Which One is More Dangerous? 120V or 230V and Why?

Which One is More Dangerous? 120V or 230V and Why? . Electricity is vital in modern life, but it also presents inherent dangers if not handled properly. A common question arises when comparing different electrical systems: Which is more dangerous, 120V or 230V? This article explores the differences between these two voltages, their potential hazards, and key safety considerations.

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Which AC Voltage Level is Safer? 230V or 120V in Domestic and Residential Applications

We all know that the domestic and residential voltage levels at the homes are 230V AC (in EU – IEC) and 120V and 240V AC (in US – NEC). The most frequently asked question is which voltage level is more dangerous (or safer) to use and what are the reasons. To clarify the confusion, let’s see the following statements and examples.

First of all, the confusion arises when we see the statement “According to Ohm’s Law, Current Increases when Voltage increases (I=V ÷ R), but Current decreases when Voltage increases according to (P = V×I) formula

In addition, keep in mind that Amperes are responsible for electrocution, Not the Volts. In other words, voltage is responsible to drive the current i.e. current kills, not the voltage. Keep in mind that don’t fall for the next confusion about which one is more dangerous AC or DC voltage levels as there are some differences between AC and DC but the effect of electric shock is almost the same on the human body. Now let’s move to the actual scenario.

One thing is clear that the more current is flowing in the circuit, the higher chance of worst electrocution when one of the live wires comes in contact with the human body. Now let’s see which circuit has more current flowing in it when connected to the 230V and 120V respectively.

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What Happens When the Human Body Encounters Electricity?

The human body conducts electricity, and even low-voltage currents can disrupt physiological functions. Effects of electrical exposure include:

1. Tingling Sensation: Caused by minor currents.
2. Muscle Contractions: Can lead to inability to release the source of the shock.
3. Respiratory Arrest: High currents can impair breathing.
4. Cardiac Arrest: Electricity can disrupt the heart’s rhythm, leading to fatal arrhythmias.

It really confuses the newbies when we assume a circuit of 80W bulb connected across 120V and then 230V as it clearly shows that there is more current flowing in the 120V circuit as compared to the 230V circuit. Let’s see the following example.

Suppose, there is an 80W bulb which is first connected across 120V and then 230V supply voltage. Now let’s determine the amount of flowing current in both circuits as follows.

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100W bulb in 120V Circuit

To calculate the current in amperes, we may use the basic power equation (P = V×I) as follow:

I = P ÷ V ⟹ I = 100W ÷ 120V ⟹ I = 833 mA

100W bulb in 230V Circuit

I = P ÷ V ⟹ I = 100W ÷ 230V ⟹ I = 435 mA

Well, we see that more current (almost double) is flowing in the 120V circuit as compared to the 230V circuit in case of 80W bulb load connected across them. Right? but this is not the actual case.

This is OK only in case when power is constant (like input and output of a transformer is the same) but the supplied power varies from the power house. In other words, the above scenario is OK if wattage is the same. If resistance is the same, the case will reverse (V=I×R) and if its current goes through the human body, the resistance is the same, so the current will double from 120V to 230V.

These different currents will flow in the bulb as they have different resistance, but when you touch with these voltages, current will depend on your body resistance and current will flow as per ohm law. The example above only happens and is suitable when the power(W) of the circuit is constant.

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P = V × I … (where P = power, V = voltage, I = current)

P = V × I … if “P” in watts is constant, then P with I is inversely proportional .

As an example = (When maintaining the power of 100W as constant)

100W = 120V × 0.833A

We have to keep 100W as constant and change the value of current and voltage.

Then , 100W = 230V × 0.435A

It is similar like a transformer i.e. if we step down voltage then automatically the current is step up and vice versa).

The above statement is right when we connect the 80W light bulb in both circuits as both bulbs in both circuits will produce the same light Intensity (energy density) as the wattage rating of both bulbs are the same. But if the bulb is only rated for 120V, it will blow when connected in a 230V circuit (see the upcoming example below). Similarly, if the bulb is rated for 230V and connected to a 120V supply, it will glow dimmer as compared to the 230V supply.

Let’s go deeper. If you have a 120 Watt lamp from the US rated at 120V, it’s gonna run 1 Amp. If you take that same lamp to the UK and plug it into 230V, it’ll draw almost 2 amps, and 230 Watts (and probably blow very quickly).

Likewise a 120 Watts lamp from the UK rated for 230V will draw 0.52 Amps on 230V. Bring that to the US and it’ll draw 0.26 Amps, 60 Watts, and be very dim. The statement is OK when resistance is constant (and power is variable, same in the case of the human body). It shows 120V needs higher (which is low) current for the same wattage lamp as compared to 230V circuit (where current is almost doubled). In short, a same wattage rated light bulb drawing 1 amp on 120V will draw almost 2 amps on 230V supply voltage.

Read More : 120V vs. 230V vs. 240V AC Power

Each material has its own resistance and when the manufacturer designs an appliance, they consider the available voltage level for the suitable operation as resistance comes first than the current and voltage. In this case, the resistance of the bulb’s filament will be almost half in case of 120V circuit as compared to 230V circuit. This way, lower current will flow in the 120V circuit.

If we connect a 80Ω bulb in both (120V & 230V) circuits, the bulb connected to the 230V will glow brighter than the bulb connected across 120V. This is because low current is flowing in the 120V circuit which is unable to deliver the required amount of current which is needed to glow the bulb. In other words, a bulb having the same resistance will glow dimmer in case of 120V as compared to the 230V. Let’s see the following example.

