Installation of current transformers - Janitza electronics (2023)

Installation orientation

Determine the flow direction of the energy in the cable that you wish to measure. P1 indicates the side on which the current source is located, whilst P2 indicates the load side.

Installation of current transformers - Janitza electronics (1)

Terminals S1/S2 (k/l)

The connections of the primary winding are designated "K" and "L" or "P1" and "P2", and the connections of the secondary winding are designated "k" and "l" or "S1" and "S2". The polarity must be established such that the "flow direction of the energy" runs from K to L.

(Video) Current Transformers (CT)

Inadvertently swapping the terminals S1/S2 leads to erroneous measurement results and can also cause incorrect control behaviour with Emax and PFC systems.

Installation of current transformers - Janitza electronics (2)
Installation of current transformers - Janitza electronics (3)

Line length and cross-section

The power consumption (in W) caused by the line losses is calculated as follows:

  • specific resistance
    for CU: 0.0175 Ohm *mm2 / m for AI: 0.0278 Ohm * mm2 / m
    L = Line length in m (outward and return line) I = Current in Amperes
    A = Line cross-section in mm2
Installation of current transformers - Janitza electronics (4)

Brief overview (power consumption copper line) for 5 A and 1 A:

With every temperature change of 10 °C the power consumed by the cables increases by 4 %.

(Video) How to wire multifunction 3 phase power meter and current transformers - NEMO (subtitles)
Installation of current transformers - Janitza electronics (5)

Serial connection of measuring devices to a current transformer

Pv = UMG 1 + UMG 2 +....+ PLine + PTerminals ....?

(Video) Rogowski current transformer for retrofit

Operation in parallel / summation current transformer

If the current measurement is carried out via two current transformers, the overall transformer ratio of the current transformers must be programmed into the measuring device.

Example: Both current transformers have a transformer ratio of 1,000/5A. The total measurement is carried out using a summation current transformer 5+5 / 5 A.

The UMG must then be set up as follows:

(Video) The new modular and compact measurement device UMG 801 - Janitza Electronics

Primary current: 1,000 A + 1,000 A = 2,000 A
Secondary current: 5 A

Installation of current transformers - Janitza electronics (6)

Grounding of current transformers

According to VDE 0414, current and voltage transformers should be secondary grounded from a series voltage of 3.6 kV. With low voltage it is possible to dispense with grounding if the current transformers do not possess large metal contact surfaces. However, common practice is to ground low voltage transformers too. Customary is grounding on S1. However, grounding can also take place on the S1(k) terminal or S2(k) terminals. Important: Always ground on the same side!

Installation of current transformers - Janitza electronics (7)

Use of protection current transformers

In the event of retrofitting a measuring device and the exclusive availability of a protective core, we recommend the use of a winding current transformer 5/5 for decoupling the protective core.

(Video) Introduction to Current Transformers Part 1: What are CTs and why use them?


What happens when a CT is overloaded? ›

Most CTs retain accuracy up to 120-130% of their rated capacity. Beyond the maximum rating, the CT will "saturate" and measurement accuracy will fall rapidly.

What is P1 P2 and S1 S2 of current transformer? ›

The connections of the primary winding are designated "K" and "L" or "P1" and "P2", and the connections of the secondary winding are designated "k" and "l" or "S1" and "S2". The polarity must be established such that the "flow direction of the energy" runs from K to L.

How do I choose CT and PT? ›

Important Points for Selecting a CT
  1. Current Transformer Output.
  2. Conductor Size.
  3. Load Size or Amperage Range.
  4. Accuracy Rating.
  5. Form Factor.
  6. Regulatory Requirements.
  7. Using Rogowski Coils.
Nov 4, 2021

What is the direction of CT installation? ›

These CT's should be installed such that the arrow is pointing toward the load to be measured. The Arrow points downstream, the load side, the low side. White Dot - Some CT's may have a white dot, or a dot of another color, like green, blue, or red.

How do you connect CT to a circuit? ›

Make sure the mating surfaces are clean. Debris will increase the gap, decreasing accuracy. Place the CT around the conductor and rotate the top back to the closed position until the latch snaps closed. Secure the CT on the conductor using a cable tie through the CT's window and around the conductor.

