SPD for field instruments are installed by thread. The following contents need to be confirmed.

1.    Number of wires to be protected

Select 2 wires, 3 wires, 4 wires accordingly.

2.     Is there a backup electrical interface?

Yes——select parallel mounted SPD 

No——select series mounted SPD

3.    Check the type of the thread

The type of the thread needs to be specified, such as 1/2’NPT，3/4’NPT，which are commonly used.