PC Type ATS vs CB Type ATS: Definition
What Is a PC Type Automatic Transfer Switch?
A PC type ATS is a dedicated transfer switching device. It is designed primarily to connect the load to one source at a time and transfer that load to an alternate source under controller command.
In practical engineering terms, a PC type ATS is switching-focused. It can be designed to make and withstand short-circuit currents, but it is not intended to break short-circuit current as a protective device. That means a separate upstream short-circuit protective device (SCPD), such as a fuse or circuit breaker, is responsible for interrupting faults.
The design consequence is straightforward: if you select a PC type ATS, you must also define the upstream protection that keeps the ATS and load-side conductors within withstand limits during downstream faults.
What Is a CB Type Automatic Transfer Switch?
A CB type ATS is a circuit breaker based transfer assembly. It is typically built around two interlocked circuit breakers (often molded-case or air circuit breakers depending on current and application). The controller transfers the load by opening one breaker and closing the other.
In practical terms, CB type ATS is switching plus protection. Because the transfer elements are circuit breakers, the assembly can provide overload and short-circuit interruption at the transfer point, within the breaker interrupting rating and trip unit configuration.
The design consequence is also clear: if you select a CB type ATS, you are making the ATS part of your overcurrent protection hierarchy, and settings control becomes part of system reliability.
Working Principle
Both ATS types share the same control loop: monitor source acceptability, apply time delays to avoid nuisance behavior, enforce interlocking, and execute an open-transition transfer unless the system is explicitly designed for closed transition.
The difference is not the concept of transfer. The difference is what the switching element is designed to do during faults, and what the system expects to clear abnormal current.
PC Type ATS Working Principle
A PC type ATS controller monitors each source (commonly voltage and frequency, plus phase checks on three-phase designs when provided). If the preferred source is outside limits for longer than the dropout delay, the controller commands a transfer.
The switching mechanism disconnects the load from the preferred source and then connects it to the alternate source using a break-before-make sequence. Mechanical and electrical interlocks prevent both sources from being connected simultaneously.
During downstream faults, the PC type ATS is not the primary interrupter. The system expects an upstream SCPD to clear fault current. For OEM documentation, that upstream responsibility is not optional: it should be explicit in schematics and service notes so installers and maintenance teams do not assume the ATS provides protection.
CB Type ATS Working Principle
A CB type ATS controller also monitors source acceptability and uses delays and permissives to prevent nuisance transfers. The transfer sequence is executed by operating two interlocked breakers.
In a typical sequence, the active breaker opens, the controller confirms position feedback, and then the alternate breaker closes. Interlocks prevent simultaneous closure.
Because the switching elements are breakers, overload and short-circuit interruption is available at the transfer point. This can simplify certain architectures, but it also means that breaker settings, selectivity, and trip verification are part of correct ATS operation, not separate concerns.
Switching Mechanism
Switching mechanism determines endurance, typical transfer timing, and maintenance focus. In selection reviews, mechanism is where you connect abstract requirements to physical reality: what fits in the enclosure, what can be serviced, and what will still operate reliably after repeated tests.
PC ATS Switching Mechanism
PC type ATS products commonly use contactor-based or changeover-switch mechanisms optimized for transfer duty. Because the device is switching-focused, the mechanism can prioritize fast actuation and high mechanical endurance.
Practically, you should expect:
A dedicated transfer actuator that moves quickly.
Interlocking that is built into the mechanism so source overlap is prevented.
Contacts designed for repeated transfer operations.
From an OEM perspective, PC ATS mechanisms often fit well in applications that see routine transfer tests or more frequent operations, as long as the protection plan is handled by upstream devices. The key requirement is not the mechanism itself, but the system agreement: the upstream protective device must clear faults, and the ATS must be rated and coordinated accordingly.
CB ATS Switching Mechanism
CB type ATS products use circuit breaker mechanisms, typically with motor operators or stored-energy operating systems. The mechanism must carry current, switch under load, and interrupt under fault conditions when required.
