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# Alternating Current

## Discussion

### introduction

In the US

• center tapped neutral: +120 V hot/neutral/−120 V hot
• hot + neutral = 120 V, standard voltage
• hot + hot = 240 V, high voltage for residential use (electric ovens, electric clothes dryers, etc.)
• three phase: neutral/120 V, ϕ = 0° hot/120 V, ϕ = 120° hot/120 V, ϕ = 240° hot
• hot + neutral = 120 V, standard voltage
• hot + hot = 120√3 V ≈ 208 V
• three phase motors

root-mean-square

The root mean square (rms) value of a quantity is a measure of its average magnitude determined by taking the root (r) of the mean (m) of the square (s) of the quantity (x).

According to the Merck Manual of Medical Information, Second Home Edition

Alternating current… is more dangerous than direct current. Direct current tends to cause a single muscle contraction often strong enough to force the person away from the current's source. Alternating current causes a continuing muscle contraction, often preventing people from releasing their grip on the current's source. As a result, exposure may be prolonged. Even a small amount of alternating current — barely enough to be felt as a mild shock — may cause a person's grip to freeze. Slightly more alternating current can cause the chest muscles to contract, making breathing impossible. Still more current can cause deadly heart rhythms.

Merck Manual of Medical Information, 2004