Free engineering tool
Voltage sag ride-through checker
against ITIC and SEMI F47.
Enter the residual voltage and duration of any dip, swell or interruption. See its IEEE 1159 class and whether your equipment should have ridden through it.
Events
| # | Residual voltage | Duration | Unit |
|---|
Where each event falls
| # | Event | IEEE 1159 class | ITIC | SEMI F47 |
|---|
What the checker tells you
For each event you enter (residual voltage and duration), the checker returns three answers:
- The IEEE 1159 class: sag, swell or interruption, and whether it was instantaneous, momentary or temporary.
- ITIC: whether the event was inside the tolerance envelope that typical information-technology and control equipment is expected to survive.
- SEMI F47: whether equipment built to the semiconductor-industry immunity requirement should have ridden through it.
Use it after a trip: take the event from your power quality recorder, enter it, and see whether the supply or the equipment is the weak link.
The ITIC (CBEMA) curve
The ITIC curve, published by the Information Technology Industry Council, replaced the older CBEMA curve in 1996. It describes the voltage events that typical IT equipment at 120 V should tolerate:
| Duration | Equipment should tolerate a residual voltage down to | And swells up to |
|---|---|---|
| Up to 20 ms | 0 % (a complete dropout) | 120 % after the first half cycle |
| 20 ms to 0.5 s | 70 % | 120 % |
| 0.5 s to 10 s | 80 % | 110 % |
| Longer than 10 s | 90 % | 110 % |
Sources: Power Monitors, CBEMA and ITIC curves, PG&E, Voltage Tolerance.
The curve is a reference for what equipment should survive, not a design specification for the supply. Industrial drives, contactors and PLC power supplies are often less tolerant than the curve suggests, which is exactly why an event inside the envelope can still stop a line.
SEMI F47
SEMI F47 is the voltage sag immunity specification for semiconductor processing, metrology and test equipment. It is widely used beyond semiconductors as a benchmark for industrial control equipment. Equipment must continue operating without interruption through sags to:
| Residual voltage | Duration at 50 Hz | Duration at 60 Hz |
|---|---|---|
| 50 % | 200 ms (10 cycles) | 200 ms (12 cycles) |
| 70 % | 500 ms (25 cycles) | 500 ms (30 cycles) |
| 80 % | 1 s (50 cycles) | 1 s (60 cycles) |
Source: Advanced Energy application note AN1401 on SEMI F47-0706. The specification covers sags only, not swells or interruptions.
Reading the result
- Inside ITIC and the equipment tripped: the equipment, or a component inside it, is less tolerant than it should be. Typical fixes are ride-through settings on drives, a small UPS or DC supply for control circuits, or contactor coil hold-in devices.
- Outside ITIC: the event was severe enough that ordinary equipment is not expected to survive. The fix is on the supply side: ride-through equipment such as a UPS or dynamic voltage restorer, or a discussion with the utility about the fault behind the dip.
- Below the SEMI F47 requirement: compliant equipment is not required to survive this event either.
Our guide on voltage dip vs sag vs interruption explains the definitions behind the classes, and voltage sags and production stops explains how to link events to stoppages.
Frequently asked questions
Is “residual voltage” the same as the depth of the sag?
No. Residual voltage is what remained (a sag to 70 %). Depth is how far it fell (a 30 % sag). This checker uses residual voltage, as IEC instruments report it.
Can I use the ITIC curve at 230 V or 400 V?
The curve was written for 120 V equipment, but in percent of nominal it is widely used as a reference at other voltages. Treat it as a guide, and use the equipment’s own immunity data when you have it.
Why does a 100 ms event matter for a process that takes hours?
Because a contactor, drive or controller that drops out in 100 ms stops the process, and restarting it can take hours. The event is short; the cost is not.
Want every event recorded and plotted automatically? Talk to an Inspector engineer.