What is the voltage on a current transformer? ›

In a current transformer, the input value is a constant current, while in a potential current, the input value is a constant voltage. In the current transformer, the range is 1A or 5A, and in the potential transformer, the range is 110V.

How long do current transformers last? ›

For the prior part, the average lasting of transformers is about 35 years. But, when operated under ideal conditions, including temperature, weather patterns and setting, the expectancy can be 30-40 years. However, this decreases a bit for industrial transformers making it 20-25 years.

What happens when a current transformer saturates? ›

Saturation of the protection core of the current transformers can cause a malfunction in the protection relays. To prevent malfunction of the protection relays caused by the current transformer saturation, software and hardware methods can be used.

What does R and C mean on a transformer? ›

In the most basic form of control, the C or common terminal of the low voltage transformer is connected in parallel to all of the control relays.. The R terminal of the low-voltage transformer is connected through the thermostat to each control relay.

What color wire is on a current transformer? ›

While the FCL series current transformers have a black lead wire designated as X1 or positive, the other current transformers with lead wires like 2RL, 5ARL, 7RL series of solid-core, and the 615 and 616 split-core series current transformers have the white lead wire as the X1.

What does H1 and H2 mean on a transformer? ›

The numbers "1" and "2" indicate voltage polarization. Looking closely, we notice that "H1" and "X1" mark the starts (noted by the letter "S") of the primary and secondary windings, respectively, and that "H2" and "X2" mark their finishes (noted by the letter "F"), respectively.

How do you size a current transformer? ›

Current transformers are specified by size (VA rating), ratio and accuracy. The VA rating determines the maximum secondary impedance (burden) that can be driven at the stated accuracy. The typical transformer-rated analog ammeter has a 5A AC movement (M).

Why CT secondary is 1A or 5A? ›

In this case, as the CT secondary has a current of 1A, to achieve ampere-turns balance, we need to have 100 turns of secondary winding. Moreover, the voltage output of a CT secondary, for a given primary current is constant.

How do you calculate CT size? ›

Required Accuracy Limit Factor = KTDF X (IF/IP) Calculated Accuracy Limit Factor = KALF X (Selected burden + ISEC X RCT) (Required burden + ISEC X RCT) Note – For correct CT sizing Calculated ALF is greater than Required ALF.

What happens if a CT is installed backwards? ›

The CT are not placed with the arrow pointing to consumer appliances. It occurs negative energy measurements and lead to an incorrect regulation.

What happens if we connect CT in parallel? ›

Connecting CTs in parallel has a negligible effect on accuracy. In fact, parallel operation tends to average out the nominal errors of the individual CTs.

Do CT wires need to be twisted? ›

Shielded and twisted – Adding a shield—in addition to the twisting—can offer some additional noise immunity, especially for long extensions. Note: for best immunity to crosstalk, the wires should be twisted in pairs.

Which wire is positive on a CT? ›

Each CT has an X1 (positive) and X2 (neutral) wire pair, and uses butt-splice connectors to attach the CT to a specific meter wire pair. The direction of the energy flow is indicated on the CT.

Why is CT placed before circuit breaker? ›

A current transformer (C.T.) is used where the current is too high to measure directly, or the voltage in the primary circuit is too high, so the galvanic isolation between primary and secondary is important for safety or technical reasons.

How CT is connected to relay? ›

The standard practice is to wire the CTs and VTs with conventional polarity connection, meaning that the primary CT polarity should be placed away from the primary protected device and that the secondary CT polarity terminal should be connected to the polarity terminal of the relay current input coils.

How much current is 240 volts? ›

Amps = Watts / Volts

3600 Watts / 240 Volts = 15 Amps.

How many amps are in a transformer? ›

Single Phase Transformer Full Load Current (ampere)
Transformer Rating Apparent Power (kVA)Full Load Current (A)
120 V240 V
20 more rows

Are current transformers AC or DC? ›

A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.

What causes current transformers to fail? ›

The most common cause of failure of transformer is insulation failure; it deteriorates due to heat, oxidation, acidity and moisture. Line surges such as switching surges, voltage spikes, line faults and distribution abnormalities.

