Touch Voltage Safety Screen Calculator

The Touch Voltage Safety Screen Calculator produces an entered touch-voltage value in volts for a grounding review:

\(\displaystyle V_{\text{touch}} = I_{\text{fault}} \times R_{\text{grid}} \times F_{\text{touch}}\)

The result is used to keep a documented touch-voltage arithmetic check with the grounding record. It combines the reviewed fault-current value, the entered grid resistance, and the portion of grid voltage represented by the entered touch fraction. The calculator then compares that calculated value with an Entered comparison value supplied by the reviewed method.

This calculation is part of a grounding-system review workflow. It is not an ampacity, conductor-sizing, voltage-drop, raceway-fill, or branch-circuit calculation. It does not select AWG or kcmil conductors, establish a grounding-electrode design, or determine an electrical worker’s exposure.

Touch-Voltage Calculation Inputs

Input	Electrical use
Entered fault current (A)	The fault-current value being reviewed for the grounding calculation.
Grid resistance (ohm)	The entered resistance of the reviewed grounding grid or grounding system.
Touch fraction (%)	The entered percentage of the grid-voltage quantity allocated to touch voltage.
Entered comparison value (V)	The voltage value from the reviewed method used for comparison with the calculated touch voltage.
Method and version	The worksheet or method identifier recorded with the calculation, such as worksheet-v1.
Source reference	The source record identifier associated with the entered values, such as record-touch.

The Touch fraction (%) is converted from percent to decimal form in the arithmetic. A touch fraction of 50% is used as 0.50.

Calculation Basis

The calculator applies the following formula:

\(\displaystyle \text{Touch voltage} = \text{Entered fault current} \times \text{Grid resistance} \times \left(\frac{\text{Touch fraction}}{100}\right)\)

It also calculates the comparison margin:

\(\displaystyle \text{Entered comparison margin} = \text{Entered comparison value} - \text{Touch voltage}\)

A positive margin means the entered comparison value is higher than the calculated touch-voltage value. A zero margin means the two entered values are equal. A negative margin means the calculated touch voltage exceeds the entered comparison value.

The margin is a numerical comparison only. Its meaning for grounding design, work practices, fault clearing, or personnel exposure depends on the method and source record entered for the review.

Calculation Example

Using the entered values shown:

Field	Entered value
Entered fault current (A)	1,000 A
Grid resistance (ohm)	0.4 ohm
Touch fraction (%)	50%
Entered comparison value (V)	250 V
Method and version	worksheet-v1
Source reference	record-touch

First, convert the touch fraction:

\(\displaystyle 50\% = 0.50\)

Then calculate touch voltage:

\(\displaystyle 1{,}000\ \text{A} \times 0.4\ \text{ohm} \times 0.50 = 200\ \text{V}\)

Touch voltage: 200 V

Next, compare that result with the entered comparison value:

\(\displaystyle 250\ \text{V} - 200\ \text{V} = 50\ \text{V}\)

Entered comparison margin: 50 V

For this example, the calculator reports:

• Touch voltage: 200 V
• Entered comparison margin: 50 V
• Source status: Source recorded
• Comparison status: Entered values comparable

Grounding Review Boundary

This calculator operates in non-independent mode. It records and compares entered values within a grounding-review worksheet, but it does not establish a safe touch-voltage limit, determine body-current exposure, validate grid resistance, calculate fault-clearing time, or make a grounding-design or work-practice conclusion.

The fault-current value, grid resistance, touch fraction, comparison value, method and version, and source reference must come from the engineering record or reviewed calculation method. Field verification, grounding-system design decisions, and any NEC, utility, site-standard, or AHJ requirements remain separate from this arithmetic comparison.