Power-Installation Safety Above 1 kV: IEC 61936-1 Boundaries

IEC 61936-1 governs the design and erection of the high-voltage installation around the equipment; it does not replace the product standard for factory-built MV switchgear or the safe-work rules used after handover. The boundary between installation, product, operation and law must be explicit.

This guide maps IEC 61936-1:2021 to MV substations: equipment selection, clearances, access, earthing, fire, ventilation, auxiliary systems, protection, lightning, escape routes, multiple sources, commissioning and documentation—while separating IEC 62271 product evidence and operational safety procedures.

Executive conclusions

IEC 61936-1:2021 applies to design/erection of AC power installations above 1 kV, up to 60 Hz, within its stated scope/exclusions.
IEC 62271-200/-1 qualify factory-built MV switchgear; IEC 61936-1 integrates it into the substation.
Installation safety includes access, barriers, clearances, earthing, fire, ventilation, escape, protection/control and building interfaces.
Human-safety distances and operating-space requirements are not obtained from an equipment impulse withstand rating.
National/regional law, grid code, fire/building rules and occupational safe-work regulations can take precedence or add requirements.
Declare normal/special service conditions and all energy sources, including backfeeds, generators, UPS, stored energy and induced voltage.
Earthing design must control touch/step voltage and withstand fault current/time; a low grid resistance alone is not the acceptance criterion.
Fire/ventilation design must account for transformers, batteries, gases, pressure relief, arc products and loss of HVAC.
IEC 61936-1 distinguishes design/erection from subsequent maintenance/live-work procedures; Annex F is informative guidance where local rules are absent.
Commissioning must prove installed interfaces and as-built safety functions, not repeat product type tests.

1. Scope and exclusions

IEC 61936-1:2021 provides requirements for the design and erection of AC electrical power installations with nominal voltage above 1 kV and frequency up to 60 Hz. It excludes specified sectors such as inter-installation overhead/underground lines, electrified rail rolling stock, mining equipment, ships/offshore installations covered elsewhere and other listed applications. Always read the current scope rather than copying an older edition.

2. Four boundaries to establish

Boundary	Typical governing source	Example
Product	IEC 62271/transformer/cable/relay standards	Panel type/routine tests and IAC/LSC rating
Installation	IEC 61936-1 + local design rules	Room, earthing, access, cable route, fire and ventilation
Operation/maintenance	Owner procedures + occupational law	Isolation, proving dead, earthing and permits
Workplace risk	National safety regulations/risk assessment	Arc-flash/shock controls and PPE

A compliant switchgear panel can be unsafe in a room with blocked pressure relief, inadequate escape, bad earthing or inaccessible cable terminations.

3. Project standards and legal register

IEC 61936-1 edition and national adoption;
applicable IEC 62271/transformer/cable/protection standards;
grid code/utility requirements;
national electrical installation and earthing rules;
building, fire, environmental and pressure regulations;
occupational safety, safe-work and live-work rules;
emergency services and insurer requirements;
owner standards and document precedence;
approved deviations and authority decisions.

4. Installation input data

single-line, voltage/frequency/earthing and maximum/minimum faults;
normal, maintenance and contingency configurations;
site altitude, ambient, pollution, flood, seismic, wind and lightning;
personnel/public access and operating/maintenance method;
transformer/insulating liquid/gas/battery hazards;
building geometry, pressure relief and ventilation;
cable/overhead interfaces and induced/backfeed sources;
protection clearing/backup time and DC reliability;
future expansion and temporary supplies;
emergency response and escape strategy.

5. Equipment selection and coordination

Um and insulation coordination;
continuous current and ambient/ventilation derating;
short-time/peak current and clearing duration;
switching/making/breaking duty and TRV;
internal arc/pressure relief where specified;
IP/IK/corrosion and accessibility;
seismic/environmental qualification;
auxiliary supply and fail-safe operation;
maintainability, isolation and earthing facilities;
environmental media handling/end of life.

Verify product evidence under the product standard, then verify installation suitability under IEC 61936-1. One does not replace the other.

