I want to replace a 115°C 250V 2A thermal fuse used in a fan motor. The only fuses available locally are 115°C 277V 15A. Can I use the higher current rated thermal fuse?

Since it is a thermal fuse, I would expect only the temperature to matter...

  • \$\begingroup\$ What is this fuse to be used in? Normally thermal fuses are used in devices that get hot as part of normal operation, such as a hair dryer. If the fan stops it will overheat and open the fuse, which is not resettable. \$\endgroup\$ – Sparky256 Dec 12 '18 at 3:05
  • \$\begingroup\$ @Sparky256 Updated question, fuse found in fan motor. \$\endgroup\$ – Jet Blue Dec 12 '18 at 3:23
  • \$\begingroup\$ The purpose of a thermal fuse is to permanently open upon reaching a certain temperature. Assuming that is the purpose of this particular thermal fuse, then the larger current rating should be OK. But you have not shared full data from both fuses so that we can confirm. Also, a larger thermal fuse may take longer to open due to thermal mass. So there could be some small uncertainties there. It is better than nothing. But may not provide exactly equivalent protection. Also, it is worth asking, why did the original fuse open? Are you sure the motor is not faulty? \$\endgroup\$ – mkeith Dec 12 '18 at 3:45
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    \$\begingroup\$ @mkeith I do not know why the fuse blew in the first place. A visual inspection of the motor shows nothing out of the ordinary... I'm thinking to replace the fuse and see if it blows again sometime soon... if it does can put more work towards narrowing down cause. \$\endgroup\$ – Jet Blue Dec 12 '18 at 4:27
  • \$\begingroup\$ Seems reasonable. If you haven't already, then you can also just bypass the fuse and run the fan under close observation for a while to see if it overheats. If it does, you may want to correct that problem before blowing another thermal fuse. \$\endgroup\$ – mkeith Dec 13 '18 at 5:17

In this case Barry partially has the correct answer, now that the OP has updated the question.

A motor can overload in many ways, but a stuck rotor (for whatever reason) needs to have a fuse that blows fast based on extreme over current. So the current rating of the fuse does matter in this case.

A motor can 'slow cook' due to an overload based on cracked or dry bearings or an over voltage condition. Not enough over current to pop the fuse but over time the motor windings become hot enough to burn the enamel coating and now you risk having a shorted motor. This is where a thermal fuse can sense a dangerous situation and open up based on extreme heat-not current.

Normally a motor is on a circuit being fed by a breaker panel, but tripping a breaker is a last resort, as they can only trip OFF so many times before the contacts wear out.

Be smart and take the time to find the right thermal fuse. Contact the motors manufacture and search fuse manufactures for something much closer to the original fuse.

What made the original fuse open in the first place? Check the motor out real good or it may have a problem that will blow the next fuse right away.

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    \$\begingroup\$ Alternatively, OP could perhaps use the 115C thermal fuse and a 2A standard fuse in series. \$\endgroup\$ – Someone Somewhere Dec 12 '18 at 5:58
  • \$\begingroup\$ Tripping a breaker is to be avoided for other reasons, like shutting down the rest of the circuit and the fact that the breaker's tripping current is likely significantly more than the fan's stall current. Breakers are good for hundreds of trips as long as they're not near the kA rating. \$\endgroup\$ – Someone Somewhere Dec 12 '18 at 5:59
  • \$\begingroup\$ @SomeoneSomewhere Combining is a neat idea! That way I can get the motor running sooner than later. \$\endgroup\$ – Jet Blue Dec 12 '18 at 6:37
  • \$\begingroup\$ Update: the motor has been running daily now for quite some time using the double fuse in series approach suggested. So far so good... \$\endgroup\$ – Jet Blue Jan 16 at 8:56

A 2 ampere fuse cannot safely be replaced by a 15 ampere fuse irregardless of the type of fuse. You don't say the type of equipment using this fuse. What do you think would happen if a fault in the equipment caused it to draw, for example, 10 amperes? The specified 2 ampere fuse would blow rather quickly. The 15 ampere fuse would never blow but your equipment could either be destroyed or worse start a fire. Don't take a chance. Get the correct fuse.

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    \$\begingroup\$ It is a thermal fuse, which reacts to a too hot environment. The current itself should not heat the fuse, so current rating must be higher than max. expected current. A much higher rating is no problem here. \$\endgroup\$ – sweber Dec 12 '18 at 3:15
  • \$\begingroup\$ @Barry, updated question - fuse used in fan motor \$\endgroup\$ – Jet Blue Dec 12 '18 at 3:25

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