Look at the transformers on the pole to determine what voltage

[jar546]

Here is a pretty good video for a delta 3 phase setup

 

[cda]

Good video

being non electric, wish they would have talked about voltage

 

[Paul Sweet]

Most delta services I've seen are 120 V (N-H) / 240 V (H-P). The P is often called the "stinger" because it is 208V to ground, and the NEC requires it to be orange.