Installation Guide for CT Meters
While direct connect or whole current meters are relatively simple to install, with little to no set up required, installing a CT, (current transformer), operated meter can be a little more complex. This guide covers talks through the basic principles for installation along with some tips for troubleshooting if required.
Wiring
Three phase CT operated meters will typically have 10 or 12 terminals, 3 for each phase, 1 for the neutral, and if required, a live and neutral for the auxiliary power supply. Each phase will require connection from the two cables on each CT as well as a voltage reference.
Single phase meters will typically require 4 or 6 connections depending on whether an auxiliary power supply is required.
Please check the manufacturer's wiring diagram for terminal labels.
CT Orientation
If a CT is not oriented correctly, it may record current to the incorrect register, (export instead of import for example), or result in incorrect measurements. There is no standard for how manufacturer's indicate the correct orientation, but the list below covers the most common examples:
- An arrow indicating direction of current; an arrow that is etched on to the base of the aperture is common with many split core CT ranges such as our T24 & T36 models. It should typically point away from the grid and towards the load drawing power, (this can vary, for example in renewable applications where generation is being measured).
- P1 to P2 labels; common with solid core CT's such as our XL1B and M3N1, the P1 label should face the grid and P2 towards the load.
Connecting the CT to the Meter
Many CT's will include a meter of cable for connecting to the meter. One cable will typically be white or red, while the second is black. The white/red cable should connect to the first CT terminal and the black cable to the second.
For CT's supplied without cable, the terminals will be labelled S1, which should feed to the first terminal, and S2 to the second.
Voltage References
The voltage reference/s should be taken from the supply being measured and should match the appropriate phase. Looping across one supply from terminal to terminal will result in incorrect readings. All voltage references should be fused as per the manufacturer's instructions.
Auxiliary Power Supply
While some CT operated meters draw power from the voltage references, others require an auxiliary power supply to power the meter. This can be looped from any phase and should also be fused as per the manufacturer's instructions.
CT Ratio
A CT operated meter needs the ratio of the CT's to be programmed onto the meter to measure correctly. Some meters require you to input the the primary, e.g. 100A, while others may require the sum of the ratio, e.g. 100/5A = 20. Please refer to the manufacturer's instructions for confirmation of which is required.
As part of the Measuring Instrument Directive, (MID), requirements, most CT operated meters will only allow this ratio to be entered once, so please take care when programming to avoid errors. If an error is made, the meter will need to be returned to the manufacturer and will incur a fee.
Trouble Shooting
If you believe the measurements being recorded on the meter are incorrect, we would first recommend verifying the wiring against the manufacturer's installation guide to ensure correctness as well as checking the CT's have been oriented correctly.
When split core CT's are being used, you should also check that they are closing firmly and have not received damage to the closing mechanism.
If you still believe there to be an error, we recommend using a clamp meter to compare instantaneous values such as current and voltage. While these values are not shown on every CT operated meter, the majority do, and guidance on how to view these values will be found in the manufacturer's manual.