6. Clearances, barriers and access

electrical clearance based on insulation coordination/product design;
safety clearance/distance to live parts under installation rules;
barriers/enclosures and protection against direct contact;
restricted electrical operating area and access control;
door/gate opening and emergency egress;
operating/maintenance aisle and equipment withdrawal path;
transport/replacement route for breaker/transformer;
height/space for cable tests and safe earthing;
temporary work zones without defeating escape.

Do not infer safe approach distance from IP code or rated impulse withstand. They answer different questions.

7. Multiple sources and isolation

utility feeds, bus couplers and transformer parallels;
generators, PV/BESS/converters and emergency supply;
LV backfeed through transformers;
VT/auxiliary/control/UPS circuits;
stored spring, hydraulic/pneumatic energy and capacitors;
induced voltage and adjacent live circuits;
remote/automatic controls and auto-reclose;
multiple disconnection points with durable labels;
safe proving-dead/earthing locations and interlocks.

The 2021 edition specifically improved labelling requirements where multiple sources must be disconnected. The isolation diagram and procedure should match as-built reality.

8. Earthing system

maximum earth-fault current and distribution through grid, neutrals, screens and remote earths;
fault duration including breaker failure/backup;
soil resistivity model, seasonal variation and multilayer effects;
grid conductor thermal/mechanical/corrosion design;
touch, step and transferred potentials;
fences, gates, rails, pipes, cable sheaths and telecom circuits;
equipotential bonding of switchgear/transformers/building steel;
neutral/NGR/earthing transformer connection;
testing/inspection points and future expansion;
commissioning measurements with model correlation.

Ground resistance is an input/indicator; safety is evaluated through permissible touch/step conditions, fault current distribution, duration and body/contact assumptions under the applicable rules.

9. Protection, automation and auxiliary systems

main/backup protection zones and failure clearing;
CT/VT selection and secondary safety;
trip circuit/DC battery/charger reliability and supervision;
breaker failure, lockout, intertrip and auto-reclose;
local/remote authority and emergency trip;
alarms, SOE, disturbance records and time synchronization;
IEC 61850/network redundancy/cybersecurity where used;
fail-safe behavior on loss of supply/communication;
selectivity and equipment thermal withstand;
testing/isolation facilities and maintenance access.

10. Fire, explosion and internal arc

transformer liquid type/volume and containment/drainage;
fire separation and distance to buildings/escape routes;
battery gas/thermal runaway and ventilation;
SF6/alternative-gas decomposition/pressure handling;
internal-arc pressure/gas/particle path;
cable fire load, sealing and segregation;
fire detection/suppression compatible with energized equipment;
emergency shutdown and responder information;
post-event hazardous atmosphere and access control.

Internal arc classification of switchgear is conditional type-test evidence, not a complete room or worker arc-flash risk assessment.

11. Ventilation and HVAC

normal equipment heat load and ambient limits;
transformer/UPS/battery/charger heat and gases;
natural/forced ventilation and redundancy;
loss-of-HVAC alarm and safe operating load/time;
dust/salt/humidity/condensation filtration/control;
pressure relief separated from HVAC ducts/occupied areas;
fire dampers and cable penetration sealing;
maintenance without unsafe live access.

12. Lightning and surge protection

external lightning protection and down-conductor separation;
substation grid/bonding and surge current paths;
overhead-to-cable transition protection;
surge arrester rating/TOV/energy/protective level/location;
control/communication surge protection and isolation;
GNSS/antenna/telecom entry protection;
shielding, lead length and cable screen bonding;
coordination with IEC 60071 study.

13. Buildings, escape and maintainability

door direction, locks and emergency release;
escape route length/width/obstruction and emergency lighting;
floor loading, anchorage and seismic restraint;
cable trenches/openings and fire/water sealing;
flood level/drainage and oil containment;
pressure relief and structural response;
lifting beams/access for replacement;
illumination, working space and labels;
noise, temperature and hazardous substance controls.

