Claire
Mr.Fu
Claire
2P, 3P, or 4P? The Ultimate Guide to Pole Selection for Transfer Switches
Core Definition: What is a “Pole”？
In electrical switches, a “Pole” (P) refers to the number of independent circuit paths the switch can control or interrupt. One “pole” corresponds to one independent current-carrying path. For a Transfer Switch, its number of poles determines how many lines it switches simultaneously.
2P, 3P, 4P: Differences and Applications
2-Pole (2P) Switch: Switches one Line (L) and the Neutral (N). Primary Application: Single-phase power systems (e.g., 220V AC). It provides complete isolation of the load circuit.
3-Pole (3P) Switch: Switches three Phase lines (L1, L2, L3). Primary Application: Three-phase, three-wire systems (no neutral load, e.g., pure motor loads), or systems where the neutral is reliably grounded and codes permit a common, uninterrupted neutral.
4-Pole (4P) Switch: Switches all three Phase lines (L1, L2, L3) and the Neutral (N). Primary Application: Three-phase, four-wire systems (with 220V single-phase loads). Its core safety value: When the neutral points of two power sources may be at different potentials or could introduce stray currents, the 4P switch prevents neutral current circulation by disconnecting the neutral, mitigating shock hazards and equipment interference.
How to Choose Poles Based on Your System？
The selection follows one core principle: All possibly live conductors must be switched to ensure electrical isolation and safety.system safety.
1.Single-Phase System (1L + N): Mandatory use of 2P.
Three-Phase System:
● If ALL loads are three-phase (e.g., 380V motors) and the neutral is confirmed to be current-free and permanently, reliably grounded, 3P may be considered (subject to local codes).
● If the system includes ANY single-phase loads (220V lighting, outlets), or if the two sources are from separate transformers, the backup is a generator, or codes require complete isolation, 4P is MANDATORY.
Rule of Thumb: When in doubt or for high-safety applications, choosing 4P is generally the safer and more compliant option.
Practical Guide: How to Choose Our SJKQ-Series Products？
Our ATS Automatic Transfer Switch product series covers all scenarios with clear selection logic:
SJKQ1 Series (2P, 3P, 4P available): Suitable for general-purpose loads with low to medium current ratings. Choose 2P for single-phase; for three-phase, prioritize 4P for safety and compliance unless specific conditions for 3P are met.
SJKQ2 / SJKQ2Z / SJKQ5 Series (3P & 4P available): Designed for higher performance and demanding applications (e.g., inductive loads, high short-circuit currents, or requiring bypass isolation).
Core Selection Steps: First, determine if 3P or 4P is required based on your system (see previous section). Then, select the specific model/specification within that pole-count category based on electrical parameters like load current and breaking capacity.
About Us:
Mingri Electric Co., Ltd. is a leading provider of high-quality electrical components and solutions, specializing in switchgear,circuit breakers,switches, etc. We are dedicated to delivering innovative products that meet the evolving needs of the global power industry.