What is the minimum size service cconduit for a 100 amp service?

If the service stack is supported by a support structure and the utility feed drop is not supported from the conduit, the size of the conduit can be 1 1/4". If the service stack is used to support the utility feed drop then the conduit has to be 2" schedule 40 conduit. The reasoning behind this is that if in a storm a tree limb falls across the service drop, the lighter weight conduit could bend and pinch the wires in the stack and short out. This would be ahead of the main service breaker and the only protection for the wire would be the primary fuse at the transformer. Theoretically this amperage could rise to 50000 amps before the primary fuse blows. A schedule 40 service stack if supported, as the code requires, will withstand most tree falls. What is most likely to happen is that the utility connectors will pull apart leaving the service stack intact.