Contacts

  

Contacts are the point where a switch throw makes or breaks a circuit. Switch contacts are always found in pairs. The contact that moves with the switch actuator is the movable contact or lever; the contact that is fixed is called the stationary contact.

Contact Materials

Contacts are subject to heat, arcing, corrosion, welding, pitting, and contaminating materials. The most appropriate contact material will differ depending on load type. Carling offers a variety of contact materials ranging from gold for dry circuits (low current circuits that do not produce an arc) to various silver alloys for high inrush loads. The most commonly used contact material is silver. Silver has low resistance and is one of the best conductors for electricity.

Contact Functions

Contact functions can be described as make-before-break or break-before-make.

Make-before-break switches are those that will complete a new circuit before breaking an old one. With this type of function, the next contact is made or closed before the previous contact is broken or opened. This can also be referred to as a shorting type switch. A typical application example for use of this type of function would be a computer switching from AC to a DC backup system.

Break-before-make switches are those that will only complete one circuit at a time, leaving an interval of time between the time one circuit opens and the next circuit closes. This can also be referred to as a non-shorting type switch. In general, all Carling Technologies' switches are break-before-make switches.

Single Break or Double Break

Single break / single make contacts are those that open and close a circuit at only one place.

Double break/double make contacts are those that open at two separate places on a circuit. Double break contacts dissipate heat more readily, providing longer switch life and enabling the switch to handle higher voltages.

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Double Break

Slow Break or Quick Break

When contacts separate, arcing or sparking can occur between the two contacts. Arcing can burn up the contacts and reduce the useful life of the switch. The arc resulting from a DC voltage will be greater and will last longer then the arc from an AC voltage, because DC current has a constant value in relation to ground and zero. Because of constant electrical flow, DC switches should ideally be quick break. Quick break circuits typically require less than 5 milliseconds to make or break. Carling AC/DC toggles and pushbutton switches utilize a quick break design.

AC current has a value that is always rising or falling in relation to zero. Whenever AC current reaches zero (120 times per second) it cannot create a spark. Because of this, AC switches can be either slow or quick break. Slow break circuits typically require 8-12 milliseconds to make or break. Most Carling AC rated switches utilize a slow break design.

Contact Types

Wiping action contacts are "self-cleaning" contacts that wipe or slide against each other when opening or closing a circuit. This wiping action helps prohibit the build-up of any non-conductive deposits on the contacts themselves. Wiping contacts are typically used in AC applications, but are also suitable for low voltage DC applications.

Wiping action contacts can include some limitations on current, voltage, and lifecycle, and they require some form of lubricant, such as grease, to facilitate movement. With repeated arcing, the level of contaminants can increase and be captured by the lubricant around the contact area. This could eventually affect the operation of the switch.

Carling switch series which offer wiping contacts include R , LR , 610/620, 611/621, T, LTA, TG, LTG, TTG, TLG, C, D, DK/EK, 641, 700, and 800.

Butt action contacts press "head-on" against each other when closing a circuit. They are much more versatile than other types of contacts, having the ability to handle multi-purpose loads from dry circuits up to 20 amps, and the ability to modify contact material, thickness or alloying agents. Butt action contacts are suitable for both AC and DC type switches.

Carling switch series which offer butt action contacts include: Contura II & III, Contura IV & V, Contura X & XI, Contura XII, J Series, L Series, RSC, RGS, LRGS, 611/621, 622/632, 651/652, TIL, TIG, TIH, TII, LTIL, LTIG, LTIH, LS, LT, F, G, H, I, MAAOA/215, P, PP, 170/72, P26, P27, 16-3P, and R135.

Roller contacts are a different style of butt action with an over-center, non-teasable mechanism. They are typically used on AC/DC switches that have size constraints. They are an example of a double break style contact where both the line and the load are broken simultaneously.

Carling switch series which offer roller action contacts include 110/216 and 110/316-P.

Knife-blade contacts are a quick-make/quick break , non-teasable variation of wiping contacts usually used on high voltage AC/DC type switches.

Carling's DK/EK switch series offers knife-blade action contacts.