The 4-20 mA Current Loop Explained: How a DC Current Transformer Helps

A simple 4-20 mA current loop consists of four parts: a DC power supply, a two-wire transmitter, a receiver resistor, and RWire. Unlike alternating current (AC), which changes all the time, direct current (DC) is consistent. Unless the loop uses a three-wire DC current transformer, the system may not recognize changes in current flow while in AC power.

The three-wire variant can hold its own in a voltage drop. The amount of voltage lost is relative to the length of the wire; the longer the wire, the more voltage lost. According to the National Electric Code, voltage drops must be no more than 3 percent of circuit voltage from the breaker box. Otherwise, operators risk pushing an appliance to its breaking point due to lack of current.
http://blog.aimdynamics.com/the-4-20-ma-current-loop-explained-how-a-dc-current-transformer-helps/

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Power Line Repair Safety Tips: Using a Reliable DC Current Transformer

Before any job, test your equipment. Malfunctioning electrical equipment is a massive electrocution risk. With that in mind, be sure to inspect your equipment carefully for peeling wiring and other forms of damage, particularly equipment you use often such as your reliable DC current transformer.

If you feel a tingling sensation when working with a piece of equipment, stop working immediately and ask for replacement equipment. In the event that you need to purchase a new DC voltage transducer or any other piece of equipment, be sure to deal only with reputable suppliers like Aim Dynamics. This assures you that you’ll be receiving both quality equipment and quality service.

http://blog.aimdynamics.com/power-line-repair-safety-tips-using-a-reliable-dc-current-transformer/