How often is the earthing network's resistance measured?

At least every twelve months, together with the continuity check at the earth connection points (NOM-022-STPS-2015, point 7.2(c)).

What values must the measurement show?

10 ohms or less for the earth resistance of lightning protection electrodes, 25 ohms or less for the earthing network, and electrical continuity at the earth connection points of equipment that can generate or store static electricity (point 7.2(c)(1) to (3); point 9.4(h)).

Is my workplace within the scope?

The standard applies in areas where flammable or explosive substances are stored, handled or transported, or which can store or generate static charges because of their processes, materials and equipment (point 2.1). It does not apply to motor vehicles, rail vehicles, vessels or aircraft (point 2.2).

Who may carry out the measurement?

The standard places the duty to measure on the employer (point 5.3) and requires instruments with a valid calibration certificate (point 9.3) and a record signed by the person who measured (point 9.5). Optionally, an accredited and approved testing laboratory or verification unit may be hired (point 11.1); its favourable report is valid for one year (point 11.5).

How long are records kept?

Documentary evidence and records may be shown on paper or electronically and are kept for at least one year (point 12.5).

MX · Expiry & renewal tracking

Never let the annual earthing measurement slip past twelve months

In Mexican areas with flammable or explosive substances or static electricity, the employer measures earthing resistance and checks continuity at least every twelve months, with calibrated instruments and a record (NOM-022-STPS-2015, points 7.2, 9.3 and 9.5). Records are kept for at least one year (point 12.5).

NOM-022-STPS-2015, Static electricity in workplaces - Safety conditions (DOF 01/04/2016), applies throughout Mexico in workplace areas where flammable or explosive substances are stored, handled or transported, or which, because of their processes, materials and equipment, can store or generate static electric charges (point 2.1). It came into force six months after publication and repealed NOM-022-STPS-2008 (transitory articles one and three).

The employer must measure the earth resistance of the earthing network under Chapter 9, check continuity at the earth connection points and, where relevant, measure relative humidity (point 5.3). One of the required safety measures is to carry out that measurement and check at least every twelve months (point 7.2(c)). Values must be 10 ohms or less for lightning protection electrodes, 25 ohms or less for the earthing network, and there must be electrical continuity at the connection points of equipment that can generate or store static electricity (point 7.2(c)(1) to (3)).

The measurement uses the fall-of-potential method under the least favourable soil moisture condition (point 9.1), with instruments holding a valid calibration certificate (point 9.3), following the procedure in point 9.4. Lightning protection electrodes must be disconnectable for the measurement (point 8.7).

The result is recorded with at least the workplace details and date, the name and signature of the person who measured, the instrument details and calibration certificate, the resistance values and continuity indication, a sketch of the measurement points and, where relevant, the lightning protection system's characteristics (points 5.6 and 9.5). Where relative humidity is a control measure, it is also measured and recorded at least every twelve months (point 7.3(b)).

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At a glance

Who it applies to	Areas with flammable or explosive substances, or that generate or store static electricity (NOM-022-STPS-2015, point 2.1)
Frequency	Earth resistance measurement and continuity check at least every twelve months (point 7.2(c))
Limit values	Up to 10 ohms for lightning protection electrodes; up to 25 ohms for the earthing network; continuity at connection points (point 7.2(c))
Method	Fall of potential, under the least favourable soil moisture condition (points 9.1 and 9.4)
Instruments	With a valid calibration certificate (point 9.3)
Record	Workplace, date, who measured, instruments, values, continuity, sketch and lightning protection (point 9.5)
Verification report or test report (optional)	Valid for one year if conditions do not change (point 11.5)
Record keeping	At least one year, on paper or electronically (point 12.5)

Workplaces or areas classified as high fire risk under NOM-002-STPS-2010 must install a lightning protection system such as lightning rods (point 8.1), whose earthing network is interconnected with the other earthing networks (point 8.6) and is also covered by the annual measurement. Training for workers involved in these tasks is refreshed at least every two years (point 10.2).

Who is responsible?

The employer measures earth resistance, checks continuity and, where relevant, measures relative humidity (point 5.3), records the values (point 5.6), informs workers and the Safety and Hygiene Commission about static electricity risks (point 5.4) and shows the documentation to the labour authority on request (point 5.7). Workers follow the safety measures, take part in training and report any abnormal condition in the earthing or lightning protection systems (points 6.1 to 6.3). Optionally, the employer may hire an accredited and approved verification unit or testing laboratory; the laboratory may only assess the measurement-related requirements (points 11.1 and 11.3).

If the deadline passes

Enforcement of NOM-022-STPS-2015 is the responsibility of the Ministry of Labour and Social Welfare (STPS) (Chapter 13). In the conformity assessment, the employer complies by presenting documentary evidence that the measurement and continuity check are carried out at least every twelve months and that the values meet the limits (point 12.3, criterion for points 5.1 and 7). Employers must comply with the official standards on occupational safety and health (Federal Labour Law, Article 132, section XVII), and there are sanctions for employers who do not observe safety and hygiene standards (Federal Labour Law, Articles 992 and 994, section V).

Twelve months from the last measurement, not from the report

The standard counts the interval between measurements: at least every twelve months (point 7.2(c)). Record the date the last measurement was carried out, which appears in the record (point 9.5(a)(3)), plus twelve months as the expiry. If you hire a testing laboratory or verification unit, its test report or verification report is valid for one year, provided the conditions on which it was based do not change (point 11.5).

Tracking it with ExpirySuite

Add a record for each workplace or earthing network and enter the date of the last measurement plus twelve months as the expiry date.
Email reminders arrive 60, 30, 14, 7 and 1 day before the expiry date and on the day, giving time to book the laboratory or prepare instruments with valid calibration.
Whoever performs the measurement can upload the record with the values, sketch and calibration certificate through a secure link that is valid for 14 days and needs no account.
Assign a responsible person, such as electrical maintenance; if the date passes without a measurement, managers get further reminders 3, 7 and 14 days later.

Frequently asked questions

How often is the earthing network's resistance measured?: At least every twelve months, together with the continuity check at the earth connection points (NOM-022-STPS-2015, point 7.2(c)).
What values must the measurement show?: 10 ohms or less for the earth resistance of lightning protection electrodes, 25 ohms or less for the earthing network, and electrical continuity at the earth connection points of equipment that can generate or store static electricity (point 7.2(c)(1) to (3); point 9.4(h)).
Is my workplace within the scope?: The standard applies in areas where flammable or explosive substances are stored, handled or transported, or which can store or generate static charges because of their processes, materials and equipment (point 2.1). It does not apply to motor vehicles, rail vehicles, vessels or aircraft (point 2.2).
Who may carry out the measurement?: The standard places the duty to measure on the employer (point 5.3) and requires instruments with a valid calibration certificate (point 9.3) and a record signed by the person who measured (point 9.5). Optionally, an accredited and approved testing laboratory or verification unit may be hired (point 11.1); its favourable report is valid for one year (point 11.5).
How long are records kept?: Documentary evidence and records may be shown on paper or electronically and are kept for at least one year (point 12.5).

Sources

Last checked: Oct 11, 2026 · This page summarises official sources for general information and is not legal advice. Check the linked sources for current rules and fees.

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Reminders on time

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