What Is a GTEM Cell? Compact EMC Testing for Small Products
GTEM cells used for emission and immunity pre-testing of small products in space-limited labs, with their advantages and limits.
3 min readNovember 6, 2026
Where Do the Pulses Come From?
When a relay, contactor or motor switches, the line's inductance creates very short, fast-rising voltage pulses. They don't come one by one but in bursts of thousands of pulses per second, reaching other devices connected to the same line.
In industrial environments this happens many times a day. The IEC 61000-4-4 test measures under lab conditions whether a device keeps working when exposed to these bursts.
How Is the Test Applied?
The burst generator is connected to power lines through a coupling network, and to signal and data lines with a capacitive coupling clamp. Typical test levels are around 1 kV for household products and 2 kV for industrial products.
During the test, the device stands at a set height above the reference ground plane and cables are arranged at the lengths described in the standard. This setup makes the result repeatable across labs.
Why Do Products Fail?
The most common problem is the pulse reaching the board by a short path from the power input and resetting the microcontroller. Inadequate input filtering, long unprotected signal cables and weak grounding are the main causes.
The fix is usually a better input filter, ferrites or suppression parts at cable entries and short ground returns on the board. We've gathered similar problems in our article on why products fail EMC tests.
Is a Shielded Room Needed?
Since the EFT test doesn't produce radio-frequency fields, a shielded room isn't required, but a proper reference ground plane and a controlled bench are. Many labs run this test in an area next to the chamber used for radiated tests.
When planning your in-house pre-test setup, we recommend considering a separate bench for EFT, ESD and surge tests together with your EMC test chamber.
Frequently Asked Questions
Are EFT and surge testing the same?
No. EFT is bursts of very short, fast pulses; surge is longer, very high-energy single pulses representing lightning and large switching events.
How many minutes does the test take?
Applications usually last one minute per line and polarity; total time depends on the number of connections.
Does a reset during the test count as a fail?
It depends on the performance criterion in the product standard. Industrial products are usually expected to recover by themselves.
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