NTC388 – FUSE LINK

One-shot thermal fuse link – backup overheat protection in electric furnaces and air handlers. It never resets: once open, the heater circuit stays dead until the link is replaced, and a blown link means something else (restricted airflow, a failed blower) caused the overheat, so find that fault before fitting a new one. No datasheet is published, so amperage and voltage are unconfirmed. Fit only an identical temperature rating.

Specifications from our own stock records. The manufacturer does not publish a public page for this item.

Specs

• TypeThermal fuse link (one-shot thermal cutoff)
• Rated opening temperature388 F per our stock records - verify the marking on the part
• ResetNone - non-resettable, must be replaced once opened
• ContactsNormally closed; opens permanently on overtemperature
• Current / voltage ratingNot published - read the markings on the link
• Typical useElectric furnace or air handler heater element circuit
• Data SourceOTP stock record - not manufacturer-verified

What kind of fuse is on my control board?

On most furnaces and air handlers it is a 3 amp or 5 amp automotive blade fuse protecting the 24 volt side. Match the printed amp rating exactly. That fuse is sized to the transformer, not to how badly you want the equipment to run.

It blew again as soon as I replaced it. What am I looking for?

A short on the low voltage side. Usual suspects are thermostat wire pinched under a panel or stapled through, thermostat wire rubbed bare where it enters the condenser, a bare conductor in the disconnect, a wet or corroded splice at a float switch, and a shorted contactor coil. Shut off the breaker and the disconnect, then disconnect the thermostat wire at the board and at the outdoor unit and add loads back one at a time.

My rollout switch or thermal fuse link opened. Can I just replace it?

Replace it, yes, but not before you learn why it opened. A one-shot link is a record that something got hot enough to need it - a plugged burner or heat exchanger, a blocked flue or vent, a cracked heat exchanger, a dead inducer, or a blower that never came on. Rollout means flame was outside the burner box. Put a new link in without fixing the cause and you will be back for another one.

Can I go up one size or twist in a piece of wire?

No. A fuse is a designed weak point. Oversize it and the next fault cooks the transformer or the traces on the board instead of costing you a dollar.