An electrical inspection is not about finding a fault. It is about written proof that a fault is or isn't there — for the insurer, under Decree 508/2009, for the building authority at occupancy approval, for the employer during periodic checks. Clients often hear "the inspection failed" and think the inspection technician is bad. In reality, in 95% of cases the fault is in the installation, and it was documentable 6 months before the inspection.
This article is the list we give clients before a planned inspection. It summarizes the 12 most common findings we identify on every other audit, and the precise measure that fixes them before the technician arrives.
Legislative framework — what applies in 2026
The main documents the inspection technician applies (Slovak / EU standards): - **Decree of the Ministry of Labour No. 508/2009 Coll.** — inspection periodicity, classification of premises (A, B, C, D, E) - **STN 33 1500: 2024** (Slovak equivalent of IEC requirements) — inspections and checks of electrical equipment (deadlines, scope, methodology) - **STN 33 2000-6** (IEC 60364-6) — verification of low-voltage installations (initial and periodic verification) - **STN EN 60204-1: 2018** (IEC 60204-1) — safety of machinery, electrical equipment of machines - **STN EN 62305** (1–4) (IEC 62305) — lightning protection - **Decree ÚBP No. 718/2002** — qualification for professional competence
In 2024, an amendment to STN 33 1500 was published with substantially stricter requirements on insulation resistance measurement on networks with frequency converters and on checking type B/B+ residual current devices on PV inverters. If your last inspection was before 2024, some measurements that passed then would not pass today.
Inspection intervals — the most common confusion
Clients remember "inspection every year". Reality per STN 33 1500 and Decree 508/2009:
- **Regular office space (premises C)** — periodic inspection every **5 years**
- **Production space (premises B)** — every **3 years**
- **Spaces with explosion hazard (premises E, ATEX zones)** — every **year**, check every 6 months
- **Healthcare facilities** — every **2 years** + annual check
- **Assembly spaces (cinema, theatre, school)** — every **2 years**
- **Outdoor installations (parking, construction sites)** — every **2 years**
- **Machines (per STN EN 60204-1)** — after every modification + at least once every **2 years** by category
Don't base periodicity on memory. Request the previous inspection report from the facility manager with a date — the period runs from there, not from installation.
12 most common findings and how to prevent them
1. Missing or unreadable documentation (60% of inspections)
Most common cause of longer inspection and higher price. The technician needs: - Original project documentation (electrical design + statics) - Previous inspection report - Switchgear schematics (current, not from 1998) - Records of maintenance and repairs - For machines: declaration of conformity + documentation per the Machinery Directive 2006/42/EC
**Prevention:** Complete the file before the inspection. If documentation doesn't exist, the technician will create a current schematic for you (= twice as long an audit and 2–4× higher cost).
2. Incorrectly sized breakers (45%)
After adding load (air conditioning, EV charger, server) nobody recalculated the breaker. Most common: 16 A C-characteristic in front of a 32 A motor = trip on every startup. Or the opposite: 25 A B characteristic in front of a 1.5 mm² conductor = the breaker reacts later than the insulation catches fire.
**Prevention:** After every load change, recalculate per STN 33 2000-4-43 (IEC 60364-4-43). Ready calculators: ETI Configurator, Hager Calc, OBO BetterDesign — all free, produce a list of breakers for the given load.
3. Missing or non-functional RCD (40%)
Apartment installations from the 90s don't have an RCD, or have type AC, which doesn't react to pulsed and DC currents from modern electronics (inverter washing machines, EV chargers, photovoltaics).
**Prevention:** Test with the T button monthly (this shouldn't be done by the inspection technician, it should be done by the user). For EV chargers, the decree and STN EN 62752 require at minimum **type B RCD** or A + 6 mA DC monitor. A regular type AC for €12 isn't enough.
4. Unsuitable socket type vs. environment (35%)
A regular IP20 socket in a workshop with dust and humidity (premises B or C per STN 33 2000-7-704). After two years there's dust inside corroding the contacts.
**Prevention:** Minimum IP44 in all wet spaces (bathroom zones 2/3, garage, exterior, workshops with liquid processing). In bathroom zones 0 and 1, NOTHING may be installed except SELV lights at IP67. Specifically: STN 33 2000-7-701 was amended in 2023, some installations from 2015–2022 no longer comply with the current standard.
5. Improper grounding / insufficient bonding network (30%)
Grounding value > 5 Ω at normal installation, or > 1 Ω at TN-C-S with PEN conductor. Often a problem in old buildings, where the ground rod is only 0.5 m deep in urban-type soil.
