various lubricants that are compatible chemically and electrically are used. Lubricant used is dependent on switch specification and operation. If customer switch specification specifically calls for no lubricant, none will be applied.

Soldering to Electroswitch Switches

Care must be exercised when soldering to Electroswitch's switches. Soldering irons, which can produce temperatures above 600F should not be used. Excessive heat or prolonged periods of heating (above 5 seconds) can cause clips to loosen, and contribute to an increase in contact resistance due to a loss of contact pressure.

Never clean rosin from soldered connections on a switch or any other contacting device with solvent. Rosin dissolved by a solvent may float down onto the contacts where it cannot be removed easily, and no amount of contact pressure can cope with a rosin coating.

Type of Detent

Unidex - a dual ball detent indexing on a starwheel. This detent offers 100,000 cycles of mechanical life, with the torque remaining constant and crisp throughout the life of the switch. It should be used in place of ball index where possible.

Ball Index - single, dual or tri-ball indexing with ball bearing indexing over a hill and valley or punched hole plate. This index is common to the Type L and MF switches. The tri-ball index must be used for military switches.

Detenting Torque

Proper detenting torque is necessary to give the right feel to the switch. An approximate torque figure can be obtained by adding all the clips which are in contact with the rotor blade(s), and then adding the maximum number of clips entering in any one detented position. This figure, multiplied by 1 inch-ounce, will give an approximate but usable torque value. In order to mask out this drag, the detent mechanism itself must have at least 1 times the torque of the section(s). This means that the total switch torque should be at least 2 times the section torque for a crisp feel. The typical tolerance on the torque requirement is 40%. If a closer torque tolerance is required, adjustments will be necessary (at additional cost).

In cases where clip and blade drag is greater than can be accommodated by a specific index, definite feel of index position becomes vague and there is a tendency to skip positions. Thus, in order to obtain a definite detent "feel," it is necessary to reduce section drag by using a thinner clip material or special slotted, low torque clips. (Consult our Application Engineering Department. They will gladly provide any information or assistance you might request.)

Maximum torque is related to the size and type of knob being used on the front panel. For a comfortable turning force, the following torque values are recommended:

in. dia. knob 8 to 15 in.-oz.
in. dia. knob 10 to 20 in.-oz.
1 in. dia. knob 15 to 35 in.-oz.
1 in. dia. knob 20 to 50 in.-oz.

(Bar knobs or deeply knurled knobs can be used with higher torques for the same size knob.)

Identification Marking of Switches

Electroswitch switches are marked "249," our registered trademark, or "Electroswitch." Our manufacturer's federal identification code number is 76854. These numbers do not identify any particular switch or item.

When specified, rotary switches may be marked with either the Electroswitch part number or customer's part number. Since changes made in production might cause obsolescence of parts already marked, it is impractical to stamp revision letters.