Paper Shredders


Shredder Motors

Shredder Motors Explained (courtesy of Acco Rexel UK)

Shredder Duty Cycles

Shredder Duty Cycle - This is declared to the Approvals Body (RBM use BSI) to meet the Safety Standard BS EN 60950.  It is marked on the product typically 15min On / 20 min Off but can be Continuous.  This takes account of the time taken to empty the Bin when Full.  Therefore, the smaller the waste bin - the longer duty cycle.  If you shred for 15 minutes and rest for 20 minutes, then it will shred all day long.

Small shredders have duty cycles because the motors are smaller, and heat up quicker.  Larger machines have a Continuous Duty Cycle and don’t require resting.  The shredder can run for more than the shred On time i.e. 15 minutes from cold, because the Motor Duty Cycle can be longer.  If you shredded continuously, emptying the bin without the rest cycle, the motor would eventually heat up, and trip the Thermal Cut Out.

Shredder Motors - Duty Cycle

Motors have a Duty Cycle as well.  This is nothing to do with the “Shredder” Duty Cycle.  Motor Duty Cycle - is that declared to the Approvals Body to meet the Safety Standard for Motors.  This is the time taken from cold for the motor to reach the Thermal Cut Out Temperature.  This can be longer than the On cycle of the Shredder Duty Cycle.

Shredder Motors - Thermal Cut Out

The motor has a Thermal Cut Out inside the electrical windings; it is a Safety device.  It prevents the motor from overheating and damaging the windings.  If you run the shredder for longer than the Shredder Duty Cycle it will eventually reach the Thermal Cut Out Temperature, and the motor will automaticaly switch off.   You will have to wait until it cools down before the cut out closes and lets the motor run again.

What are the WATTS?

Motor Watts - is that declared to the Motor Approvals Body. It is the watts at which the motor will run continuously without exceeding a maximum temperature rise i.e. 100Watts.   Input Watts is the current in Amps i.e. 2.0 amp multiplied by the Supply Voltage i.e. 230v therefore 460Watts say, at maximum sheets.  Output Watts are always lower than input watts because up to 50% of the energy is lost, (resulting in the motor heating up), not in shredding i.e.230Watts.


Shredder Motors

General Comments (Not from Acco Rexel)

The size of a larger shredder's motor is measured in kilowatts or horsepower and is often given more emphasis than it should be given.  A portion of a motor's power in a paper shredder  must first be applied to overcome the friction and internal resistance of the cutting head and drive train before any remaining power can be used for shredding paper.


This is one of the reasons why oiling increases the cutting

capacity; reducing the friction of the cutters, and consequently more power remains to cut paper.


In some precision built shredders such as the larger Dahle shredders, ball bearings, precision aligned frames, and a sealed oil-filled gearbox work together to minimize the internal friction created. The result is that more of the motor's power is available for shredding paper and a smaller, more efficient motor can be used to obtain the same results.


A competitor having a larger motor may not be providing the user with any additional speed or cutting capacity (true benefits to the user). The larger motor may simply be required to overcome the internal friction caused by inexpensive design or flimsy construction.


Some manufacturer's express the power of their shredders' motor with reference to INPUT Watts rather than OUTPUT Watts.  This of course does not take into account the power lost in overcoming friction and internal resistance as mentioned above.  It is wise to look more to the claimed cutting capacity per pass of a shredder rather than be "confused" by the claimed power of a shredder's motor.