When is a separate utility service required instead of a subpanel?

A separate utility service — the ADU getting its own meter and its own connection to the utility's distribution system — becomes necessary when a subpanel fed from the main house simply won't work, either electrically, practically, or because a policy requires it.

The three main triggers

• Insufficient main service capacity. If the load calculation shows the existing service can't carry both the house and the ADU even after a panel/service upgrade, a separate service may be the only viable route.
• Distance. When the ADU sits far from the main panel (often cited around 150 feet or more), a subpanel feeder becomes inefficient — heavy voltage drop forces large, expensive conductors — and a dedicated service can be cleaner.
• Utility or local policy. Some utilities or jurisdictions require separate metering under certain conditions (for example, certain detached configurations or when the ADU will be separately billed). Policies differ by provider — verify with yours.

What a separate service actually involves

A separate service is a bigger lift than a subpanel. It typically requires:

1. Its own meter socket sized and located per utility standards.
2. Service-entrance conductors running from the utility transformer or point of connection.
3. Utility engineering review, approval, and scheduling of the connection.
4. Building department permits and inspections for the meter and service equipment.
5. In some cases a transformer or distribution upgrade if the existing infrastructure can't carry the new service.

Because it involves the utility's own equipment and crews, you don't control the schedule the way you do with a subpanel your electrician installs in a day. That loss of control is the main reason to decide on a separate service early and submit the utility request in parallel with permitting.

Subpanel vs. separate service — quick comparison

The separate-billing benefit is real for rental ADUs, but the trade-off is cost and the utility's timeline, which can become the longest item on your project schedule. Start utility coordination the moment you begin permitting, not at the end of construction.

Requirements vary by jurisdiction and utility — confirm with your local building department and serving utility. Our electrical plans document whichever configuration applies, including the metering layout.