Stray Voltage Definition

Stray voltage is a relatively small voltage difference (less than 10 V) between two points an animal can contact simultaneously. Animals respond to the current through their bodies produced by this voltage difference and not to that voltage directly. Therefore, the conductivity of the animal really sets a limit on how small this voltage difference is before it is sensed.

The original definition of the term "stray voltage" was to describe the phenomenon where these voltage differentials exist in the farm environment even when the farm was wired according to existing electrical codes. This concept of stray voltage was gradually expanded to include all low-level voltages found on farms regardless of their source. High-level voltages such as might be encountered if a 120-V hot wire were inadvertently wired to an electrically isolated milk line were not considered to be stray voltages. The purpose of the 10 volt limit is to eliminate these types of high voltage problems from being considered stray voltage.

This definition is still workable. It is electrically correct, reflects the original intent of the term "stray voltage, and is consistent with colloquial use of the term.

The terms 'stray voltage' and "neutral-to-earth voltage" are often used interchangeably. This mix-up occurs because on most farms with a stray voltage/current problem, the immediate source of the stray voltage is an elevated neutral-to-earth voltage. However, an elevated neutral-to-earth voltage does not necessarily result in stray voltage that affects animals. And, the existence of stray voltage is not always related to an elevated neutral-to-earth voltage. Still, the relationship between an elevated neutral-to-earth voltage and stray voltage is very strong. In fact, it is so strong that the reduction of elevated neutral-to-earth voltages should be considered to be within the context of normal farm management programs, regardless of a proven stray voltage/current problem. Reduction of neutral-to-earth voltages need not be done immediately unless a stray voltage/current problem has been identified (or is suspected). However, a very high neutral-to-earth voltage may indicate a serious malfunction of the electrical system and/or may be a safety hazard, both requiring quick investigation.