**Prevention:** Measure ground resistance every 2 years with your own tester (Fluke 1623-2, Metrel MI 3290). If the value rises, drive an additional ground rod or switch to a TT network.
6. Missing identification and labeling of the switchgear (50%)
Decree 508/2009 and STN EN 60204-1 require unambiguous identification of every breaker, motor starter, contactor. "Breaker 1, breaker 2, breaker 3" = a finding. It must be: what it protects, where the consumer is, conductor cross-section, date of last check.
**Prevention:** Professional label printer (Brady BMP41, Brother PT-E550W). Cost: €0.15 per label. Investment of €60 on labels + 90 minutes of sticking them before inspection — saves €200–500 on a prolonged audit.
7. Improper motor protection (20%)
11 kW motor on a 25 A motor starter set to 18 A instead of the required 22 A. The starter drops out on startup, somebody dials it to max (25 A), thereby exceeding both the cable (4 mm²) and the starter itself. Real risk of fire.
**Prevention:** Set per the motor nameplate, not per the electrician's memory. Range of measured nominal motor value + 10% reserve. More complex drives: PT100 thermistor in the motor winding that directly switches off through a protection relay.
8. Missing surge protection (75% of buildings without lightning protection)
The new STN EN 62305-4 (protection of electronic systems against lightning impulse) requires multi-stage protection at every installation connected to an external network — i.e., **every building**. Type 1 + Type 2 surge protection in the main switchgear = optional only at buildings without a lightning protection system AND in an urban location with LPS > B2 (which is 80% of Slovakia).
**Prevention:** Dehn DSH ZP TT 255, OBO V25, Iskra POL 230/12,5 — 3-stage protection, price €80–200 per set. With PV installation, a DC surge protector between panels and inverter is mandatory.
9. Conductors without color marking or with wrong colors (25%)
STN 33 2000-5-51 specifies: PEN/PE = green-yellow, N = blue, L1 = brown, L2 = black, L3 = grey. Old installations often have red or yellow everywhere. Not only is this a finding, but it's also genuinely dangerous — an electrician can mistake phase for neutral.
**Prevention:** During every partial renovation, switch to current colors. In the switchgear use heat-shrink labeled sleeves (Phoenix Contact MULTI 04, Wago 209-184) if original conductors can't be changed.
10. Open or missing switchgear covers (35%)
The IP rating of a switchgear applies only with the cover closed. Open or removed cover = IP00, which fails STN 33 2000-4-41. We often see a switchgear with the front panel ripped out, because "for better cooling".
**Prevention:** Filter-fan units (Rittal SK 3237, Schroff 17118-016) with thermostatic switching. Cheaper than a follow-up audit or an injury.
11. Cables without protective conduit in places of mechanical stress (20%)
Cables "loose" in a workshop or warehouse where a forklift can pass. STN 33 2000-5-52 requires IK10 mechanical protection (= 20 J impact) in industrial spaces.
**Prevention:** Heavy installation conduits (Kopos 1525, Schwabe 8825) in zones with impact risk. Price €1.50/m, lifespan 30+ years.
12. Missing documentation after changes (90% of inspections)
The client makes 5 small changes per year — moves a strip, relocates a socket, adds lighting — and none gets recorded in the schematic. The technician sees an installation that doesn't match the schematic = automatic finding.
**Prevention:** Logbook (Excel or paper) in the switchgear. Every change: date, who did it, what they did, signature. Schematic updated once a year (€60–120 per hour for a designer).
Practical procedure before inspection (30 days ahead)
1. **Week 1:** Request the previous inspection report. Go through the list of identified findings — have they been removed? If not, it's a recurring finding = fine + pressure on the technician. 2. **Week 2:** Self pre-inspection. Visual walk-through per the 12 points above. Cost: €0 + 4 hours of your electrical maintenance. 3. **Week 3:** Fix the trivial ones (labels, covers, documentation). For larger ones (RCD, surge protection), order material. 4. **Week 4:** Update schematics and logbook. Prepare the file for the technician.
This procedure reduces the average number of findings from 4.1 to 0.8 and shortens the audit itself from 6–8 hours to 3–4 hours — which translates into lower billing and a faster report.
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*We do inspections and help clients prepare for them. If your inspection is coming up and you'd like to walk through a checklist beforehand, the first call (45 minutes) is free — our goal is for the inspection to pass, not for you to have a bad report for a sponsorship audit.*