Transformer Overcurrent Device Size

Project:
Case Number:

Transformer Size KVA:

Transformer High Side Line to Line Voltage KV:

Transformer Low Side Line to Line Voltage KV:

Transformer Impedance %Z:

Phases:

The National Electric Code (NEC) provides for several methods of protecting both the primary and secondaries of transformers. This can be accomplished using circuit breakers or fuses protecting only the primary or a combination of primary and secondary. The code divides the requirements into transformers with a rating over 1000V or 1000V or less.

Providing the transformer impedance factor (%Z or %impedance) will also result in the calculation of both the high and low side fault current.

NOTE: The calculator currently uses Table 450.3 (B) the 1000V or less table and provides a “rule of thumb” calculation of 150% for the primary protection and 125% for the secondary protection.

The National Electric Code (NEC) specifies the minimum size for cable tray systems which includes ladder, ventilated trough, ventilated channel, solid bottom and other similar structures. It’s important to note that cable trays are mechanical support systems and not raceways. Raceways are included in another section of the code.

Proper cable tray sizing is complicated and often existing cable trays are overloaded per the code. If you have questions or would like some engineering assistance to properly size your cable tray installation please contact us.

Result here