What does the t on the residential property lamppost mean?

1 symbol t indicates that the neutral point of the power system is directly grounded, and the second symbol t indicates that the metal steel pole of the street lamp is directly connected to the earth through the grounding body, regardless of the grounding mode of the system.

In TT system, the grounding of all loads is called protective grounding.

Lamp post may be electrified due to cable insulation damage or other reasons. In order to prevent this leakage from endangering personal safety, the metal shell is connected to the earth through a grounding device, which is called protective grounding.