EARTHRINGS Frequently Asked Questions



Why does the Earthrings ™ Bearing Protection Ring last so long without wearing out?

The patented technology design of the Earthrings ™ does not use applied pressure friction for the fibres and therefore there is no direct frictional wear applied to the fibre tips. The Earthrings ™ will literally last for the service life of the motor.

How long will the Earthrings ™ Conductive Microfibre™ shaft grounding brush last?

The Earthrings ™ will last for the normal service life of the motor and continue to discharge shaft voltages to ground. In lab test the shaft grounding ring showed negligible wear, less than 0.001″(0.025mm) in a 10,000-hour test at 1800 RPM.

Why don’t the fibres wear over time?

There is virtually no measurable wear because of the almost frictionless design. Even after 8700 hours of continuous operation the wear was not measurable with an optical comparator. The patented design ensures the perfect interference fit to the shaft surface.

Is any maintenance needed for the Earthrings ™ once it is installed?

Earthrings ™ technology is maintenance free and will not wear out. It is fully effective even when oil, grease or contamination gets on the shaft surface. Once installed per manufactures recommendation the shaft grounding ring does not require periodic maintenance or replacement for the normal service life of the motor.

Are Earthrings ™ affected by oil or grease?

Earthrings ™ is effective if oil or grease is present on the shaft because the Conductive Microfibres™ cut through the grease and oil and maintain their contact on the motor shaft to discharge the shaft voltages to ground.

Why do conventional shaft grounding brushes wear out?

Whether metal bristle or carbon block, conventional shaft grounding brushes use a spring loaded mechanism to apply pressure onto the shaft while it is rotating. This causes rapid wear of the brush surface and frequent replacement.

Where do the VFD induced shaft voltages go with no Earthrings ™ brush installed?

The shaft voltages will build up on the motor shaft and discharge through the bearings. This happens because the voltages induced onto the motor shaft overcomes the dielectric of the grease film between the bearing’s ball and race.

Why are these shaft currents so destructive?

Because they occur literally hundreds of thousands of times per minute while the motor is running. Over time the bearing race becomes heavily frosted and may start to flute in a very short period of time…sometimes causing failure in only a few months

When do i use an HV ring instead of an LV ring?

For motors under 500HP (375Kw) and 600V AC, a Low Voltage (LV) product can be selected.Above 500HP (375Kw) and 600V AC a HV ring must be used.

Will electrical bearing damage always occur in a VFD application?

Yes – with no alternate path to discharge shaft current, pitting of the motor bearing will take place during VFD operation. These discharges will continue and will always seek the path of least resistance – usually through the motor bearings. Installing Earthrings ™ will create an alternate path for these discharges and divert current away from the motor bearings.

We just installed VFDs on many of our motors and so far, everything is OK, should I be worried about shaft current?

Yes – even if you have not experienced excess noise, vibration or bearing failure so far, the VFD induced shaft currents continuously discharge through the motor bearings during operation and may cause an unplanned failure unless you have a means to discharge them. By installing the Earthrings ™, you will provide the best means of protection and prevention to avoid potential failure

From a preventative maintenance perspective what would you recommend?

In order to prevent potential catastrophic failures, install an Earthrings ™ Conductive MicroFibre™ brush to all motors controlled by a VFD.

Should one or two Earthrings ™ be installed on the motor?

For smaller frame motors (up to and including 90kw motors) install one Earthrings ™ on either the drive end or the non-drive end of the motor. For larger motors you must insulate one of the bearings to stop the circulating currents and install an Earthrings ™ on the opposite end. However, when insulation on the non-drive end is not designed into the motor or cannot be easily installed, two Earthrings ™ are recommended – one on the drive end (DE) and one on the non-drive end (NDE).

If Earthrings ™ is installed outdoors, will water affect performance?

There is no problem with water or moisture – Earthrings ™ will continue to perform even if some water gets inside Earthrings ™.


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