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Monday, October 26, 2020

Electrical Safety Guidelines

Electrical  Safety and Preventive Measures

  • 30 ma used for portable tools (1 Ampere = 1000 MA)
  • 1 ohm required for Diesel Generator or portable diesel engines
  • 25 mili ohms is enough to kill a person
  • Min 3 mtrs clearance from electric to the person when passing. HV
  • Low voltage. <250 V 
  • Medium voltage. 250 V – 650 V 
  • High voltage. 650 V – 33 KV 
  • Extra high voltage. Above 33 KV 

Precaution:

  1. PTW 
  2. Isolation 
  3. LOTO 
  4. Insulation 
  5. RCD (Residual current device) circuit breaker 
  6. Bonding & Grounding 
  7. Guarding 
  8. Electric resistant PPE’s 
  9. Safe work practice 
  10. ELCB (Earth leakage circuit breaker) 
  11. GFCI (Ground fault circuit interrupter) 
  12. OCB (oil circuit breaker) 
  13. VCB (Vacuum circuit breaker) 
  14. Use flameproof apron while putting ON/OFF 

Points to Remember:

  1. The equipment itself should be checked to ensure that it is suitable and conforms with recognized standards such as CE marking and European standards, 
  2. Vertical clearance above walkways shall not be less than 3 mtrs (10ft) for circuits carrying 600 volts or less.
  3. Current: the flow of electricity through a conductor 
  4. Voltage: the potential difference between two points of a conductor 
  5. HIPOT TEST: It is the insulation leakage test done for high voltage electrical

Standard Electric Boards Colour Code:

  • Purple. 24 v dc
  • Yellow. 110 v ac
  • Blue. 220 v ac
  • Red. 440 v ac

Effects of Amount of A/C Current 60 Cycles/Seconds: 

  • More than 3 ma. Painful shock, incident, accident
  • More than 10 ma. muscle contraction can’t go
  • 25 mA can kill a person
  • More than 30 ma. Temporary lung paralysis 
  • More than 50 ma. Heart dysfunction, usually fatal
  • More than 100 ma – 4 a. Heart dysfunction, fatal 
  • Over 4 a. heart paralysis, severe. burn
  • 50 – 100 a. for a person will be fatal.  
  • For earth rod (D.G. or welding gen) required 1 ohm 
  • ARC: Electrical passing through the air
  • Minimum acceptable value of insulation resistance, 1 megohm for each 1000 V 
  • e.g. one motor 2400 V so you should have a minimum insulence resistance megohms
  • Clearance a person from live 50 kv lines shall be 10 feet 0.4 inches

Difference Between Grounding & Bonding?

Earthing is the attachment of a bonded metallic system to earth, typically through ground rods or other suitable grounding electrodes. The NEC prohibits earthing via isolated ground rods. As the only means of equipment grounding.

  1. Transformer requires min 4 earthing. 
  2. Grounding deep 10.  
  3. Ground rods shall not be less than 5/8 inch in diameter by 8 feet in length. 
  4. Ground rods shall be driven into the ground so that one end of the ground rod is at a minimum depth of 8 feet below the surface of the ground.
  5. Distance (away) from other grounding is 50. 
  6. Rod: copper or galvanized
  7. Transformer requires min 4 earthing standard ground resistance value of 5.0 ohms or less
  8. Bonding: grounding one equipment’s to another to avoid static electricity
  9. The telecommunications industry has often used 5 ohms or less as their value for grounding and bonding while electric utilities construct their ground systems so that the resistance at a large station will be no more than a few tenths of one ohm.
  10. Platform wide enough with guard rails (39 – 43”) and toe boards (4’’ - 6”)

Download File

 Electrical Safety Guidelines

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