Practically, you should expect:
Mechanical and electrical interlocking between two breaker poles.
Transfer sequences that depend on breaker opening and closing time plus position confirmation.
A stronger dependency on maintenance discipline for mechanism and trip system verification.
For OEM use, CB ATS mechanisms are often chosen when the transfer point must also behave like a local protective device. The tradeoff is size and complexity, plus the need to keep settings consistent with the original design intent.
Protection Capability
Protection capability is the criterion most closely tied to risk. It answers three questions that matter in every design review: what clears faults, how fast, and where that responsibility is documented.
PC ATS Protection Features
A PC type ATS typically does not provide overcurrent protective functions. It may provide monitoring such as undervoltage, frequency, and phase checks, but those are source qualification features, not fault interruption.
For PC ATS systems, the protection map should be explicit:
Protection function | Typical device responsible in a PC ATS system | Practical selection note |
|---|---|---|
Overload protection | Breaker(s) sized to conductors and load profile | Document ampacity basis and settings |
Short-circuit interruption | Upstream SCPD (breaker or fuse) | Confirm interrupting rating vs available fault current |
Coordination/selectivity | Achieved through protective device selection and settings | Record intent and verification approach |
Source qualification | ATS controller sensing | Configure thresholds and time delays to avoid nuisance transfers |
The advantage is a clean separation of roles. The risk is assuming the ATS covers protection when it does not.
CB ATS Protection Features
A CB type ATS integrates overload and short-circuit interruption through its breaker elements. This can deliver local fault isolation at the transfer point and can reduce dependence on upstream devices for fault interruption of the load-side circuit.
That does not remove the need to coordinate the system. You still need to ensure:
Breaker interrupting ratings match available fault current.
Trip settings protect conductors and align with selectivity requirements.
Settings are controlled and documented so field changes do not undermine coordination.
For OEMs, the biggest practical benefit is localized protection behavior. The biggest practical risk is treating integrated protection as automatic coordination.
Transfer Speed
Transfer speed should be treated as an end-to-end system behavior: sensing delay, dropout delay, source acceptance delay, and mechanical open interval. The relevant requirement is what the load can tolerate.
PC ATS Transfer Speed
PC type ATS designs are commonly faster in mechanical transfer because the mechanism is optimized for switching. Many designs achieve transfer intervals that are short enough for loads with reasonable ride-through to stay energized, especially when control power supplies have capacitance or are UPS-backed.
In practice, PC ATS speed is most valuable when:
The transferred load is control power, PLC power, or similar electronics that reset on short interruptions.
The design minimizes nuisance transfers so contact wear is not accelerated.
The protection architecture already exists upstream.
Do not select based only on a single catalog timing figure. Validate transfer behavior with your intended controller delays and your real load profile.
CB ATS Transfer Speed
CB type ATS designs are often slower in mechanical operation because breaker actuation involves more complex motion and because position confirmation is typically part of the safe sequence.
For many feeder and mixed-load applications, this is acceptable. For sensitive control loads, it can be a risk if you do not add ride-through design (for example, a control UPS) or if you do not validate interruption tolerance.
In a consideration-stage decision, the key is not whether CB is slower, but whether the slower transfer is still inside the load tolerance envelope.
Size and Installation Requirements
Size is not only the device outline. It is bend radius, heat rise, service clearance, and the additional equipment required to complete the protection plan.
PC ATS Size and Installation
PC type ATS units are often compact for a given current rating. That can make them attractive for panel-level transfer functions.
However, PC ATS selection implies additional protective devices exist elsewhere. Installation should be evaluated as a package:
Integration topic | Typical PC ATS impact | Practical installation note |
|---|---|---|
Space | Smaller transfer device | Confirm upstream protection space and wiring clearance |
Wiring | Clean transfer wiring path | Dress conductors to protect terminations from vibration and strain |
Heat | Depends on enclosure and current | Verify temperature rise in the actual enclosure layout |
Commissioning | Transfer logic plus protection verification | Confirm thresholds, delays, and upstream protection intent |
For OEMs, the most common mistake is placing a compact PC ATS into a layout without leaving room for protection, service access, and thermal margin.
