Power Isolation & Bleeding

Safe isolation procedures, LOTO (Lockout/Tagout), power bleeding, capacitor discharge, and permit-to-work requirements for UAE construction sites.

Regulatory Basis

Safe isolation and power bleeding are mandatory before any electrical work is carried out on site. ADOSH-SF CoP 15.0 Section 4 requires that all electrical work be carried out only after the circuit or equipment has been made dead, isolated, and proved dead. The Dubai Municipality Code of Construction Safety Practice and the UAE Fire and Life Safety Code both reinforce this requirement. Failure to isolate is the leading cause of electrical fatalities on UAE construction sites.

Governing standard
ADOSH-SF CoP 15.0 — Section 4 (Electrical Safety)
critical
Dubai standard
DM Code of Construction Safety Practice
critical

Safe Isolation Procedure (5-Step)

The internationally recognised 5-step safe isolation procedure must be followed on all UAE construction sites before any electrical work begins. This procedure is referenced in ADOSH-SF CoP 15.0 and aligns with IEC 60364 and BS 7671 requirements.

Step	Action	Severity
1	Identify the circuit or equipment to be isolated — confirm correct identification using circuit schedules and labelling	Critical
2	Switch off and isolate — open the isolator, MCB, or MCCB and lock off using a padlock and lockout hasp	Critical
3	Prove the voltage tester is working — test on a known live source before and after testing the isolated circuit	Critical
4	Test for dead — use an approved voltage indicator (GS38 compliant) to confirm all poles are dead at the point of work	Critical
5	Prove the tester again — retest on the known live source to confirm the tester still functions	Critical

A non-contact voltage tester alone is not sufficient for safe isolation. A two-pole voltage indicator complying with GS38 (or equivalent) must be used.

Lockout / Tagout (LOTO)

ADOSH-SF CoP 15.0 requires a formal LOTO system for all electrical isolation on construction sites. Each person working on isolated equipment must apply their own personal padlock to the lockout hasp. No one may remove another person's lock. A danger tag must be attached to the isolation point identifying the worker, the date, and the reason for isolation.

Personal padlock
Each worker applies own lock — unique key
critical
Lockout hasp
Multi-lock hasp required when more than one person is working
critical
Danger tag
Name, date, reason for isolation — attached to isolation point
critical
LOTO register
Written record of all active isolations maintained on site
critical
Permit to Work
Required for all HV work and complex LV isolation on UAE sites
critical

Power Bleeding (Capacitor Discharge)

After isolation, stored energy in capacitors, UPS systems, variable speed drives (VSDs), soft starters, and power factor correction banks must be discharged before work begins. Many modern VSDs retain dangerous DC bus voltages for several minutes after isolation. The equipment manufacturer's discharge time must be observed and confirmed with a voltage tester before touching internal components.

VSD / inverter discharge time
Minimum 5 minutes after isolation — confirm with voltage tester
critical
UPS systems
Isolate both input and bypass; discharge capacitors per manufacturer instructions
critical
Power factor correction capacitors
Discharge resistors must be fitted or manual discharge procedure followed
critical
Voltage confirmation
Measure DC bus voltage with approved meter before touching internal components
critical

Never assume a VSD or UPS is safe to work on immediately after switching off. The DC bus can retain 400–800V for several minutes. Always measure before touching.