Parallax ATS301 & ATS503 RV Transfer Switch Wiring Guide

Parallax ATS301 and ATS503 automatic transfer switches both choose between RV shore power and a suitable generator, but they serve different AC systems. The ATS301 is a 30A, 120V switch; the ATS503 handles 50A, 120/240V service. Compare the factory connection groups and exact model photos below.

How the transfer switch supplies the RV

One transfer switch accepts two separate AC sources and selects one to feed the downstream AC distribution. It prevents the connected sources from backfeeding each other; it does not combine their available power.

Shore or utility AC

Shore power inletAC input from the RV shore cord
ATS utility inputSeparate shore/utility connection group
AC load outputSupplies the RV breaker panel when selected

Generator or alternate AC

Onboard generatorSource and voltage compatible with the exact ATS
ATS generator inputSeparate GEN connection; delayed switch-over
AC load outputSame downstream distribution, not a second simultaneous feed
Parallax ATS models normally select shore power until a generator or other approved alternate source takes command. They have different 30A and 50A internal wiring layouts. Functional flow only, not a physical wiring or terminal position diagram; use the unit's factory wiring label for conductor placement and grounding.

Which Parallax ATS model fits your AC system?

Model Current AC service Switching design Connection identification
ATS301 30A 120 VAC, single leg DPDT relay; generator command Shore / GEN / LOAD groups and protective ground
ATS503 50A 120/240 VAC, two legs Heavy-duty relays; generator command UTILITY / GEN / LOAD L1, L2, neutral and auxiliary terminals

ATS301 and ATS503 connection identification

ATS301: The manufacturer labels the three main circuits A (LOAD), B (GENERATOR input) and C (SHORELINE input), plus D for the equipment ground. Its 30A supply is 120V; it does not handle two independent 50A hot legs.

ATS503: The factory drawing distinguishes UTILITY, GEN and LOAD groups with L1, L2, NEUTRAL and auxiliary terminals. Its NJ1–NJ3 neutral jumpers and timer jumper are specific to different operating configurations, so installation must follow the actual wiring label rather than a generalized diagram.

Generator power is normally the command source. A stabilization delay is provided before transfer, while the default position supplies loads from shore/utility power.

Check the original equipment: Match the exact case label, AC voltage, hot-leg count, generator type, terminal arrangement and mounting requirements. These switches are not universal drop-in replacements across manufacturers or between 30A and 50A RV electrical systems.

View the matching transfer-switch listings

These are the two exact model-number listings on NewRVParts, with their respective catalog photographs. Select the required AC service and wiring style rather than the housing appearance.

Original manufacturer connection drawings

Parallax's factory drawings show the source terminals, load circuits and specific ATS503 jumper configurations. Use the drawing attached to the actual unit for conductor order and torque requirements.

Parallax ATS301 official model page · Parallax ATS503 official model page · Parallax ATS301 owner and terminal drawing (PDF) · Parallax ATS503 owner drawing (PDF)

Electrical safety: Disconnect shore, generator and inverter AC supplies before service. These switches are not ignition protected and must not be mounted with combustible materials or in battery/generator compartments. AC wiring and testing require a qualified RV electrician following the exact manufacturer instructions.

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