How to Select Transformer Disconnect Switches

Check the single line diagram for the location and quantity of disconnect switches needed. Make a list of the switches and the transformers to which they are connected. Make sure that you have the technical specifications or nameplate information for all the transformers on the list. Check the short circuit calculations to make sure they include the locations of the disconnect switches. Check the single line diagram to see if it specifies whether each switch should be motor-operated or not. If the single line diagram does not include this information, check how the technicians will operate the system to determine whether remote disconnect switch operation is required.

Add columns for voltage, current, short circuit current and motor operator to the list of disconnect switches. Check the transformer specifications or nameplate information to find primary and secondary voltages and primary and secondary full load currents for each transformer on the list. Fill in the corresponding voltages and currents for each disconnect switch from the primary or secondary transformer data, depending on where the switch is connected. Fill in the short circuit current for the location of each disconnect switch from the short circuit calculations. Add whether a particular disconnect switch requires a motor operator.

Identify at least three potential suppliers, such as Southern States, Joslyn or HEAG, for the disconnect switches. Check the requirements from the list of disconnect switches against the manufacturer's specifications, rounding up the requirements from the list to the next larger value available from each manufacturer. Check the prices of each of the switches with the rounded up values. Select the switches that offer the best price while meeting or exceeding the requirements for voltage, current, short circuit and motor operator. Select the switches from the manufacturer that can supply the most switches matching your specifications at the lowest price.