1. Auxiliary Contact Configuration: The model description indicates that the APV500-EA explicitly has "NO AUX CONTACT," while the APV500-E documentation does not mention this feature. The APV500-E may integrate a set of independent low‑current contacts for status feedback. What this means: Auxiliary contacts are used to feed back the open/closed state of the main contacts to the control circuit, enabling interlocking, status indication, or PLC signal acquisition. If the original design relies on the "no auxiliary contact" characteristic of the APV500-EA (i.e., it does not require or intentionally avoids such a signal), replacing it with an APV500-E that includes auxiliary contacts could introduce wiring redundancy or require handling of additional terminals. Conversely, if the original design mistakenly used the APV500-EA but actually requires status feedback, the replacement could resolve a functional gap. The highest risk scenario occurs when the existing control logic depends on the absence of this signal; an unintended contact signal introduced after replacement could cause system misinterpretation. 2. Coil Drive Interface Form (Unconfirmed): There is a discrepancy between the "PCB MOUNT" description for the APV500-E and the "Chassis Mount" and "Stud" entries in its parameter table. It is reasonable to speculate that this description may refer to a coil termination suitable for PCB soldering, rather than traditional wire leads or terminal blocks. What this means: If this speculation is correct, the coil of the APV500-E would need to be soldered directly onto the main control PCB, whereas the APV500-EA likely uses wire connections. This affects the entire drive‑circuit layout and mechanical design. Substitution would require redesigning the electrical and physical connections for the coil drive section; a direct interchange is not possible. Recommendation: Before proceeding with the substitution, obtain official drawings or detailed specifications for the APV500-E from the manufacturer or supplier to confirm its exact terminal definitions (including whether an auxiliary contact is present) and the precise physical form of its coil terminals.