Reading and Configuring Time-Current Curves
You can create selective coordination graphs in ElectroBIM to coordinate time-current curves for the circuit breakers in your project. Selective coordination graphs are made using the Graph Insert command.
The time-current curves for a piece of distribution equipment or equipment connection are set in the dialog box for the device. Once a curve has been inserted on the drawing, you can make changes to it with the Curve Edit command.
This article describes how to read time-current curves and how curves are affected by the settings available.
Most of the settings below can only be configured for electronic circuit breakers. If you have selected a fuse or non-electronic circuit breaker, you can only set the Instantaneous Pickup.
Trip times and current thresholds for breakers vary and are therefore represented on the graph as shaded areas rather than single points. For example, a breaker with a Short-time Delay ☰ of 0.22 could take anywhere from 0.22 to 0.32 seconds to trip.
Long-time Pickup​
Long-time Pickup refers to the trip current for the breaker.
On the curve, the long-time pickup is represented by a vertical line between the top of the graph and the long-time delay segment of the curve.
On electronic breakers, this value is a fraction of the maximum rating for the breaker. To specify this value in ElectroBIM, set the breaker size to match the trip rating for the setting you want. For example, a breaker with a maximum rating of 200A and a long-time pickup of 0.75 would be modeled as a 150A breaker in ElectroBIM.
Long-time Delay​
Long-time Delay ☰ refers to the length of time the breaker will allow weaker current surges, such as a motor starting, before the breaker trips; the higher the current, the faster the breaker will trip.
On the curve, the long-time delay is represented by a slope on the leftmost part on the graph below the long-time pickup segment of the curve. Changing this value will move the slope along the y-axis:
- Faster trip times move the slope down.
- Slower trip times move the slope up.