Current Coil


A circuit breaker is an electrical switch that automatically opens a circuit when certain electrical conditions are met. In general, circuit breakers open (trip) when the electrical current through a sensing device exceeds a pre-established current rating. Measured in amperes, electrical current is the flow of electrons through an electrical conductor. Carling Technologies manufactures hydraulic/magnetic circuit breakers where the current sensing device used is an electromagnetic solenoid, or coil.

The current coil rating of a Carling circuit breaker is the maximum current in amperes the breaker will carry continuously without tripping. Carling circuit breakers will not trip at 100% of this current rating, are guaranteed to trip at 125% to 135% of the current rating (depending on your choice of trip delay), and may trip between 101% through 134% of current rating. For more information on what makes a magnetic circuit breaker trip, see the Learn More - Trip Time Delay page for Circuit Protection.

Temperature Stable

Because Carling Technologies' circuit breakers are hydraulic/magnetic circuit breakers, their precision mechanisms are temperature stable, not adversely affected by temperature changes in their operating environment. They will trip at the same current regardless of ambient temperature, providing consistent trip point operation from temperatures ranging from -40°C to +85°C. With this stability, derating considerations due to temperature variations are not normally required and heat induced tripping is avoided.

Their hydraulic/magnetic construction is also generally more application flexible since the current rating, inrush tolerance, and trip delay can be specified relatively independently.

Available Current Ratings

Carling Technologies circuit protection product lines cover a wide range of coil ratings - from .01 amps to 25 amps (M-Series, Q-Series) to 50 amps (A-Series, B-Series, D-Series) to 100 amps (C-Series, E-Series) up to 700 amps (F-Series).

Selection Guidelines

Current coil rating represents the electrical load requirement. You may find the following general guideline helpful in determining the appropriate current coil rating for your application:

  1. What is the normal (stabilized) operating current the breaker will encounter?
  2. Using the list below, what is the "safety factor" to preclude surge-induced nuisance tripping? Typical safety factors:
    • 1.20 on resistance loads
    • 1.75 on inductive & transformer loads
    • 1.5 on linear power supply circuits
    • 2.0 on switching power supply circuits
    • 1.75 on single phase induction motors
    • 1.25 on other motors
  3. Final current rating = normal operating current X safety factor.
  4. To minimize your cost, we suggesting choosing the next highest standard current rating shown in our catalog for the specific series in which you are interested. However, you may also contact your Carling Technologies Sales Representative for available non-standard ratings, should you require them.

Voltage Trip Ratings

Carling Technologies also offers AC and DC voltage trip ratings on A-Series, B-Series, C-Series, & D-Series breakers. Voltage trip circuit breakers are factory calibrated to trip at a specified voltage value and are not rated for continuous duty. Voltage trip ratings are often used for "Dump Circuit" or "Panic Trip Circuit" applications where there is a need to open the main power contacts with low power input from one or more sources. Use the Carling Technologies' on-line valid part number configurator, CONFIGURIT®, for specific voltage trip ratings offered or contact your Carling Technologies Sales Representative.

Multi-Pole Breakers

Multi-pole breakers where poles are electrically isolated are also available. Such multi-pole construction provides the capability of assigning a different current coil rating to each pole. This is called dissimilar pole construction. To learn more about dissimilar pole construction, see Learn More - Poles, for Circuit Protection.

For dissimilar multi-pole breakers, Carling assigns special catalog numbers that fall outside the convention of our standard catalog-ordering scheme. However, you can still configure valid dissimilar pole constructions using our on-line Configurit.

Dual Coil

Carling Technologies also offers circuit breakers of Dual Coil construction, where a circuit breaker has two coils in the space normally occupied by a single coil. By combining two electrically independent coils on a common magnetic circuit, it is possible to provide contact opening when either an over-current or trip voltage is applied to the respective coils. One coil will be a current trip coil operating according to the standard circuit rating specifications; the second coil can be used to provide a remote shutdown function. See Learn More - Circuits for more information regarding the function of Dual Coil circuits, or contact your Carling Technologies Sales Representative.