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80Ω bulb in 120V Circuit

To calculate the current in amperes, we may use the basic Ohm’s law (V = I × R) as follow:

I = V ÷ R ⟹ I = 120V ÷ 80Ω ⟹ I = 1.5 A

80Ω bulb in 230V Circuit

I = V ÷ R ⟹ I = 230V ÷ 80Ω ⟹ I = 2.875 mA

We see that more current is flowing in the bulb’s filament when connected to 230V supply voltage. That is the reason the bulb connected to the 230V circuit is brighter while the same bulb is dim when connected to the 120V circuit. In short, the more the current, the higher the power dissipation in the form of heat and light.

This shows the bulbs are rated for specific voltage levels. In short, the 230V rated bulb connected to the 120V circuit will glow dimmer and the 120V rated bulb connected to the 230V circuit will blow it at all.

Let’s move to the final stage as now we know that the things which have to be considered are voltage, current and resistance when talking about the electric shock and human body.

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Good to Know:

The average resistance of a human body in dry condition is almost ≈ 100,000Ω while the resistance of a human body in wet condition is 1000Ω.

Also, the voltage above 50V (in dry condition) and 25V (in wet condition) is enough to shock a person. Also, 30 mA (RCDs are set in the UK) is enough for respiratory paralysis while 75-100 mA will cause ventricular fibrillation (rapid & ineffective heartbeat).

Anything higher than 300mA is fatal and kills in seconds. 4.5 to 10A will instantly lead to cardiac arrest, severe burns and finally death.

Overall, it is mainly the eclectic power (a mixture of current and voltage) where voltage (as a pressure) pushes electric current (as a flow of charge) is responsible for electric shock.

Now let’s see what happens when a human comes in contact with 120V and 230V supply voltage levels. Let’s assume a person in wet condition (standing in a rain, puddle of water or sweating having a resistance of 1kΩ) makes a contact to the 230V and 120V circuit and analyze the results.

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Human Body in Contact of 120V Supply

• I = V ÷ R
• I = 120V ÷ 1kΩ
• I = 120 mA

Human Body in Contact of 230V Supply

• I = V ÷ R
• I = 230V ÷ 1kΩ
• I = 230 mA

We see that more current is flowing in the human body when contacted to the 230V as compared to the 120V supply voltage. Hence, it proves that 120V supply voltage is safer than 230V supply voltage. In other words, 230V is more dangerous than the 120V voltage.

It shows the human body has a resistance, and with V = I×R, if we double the voltage, we double the current. So current kills, but you get twice the current through your body with 230V as you do with 120V.

As shown in the first trap example, the 100W bulb has different resistances for 120V or 230V. When we touch the live conductor of 230V, the current flows 2 times higher than 120V. Remember the resistance of our body is the same in both cases as compared to the bulb or any other electrical appliance which has different values of resistances and operating voltage as well as wattage ratings. As a human body, we have only a constant value which is resistance whereas the resistance is variable (different values for specific and different voltage levels by designers and manufactures).

To keep things simple, think of voltage as pressure, the higher the volts the more pressure that is behind it. Technically the current does the damage, yes, but you get more current from more volts. It is similar to asking which voltage level is more dangerous, 1V or 1000V? This is why you see “Warning signs” at high voltage appliances and equipment i.e. higher voltage ⟹ higher danger.

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Why 230V Is More Dangerous Than 120V

1. Increased Voltage = Higher Risk

Higher voltage increases the likelihood of current passing through the body. At 230V, even brief contact can result in severe injury or death, as it forces more current through the body compared to 120V.

2. Higher Energy Transfer

230V systems transfer energy more efficiently, but this also means that accidental exposure delivers more energy, increasing the severity of burns and internal damage.

3. Lower Resistance Thresholds

The human body’s resistance decreases with higher voltages. At 230V, the body offers less opposition to current flow, amplifying the danger.

4. Arcing and Flashover

High-voltage systems are prone to arcing—electric discharge through the air—which can cause severe burns or fires even without direct contact.

When Is 120V More Dangerous?

Although 230V is generally more hazardous, certain conditions make 120V equally dangerous:

• Prolonged Exposure: Extended contact can cause serious injuries or death.
• Wet Conditions: Lower resistance amplifies current flow.
• Faulty Systems: Malfunctions can elevate risks regardless of voltage.

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Practical Safety Measures for 120V and 230V Systems

1. Use Proper Insulation

Electrical systems should always be insulated to prevent accidental contact.

2. Install Residual Current Devices (RCDs)

These devices detect leaks in current and shut off power to prevent electrocution.

3. Regular Maintenance

Inspect wiring and outlets to identify and resolve potential hazards, regardless of the voltage system in use.

4. Training and Awareness

Educating users about electrical safety is critical, especially in regions where high-voltage systems like 230V are standard.

5. Protective Gear

Use insulated gloves and tools when working near electrical systems.

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Frequently Asked Questions (FAQs)

1. Can 120V Kill You?
Yes, 120V can be fatal if exposure is prolonged, occurs in wet conditions, or flows directly through vital organs.

2. Why Is 230V Common in Europe?
230V is more efficient for power transmission and heavy appliances, which is why it’s the standard in Europe.

3. How Does Current Affect Safety?
Current determines the intensity of an electric shock. Higher currents cause severe injuries, even at lower voltages.

4. Are 120V Systems Safer for Homes?
Yes, 120V systems are generally safer for residential use due to lower voltage levels, which reduce the risk of fatal shocks.

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