Stray Voltage Mitigation

Stray Voltage Mitigation


Small AC voltages on the power company's grounded primary neutral can appear on the customer's secondary neutral, as these are normally bonded together. This voltage may affect dairy cattle and other livestock.


The Dairyland Variable Threshold Neutral Isolator (VTNI) blocks AC and DC current, when installed between the primary and secondary neutrals at the power company transformer by the utility. This results in the farm grounding system being isolated from the power company ground under normal conditions, but reconnected if the voltage rises on either system to the device threshold. The VTNI reverts back to the blocking mode when the event is over.

The VTNI is the preferred solution by utilities for primary-to-secondary isolation, based on its reliable solid-state design. It meets the U.S. requirements for an isolation product, as stated in National Electric Safety Code (NESC) 97D2.

Note: The Dairyland model VTNI is not authorized for use in solving nuisance shock to persons at swimming pools or similar human health situations where structure to ground voltage is present. Instead, proper bonding and grounding techniques need to be applied to solve such problems.

To implement primary-to-secondary isolation, the following issues need to be examined to verify product ratings:

  • Examine AC fault current exposure and compare to the VTNI ratings.
  • Install the VTNI between primary and secondary neutrals with no bypass around the device.
  • Test to assure that isolation has been achieved.