The short answer
A standard MOV is not a drop-in equivalent for a thermally protected MOV (TMOV). A TMOV combines a varistor with a thermal disconnect and, on many part numbers, a status indicator pin. A standard MOV provides the clamping element only. Before substituting, an engineer needs to re-check the protection design as a system — not just match disc size and surge rating.
The substitution checklist
- Electrical match first: maximum continuous operating voltage (MCOV, AC and DC), varistor voltage, clamping voltage at the specified test current, energy rating, and peak surge current (8/20 µs) — in that order. The same disc diameter does not mean the same ratings.
- The thermal protection gap: identify how the original design disconnects a degrading MOV. If the TMOV's internal thermal element was the only disconnect, the replacement design needs a disconnector at the module or equipment level.
- Indicator and monitoring pins: if the original part provided a status pin, a standard MOV cannot reproduce that signal — the monitoring circuit must be redesigned, or the feature dropped deliberately.
- Footprint and leads: disc diameter, thickness, lead spacing, lead form and coating can differ between series even at the same nominal size.
- Certification status: confirm the replacement component's own recognition. Flyboat MOVs are UL 1449 Recognized, File E335803 — verifiable in UL Product iQ under that file number. A component change inside a listed end product may also require the end-product file holder to update its own certification file; check with your certifier before committing.
- Samples and testing: evaluate samples in the actual end-product thermal environment before approving the substitution.
How Flyboat can help
Our engineering team can line a standard MOV up against the ratings of the part you are replacing, and discuss disconnector-based module designs where thermal disconnect is handled at the module level. Flyboat MOVs themselves carry no built-in thermal protection, and we say so plainly. Full range: www.flyboatmov.com
Working on a substitution? Contact our North American team — Thomas Dong, [email protected], +1 267-809-2765.
