Quick answer
Size the ATS from the electrical design and the manufacturer’s model data—not from a single headline rating. Confirm continuous load current, system voltage, phase arrangement, required poles, source type, utilization category and site conditions before the final selection.
An automatic transfer switch sits between two power sources and the protected load. A good selection process therefore has to look at the load, both sources, the switching arrangement and the installation environment together.
01 Define the design load
Begin with the project’s calculated load and applicable design rules. Identify which circuits are essential, whether large motors or inrush loads are present, and what future capacity the project requires.
02 Confirm voltage, frequency and phases
The ATS must match the system it will switch. Send the supplier the line voltage, frequency, single- or three-phase arrangement, and control-power requirement.
| Project item | What to confirm | Why it matters |
|---|---|---|
| Voltage | Line and phase voltage | Device and control compatibility |
| Frequency | 50 Hz or 60 Hz | Control and application review |
| Phases | Single or three phase | Pole arrangement and wiring |
| Sources | Mains, generator, solar or storage | Transfer logic and coordination |
03 Decide whether the neutral must switch
The correct pole count depends on the electrical design and earthing arrangement. Do not assume that every three-phase project needs the same pole configuration; ask the project engineer to confirm whether the neutral is solid or switched.
Buyer tip: Include a single-line diagram with your inquiry. It helps the supplier review the proposed source and neutral arrangement.
04 Review the transfer and installation requirements
Clarify automatic or manual operation, expected transfer sequence, generator start signal, panel space, mounting method, ambient conditions and any interlocking or communication needs. The final choice should then be checked against the current manufacturer’s datasheet.
05 Send a complete inquiry checklist
- Calculated or design load current
- System voltage, frequency and phases
- Required pole arrangement
- Normal and standby source types
- Panel dimensions and mounting constraints
- Single-line diagram when available
- Destination market and required documents
- Branding, packaging and order quantity
Want LSP to review your starting configuration?
Send the checklist above with your project files. We will use it to recommend the next model and document set to review.
Send project detailsFrequently asked questions
Should I select an ATS only by amp rating?+
No. Current is one input. Voltage, phases, poles, application, transfer sequence, installation and model-specific ratings also need review.
What if the project includes motors?+
Provide the motor and starting information to the project engineer and ATS supplier so switching and protective-device coordination can be evaluated.
Can LSP recommend a model from a single-line diagram?+
A single-line diagram is very useful, but it should be accompanied by the load, source, voltage, frequency, pole and installation details.
Engineering note: This guide is general purchasing and selection information. Final equipment selection and system design should be completed by qualified professionals using current project requirements, applicable standards and model-specific manufacturer documentation.