KBH ENERGY Design tool

Current transformer secondary wiring design

Calculation of the secondary circuit burden and the maximum wire length between the CT, terminal block and measuring instrument.

Input

TRANSFORMER

Secondary currentA

Rated burden VA

Accuracy class

You will find these values on the transformer nameplate. The burden is specified at rated secondary current.

LOADS IN THE CIRCUIT

Instrument burden VA

Additional meter in series VA

Terminal block in circuit VA

The instrument burden is stated in its documentation. The terminal block loss covers contact resistances.

SECTION A · FROM THE TRANSFORMER

Wire length m

Conductor cross-sectionmm²

Conductor material

SECTION B · FROM THE TERMINAL BLOCK

Wire length m

Conductor cross-sectionmm²

Conductor material

Enter the length as the distance between components. The calculation covers the go and return path (2× length).

Circuit and results

Secondary circuit: transformer, wiring, terminal block and measuring instrument

Wire resistance (go and return)
Wire burden
Instrument and terminal block burden
Total circuit burden
Margin to rated burden

0 %25 %Utilization: 0 %

OVERLOAD

Maximum wire length

Section A (from the transformer)

Section B (from the terminal block)

The maximum length of one section is calculated with the other section's length as entered and the transformer's rated burden fully used.

WARNING

The secondary circuit of a current transformer must never be opened while the primary carries current. Breaking the loop produces dangerously high voltage at the terminals and can destroy the transformer. Connect instruments only with the primary circuit switched off or via a shorting terminal block.

This tool assists with designing secondary wire lengths for current transformers. It does not replace a detailed electrical calculation or verification by a design engineer. The calculation uses a copper resistivity of 0.0175 Ω·mm²/m and aluminium of 0.0278 Ω·mm²/m at 20 °C. Measurement accuracy is guaranteed at a burden between 25 % and 100 % of the transformer's rated burden (IEC 61869-2).

Current transformer secondary wiring design

Current transformer secondary wiring design

Input

Circuit and results

Maximum wire length

Online calculator: size the secondary wiring of your current transformers

Compensation

Janitza® UMG

CT

Components

Switchgear

Services

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