AC Solid-State Relay Is Off but the Load Glows? Check Leakage
An off-state solid-state relay can pass a small current. A sensitive load may glow or fail to release even though the control input is off. Compare leakage specifications with the load behavior before declaring the relay shorted.
AC SSR example; leakage and failure behavior are product-specific.
What is happening?
Semiconductor output circuits and internal snubbers can contribute off-state leakage. The amount and acceptable load types depend on the model. Off-state indication is not electrical isolation.
Check these five things
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Confirm the SSR output type and exact part number.
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Read leakage and minimum-load specifications.
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Compare the load holding or response characteristics.
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Have qualified personnel use an approved diagnostic method.
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Select a manufacturer-supported load-interface solution if needed.
Worked example
A teaching indicator draws so little current that SSR leakage produces a faint light while the control input is off. A larger lamp behaves differently. The observation can be compatible with the specification, but a failed-short SSR must still be distinguished through the approved test.
Quick diagnostic reference
| Evidence | Question |
|---|---|
| Small residual effect | Specified leakage sufficient? |
| Full load operation | Possible failed output? |
| Control input off | Does not establish isolation |
The mistake to avoid
Do not add an arbitrary resistor or treat the output as safe to touch. Any load adaptation needs voltage, power, protection, and installation review.
How to verify the fix
Confirm both commanded operation and off-state behavior with the intended load. Document the approved interface and isolation method separately.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
OMRON: Solid-state relay technical guide. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.