What is a CT Meter?
A CT meter is a device that measures amperage in one or more conductors using sensors called current transformers (CTs). Current transformers come in many sizes and amperage ratings which allows a single meter to measure all kinds of electrical loads. In addition to amperage, these metering devices measure voltage so they can ultimately calculate power. Typically, these meters are used to monitor the power of individual circuits in an electrical distribution panel. They come in a wide variety of form factors and can accomplish things like measuring kWh usage of server racks or submetering tenants. The versatility of CT meters makes them a popular choice for many energy professionals. However, versatility can make them complicated to install and configure. Installers who adhere to the three tips below find themselves with fewer headaches and happier customers.
A phase of an electrical system represents one line of power. Typically, electrical panels have multiple phases powering the breakers within it. For example, a 120/240VAC residential panel has two distinct phases (often referred to as phase “A” and phase “B”), and the breakers in that panel are powered by one phase or the other. When metering the power of a circuit, you must multiply a voltage measurement by a current measurement. Further, to calculate power correctly, the current for a breaker on phase A must be multiplied by the voltage of phase A. This means that power calculations will be inaccurate if you multiply a current measurement by the voltage of a different phase.
To avoid mixing up your current and voltage phases, bring a handheld ammeter with you to the install site and check the potential difference (volts) between the phase A lug on the main breaker and the breaker where the current transformer is located. If the potential difference equals zero, then they are in phase.
Record Your Work
Write everything down before leaving the install site. Include information about the location and model number of CTs, which input position the CT connects to on the meter, the service voltage, etc.… Use your phone to take some photos if you have the chance. Having this information on hand after leaving the install site can prevent truck-rolls for troubleshooting later on. Remember, some CT metering systems can have dozens of CTs connected to them, so recording information is important for keeping everything organized.
Speak with Network Administrators
If you want to upset a network administrator, the best thing to do is to start plugging random devices into their network, and not tell them about it. A healthier approach is to ask your meter manufacturer if they have a security whitepaper or statement describing the technical details of the network connection and deliver it to the network admin. Also, they’ll want time to look it over, so it’s best not to wait until you’re installing the system to deliver it to them.
Written By: Ed Pantzar, Marketing Manager at eGauge Systems