What LV-Only Means: Where a Voltage Sag Protector Actually Goes

A voltage sag protector rated for low voltage (LV) service is designed to operate at 1kV or below. WESCO’s TSP® is installed not at the utility incoming point, but directly in front of the sensitive load it protects, and it does not cover medium- or high-voltage systems at 3.3kV and above. “LV-only” is not just a spec limitation — it defines where the unit belongs on the one-line diagram and what it is meant to protect.

Picture a semiconductor fab where a voltage sag ripples through the plant. Chamber controllers, vacuum pump drives, and robot controllers pull their power from the low-voltage side, and they can all trip or reset at once. The failure isn’t caused by the voltage at the incoming switchgear — it’s caused by the sag reaching each device’s input terminals. That is exactly where a TSP unit is installed: immediately upstream of the load that needs protecting.

What “LV-only” actually scopes

TSP® is built for systems at 1kV or below. Voltage sag compensation for medium- or high-voltage systems (3.3kV and above) is outside its scope.

This scope determines placement. In most industrial facilities, power arrives at medium or high voltage, steps down through a transformer, and is then distributed at low voltage to individual equipment. TSP sits in that low-voltage distribution segment — from the transformer’s secondary side through to the load.

Not the incoming point — the load itself

A common misconception is that a single TSP unit at the main switchgear will protect an entire facility. In practice, TSP is not a plant-wide compensator; it is installed in front of a specific load to condition the voltage reaching that load.

There are two reasons for this approach:

• Sensitivity to sags varies by equipment. Semiconductor and display process tools can trip from a sag lasting only a few milliseconds, while general lighting or low-speed motors are comparatively tolerant.
• Installing at the load concentrates capacity where it is actually needed, keeping equipment sizing and cost proportional to the risk.

As a result, TSP units are typically deployed line by line, or panel by panel, wherever protection is required.

Why the protection logic centers on the load

WESCO TSP is primarily supplied to the semiconductor, display, automotive, battery, and data center industries. These sectors share a common trait: precision control equipment fed from the low-voltage side, where even a brief sag can interrupt a process.

IEEE studies report roughly 60-70 voltage sags per year at a typical industrial site. At that frequency, protecting only the incoming point leaves each line’s actual exposure largely unmanaged. Installing at the load directly shields the equipment from these recurring events.

What SEMI F47 and the ITIC curve point to

Equipment tolerance to sags is also codified in industry standards. SEMI F47 sets ride-through points for semiconductor equipment at 80% of nominal voltage for 1 second, 70% for 0.5 seconds, and 50% for 0.2 seconds. The ITIC (CBEMA) curve similarly publishes a tolerance envelope for general information technology equipment.

Both standards reference voltage at the equipment’s input terminals, not at the utility incoming point. That is precisely why sag protection needs to sit at the load — matching the placement logic behind TSP.

Practical considerations at the load

TSP uses an EDLC ultra-capacitor, battery-free design, unlike conventional UPS units built around lead-acid or lithium batteries that require periodic replacement. The energy storage stage carries a 10-year design life, and response time is within 2ms for small/mid-capacity units and within 4ms for larger units.

Since each unit sits at the load, it’s worth reviewing a few things during installation:

• Rated current and peak momentary load of the protected equipment
• Available panel space and switchgear configuration
• Which loads on a given line need priority protection

Key takeaways

• TSP® is an LV-only (≤1kV) voltage sag protector; medium- and high-voltage systems (3.3kV and above) are outside its scope.
• It installs in front of the sensitive load, not at the utility incoming point.
• Load-level installation matches protection to each device’s actual sag sensitivity and keeps capacity proportional to need.
• IEEE data puts sag frequency at roughly 60-70 events per year at a typical industrial site, which argues for load-level rather than single-point protection.
• Standards like SEMI F47 and the ITIC curve reference voltage at the equipment terminals, reinforcing why TSP belongs at the load.

Frequently Asked Questions

Q. Can TSP be installed on medium- or high-voltage equipment?

No. TSP is designed for LV systems at 1kV or below; voltage sag compensation for systems at 3.3kV and above is outside its scope.

Q. Is TSP installed at the main switchgear?

No. TSP does not compensate the entire incoming supply. It is installed directly in front of a specific sensitive load to condition the voltage reaching that load.

Q. Why install a separate unit at each load instead of one central unit?

Because sag sensitivity varies by equipment. Installing at the load concentrates capacity where it's needed, keeping equipment sizing and investment proportional to actual risk.