Electric Panels and Service Upgrades for ADUs

Thinking about adding an accessory dwelling unit (ADU) to your property? One important consideration is ensuring that your existing electric panel can accommodate the additional electrical requirements of the ADU. If not, you’ll need to address this issue as part of moving forward with your ADU project, and it’s important to understand and budget for this expense upfront.

This can involve increasing the Amperage that currently services your property. This typically costs around $11,000 for an overhead electrical service upgrade, plus an additional $5,000 to $10,000 if your existing service wire is underground and the conduit is too small to accommodate the larger wire that will carry the increased Amperage. (See more on this below.) Additional costs may apply if upgrading the underground service conduit requires any work in the public right-of-way. While determining whether your property is ready for an ADU can be a complex process, rest assured that SnapADU has you covered. Keep reading for more detailed information on this important topic.

Existing power source: underground vs. overhead power lines?

Before starting the construction of an ADU, it’s crucial to assess the existing power source & type for two reasons:

  1. Determining the best location for the ADU should factor in any potential interference with the existing power source, which will have to either be avoided or be rerouted.
  2. Upgrading the electrical service (if necessary) will vary in complexity & cost based on the type of power line.

There are two ways that power can service your property: underground power lines or overhead power lines.

Underground lines

One of the most common issues that can arise is the presence of underground power lines running through the area where the ADU is planned to be built. In such cases, it’s essential to map out the location of the underground power lines early on in the feasibility process to either avoid or plan a move if needed.

Overhead lines

Similarly, overhead power lines can also intersect with the proposed ADU and may need to be relocated. This typically costs between $2,000 and $3,000 if no work to the existing service panel is needed. The presence of these lines can make it challenging to move large equipment and materials, which can delay the construction process. To avoid this issue, it’s important to identify the location of the overhead lines and plan the construction around them.

SDGE outlines clearances over buildings & structures that must be maintained. Notably, we would be looking at the “service drop,” meaning just the one wire from the power pole to the primary dwelling. See the image below specifying the 8′ minimum vertical clearance requirement from a structure.


High voltage power lines

High voltage power lines are typically carried on tall metal towers or wooden poles that are erected along a path known as a right-of-way (ROW) or easement. In the context of high voltage power lines, an easement grants the utility company the right to install and maintain power lines, transformers, and other equipment on the property owner’s land. You can never encroach on a utility easement; building a structure too close to the power lines can interfere with the proper functioning of the lines or pose a safety risk.

When will I need to upgrade my electric service for an ADU?

The required size of your electric service for the ADU is determined by several components, including the main service panel, service size, and service conduit. We’ll explain what these terms mean and how they relate to a potential upgrade to your electric service. We’ll also discuss the circumstances under which you may need to upgrade your electric service and the steps involved in doing so.

First, let’s establish terminology:

  • Main Service Panel (MSP) – The primary panel, typically located on the PDU, which houses the meter bubble and accepts the SDGE service.
  • Service Size – The amperage being brought to the MSP. This is either 100A, 200A, or 400A. Nothing in between.
  • Service Conduit – The conduit which houses the underground service wire. This conduit connects the MSP to the SDGE transformer, handhole, or vault at the street.

All of these components are proportional to the service size:

  • 100A service size means 100A MSP and 2” conduit.
  • 200A service size means 200A MSP and 3” conduit.
  • 400A service size means 400A MSP and 3” conduit.

If a service upgrade is necessary:

  • When upgrading from 100A to 200A and service is 2” underground conduit, it is likely that it will require an upgrade to 3” conduit. SDGE will always need to field the site to determine if a conduit upsize is needed.
  • When upgrading to 400A, the conduit will always need to be upgraded because 400A requires 3” conduit. Unless the existing service is 200A and it was installed after 2015, in which case it may already be 3.”

If the existing service size needs to be upgraded and the service is underground from the main panel to the connection point at the street, one of several outcomes will happen:

  1. Existing conduit size is adequate for the new upgraded service and we do not need to touch anything but the panel.
  2. Existing conduit is undersized for the new upgraded service and we need to replace the conduit from MSP (main service panel on PDU) to an SDGE handhole/transformer/vault that exists:
    • in an easement on the client’s property. In this case, there is no work that needs to be performed in the right of way (ROW).
    • across or down the street from the client’s property. In this case, ROW work will be required to install a new upsized conduit to said handhole/transformer.

There’s also important context to note on conduit upgrade requirements. Sometimes the underground service is not in conduit at all and is SIDA, DBC cable – “direct-burial cable.” Because the DBC cable is stubbed up into the panel with a 90deg conduit sweep through the foundation and into the wall, we cannot tell the difference between SIDA and conduit. This information can only be obtained through an SDGE service order request. If the underground wire is determined to be DBC by SDGE, any change/upgrade to the MSP will trigger a conduit upgrade.

All of this information is what SnapADU has gathered from recent service upgrades. These rules are always changing. While there is an SDGE Service Standards & Guide, many of the requirements and the parameters are largely set by the planner assigned to the project, so each case will be different. This is yet another reason it is so crucial to work with an experienced contractor on your ADU build so your team can find workable solutions – and advocate for you – in these complex scenarios.

Why should your ADU contractor upgrade your main electrical panel?

An upgrade to your existing Main Service Panel can occur for a variety of reasons – undersized, unsafe, too few breaker slots, need for a solar-ready panel. Whatever the cause it is best to have your ADU contractor manage the scope of work for several reasons.
  1. Coordination with the utility provider which has long, long lead times, typically 6 months at a minimum. We initiate a work order for every project as soon as a sales proposal is signed and begin coordination with them so that there is no delay caused by the long lead time
  2. The utility provider does not allow duplicate service orders on the same property. Since the ADU contractor immediately requests a work order, any other provider would not be able to do so.
  3. Every ADU requires its own, stand-alone Sub Electrical Panel (“sub-panel” for short) which needs to be of the correct capacity and model to accept the electrical circuits from the ADU as well to connect to the Main Service Panel.
While it can take six months or more to complete the work from application to re-energization, the physical work onsite typically take only two days, for which power is out for only several hours on average. Costs for an upgrade will range widely depending upon the reason for the upgrade and proximity to the High Power Transmission Lines.