Arkansas HVACR NewsMagazine November 2020

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 High Resistance and Low Voltage = Safer  Low Resistance and High Voltage = Danger This is why working around live electrical should only be done with insulated tools, proper PPE and in dry conditions. These all serve to keep the resistance up to reduce the likelihood of a fatal shock. The higher the voltage the more diligent you need to be. Some people may bring up high voltage shocks from a taser or static electricity as proof that “voltage doesn’t kill”. In these cases, the power supply is either limited, intermittent or instantaneous. This means that while the voltage is high it is only high for a very short period. Unfortunately in our profession, those sorts of quick high voltage discharges aren’t the big danger we face, most of the electrical work we do is on systems that will happily fry us to a crisp before the power supply cuts out. A circuit breaker or fuse will never protect us because we draw in the milliamp range when we are being shocked as almost all fuses or breakers don’t trip or blow until much higher levels are reached. Be safe around high voltage and keep your resistance high.

50 – 150 milliamps (continued)

Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Death is possible. Ventricular fibrillation (heart pumping action not rhythmic) occurs. Muscles contract; nerve damage occurs. Death is likely.

1,000- 4,300 milliamps

(1-4.3 amps)

10,000 milliamps (10 amps)

Cardiac arrest and severe burns occur. Death is probable.

*Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns. †Differences in muscle and fat content affect the severity of shock. Let’s say that a particular shock is traveling through a 20 KOhm (20,000 ohm) path in your body

• At 120V this would produce a 6mA shock

• At 240V it would be 12mA • At 480V it would be 24mA

Bryan Orr, HVAC School ( Founder / Podcaster / Dad of 10 ) Bryan Orr is a lifelong learner, proud technician and advocate for the for the HVAC/R Trade

It becomes clear pretty quick that higher voltage does lead to more dangerous shocks as does the resistance of the path.