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Current Transformers

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  1. TYCO SC5 Split Core Current Transformers

    TYCO SC5 Split Core Current Transformers

    Tyco Split Core Current Transformers offer a fast installation, cost effective solution for applications including Switchgear, Distribution systems and Control Panels. Learn More
    Excl. Tax: £47.65 Incl. Tax: £57.18
  2. DBP 816 Split Core  Current Transformer

    DBP 816 Split Core Current Transformer

    Split Core Current Transformer. Available ranges 2000-5000/5A Learn More
    Excl. Tax: £44.08 Incl. Tax: £52.90
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Current Transformers


We supply a huge range of Current Transformers (or CT's) most of which are available to buy on line. Specials are also available please email us or call us on +44(0)1244 393800 if you can't find a Current Transformer that you need. Use the sub categories on the left to view our range or read on to find out more.

Current transformers are used when the primary circuit rating of the feeder that is being monitored is too large to be connected directly to a meter. We supply Current Transformers with primary ratings from 1 - 5000A. There are a few important points to note when specifying and installing CT's, but first we will mention the different types that are available.

  • Solid Core Current Transformers - These are generally the cheapest type available and can either have a round aperture for installation onto a cable or a slotted aperture for installation on a bus bar. This type of CT has to be fitted over the end of a cable or bus bar and therefore the circuit needs to be switched off and disconnected in order to complete the installation. A single CT will monitor 1 phase therefore for a 3 phase application, 3 Current Transformers would be required. View our Solid Core range here.


  • Split Core Current Transformers - These units are usually a bit more expensive however by design they split into two parts. This allows installation onto a cable or bus bar without it having to unconnect it. This makes for easier installation in retro fit applications. A single CT will monitor 1 phase therefore for a 3 phase application, 3 Current Transformers would be required. View our Split Core range here.


  • 3 Phase Block Current Transformers - These are similar to the solid core current transformers and are generally used in low voltage switchboards. They are meant for 3 phase applications where all three CT's are molded into a single unit to save space. This type of CT can be mounted directly next to a molded case circuit breaker but care needs to be taken to make sure the pitch of the cables exiting the MCB line up with apertures in the 3 phase block CT. View our 3 phase block CT range here.


  • Summation CT's - These units are for special applications in which it is desired to monitor two or more identically rated circuits on a single meter. Summation current transformers would be used in conjunction with standard CT's to "electrically add" the current flowing in each phase of each circuit together. View our summation CT range here.


Our CT range is split into several different categories which can be viewed by clicking the links in the text above or  from the sub menu to the left. We supply solid core, split core and ring type CT designs covering all common currents ratings from 40 to 4000A. Call us on +44(0)1244 393800 or email us if you can't find what you need.

A 100/5A CT mounted on a 100A circuit would give 5A into the meter connected to it when the circuit is running at full load. If the circuit was running at half load then the meter would see 2.5A on the CT's secondary. In turn the meter would have the ratio of the CT set into it so that it was able to determine that at 5A it would actually read 100A on its display. CT's are used as it would be difficult/ expensive to connect cables that carry more than 100A directly onto the meter itself.

There are some important points to note when installing these units. Firstly CT's should be installed by a suitably qualified electrician as the currents and voltages involved can be potentially lethal.

In normal service CT's are extremely safe however the secondary connections should never be open circuited when their is current flowing in the primary conductor. If this occurs the potential difference across the secondary terminals will rise exponentially and eventually will try to break down the air gap leading to excessive heat and arcing. A CT left in this state could destroy itself. To ensure this is never a problem we also provide specialist metering test blocks which serve to provide CT shorting link facilities should the need arise to take a meter out of service.

Care should also be taken in selecting a CT with the correct accuracy. As with all measuring instruments there will be some error in its reading. CT's are catagorised in classes of accuracy. A CT with and accuracy of 0.5% means that it will be accurate to plus or minus 0.5% of the true reading. CT's due to their passive nature are less accurate at low loads (typically 10% or lower depending upon the CT).

In addition the accuracy of a CT can be affected by the load of the meter it is driving. Again because the units are passive care must be taken to install the correct cable in terms of  conductor size and length between the meter and CT to ensure that the accuracy is not compromised. 

Finally CT's need to be installed and wired correctly. Fitting a CT the wrong way round or reversing the secondary wiring will mean on some meters that it will fail to register any current. 

If you need help or advice in selecting or installing any of the equipment we sell - get in touch via email or call us on +44(0)1244 393800 when our friendly and informative team will be happy to help.