CB ATS Size and Installation
CB type ATS units typically occupy more volume because they include two breakers, interlocks, and operating hardware. In some architectures, that can be offset by reducing separate protective component count.
Installation evaluation should include:
Termination space for two breaker line sides plus load side.
Access to interlock assemblies.
Space and procedure for breaker inspection and trip verification.
For enclosure design, treat CB ATS selection as a mechanical constraint early in CAD, not a late-stage BOM substitution.
Cost Comparison
Cost should be modeled as system cost: device cost, protection devices, wiring labor, commissioning, and maintenance.
PC ATS Cost Advantage
PC type ATS devices are often lower in unit cost because they are switching-focused. If your design already includes upstream protection and coordination effort, the incremental cost of adding a PC ATS can be favorable.
PC ATS can also reduce indirect costs when fast transfer prevents nuisance downtime events in sensitive control loads. For OEMs, that value is often more important than the component delta.
The caveat is simple: if the PC choice forces you to add protection devices that you would not otherwise need, the system cost advantage can shrink or disappear.
CB ATS Cost Considerations
CB type ATS devices often cost more due to dual breakers and mechanisms. The value proposition is integrated protection and fault isolation at the transfer point.
System-level cost considerations include:
Reduced need for certain external protective devices, depending on architecture.
Increased need for settings control, documentation, and periodic verification.
Potential nuisance trip risk if the load profile is not matched to breaker settings.
For consideration-stage decisions, compare BOM and labor with the same level of seriousness you apply to any protective device choice.
Maintenance and Service Life
Maintenance planning should assume the ATS will be tested. Many failures occur because transfer equipment is left unexercised until an outage.
PC ATS Maintenance Requirements
PC type ATS maintenance focuses on switching wear and mechanical integrity:
Inspect for heating and contact wear indicators.
Verify interlock operation and correct travel.
Check and retorque terminations per maintenance procedure.
Functionally test transfer and retransfer sequences.
Because a PC type ATS is not intended to clear faults as a protective device, its wear is mainly driven by switching operations and thermal conditions. In frequent-test environments, this can be a practical advantage.
CB ATS Maintenance Requirements
CB type ATS maintenance includes breaker maintenance plus transfer verification:
Exercise operating mechanisms and verify smooth operation.
Verify trip unit behavior and settings match documentation.
Inspect interlocks and position feedback.
Test transfer and retransfer sequences.
Service life is influenced by switching duty and any fault interruption events the breakers see. For OEMs, the key is to provide a clear maintenance and settings-control recommendation so field teams do not unintentionally drift from the original coordination intent.
PC Type ATS vs CB Type ATS: Application Comparison
Application fit is where you convert the criteria into a simple answer: which one you should use in this design, and why.
PC ATS Applications
PC type ATS is commonly selected when the design priority is fast, repeatable transfer and high switching endurance, and when the protection responsibility is clearly assigned to other devices.
Typical fits include:
Control power and auxiliary loads inside an industrial cabinet.
Circuits where load ride-through is limited and interruption must be minimized.
Systems with routine test transfers where switching endurance is a practical reliability requirement.
In these applications, the must-have is a documented protection plan: identify the upstream breaker or fuse that clears faults and confirm ratings and coordination intent.
CB ATS Applications
CB type ATS is commonly selected when integrated overload and short-circuit interruption at the transfer point is desired or required.
Typical fits include:
Feeder-level transfers feeding mixed loads.
Distribution points where local fault isolation simplifies service.
Architectures where the ATS is expected to behave like a protective device, not only a transfer device.
In these applications, the must-have is settings control: ensure trip settings are documented, verified in commissioning, and protected against undocumented changes.
