Which One is More Dangerous? 50Hz or 60Hz in 120V/230V & Why?

Electrical Technology

Which Frequency Level is Safer? 60Hz or 50Hz in 230V & 120V Circuits?

Here is another silly question because there is no significant difference between 50Hz and 60Hz. It would have made a sense if the comparison was between 50Hz to 500 Hz with high voltage and large capacitance in farads or microfarads and so on for 60Hz to 600Hz. The human body is not that much sensitive to differentiate between 60Hz and 50Hz i.e. the heart fibrillation risk is almost same for both cases.

Anyhow, we got the question and let’s analyze the exact result of both frequencies even if the difference(s) is very small.

Well, we will discuss the 50/60Hz in two ways

120V – 50 Hz vs 120V – 60Hz
120V – 50 Hz vs 230V 60Hz

As we know that there is no frequency in DC voltage i.e. frequencies only applicable to AC voltage. This way, we will not talk about DC voltages and DC electric current shock effects on the human body. We will stick only to the AC and its related characteristics.

This is because a human body may act as a capacitor to the AC supply due to the existence of frequency. When DC current flows in the human body, only resistance opposes it. On the other hand, when AC current flows through the human body, impedance (resistance “R” and capacitive reactance “X_C“) opposes the flow of current.

Capacitance of Human Body

Unlike the DC voltage, the human body (from live wire to ground) acts as an insulating medium like a capacitor in case of AC voltage. If the value of current is too small (like micro amperes) in the victim body to the ground, the body will discharge to ground and the potential will lead to zero and the whole process is barely sensible.

The average capacitance of a human body is 100 pF (e.g. 100 pF = 100 x 10^-12 = 0.0001µF = 0.0001 x 10^-6 = 1 x10^-10 Farad (where one farad is Coulomb / Volt) which is too small to be considered. Where the resistance of the human body is up to 100,000 Ohms in dry condition (and up to 1kΩ in throughout wet conditions).

The capacitance of human body can be calculated using the flowing formula.

C _Body = (( R _Body + R _Source ) × Tanθ ) ÷ ( R _Body × R _Source × ω )

Where:

C _Body = Capacitance of body
R _Body = Resistance of Body
R _Source = Resistance of Source
Tanθ = where θ = 2π ( Time period ÷ time delay)
ω = 2πf and f = frequency in Hertz

As we know that in a capacitive circuit, current increases when frequency increases. Similarly, current Increases when capacitance increases or capacitive reactance decreases. But still that won’t make any significant changes and have a sensible effect on the human body if the frequency increases from the 50Hz to 60Hz or even 500Hz. For example, the capacitance of the human body is 4.60nF at 50Hz and 4.55nF at 60Hz. These values won’t let you decide which one is safer. Stay away from these trap myths as both are bastards.

This will only make changes in high voltage circuits or when the value of capacitor is high e.g. microfarads or more.

120V – 50 Hz

The common residential single phase supply in the US is 120V – 60Hz (where it is 230V – 50Hz in the EU & UK – IEC). It is actually the RMS voltage means the 120V – AC would have the same heating effect as 120V DC (Same is the case for 230V AC and DC).

Example: Suppose the resistance of the human body is 100,000 ohms and capacitance of 100 pF. Let’s calculate the amount of current if he makes contact with the live wire of 120V.

X_C = 1 ÷ 2πfC in Ω

X_C = 1 ÷ (2π × 50Hz × 100 pF in Ω
X_C = 1 ÷ (2π × 60 100 pF) in Ω
X_C= 31.83 MΩ

R = 100,000Ω

As both resistance and capacitive reactance will be acting in parallel circuits. So the total impedance in parallel capacitive and resistive circuit is:

Impedance Z = (R² + X_C²) ÷ (√ (R² + X_C²))
Impedance Z = 99.9kΩ

Now, the flowing amount of current in the body

I = V ÷ Z
I = 1.2 mA

120V – 60 Hz

The value of current is the same if we change the value of frequency from 50Hz to 60Hz.

I = 1.2 mA

No wonder, the same 1.2 mA current will flow through the human body if we increase the supply frequency from 50 to 500Hz. In short, the RMS value and Peak to Peak value is not dependent on the supply frequency.

The above theoretical calculations shows that If we put frequency as 50Hz, 60Hz or 500Hz, the overall impedance (i.e. resistance) would decrease. This way, AC has the ability to easily pass through the capacitor where the capacitor blocks the DC voltage. As we are talking about AC with frequency, it means AC is more dangerous than DC in cases when the human body acts as a capacitor.

120V – 50Hz Vs 230V – 60Hz

Now, if we talk about the 120V – 60Hz and 230V-50 Hz. We already discussed that 230V is more dangerous than 120V as in case of a resistive load (like the human body) the higher the potential difference, the more the flow of electrons will be.

Conclusion:

The electric shock will be almost the same for both frequencies of 50Hz and 60Hz at 120V supply voltage. Despite the frequencies of 50 & 60 Hz, both 120V and 230V / 240V are dangerous and one may never ever touch the live wire at any cost.

In short, it is not the frequency in hertz, but electric power i.e. the amount of voltage which pumps the electric current into the victim body to the ground. Overall, it is the electrical energy which is responsible for all these bad things (electrocution).

Keep in mind that impedance and resistance decreases when frequency increases. This way, stay away from high voltage and capacitive appliances as the higher the frequency and voltage, the more will be the current.

This is why birds can safely sit on the medium voltage lines (up to 50kV) but not on +200kV power lines as the field intensity of EHV is fatal to anyone even in free air. That’s why a standard distance should be kept between an energized line and the line workers.

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