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Appropriate fusing?

R

RayP(MI)

Well-known Member
Was checking fusing on my water pump the other day, after a fuse blew - probably due to fatigue. Blowing fuses has not been a problem with this installation, but want to just clean up my act. Pump is 3/4 hp, 220 volts, submersable, so reading nameplate isn"t an option.

Is fused at the pole on it"s own switch box, underground wiring over to pump,and also in well house where is secondarily switched.

What fuse rating is appropriate for 3/4 hp 220v - fuses on both legs of line?
 
The fuses I believe you are speaking about should be sized to protect the underground wiring. If it's 12 gauge then it should be 20 amp fuse, 14ga. wire 15A, fuse, 10 ga. 30A.
Also fuses do not do well with motor starting current, a circuit brkr. would be a better choice
 
There is sometimes confusion regarding motor protection.
There is short circuit protection which is just protection against a near or dead short. Fuses are breakers are sized well above actual wire current capacity. IIRC as I"m on the road away from my code book. Something like 300% for ordinary fuses and 175% for breakers and slow blow D fuses.
There is thermal protection to protect electric motors from overloads. Usually a 115% heater on the motor starter. or built into a small motor"s junction box.
30amp fast blow P fuse or 20amp slow blow D fuse.
Has anything happened to drop voltage to the pump while starting? Has the pressure switch contacts started arcing?
2 wire or 3 wire pump?
 
For the most protection, you're better to install a circuit breaker. Not that much money, and it provides both magnetic (inrush overload) and thermal (slow overload) protection.
For 3/4 Hp, 230-volt, the NEC Code says your full-load-current is 6.9 amps, and you ought to install NO LARGER than a 15-amp circuit breaker.
Minimum copper wire size for this size motor = 14-gage, but you ought to have as large a wire size as you can. 12 or 10 is great.
 
Thanks guys. The 6.9 amp rating on the motor was the figure I"m needing. Starting current will be approximatly double that. Installation has not been a problem. #12 undergound wire from meter to well, fused at meter, and also at well. Just that fuses were getting old, from exposure in outside enclosure. Then, I don"t think fuse issue was even addressed when we changed over to new pump and well a few years back. So, it had been running with 15 amp fuses at the pump for all that time. As far as fuses and breakers, fuses will do just fine, just a little inconvenient whan they blow after store closes!
I keep a stock around for just such emergencies!
Would cost me a bunch to change out both boxes to use breakers. In short, (no puns intended,) the system ain"t broke.
 
I'm surprised no one asked if you are using "dual element" fuses (Fusestat/Fustron) in this motor starting application.
Fusetron
 
The breaker does not provide thermal protection.
How is a 6.9amp motor protected when the breaker will allow it to operate at 200% OVER LOAD continouisly until the motor burns out?
A breaker will not isolate the cicuit as fast as a fuse either. Breakers will on occassion weld the contacts shut and prodice no protection.
Breakers with age, exposured to agressive enviroments or if used as a switch. The breakers ame plate rating is no long valid. It may vary from 2 to 100amps after a while.
 
I keep a jar full of Fustrons on hand for my planer motor.The 5hp motor will blow fuses on a hot day.nothing wrong with the motor.When a fuse blows I stop running the planer.When I did appliance service I found that washing machines needed a time delay fuse.Fuses can get hot in operation.Ive seen 30 amp fuses on a coffee maker get too hot to touch.Cartridge fuses seem to stand up better under heavy loads
 
OT- This is probably not the correct way to get a message to Buickanddeere, but this is on one of your last posting and I thought I'd try.. I've been chasing leads for over a year to find a cam to fix my Granddad's Standard Monarch walking tractor. I recently saw a posting from someone who I think said he had several parts machines. That someone is Jdemaris. I've read all about Jdemaris and hope he will return.
I know this is a long shot, but is there any way to contact him to see if he may have the cam I'm searching for?? Thanks Bert
[email protected]
 
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