NR-10 Controlled Zone Radius

NR-10 Electrical Controlled Zone Calculator

Brazil’s Regulatory Norm NR-10 draws two safety boundaries around energised electrical parts. The Risk Zone (Dr) is the inner one, where getting close means the part has to be de-energised or specific control measures put in place. The Controlled Zone (Dc) sits further out and only authorised personnel may cross it. How far each line falls depends on the voltage of the installation. At 13.8 kV, for instance, the values come out to Dr = 0.20 m and Dc = 0.96 m; bump that to 138 kV and they climb to roughly 1.10 m and 3.00 m. Anything above 1 kV counts as high voltage (AT) under NR-10 and anything below as low voltage (BT), with the rules tightening step by step once you pass 50 V AC.

Inside the controlled zone, only workers classified as qualified, capacitated and authorised are allowed to operate. The norm asks for the basic NR-10 course of 40 hours and an 8-hour refresher every year; anyone working on the Electrical Power System (SEP) also has to take an extra 40-hour module. On paper, that means keeping the Electrical Installations Prontuário (PIE), the single-line diagrams and the Risk Analysis Report.

Applications

Electrical engineers, safety technicians and maintenance planners lean on it to set where the isolation tape goes, pick the right insulating tools, size permanent barriers, plan switching manoeuvres and put together the Work Permits (PT) for tasks done live or close to it.

FAQ

Can the controlled zone overlap walkways? No. Whenever the controlled zone runs into areas where people walk or vehicles pass, NR-10 calls for physical barriers, signs or grounded screens.

Does the certificate from another company count? It does, but not on its own. Every new employer still has to validate it, enter the worker in the Prontuário and run a complementary course covering the local procedures and the specific equipment in use.

What about DC (direct current) installations? DC falls under NR-10 too. The voltage thresholds look much the same, but for the safety distances you pull the figures from ABNT NBR 5410 (low voltage) and NBR 14039 (1 to 36.2 kV), applied to the DC nominal value.