Heat pump cartridge fuse box is humming

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Old 12-31-13, 04:34 PM
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Heat pump cartridge fuse box is humming

Just noticed this for the first time, today.

On the outside garage wall is a disconnect switch with two 40A slo-blow fuses. There is a slight, high pitched hum in this switch box. Heat Pump was OFF.

Anything to worry about?

Thank you
 
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Old 12-31-13, 06:07 PM
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It would be extremely rare for any sound to come from the two fuses..... it would be even rarer if the heatpump wasn't even running.

Is there any name on the disconnect ?
There may be some kind of load shedding device in your disconnect based on your power company.
 
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Old 12-31-13, 07:09 PM
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I went back and checked. I had it wrong. The two 40A fuses are for the POOL motor and filter. The heat pump box is close by and I confused the two.

Anyway, I went back and the noise was still there. I pulled the disconnect and placed it back in. The noise stopped. The pool motor was not running on either occasions.

As an aside, the fuse (or fuses) in the box conked out about 8 days ago. I replaced both.

The box is a Midwest Electric Products, Mankato MN #U065F1, circa 1993.

Thank you PJ for your input and I will check tomorrow and see what's what.
 
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Old 12-31-13, 09:49 PM
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The U065F1 is just a standard two pole 60A fused disconnect.

So is this disconnect that is making the noise the one that runs the pool ?
It shouldn't be making any type of noise especially with no load connected.

I am concerned when you say the two fuses conked out. If your pool isn't running then those fuses shouldn't be doing any work. To expand further..... 40 amps to a pool pump is exceptionally high. There must be something else on that circuit.
 
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Old 01-01-14, 10:12 AM
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Hi again PJ.....and anyone else reading this thread. Happy New Year !

Yes, the pool disconnect makes the noise. It is not a steady hum, it modulates a bit, louder to softer to louder, etc.

When pool motor stopped running last week I checked both fuses with my digital multi-meter. Only one showed a jump in the continuity numbers. I am not the best at checking this......so I replaced both fuses.

(The pool motor was running 24x7 last week because of 20 degree weather and ice forming on the pool surface. It was running when the fuse conked out).

I checked the main panel INSIDE the garage and there are two 40A breakers pinned together into one. Nothing else on the circuit.

I will probably call a licensed electrician that we know well and have him take a look after New Years.

Any comments are much appreciated.
 
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Old 01-01-14, 11:30 AM
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What else is on that circuit ??

A single pool pump doesn't draw anywhere near 40A at 240V.
Technically, since you have a two pole 40A breaker at the main panel.... you only need an unfused disconnect there. You don't need to fuse the circuit twice.

It might be possible to hear a hum from the fused disconnect if the slide contacts aren't tight and clean. Inspect the fuse holders and the contacts in the disconnect box for discoloring.
 
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Old 01-05-14, 06:07 AM
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Well, I was wrong again.......There is a sub-panel outside for the pool equipment with the disconnect wired in a few feet away. This sub-panel feeds the pool equipment, pool light AND the RV shed 30A service AND a sub-panel in the backyard that feeds the fountain pump and four 110v outlets in the backyard.

I did pull the disconnect again and fuses and contacts appeared clean and not discolored. Thanks for your help. I will call our electrician one of these days.
 
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Old 01-10-14, 08:24 AM
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No buzz for 4 days. I did some checking and pushed GFI resets on all the outlets.....and that is when the buzz stopped.
 
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