Basic: 100A indoor replacement — Panel, new breakers, basic wiring; 6–8 hours; total $1,200–$2,000; includes standard permit where required. Key cost drivers include panel amperage, indoor vs outdoor location, wiring length, and whether a full panel upgrade or rerouting is needed. The article outlines cost ranges, per-unit pricing, and practical. It is the policy of the Company to serve all its customers in an orderly manner and assist in securing a more beneficial use of electricity. Uniform. Electrical power enters a distribution box through the incoming lines using what we call a five-wire system. Each of these wires has a specific, non-negotiable purpose: The Phase Lines : You've got three of these bad boys – A, B, and C phases. By convention, we use yellow for A phase, green for B. This document represents the minimum requirements and specifications for the installation of the electrical underground distribution systems fed from padmounted transformation, serving Secondary Service Accounts, to be transferred to Oncor Electric Delivery Company ownership. Done right, it ensures safety, compliance, and long-lasting performance. If you have any questions, please contact your Ameren Illinois Representative at the number listed on the back of this brochure, or call 1-888-659-4540 or visit us at.