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I have 240v circuit with 12awg wire that will service a 3/4hp motor (about 5amps max at 240v). That circuit is protected by a standard 20amp breaker.

I was wondering if it is a good idea/warranted to put in a 10amp time-delay fuse at the motor as extra protection?

Like this for example. 600V Slow Blow Class CC Time Delay Fuse

Problem with this style fuse I can't find a single fuse holder/block and the three place ones are 6 times the price of a fuse on ebay.

Can one use a more standard glass/ceramic type fuse for this application? like this Bussmann MDA 10A 250v Slow Blow Time Delay Ceramic Fuse because holders for this are common and cheap.

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  • Does the motor have thermal overload protection built in? Can you post a photo of the nameplate? – ThreePhaseEel Apr 3 '19 at 11:39
  • Don't have the pump yet. But manual says "For safety, the pump motor has resetting thermal protector that automatically will turn off the pump if it becomes too hot." so I guess that is a yes. – DKebler Apr 3 '19 at 14:37
  • Most motors have a resetting thermostat. Pumps are water cooled. If they run in a dry well, they burn out if not thermally protected. – Sherwood Botsford Apr 3 '19 at 21:42
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There is no real need to put a 10A fuse on it in addition to the breaker. The 20A breaker will be enough protection regarding overload and short circuits.

The only recommendation I would give is to put it on a GFCI because it's for a pump in a presumably wet location.

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Regular breakers are already time-delay/dual-element, so you don't need an extra device for this. You could just downbreaker at the panel. Change the 20A breaker for a 15, or if you're willing to hunt down a 10A, do that.

Each series point in a circuit has exactly the same current, so it doesn't matter where the breaker/fuse is located.

Besides, fuseholders may be readily available as components, but that doesn't mean it's easy to mount them in a safe, Code-legal and serviceable manner.

Speaking of components.... You must stop buying electrical components on eBay, AliExpress/AliBaba, or Amazon Marketplace. (For the difference see this post). This stuff is almost all cheap Cheese junk that has never, and will never, see the inside of a reputable testing lab like Underwriter's Laboratories (UL).

For mains wiring this type of imported junk is prohibited by NEC 110.2, which requires items be approved (by your local authority, but they defer to UL and comparable labs such as CSA or TUV). CE is not a testing lab.

Sellers on Amazon Marketplace lie constantly about "By (manufacturer)", but in all fairness, this one looks legit. Here, it appears the US factory is using Amazon's warehouse as a drop-shipper so they don't need to staff their own shipping department. When you do this -- a few more clicks and you're on Amazon Marketplace, and Prime members get free 2-day shipping.

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  • Actually, the first link looks like manufacturer ship via Amazon warehouse. The second one appears to be generic stuff of possibly dubious quality. – manassehkatz-Moving 2 Codidact Apr 3 '19 at 17:56
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    @manassehkatz Good catch, I clarified.. – Harper - Reinstate Monica Apr 3 '19 at 18:13
  • Actually, it looked to me like the other way around. Unless I'm really confused... – manassehkatz-Moving 2 Codidact Apr 3 '19 at 18:19
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    @manassehkatz oh I see what you mean. "Sold from and ships by X" is safer if they ship from the United States [or other country with good safety and import standards]. However many are ePacket delivery from China, usually Shenzhen where the US Postal Service has a facility with very low shipping rates. – Harper - Reinstate Monica Apr 3 '19 at 18:28
  • Bottom line is caveat emptor. – manassehkatz-Moving 2 Codidact Apr 3 '19 at 18:33
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In passing: If you haven't bought the pump yet, give thought to the 3 phase variable frequency drive pumps. They are more expensive, but they use frequency control to keep the pressure nearly constant if you are drawing more than 1 gpm. This reduces pump cycling, and keeps the water level in the well more constant. Net result: fewer future problems. Here, the main supplier of these is Gould.

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Thermal protection matters

Since your pump motor, according to its documentation (assuming it is accurate) has integral thermal overload protection, then you don't need to provide anything besides the branch-circuit short-circuit (and possibly ground-fault) protection at the panel. This means that your existing 20A breaker is fine provided the wiring is sized appropriately: there is no need for a fuse or a downsized breaker to protect the motor from overload.

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