Plant maintenance
Shaft-voltage survey and motor grounding rings
Early bearing wear on a VFD-driven motor is sometimes electrical. A shaft-voltage survey shows whether that is likely, and whether a grounding ring is the right next step.
About this service
Star Automations is a multi-brand servo motor repair company with 25+ years of work on industrial machines. We see VFD-driven motors in the same plants as the servo motors we repair. This page is for the shaft-voltage work that sits beside that motor repair. The core motor service is described on our servo motor repair page.
A variable-frequency drive can place a common-mode voltage on the motor shaft. If that voltage finds its path through the bearings, the discharge can frost or flute the raceways and shorten bearing life. A shaft-voltage survey measures what is present on the running motor. Where a path to ground through a shaft grounding ring is appropriate, we can supply and fit a ring that matches the shaft.
Puducherry operations are ISO certified. We take survey enquiries for plants served from Puducherry, Chennai, Bengaluru, Hyderabad and Delhi, and from other cities by arrangement.
Why it matters
If a VFD-driven motor keeps taking new bearings, or the old bearings show frosting or regular fluting marks, electrical discharge is one of the causes worth checking. Changing bearings alone does not remove the voltage that damaged them. A short survey on the running machine tells you whether shaft voltage is present and whether a grounding ring, or another change to the installation, should be considered.
This is an investigation and a parts-and-fitting service. We do not claim that a ring will prevent every future bearing failure, because mechanical load, lubrication and alignment also matter. We will report what we measured and what we recommend.
Who it is for
- Plants running groups of VFD-driven motors on process, packaging, HVAC, fans, pumps and conveyors.
- CNC shops and machine builders with inverter-fed spindle or axis motors that have had repeated bearing work.
- Maintenance teams who want a recorded survey, not only a part fitted in isolation.
- MRO buyers who want a motor list handled in one visit, including a later fitting visit if you approve the rings.
How the work runs
- 1. Send the list. Send the plant city, a list of the VFD-driven motors you want checked, and any notes on bearing history or fluting.
- 2. Plan the visit. We plan a visit at a time when the machines can be observed in their normal running condition.
- 3. Measure and review. We measure shaft voltage and review the installation, including cabling and earthing as they appear on site.
- 4. Written report. We issue a written report of the findings. Where a grounding ring is appropriate, we propose the ring size and the fitting method.
- 5. Supply and fit. If you approve, we supply and fit the rings, or we supply them for your team to fit to the method in the report.
What to send us
The plant city, the number of motors, nameplate data or photos, whether the motors are VFD-driven, and a short note on bearing changes or observed fluting. A list is better than one motor if you have a group on the same type of drive. If a motor is already noisy, hot, or out of service, say so; it may also need servo motor repair or other mechanical work.
Frequently asked questions
What is a shaft-voltage survey?
A shaft-voltage survey is a set of measurements on a running VFD-driven motor to see whether voltage is present on the shaft that could discharge through the bearings.
Why do VFD-driven motor bearings fail early?
One cause is electrical discharge through the bearing, which can frost or flute the raceways. Lubrication, load and alignment can also cause early wear, so a survey is used to see whether shaft voltage is part of the picture.
What is a motor grounding ring?
A motor grounding ring is a ring fitted around the shaft to give a path to ground for shaft current, so that current is less likely to pass through the bearings. We supply and fit a ring when the survey, or a clear installation need, supports that step.
Can you survey several motors in one visit?
Yes. Send the list and the plant layout notes. A group of motors on the same site is a normal enquiry.
Do you only fit rings, or do you measure first?
We prefer to measure first, then recommend. If you already have a known fluting problem and a clear shaft size, we can discuss supply and fitting from the nameplate and photographs. We will still say when a measurement visit would be wiser.
Are prices for rings listed here?
No. Prices are not published on this page. Send the shaft details or the motor list and we will come back with the next step.
Brand names identify the equipment and parts we work on. Star Automations is an independent multi-brand repair and maintenance company and is not an OEM service centre.