PC vs CB Automatic Transfer Switch Comparison Table
Selection criterion | PC type ATS | CB type ATS |
|---|---|---|
Core role | Transfer switching | Transfer switching plus protective breaker function |
Fault interruption | Upstream SCPD/OCPD clears faults | Breakers can interrupt overload and short circuits |
Typical best-fit | Panel-level or protected assemblies | Feeders and distribution with local protection needs |
Transfer behavior | Often shorter mechanical open interval | Often longer mechanical open interval |
Endurance | Often strong for frequent transfer duty | Dependent on breaker frame and maintenance |
Space | Often compact device | Typically larger due to dual breakers/interlock |
Engineering focus | Protection coordination outside the ATS | Breaker coordination and settings control at the ATS |
Common selection error | Treating ATS as overcurrent protection | Treating integrated protection as automatic coordination |
How to Select the Right ATS Between PC and CB Types
Use PC type ATS when your system already assigns fault clearing to upstream protective devices and your transferred loads benefit from fast, repeatable switching and high endurance. In this design, the most important documentation is the protection responsibility map: what clears faults, with what rating, and how coordination intent is preserved.
Use CB type ATS when you need the transfer point to also provide overload and short-circuit interruption, or when local isolation at the ATS is a functional requirement. In this design, the most important control is settings governance: trip settings, verification, and maintenance must be treated as part of ATS reliability.
If you need a simple design-review test: if your one-line diagram expects the ATS to behave like a protective device, CB is usually the cleaner architectural fit. If your one-line diagram already assigns protection elsewhere and you are optimizing transfer performance and endurance, PC is usually the cleaner fit.
Why Choose LSP Automatic Transfer Switches for Reliable Power Switching Solutions?
LSP automatic transfer switches are designed with high-quality components, precise manufacturing processes, and strict quality control standards to ensure stable switching performance under various operating conditions. Our ATS solutions support single-phase and three-phase applications, covering residential backup power, commercial buildings, industrial facilities, solar energy systems, and generator backup applications. With carefully optimized switching mechanisms, reliable interlocking structures, and advanced control technology, LSP ATS products provide fast and secure power transfer between normal and standby power sources.
Beyond standard ATS solutions, LSP provides flexible OEM and ODM customization services to meet different project requirements, including product specifications, current ratings, enclosure designs, branding, and packaging solutions. Supported by our 1600㎡ manufacturing facility, automated production lines, and professional engineering team, we are capable of delivering consistent product quality and customized solutions for global electrical brands, distributors, and system integrators.
FAQs
Is a PC type ATS the same as a contactor ATS?
A PC type ATS is often implemented with contactor-based or changeover-switch technology, so the terms overlap in catalogs. The engineering distinction is that PC type transfer equipment is switching-focused and is not intended to interrupt short-circuit current as a protective device.
Does a CB type ATS always eliminate the need for upstream protection?
A CB type ATS integrates overload and short-circuit interruption at the transfer point, but upstream protection and coordination still matter. Upstream devices may be needed for feeder protection, selectivity, or system short-circuit rating strategy. Upstream protection can also limit let-through energy and reduce stress on downstream conductors and equipment.
Which ATS type is better for control power inside an OEM panel?
For control power, the main risk is a brief interruption causing PLC resets, drive faults, or communications dropouts. PC type ATS designs often have shorter mechanical transfer intervals and strong switching endurance, which can help when protection is already defined elsewhere. CB type ATS can work, but you must evaluate transfer timing, breaker settings, and nuisance trip risk.
When does a CB type ATS make more sense for compliance and documentation?
CB type ATS can fit better when specifications expect overcurrent protection at the transfer point, require local fault isolation, or demand a protective disconnecting means at the ATS location. It can also simplify narratives where load-side conductor protection is assigned to the ATS breakers. However, compliance still depends on correct ratings, markings, and coordination.
Which ATS type tends to have longer service life in frequent-transfer applications?
In frequent-transfer applications, service life is driven by switching endurance, temperature rise, and maintenance discipline. PC type ATS designs often use dedicated switching mechanisms that tolerate repeated operations well, provided faults are cleared by upstream protection.
