Transformer

Figure 1: Auto Coordination Options - Transformer

Option Descriptions
Option Description

NEC Requirements for Transformer Protection

The table is the NEC Table 450-3(A) for transformer primary over 600V. The table shows the maximum rating or setting of over current protection for transformers. You can change the values in the spreadsheet.

With SSTs, apply transformer FLA NEC limits using

When setting SST for transformer FLA, the LTPU is set based on the following selections:

  • LTPU setting amps: LTPU setting is set based on LTPU amps.
  • LTPU min tolerance amps: LTPU setting is set based on LTPU minimum clearing curve amps.

Allow one setting past transformer FLA NEC limit for LTPU selection

Selecting the check box increases LTPU setting by one past the selected transformer FLA NEC limit. If the check box is not selected, LTPU is set as originally specified.

How should the LTPU selection of LV devices be prioritized?

LTPU coordination is selected by coordinating with other protective devices or with maximum transformer FLA.

  • Use closer selectivity with downstream protective devices: LTPU setting is set based on coordination with downstream protective devices.
  • Use Max transformer Amps: LTPU is set based on maximum transformer amps.

Minimum gap between inrush and relay

Sets the relay time delay at specified seconds higher than the transformer inrush time.

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