PAT Testing Intervals Guide
Risk-based testing frequencies, equipment classes, test limits, and legal requirements
IET Code of Practice 5th Edition & Electricity at Work Regulations 1989
PAT vs EET — What Changed?
The IET 5th Edition (2020) renamed PAT to Electrical Equipment Testing (EET) and shifted from fixed annual schedules to a risk-based approach. There is no law requiring testing at a specific frequency — the duty holder must justify intervals through a documented risk assessment. The old prescriptive frequency tables have been removed.
Key change: Universal leakage limit simplified to 5 mA for all classes (was 0.25 mA for Class II).
Suggested Testing Frequencies
These are industry benchmarks, not legal requirements. Actual intervals should be based on risk assessment.
| Environment | Item Type | User Check | Formal Visual | Combined Test |
|---|---|---|---|---|
| Construction site | 110 V tools | Daily | Monthly | 3 months |
| Construction site | 230 V tools | Daily | Weekly | Monthly |
| Industrial / factory | All portable | Daily | 6–12 months | 6–12 months |
| Office / shop | IT equipment | No | 2–4 years | Up to 5 years |
| Office / shop | Kettles / fans / heaters | Yes | 1–2 years | 1–2 years |
| School / college | Shared equipment | Yes | 6–12 months | 1 year |
| Hotel | Bedroom items | No | 2 years | 3–5 years |
| HMO / rental | Shared area appliances | No | Annual | 1–2 years |
Risk Assessment Factors
| Factor | Higher Risk (test more often) | Lower Risk (test less often) |
|---|---|---|
| Environment | Construction site, workshop, outdoors | Office, hotel bedroom, archive |
| Equipment type | Hand-held power tools, portable heaters | Desktop computer, desk lamp |
| Construction class | Class I (relies on earth) | Class II (double insulated) |
| Users | Public, students, multiple users | Single trained employee |
| Movement frequency | Frequently moved / coiled | Stationary (rarely unplugged) |
| Previous failures | History of similar faults | Clean track record |
Equipment Classes & Test Limits
| Class | Description | Earth Continuity | Insulation Resistance | Leakage Limit |
|---|---|---|---|---|
| Class I | Earthed (metal chassis connected to earth pin) | ≤ 0.1 Ω + R | ≥ 1 MΩ (500 V DC) | ≤ 5 mA |
| Class II | Double insulated (no earth connection) | N/A | ≥ 2 MΩ (500 V DC) | ≤ 5 mA |
| Class II FE | Double insulated with functional earth | N/A (safety) | ≥ 2 MΩ (500 V DC) | ≤ 5 mA |
| Class III (SELV) | Extra-low voltage (battery/transformer) | N/A | Test the charger/PSU | N/A |
| IT / Sensitive | Computers, servers, monitors | ≤ 0.1 Ω + R | ≥ 1 MΩ (250 V DC) | ≤ 5 mA |
Landlord & Business Obligations
Scotland: Housing Act 2014 mandates PAT testing every 5 years or at change of tenancy.
England & Wales: No specific frequency mandated, but landlords must ensure supplied appliances are safe throughout the tenancy.
HMOs: Many local authorities require annual testing for shared appliances as an HMO licence condition.
EAWR 1989 Regulation 4(2) requires all electrical systems be maintained to prevent danger.
PAT testing is the accepted way to demonstrate due diligence and “all reasonable steps.”
Insurance: Most policies require compliance with safety regulations — untested equipment can invalidate claims.
Common PAT Failures
| Fault | Cause | Risk |
|---|---|---|
| Damaged cable | Abrasion, crushing, or excessive bending | Fire and electric shock |
| Wrong fuse fitted | Over-fusing (e.g. 13 A fuse in a 3 A lamp) | Cable overheating / fire |
| Earth path failure | Corroded or loose terminal in plug | Casing remains live during fault |
| Insulation breakdown | Moisture ingress or component aging | Electric shock to user |
| Poor cable grip | Incorrectly assembled rewireable plug | Internal arcing at terminals |
| Counterfeit plug | Non-BS 1363 plug, substandard materials | Melting / fire under normal load |
Common Misconceptions
- - “Annual testing is a legal requirement” — There is no law mandating a specific frequency. Intervals must be justified by risk assessment.
- - “New items need testing immediately” — New equipment from reputable manufacturers is generally exempt from the first test cycle.
- - “Only electricians can PAT test” — The law requires competence, not a specific qualification, though C&G 2377-77 is recommended.
- - “A pass sticker means it’s safe forever” — Testing is a snapshot in time. Damage can occur at any point after testing.
Key Points
- - The IET 5th Edition replaced fixed schedules with risk-based intervals
- - ~95% of defects can be found through visual inspection alone
- - Never earth-test Class II equipment — there is no earth path to measure
- - Use 250 V DC (not 500 V) for insulation testing on IT and sensitive equipment
- - Document everything — an asset register is your primary defence in litigation
- - Recommended qualification: C&G 2377-77 (Level 3 In-Service Inspection & Testing)