Yes, a different rate for "construction" supplies, about double the regular rate.
For a permanent supply you need to pass an "inspection", by the authority.
IIRC the meter "type" on your bill should tell you what rate you are on. Alternatively, from your total cost and consumption in kWh you should be able to calculate a rough per-unit rate. If it's over about 6Baht per unit you are likely on a construction supply.