When Your Internal Team May Not Be Enough
Most plants have their own electricians for routine work. The faults that need a specialist field service technician usually fall into four groups.
Intermittent faults
The line stops at random, the fault clears itself and nobody can make it happen again. Short stoppages add up. Finding the cause takes a method, data loggers and experience of the patterns.
Power quality issues
Voltage sags, harmonic distortion, transients and imbalance rarely show on a standard multimeter. They turn up as drive faults nobody can explain, motors that fail early and PLCs that behave erratically. You need a power quality analyser and the experience to read what it logs.
Medium voltage systems
Work above 1,000 V AC needs authorised people with the qualifications and PPE for it. Most in-house teams are qualified for low voltage only.
Complex drive and motor systems
Servo systems, high-power drives and regenerative configurations fail in ways that go well beyond an open circuit. You need the electrical knowledge and familiarity with the particular drive platform.
What Diagnostic Technicians Do on Site
A diagnostic visit usually follows the same sequence:
- 1.Review fault history and any available data
- 2.Inspect visually
- 3.Take measurements
- 4.Fit data loggers where the fault is intermittent
- 5.Analyse the collected data
- 6.Present findings with recommended corrective actions
You get a report with the root cause, the evidence and the recommended fix. That is what stops the fault coming back, and it supports an insurance or warranty claim.
Common Diagnostic Disciplines
Qualifications to Consider
Electrical qualifications are set nationally across Europe. Check for:
- National electrical authorisation for your installation voltage
- Thermography certification for thermal survey work
- Manufacturer-specific training where VFD diagnostics are involved
- CompEx or a national equivalent for hazardous (ATEX) zones, which most European sites require
Field Notes
Three faults from my own years on site. None of them was random.
The servo fault that kept coming back
Intermittent overspeed fault on a servo motor. Cycle the power, fault clears, runs fine for a few days, then it's back. Drive replaced. Motor replaced. Wiring "checked".
When someone says they checked the wiring, it's usually a visual check. Doesn't catch this.
My trick: run a long wire to the pin at the motor plug, continuity test from the far end, measure resistance on each wire individually. Should be around 1 ohm.
Pink wire came back at 70 ohms. That's not a wire fault, that's a connection fault. Pin wasn't properly seated in the plug.
Faults like this get power-cycled away for years without ever getting fixed. The drive and motor were never the problem.
Bare copper in a live connector
Bare copper. Sitting inside a live 110V connector. For who knows how long.
Mid-upgrade, swapping old cables for new. The 110V circuit wasn't even part of the work.
Powered up, breakers started tripping. No obvious reason.
Went through every connection on the 110V circuit. Hours of it. Eventually found a crimp that had never been properly terminated. Copper exposed, sitting right inside the plug.
It had been like that for years. Done nothing. Then cables get moved around during other work, wires shift slightly, and a short that's been waiting patiently decides today is the day.
Reterminated properly. Work continued.
The frustrating part isn't finding it. It's knowing it was installed like this, ran through commissioning, and sat there undetected through every service visit since.
Nothing is random. Some faults just need the right conditions to show themselves.
Machine down repeatedly, cause unknown
Current solution: power off and on.
The signal kept dropping. No pattern, no error code. The machine would run fine for hours, then stop "randomly".
Nothing is random.
The cause is in the photo. Wire insulation was clamped under the screw instead of the copper. Sometimes the strands made contact. Sometimes they didn't.
Done right: crimped, correct strip length, nothing under the screw but copper.
A hard fault costs you an hour. An intermittent one can cost weeks, because everyone starts by suspecting the expensive parts first. That is the real price of a shortcut during installation.
Finding the right Field Service Technician can be priceless.
Cost Considerations
Diagnostic work is usually a day rate, plus rental of any specialist instruments. An intermittent fault often takes three visits, not one:
- 1.An initial assessment.
- 2.A data logging period, with the instruments left on site.
- 3.A return visit to analyse the data and report.
Disclaimer: This guide is general information, not professional, legal or electrical safety advice. Qualifications and electrical safety rules differ by country, so check what applies to your installation before acting on anything here. FindFST accepts no liability for decisions made on the basis of this guide.
From the field
Fault-finding stories from FST Life that go with this guide.
30 Dec 2026
Looks fine. No comms.
Profinet plug was in the right port, nothing obviously wrong. But the machine wasn't talking. Then look closer and you can see the profinet plug isn't...
3 Dec 2026
Terminals installed directly under a fan
Multiple signals dropping out, no obvious cause. Pulled the covers and found it straight away. Dust being blown directly into the terminals, constantly...
25 Oct 2026
Rookie mistake that cost me a full day
First time I installed new cables, I did it as fast as possible. Get to the cabinet and all the plugs were damaged, cannot connect them. Spent the...
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