Surge diverter in RTD terminal box

[NickParker]

What are these "SD" in the RTD terminal box of a Ex proof motor?
Is it "Surge diverter". Why is it provided?

 

[Gr8blu]

My best guess: "SD" stands for "stator detector".
The OEM did a poor job of identifying terminals on their wiring diagram.
What they appear to be indicating is that the 1, 2, and 3 terminals on the first group should go to the process control as "detector #1", and the unlabeled wire should be directly connected to ground at the terminal strip in the terminal box.

Note that all the detector grounds are tied together - there should be an additional wire (supplied by the user) inside the terminal box that goes from the "ground" strip to the facility ground.

Why are they labelled 1SD, 2SD, etc.? Because there is (probably) another diagram showing where they are in relation to the circumference of the stator for troubleshooting purposes. As an example, 1SD is located at top dead center; 2SD is located at roughly 60 degrees clockwise from 1SD, and so on.

 

[panter]

GR8blu ,
It seems to me that you are right.
I predict that the first 6 PT 100 detectors are two per stator phase. Last two could be for the temperature of bearings .