Multiple residual current circuit breakers connected in parallel in the distribution box

Connecting multiple residual current circuit breakers (RCBOs) in parallel is generally not recommended unless specifically designed for parallel operation, due to potential current imbalance and coordination issues.Key Considerations1. Load Distribution and Current Imbalance When standard RCBOs are connected in parallel, each breaker may not share the load evenly because of slight differences in internal resistance and trip characteristics. This can cause one breaker to trip earlier than the other, potentially disconnecting part of the circuit unnecessarily and reducing system reliability . Proper load balancing requires careful design, and in industrial applications, specialized breakers like Eaton's double wide (DW) or double narrow (DN) units are used, which integrate a common trip mechanism to ensure balanced current sharing . 2. Selective Fault Isolation RCBOs are designed to provide both overcurrent and residual current protection for individual circuits. Placing them in parallel can compromise selective protection, making it difficult to isolate only the faulty section. Each RCBO should ideally be installed in its own circuit to allow precise fault detection and minimize disruption to other loads . 3. Coordination and Safety Parallel breakers must be coordinated to trip simultaneously under fault conditions. Without coordination, one breaker may trip prematurely, or both may trip unnecessarily, which can lead to nuisance outages or reduced protection effectiveness . Standard RCBOs are not designed for parallel operation, so using them this way may violate electrical codes and safety standards. 4. Practical AlternativesUse a single higher-rated breaker: If the load exceeds a single RCBO's rating, consider a breaker specifically rated for higher current or a factory-designed parallel-capable breaker .Dedicated circuits: Install multiple RCBOs on separate circuits rather than paralleling them, maintaining selective protection and compliance with safety regulations .Professional design: For large or critical installations, consult a certified electrician or engineer to design a system with proper load sharing, thermal testing, and compliance with local electrical codes .ConclusionWhile paralleling RCBOs might seem like a way to increase capacity, it introduces risks of uneven current sharing, nuisance tripping, and compromised selective protection. The safest approach is to use RCBOs in their intended configuration—one per circuit—or to use breakers specifically designed for parallel operation with a common trip mechanism. Proper design, testing, and adherence to electrical codes are essential to ensure both safety and reliability .