What is the biggest danger from a current transformer? ›

Open circuit condition in a current transformer (CT) can result in dangerous over voltage condition at the secondary terminals of the CT. An open circuit CT especially of high ratio and carrying high currents can produce secondary open circuit voltage in the range of few kilo volts.

What will happen if a current transformer is left open circuit? ›

If CT is kept open-circuited, no current will flow in the secondary, and consequently, no secondary flux will be set up in the core. In absence of secondary current, the net flux will be higher than the flux generated in the core when CT is connected to load.

How do you test a current transformer? ›

The output voltage of a current transformer (CT) can be tested in the field using an digital multimeter with a millivolt AC (mVac) range. This test is useful to confirm that the CT is working properly and that current is flowing in the conductor that the CT is installed on.

How do you desaturate a current transformer? ›

The only way to remove this remanence is by degaussing the CT. Degaussing can be done by applying primary rated current and a variable load to the CT secondary terminals. Start the load at a high resistance to cause the CT to saturate in both the positive and negative directions.

What causes current transformer saturation? ›

Presence of DC offset in fault current is the causes of saturation in current transformer core.

What does L and N stand for on transformer? ›

There are two different name, L (Live) and N (Neutral) on the AC input terminal. Please refer to Fig. 1 for the wiring of the AC input.

Does a 24 volt transformer need to be grounded? ›

transformers for AC systems of less than 50 volts if the primary voltage exceeds 150 volts to ground or if the main transformer supplying power to the building is ungrounded. that the secondaries of all transformers that supply 24 VAC be grounded.

Where do you connect C wire to transformer? ›

The C wire should connect to the common side of the transformer.

Does it matter which wire goes where on a transformer? ›

Low voltage wire does not have polarity; it does not matter which of the two wires connects to the common terminal and which to the voltage terminal, as long as one wire goes to each. The correct voltage terminal is the one that results in an optimal voltage at the fixtures connected to that run.

Does current transformer step up or down? ›

A current transformer is a transformer used to step down the line current to make it easier to measure. The total power in a transformer is the same on the primary and secondary sides.

Does the black or white wire carry current? ›

What do the Different Color Wires Mean? Here's a rundown of electrical wires: The black wire is the "hot" wire, it carries the electricity from the breaker panel into the switch or light source. The white wire is the "neutral" wire, it takes any unused electricity and current and sends it back to the breaker panel.

Which side of a transformer is high voltage? ›

For this tutorial we will define the “primary” side of the transformer as the side that usually takes power, and the “secondary” as the side that usually delivers power. In a single-phase voltage transformer the primary is usually the side with the higher voltage.

What is X1 X2 X3 X4 in transformer? ›

Terminations, include; H1, H2, H3, and H4, which signifies the high voltage side if transformer and X1, X2, X3, and X4, which means low voltage side of a transformer.

Does polarity matter on transformer? ›

Transformer polarity is fundamental to grasping how transformers function and how they're utilized. Understanding polarity is essential to properly paralleling single-phase transformers and connecting instrument transformers (current and potential) to metering devices and protective relays.

What is the accuracy of CT? ›

1 rated Metering CT is accurate to 0.3 percent if the connected secondary burden if impedance does not exceed 0.1 ohms. A 0.6B8 rated metering-class CT will operate within 0.6 percent accuracy if the secondary burden does not exceed 8.0 ohms.

How do you calculate current size? ›

Electric current is measured in units of amperes; the symbol for the ampere is A. One ampere is equal to one coulomb passing a point in a wire in one second. We can calculate current, 𝐼 , using the formula 𝐼 = 𝑄 𝑡 , where 𝑄 represents an amount of charge passing a point in an amount of time, 𝑡 .

What happens if transformer secondary is shorted? ›

A shorted secondary results in a very large secondary current but little or no load current since the short is connected across the load (see Figure 3). The primary current is also much greater than normal since the reflected impedance is very low.

What happens when CT secondary is shorted? ›

The secondary side of the current transformer is always kept short-circuited in order to avoid core saturation and high voltage induction so that the current transformer can be used to measure high values of currents.

