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Circuit Breakers
Circuit breakers interrupt overload and short-circuit currents before cables and equipment are damaged, and protection relays decide when the larger breakers should trip. Seven Star LLC supplies both to electrical contractors, panel builders and plant engineers in Oman. This category is dominated by Schneider Electric, with Compact NSX and PowerPact molded case circuit breakers, Acti9 and Multi 9 devices and TeSys motor circuit breakers, and also lists ABB breakers and relays, SEL and Siemens SIPROTEC protection relays, Eaton fuses and Legrand miniature circuit breakers.
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Category guide
About Circuit Breakers
Circuit breakers interrupt overload and short-circuit currents before cables and equipment are damaged, and protection relays decide when the larger breakers should trip. Seven Star LLC supplies both to electrical contractors, panel builders and plant engineers in Oman. This category is dominated by Schneider Electric, with Compact NSX and PowerPact molded case circuit breakers, Acti9 and Multi 9 devices and TeSys motor circuit breakers, and also lists ABB breakers and relays, SEL and Siemens SIPROTEC protection relays, Eaton fuses and Legrand miniature circuit breakers.
Types of circuit breaker and protection device listed
- Miniature circuit breakers, RCBOs and RCD modules: final circuit protection against overcurrent and earth leakage.
- Molded case circuit breakers (MCCB): distribution and feeder protection, with thermal-magnetic or electronic trip units such as MicroLogic.
- Motor circuit breakers: short-circuit and adjustable overload protection for a single motor.
- Load break and disconnect switches: isolation under load, without protective tripping.
- Vacuum circuit breakers and protection relays: medium-voltage switchgear, with feeder, motor and transformer relays.
- Fuses: Class J time-delay fuses for North American style panels.
How to select a circuit breaker
Five values define a low-voltage breaker: rated current, number of poles, rated voltage, breaking capacity and the trip characteristic. The breaking capacity must be at least equal to the prospective short-circuit current at the point of use, a figure that comes from the fault level study and not from the load. The trip curve or trip unit settings are chosen so that the breaker nearest the fault opens first, which is called selectivity or discrimination, and manufacturers publish tables for combinations of their own devices. Ambient temperature affects thermal trip units, so breakers in hot outdoor panels in the GCC may need derating or an electronic trip unit. For medium-voltage breakers add rated voltage, short-time withstand current, control voltage for the coils and motor, and fixed or withdrawable construction.
Data needed to quote a breaker or protection relay
Send the full reference, including the trip unit and accessories. For relays, send the complete order code, since CT rating, auxiliary voltage and protocol are fixed at ordering.
What to include in your inquiry
These details let us quote the right item the first time.
- Manufacturer part number or catalogue reference
- Rated current and voltage
- Breaking capacity and number of poles
- Trip unit and accessories
- Quantity
Missing some of them? Send what you have. A nameplate photo or an old part number is enough to start.
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Request a Quote for Circuit Breakers
Looking for a specific model, part number or brand in Circuit Breakers? Send us your requirements and quantities. Seven Star LLC sources genuine industrial equipment for customers across Oman and the GCC and replies with a formal quotation.
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Frequently Asked Questions
What do the letters B, C and D mean on a miniature circuit breaker?
They indicate the instantaneous trip curve defined in IEC 60898-1, that is, the multiple of rated current at which the magnetic release trips. Type B trips at the lowest multiple and suits resistive loads and long cable runs. Type C is the general choice for mixed loads. Type D tolerates high inrush from transformers and motors. The thermal overload part is the same for all three.
What is the difference between Icu and Ics on an MCCB?
Both are breaking capacities under IEC 60947-2. Icu is the ultimate short-circuit breaking capacity, the highest fault current the breaker can clear, after which it may not be fit for further service. Ics is the service breaking capacity, a fault level the breaker can clear and then continue in normal service. Ics is stated as a percentage of Icu and matters for supply continuity.
Can I replace only the trip unit on a molded case circuit breaker?
On many frame types the trip unit is interchangeable and has its own reference, so a thermal-magnetic unit can be replaced or upgraded to an electronic one of the same frame. On others the trip unit is factory-sealed to the breaker. Give us the breaker reference and frame size, and we check the manufacturer's catalog to see which trip units are offered for that frame.
What is the difference between an RCD, an RCBO and a Vigi add-on module?
An RCD detects earth leakage current and trips, but gives no overcurrent protection. An RCBO combines earth leakage and overcurrent protection in one device for a single circuit. An add-on residual current module is clipped to a compatible miniature or molded case breaker and uses that breaker's mechanism to trip. All are chosen by sensitivity in milliamps and by type, such as AC, A or B.
What do you need to quote a circuit breaker or protection relay?
The manufacturer reference is best. Otherwise send the rated current, poles, system voltage and frequency, breaking capacity, curve or trip unit type, fixed, plug-in or withdrawable version, and accessories such as auxiliary contacts, shunt or undervoltage release, rotary handle or motor mechanism. For protection relays send the complete order code or the CT secondary rating, auxiliary voltage, I/O count and protocol.