Meter Burden Voltage Calculator

A meter burden voltage calculation determines the voltage developed across an instrument’s input resistance while test current flows through it. The primary result, Burden voltage, shows the voltage the meter imposes on the circuit or signal source because the meter is not an ideal zero-resistance load.

Enter Meter input resistance in ohms and Meter current in amperes. The calculator returns:

• Burden voltage in volts
• Resistive burden power in watts
• Input resistance used
• Current used

This calculation is used when evaluating whether a meter, test instrument, transducer output, current source, CT secondary circuit, PT-related measurement circuit, or low-level control signal can supply the required current without unacceptable loading or measurement error.

A high input resistance generally reduces loading in voltage-measurement applications. In current-driven circuits, however, the voltage developed across that resistance may be significant relative to the available source voltage, instrument range, or intended operating point.

Meter Input Resistance and Circuit Loading

Meter input resistance is the effective resistive opposition presented by the meter input. When current passes through that resistance, the meter produces a voltage drop and dissipates power.

The calculated burden voltage is not necessarily an error by itself. It is the voltage required to drive the stated current through the meter input. Whether that voltage is acceptable depends on the circuit being tested and the instrument’s specified operating characteristics.

For example, burden voltage may be reviewed when:

• A low-voltage source must drive a meter input at a known current.
• A current loop or sensor output has limited compliance voltage.
• A test setup uses a series instrument that adds resistance to the circuit.
• An instrument transformer secondary circuit may be affected by connected metering equipment.
• A technician needs to estimate heat dissipation in a resistive meter input during a test.

The result does not determine conductor ampacity, AWG or kcmil selection, branch-circuit sizing, feeder sizing, raceway fill, voltage-drop compliance, or overcurrent protection. It can, however, support a broader load and voltage-drop review of the measurement circuit.

Burden Voltage Formula

The calculator applies Ohm’s law to the meter input resistance:

\(\displaystyle \text{Burden voltage (V)} = \text{Meter current (A)} \times \text{Meter input resistance (ohm)}\)

It also calculates the resistive power dissipated at the input:

\(\displaystyle \text{Resistive burden power (W)} = \text{Meter current (A)}^2 \times \text{Meter input resistance (ohm)}\)

Where:

Field or Result	Meaning
Meter input resistance	Resistance presented by the meter input, in ohms
Meter current	Current through the meter input, in amperes
Burden voltage	Voltage developed across the meter input resistance
Resistive burden power	Resistive power associated with the stated current and input resistance
Input resistance used	The entered meter input resistance used in the calculation
Current used	The entered meter current used in the calculation

The formulas treat the meter input as a resistance. They do not model reactive impedance, phase angle, waveform distortion, frequency-dependent response, nonlinear electronics, lead resistance, connection resistance, or internal instrument protection circuits.

Calculation Example

For a meter with a Meter input resistance of 10 ohm and a Meter current of 0.02 A:

\(\displaystyle V = 0.02\ \text{A} \times 10\ \text{ohm} = 0.2\ \text{V}\)

\(\displaystyle P = (0.02\ \text{A})^2 \times 10\ \text{ohm} = 0.004\ \text{W}\)

Result	Calculated Value
Burden voltage	0.2 V
Resistive burden power	0.004 W
Input resistance used	10 ohm
Current used	0.02 A

The meter requires 0.2 V across its assumed 10-ohm input resistance to pass 0.02 A. Its calculated resistive burden is 0.004 W, or 4 mW. In a low-voltage test circuit, that 0.2 V may be material; in a higher-voltage circuit, it may be negligible. The circuit’s source capability and the instrument’s specified limits determine the practical conclusion.

Instrument Transformer and Test-Circuit Review

A burden calculation can be relevant to CT and PT-related work, but the result cannot be treated as a complete instrument-transformer burden determination. CT secondary performance may be affected by connected instrument impedance, secondary conductors, terminals, test switches, relays, meters, frequency, waveform conditions, and the CT’s published accuracy and excitation characteristics.

For current transformer work, verify the complete secondary circuit and follow the applicable test procedure. Do not use a simple resistance-and-current result to establish CT accuracy, saturation performance, allowable secondary burden, or safe operating condition.

For PT, voltage source, and electronic signal applications, compare the burden voltage with the source’s available voltage, regulation, compliance range, specified loading limit, and required measurement accuracy. Where test leads are part of the circuit, include their resistance separately when evaluating total circuit voltage drop.

Field Verification

Use the calculator for meter burden arithmetic only. Verify the actual meter range, input specification, frequency response, accuracy class, loading effect, CT/PT behavior, connection method, lead resistance, and test procedure separately.

Where the measurement circuit is part of installed premises wiring, complete the relevant electrical design and code review independently. That review may include conductor ampacity, insulation temperature rating, terminal rating, correction factor, adjustment factor, current-carrying conductors, overcurrent protection, voltage drop, disconnecting means, equipment listing, manufacturer instructions, and AHJ requirements.