Which CT is better 5P10 or 5P20? ›

Its application which differetiate the use of 5P10 and 5P20. If the breaker is used for backup protection say incommer etc you can use 5P20, but if it is say an incommer ACB/ MCCBof PMCC, you should use 5P10 only.

How do you calculate CT current? ›

Definition: 1) The ratio of primary amps divided by secondary amps. 2) The current ratio provided by the windings of the CT. For example, a CT that is rated to carry 200 Amps in the primary and 5 Amps in the secondary, would have a CT ratio of 200 to 5 or 40:1.

How do you size a load for a CT? ›

For best accuracy, the diameter of the conductor being monitored should be more than half the opening size of the CT. For example, a 4/0 AWG conductor is typically 0.64 inches in diameter and commonly carries 200 to 250 amps. This will fit in a 0.75 inch CT and largely fill the opening (best case for accuracy).

How do you set a CT ratio? ›

How to set CT ratio in EM6436 ?
  1. After 'RmS' press "^"(Up arrow) button to reach "Clr".
  2. After "Clr" press "^"(Up arrow)button to reach "Set".
  3. After "Set" press ">"(Right arrow)button to reach "View".
  4. After "View" press "V"(Down arrow) button to reach "Edit".
  5. After "Edit" press ">"(Right arrow)button for two seconds.
Sep 1, 2017

What direction does a CT clamp go? ›

A CT clamp must be placed around the live meter tail as shown below with the arrow pointing towards the consumer unit.

Do you need a ground to wire a 24v transformer? ›

that the secondaries of all transformers that supply 24 VAC be grounded. IF a grounded secondary is mandated, ground the common (–) wire from the transformer to an equipment grounding screw in the equipment enclosure. If more than one controller is powered from the transformer, ground both at the same ground screw.

Can CT be connected in parallel? ›

CTs can be connected in parallel at the panel and a single twisted pair run to the meter.

Which rule should follow while installing transformer? ›

Operation of power transformers
  • Standard and special transformer tests.
  • Site considerations.
  • Preliminary inspection upon receipt of transformer.
  • Plan for the prevention of contaminants.
  • Making connections that work.
  • Controlling sound level.
  • Make sure the transformer is grounded.
  • Final inspection and testing.
Feb 8, 2016

How many wires go to a transformer? ›

Connections to this type of transformer are basic-three wires into the high side (H1, H2, and H3) and three wires out from the low side (X1, X2, and X3). No. 10 AWG primary-side wiring (22.6A at 480V) and secondary-side No. 8 (45.1A at 240V) will give you full use of the transformer capacity.

Do you always ground the neutral in a transformer? ›

The neutral and ground must be connected to the transformer neutral bus. Making the N-G bond at the main panel is not advised in order to segregate normal return currents from ground currents. The transformer neutral bus is the only point on the system where the neutral and ground should be bonded.

How do I choose a CT size? ›

As discussed above, the key in selecting the proper CT should be based upon the minimum and maximum load size, selecting the CT that will give you the highest amount of sensor resolution. Using a 100 Amp CT on a 100 Amp Load will give you a better sensor resolution when compared to a CT that is rated to 5000 Amps.

How is CT size calculated? ›

Required Accuracy Limit Factor = KTDF X (IF/IP) Calculated Accuracy Limit Factor = KALF X (Selected burden + ISEC X RCT) (Required burden + ISEC X RCT) Note – For correct CT sizing Calculated ALF is greater than Required ALF.

What happens if you don't ground a transformer? ›

Without establishing an effective ground-fault current path, the ground-fault current will not flow to expose the ground-fault to protective devices. This results in failure of the overcurrent protection device to operate correctly to clear the fault condition.

What happens if a transformer is not grounded? ›

If the grounded (neutral) service conductor is opened or not provided at all, objectionable neutral current will flow on metal parts of the electrical system and dangerous voltage will be present on the metal parts providing the potential for electric shock.

What does R and C mean on transformer? ›

The C wire is simply the “common” side of the transformer 24V output (there are two wires coming out of the 24V transformer, “hot” and “common”). Just tap into the “common”. The R (red) wire is really the power source. The C wire closes the circuit and allows continuous flow of 24V energy to power the thermostat.


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