Analysis of Voltage Sag Count Gathered by Innovolt Power Protection Devices

By Vincent P. Luciani, Sr. Product Architect at Innovolt

Innovolt products are unique in that they not only protect against power grid disturbances, they are also a diagnostic tool to sense and track the number of occurrences of power grid disturbances.

The purpose of this paper is to inform the users of Innovolt products on how to analyze the Voltage Sag information gathered by all Innovolt devices.

A Voltage Sag is defined as a momentary reduction or loss of voltage. Most voltage sag events last anywhere from 1 cycle (16 milliseconds) to 10 cycles (0.16 seconds). In many cases where Innovolt products have sensed voltage sags, electricians have been called in to “check the line”. They read the line voltage with a digital voltmeter, see that it is within specifications, and deem the LINE “OK”. The voltmeter is not able to react to an event that fast. So, even if a sag was occurring at the exact moment the voltmeter was inserted, it would not validate the existence of a sag at all. In order to capture a voltage sag, special equipment such as an oscilloscope or a voltage monitoring device is required.


Voltage Sags are dangerous to electronic equipment in that they cause abnormally high Current Inrushes. These current inrushes are not suppressed by the electronic equipment’s own current inrush protection circuits as they don’t have time to reset during this instantaneous event. Current inrushes have been measured to be between 10-50 times normal operating current which greatly reduce the lifespan of electronic equipment.

Voltage Sags can be broken into two categories: Those produced on the power grid, and those produced internally on a branch circuit within a building.

Grid Based Voltage Sags

Grid based voltage sags are a secondary effect of a grid fault. When a fault (a short between any two phases of electrical power) occurs, local subscribers experience a complete power outage. However, subscribers in a larger area surrounding the fault experience a voltage sag as the grid tries to feed the fault. On average, 30 to 100 grid based voltage sags occur annually across the North American power grid.
As Grid Based voltage sags are a secondary effect of a fault on the grid, there is not much the subscriber can do to prevent them. However, the subscriber can install Innovolt power protection in order to protect against the current inrush that result from voltage sags.

Branch Circuit Based Voltage Sags

Internal voltage sags occur when multiple high current loads are distributed along a single branch circuit. When a large current is requested by a “downstream” load, the voltage as seen along the branch circuit is momentarily reduced. A typical example of this is when dimming of lights is observed at the moment an air conditioning unit comes on.

Analyzing Voltage Sag Counts

By regularly reading the voltage sag disturbance count on Innovolt products, one can determine the probable cause of the voltage sag. If the count is on par with the national average of 30-100 events per year, one can assume that they are grid based.
However, if the count is building up quickly, one can point to internal building wiring issues as the probable cause. Some Innovolt customers have tracked more than 10,000 voltage sags in as small as a 6 week period indicating internal wiring issues.
In these cases, the problem was tracked to (2) common causes:
• Multiple high current loads on a single branch circuit
• Long wire runs from the outlet to the breaker panel
Even though Innovolt product will reduce the current inrush that results from voltage sags, it is best to reduce equipment exposure to voltage sag events. In order to reduce the likelihood of experiencing branch circuit based voltage sags, the following practices should be followed:
1. Request a Fully Dedicated Branch Circuit Run 
    This means that all three connections LINE, NEUTRAL, and GROUND be an independent run from the outlet to the breaker box. In some instances, electricians will run a dedicated LINE but tie on to an existing NEUTRAL and still consider this a dedicated run. This is not advised since
    load currents run on both the NEUTRAL as well as LINE wires.
2. Request an increased wire gauge for long run 
    The National Electrical Code gives guidelines for minimum wire gauge. Electricians usually use this minimum gauge for a particular run. However, larger wire sizes can be used for longer runs in order to reduce impedance which reduces the likelihood of localized voltage sags.
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