14. Operational safety handoff

Design must enable safe operation, but subsequent work is governed by competent-person procedures and local occupational rules. Handover should define:

single-line/isolation/earthing diagrams;
switching rules, permits and role authorization;
lockout/tagout/key control;
proving-dead equipment and procedure;
portable/fixed earthing points and ratings;
arc-flash/shock risk assessments and labels;
remote operation and restricted approach;
emergency/rescue/fire response;
maintenance/inspection and change control.

IEC 61936-1:2021 clarified the distinction between erection/design safety and later maintenance/repair safe-working procedures. Its Annex F is informative where no local rules exist; it does not override law.

15. Commissioning and verification

as-built equipment/rating/clearance/access review;
earthing continuity and grid measurements/model reconciliation;
protection settings, secondary injection and end-to-end trip;
breaker/interlock/earthing-switch negative tests;
DC battery/charger/loss-of-supply tests;
phase sequence, CT/VT polarity and cable tests;
alarm/SCADA/communication/time/failure tests;
HVAC/fire/pressure-relief interfaces;
labels, multiple-source warnings and escape readiness;
NCR closure, as-left state and operator training.

16. Required documentation

standards/legal/compliance and deviation registers;
single-line, layout, sections and cable routes;
earthing/lightning/fire/ventilation studies;
short-circuit, insulation, protection and arc-flash studies;
equipment data/type/routine/FAT evidence;
interlock, trip, cause-effect and SCADA matrices;
commissioning/SAT records;
operation/maintenance/emergency procedures;
hazardous materials/environmental/end-of-life data;
as-built revision and future expansion constraints.

17. Failure-scenario design review

Failure	Installation-level questions
Main protection or breaker fails	Which backup devices clear every source, in what time, and can equipment/earthing withstand it?
Station DC is low/lost	Are dual paths, battery autonomy, trip capacitors or manual emergency means required and supervised?
HVAC/heater fails	How long can load remain, which alarms act and how are condensation/overtemperature controlled?
Internal arc occurs	Where do pressure, hot gas, particles and smoke go; are escape routes and adjacent equipment protected?
One earthing connection opens	Does the grid remain continuous and are touch/step/transfer potentials acceptable?
Remote communication/control fails	What local fail-safe control remains and can automation issue stale/duplicate commands on recovery?
Fire/flood affects one area	Are redundant systems separated and is emergency isolation accessible?
Unplanned backfeed appears	Do indication, isolation points, interlocks and labels identify every source?

Document each initiating event, detection, automatic action, manual response, safe state, remaining hazard and test. A design that is safe only while every auxiliary system works is not robust.

18. Stage-gate responsibility matrix

Concept: owner defines operating philosophy, access, reliability, fault/earthing and legal basis.
Detailed design: consultant/contractor coordinates layout, clearances, earthing, fire, ventilation, protection and interfaces.
Manufacturer: supplies product evidence, installation constraints, pressure relief, heat loss, maintenance and environmental data.
Civil/building team: proves structure, escape, penetrations, fire separation, drainage and exhaust paths.
Protection/control team: proves zones, settings, DC, communications, fail-safe logic and clearing times.
Commissioning authority: verifies as-built interfaces and closes NCRs.
Owner/operator: accepts residual risk, procedures, competence, maintenance and change control.

Every safety requirement needs one accountable owner and one verification record. “By others” is not closed until the interface, deliverable and accepting party are named.

19. Common mistakes

using IEC 61936-1 as the switchgear product standard;
assuming product type tests prove room/installation safety;
using insulation withstand as human approach distance;
checking earth resistance but not touch/step/transferred voltage;
ignoring multiple/backfeed/stored-energy sources;
blocking internal-arc exhaust with building/HVAC;
no failure plan for HVAC/DC/protection/communication;
treating informative Annex F as national law;
omitting future expansion/contingency cases;
handover without as-built isolation/earthing documents.

Primary references

Safety note: Apply national law, owner rules and a competent project-specific risk assessment. This article is not a switching instruction or authorization for live work.