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Compactors & Balers · Electrical · E-3

The Motor Hums But Won't Turn

A motor that hums loudly and trips the overload within seconds has almost certainly lost one of its three legs — a blown fuse, an open breaker pole, or a burned starter contact. It can also be a seized pump or a locked rotor. Whichever it is, the single most important thing is to stop resetting the overload, because every restart attempt heats the windings further.
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All Electrical Symptoms
Tier 3 throughout. 480V three-phase. The only Tier 1 action is stopping.
Right Now

Stop Resetting the Overload

This is the whole Tier 1 action on this page, and it is the one that decides whether you are buying a fuse or a motor.

Stop pressing reset.

The overload is not being a nuisance. It is the only thing currently protecting the motor.

Shut the machine down and lock it out.

So the next person on shift does not do what you just stopped doing.

Tag it.

“Do not reset — electrical fault, service called.” Without the tag this machine gets reset four more times before anyone arrives.

Note how long it ran before tripping.

Seconds, not minutes, is the signature described on this page. A delayed trip is a different fault entirely.

Call it in as electrical.

So whoever comes arrives with the instruments and PPE for live three-phase work.

Why this is Tier 3 and not negotiable

A compactor control cabinet carries 480 volts, three phase. The control components inside it run on 120V or 24VDC, which is exactly why people open the door thinking it is low-voltage work. The 480V line side is right there beside them, and an arc flash in that cabinet is a burn injury rather than a shock.
Reading It

Hum Plus a Fast Trip Is a Signature

Motors fail in several ways and they do not all sound alike. This particular combination is specific.

Loud hum, trips in seconds

Classic single-phasing. The motor is receiving power on two legs instead of three, cannot develop starting torque, and draws locked-rotor current until the overload saves it.

Hums and turns slowly, then trips

Also consistent with a lost leg under load, or with a mechanical drag — a stiff pump, a bearing going.

Runs several minutes, then trips

Not this fault. A delayed trip points at heat, overload sizing, or the hydraulics working against a relief — a different page.
Narrowing It

Three Causes

  • A lost leg — the usual one — One blown fuse of three, an open pole in a breaker, or a burned contact in the starter. The motor itself is often perfectly healthy and the repair is upstream of it.
  • A seized pump — The motor is fine and is being asked to turn something that will not move. Frequently follows a cavitation event or a run on low oil.
  • A locked rotor — Bearing failure or internal damage in the motor. The most expensive of the three and the least common.

Why the diagnosis matters before the parts

These three look identical from the start button and cost very different amounts to fix. A motor replaced because of a blown fuse is an expensive way to not fix a problem — and the new motor will do exactly the same thing on the first start.
The Clock

What Each Reset Costs

Single-phasing damage is cumulative and it is a function of how many times someone pressed the button.

First trip, machine left alone

Diagnose the supply, replace a fuse or a starter contact. The motor is undamaged. The cheapest possible outcome.

Several resets

Winding insulation degraded by repeated locked-rotor current. The motor may run afterwards and fail early — a fault you have paid for but not yet received.

Repeated resets over a shift

Motor replacement, on top of whatever the original electrical fault was. Two invoices for one problem.
Before You Call

What We Need to Quote It

You do not need all of this — the make and model plus photos is usually enough to get started. But the more of it you have, the closer the first number is to the final one.
  • Bore — Inside diameter of the barrel. Stamped on many data plates; otherwise we measure it.
  • Stroke — Fully extended length minus fully retracted length.
  • Rod diameter — Across the chrome, measured with calipers if you have them.
  • Mount type — Clevis, cross-tube, trunnion or flange — and the pin diameter.
  • Pin-to-pin retracted — Center of one mounting pin to center of the other, ram fully in.
  • Ports — Size, thread type, and whether they face the same direction or opposite.
  • Machine make and model — Off the data plate. It often tells us the cylinder before you measure anything.
  • Photos — The whole cylinder in place, both mounting ends, and a close shot of the rod.

If you can't get the measurements

Don’t climb on the machine to get them. Send the make, the model and the photos, and we will take the dimensions when the cylinder is out — or bring a replacement with us if we already know that machine.
Safety

Where Your Checking Stops

Tier 1 · Site check

Shutting the machine down, locking it out, tagging it, and noting how long it ran before tripping.

Tier 3 · Service technician

Everything else. Verifying all three legs under load, fuse and starter work, megger testing the motor, and any work inside the cabinet.

Do not crack a fitting to check for pressure

Stored hydraulic energy is the hazard that makes this Tier 3 no matter how simple the repair looks. Loosening a fitting “to see if there’s still pressure in it” is how people get injection injuries — which do not look serious for the first hour and are a surgical emergency. Pressure gets relieved deliberately and confirmed at the gauge.
Applies To

Compactors and Balers Both

This fault lives in the power unit, so it behaves the same on a stationary compactor and on a vertical baler. One difference is worth naming.

On a baler

Identical, and the same rule applies: stop resetting the overload. Vertical balers in retail get reset repeatedly by whoever is on shift, because the machine is in the way of the job.
Questions We Get

Motor Faults, Answered

Other equipment on the same panel works fine. Doesn't that rule out the supply?
Not at all — and this is the most common reason people skip past the real cause. Single-phase loads elsewhere on the panel run perfectly on two good legs. Only the three-phase motor notices the missing one.
Yes. A fuse can open with no visible sign, and a starter contact can burn while the contactor still pulls in and sounds normal. That is why this gets verified with instruments under load rather than by inspection.
A handful of resets is not automatically fatal — motors have thermal margin and the overload is doing its job. Tell the technician how many times, honestly. It changes whether the motor gets tested before being put back in service.
It could. A motor that has been repeatedly restarted against a locked condition gets hot enough to smell, and that smell is insulation. It is a reason to treat the call as urgent rather than routine.
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T&T Weber Hydraulic Inc.
184 Stone St, Unit 5
Clinton, MA 01510

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Onsite compactor and baler service throughout New England — Massachusetts, Connecticut, Rhode Island, New Hampshire, Vermont and Maine. Cylinder reseal and replacement, domestic replacement cylinders, hydraulic, electrical and controls, and full mechanical repair.