Electrical Vaults: Sizing, Placement, and Why They Always End Up Where Your Landscaping Was

If you've done any amount of commercial or multifamily development in California, you've had this conversation. The architect has a beautiful entry plaza. The landscape architect has a bioretention planter along the south side. The civil has grading that actually drains. And then PG&E or the municipal utility drops a redline on your plans showing a vault the size of a hot tub sitting directly in the middle of all of it.

Welcome to dry utility coordination.

Electrical vaults aren't optional, and they're not small. If you understand when they're required, what they actually look like in the field, and what constraints govern where they go, you'll stop being surprised and start designing around them from day one. That's what this post is for.

what's an Electrical Vault, and When Do You Need One?

An electrical vault (also called an underground service vault or transformer vault) is a buried concrete enclosure that houses a pad-mount or submersible transformer and associated switching equipment. Unlike a pad-mount transformer — which sits above grade on a concrete pad and is surrounded by a green metal cabinet — a vault is entirely below grade, with flush-to-grade access hatches on top.

You're typically looking at a vault instead of a pad-mount when one or more of the following applies:

For smaller commercial loads — a single-story retail building, a small office, a standard fast-food pad — you'll typically get a pad-mount transformer. They're cheaper, easier to maintain, and the utility prefers them when there's space. Vaults come in when you're past that threshold or when the site physically can't accommodate above-grade equipment.

Typical Vault Sizes: What You're Actually Designing Around

This is where a lot of plans go wrong. Engineers assume a vault is roughly transformer-sized. It's not. The vault has to house the transformer plus the primary switching equipment, cable terminations, oil containment, and enough room for a utility crew to work safely.

Here are the vault dimensions you'll typically encounter on California projects:

The footprint you need to protect at grade is larger than the vault itself. PG&E's standard requires a minimum 3-foot clearance around the vault perimeter for cable access conduits and future maintenance. Add the conduit stub-outs in all four directions, and you're protecting an area that can easily hit 16 × 24 feet before you've placed a single tree or BMP.

Structural slab thickness typically ranges from 8 to 12 inches of reinforced concrete. The vault lid hatches — usually two to four of them — are each around 3 × 4 feet and must swing open 90 degrees without hitting anything. If there's a wall, a planter curb, or even a grade transition within that swing radius, the utility won't accept the location.

Placement Constraints: ROW vs. On-Site

Where a vault goes depends on who owns the infrastructure and who controls the right-of-way.

In the Public ROW

In California, it's common for the utility primary to run in the public ROW, and for vaults or junction structures to be sited within the ROW as well. If that's the case, you're coordinating with both the utility (PG&E, SCE, or the municipal utility) and the encroachment permit process through the city or county. Typical ROW constraints include:

Contra Costa County, for example, requires an encroachment permit through Public Works for any vault lid within the ROW, and the permit process adds 4–8 weeks to your schedule if you haven't started it early. Don't wait until 90% CDs.

On Private Property

When the vault is on the project site, the constraints shift to the utility's easement requirements. PG&E will require a recorded easement over the vault footprint plus the access zone. That easement area typically can't have permanent structures, trees with deep root systems, or anything that would impair emergency access. This effectively removes that zone from your usable landscape budget.

The civil engineer's job here is to get the utility company's preliminary design — even an informal one — before you finalize site layout. On projects we've worked on in the East Bay and Contra Costa area, we've seen vault locations shift two or three times between the utility's initial sketch and the final recorded easement. Every shift has downstream consequences for grading, drainage, and landscape.

Clearances: The List That Actually Governs Your Layout

Vault placement isn't just about the utility's preferences. There are separation requirements from every other utility, from structures, and from site features. Here's what you're working with in California:

Why the Vault Always Ends Up in the Landscape Area

Here's the honest answer: it's a process-of-elimination problem.

The utility's primary conduit route follows the path of least resistance — usually parallel to the street in the ROW or just inside the property line. The vault has to go where the primary route hits the load center, which is somewhere near the electrical room. That location is almost always constrained by:

What's left? The landscape strip along the south side. Which is exactly where your bioretention planter was going. And the stormwater BMP engineer spent three weeks sizing.

The fix is coordination, and it has to happen early. On dry utility projects we manage, we request a utility company preliminary service layout before the 50% SD submittal. That gives us a vault location that's at least approximately right before grading, drainage, and landscape lock in. It doesn't eliminate surprises — utilities reserve the right to move things through design — but it cuts the late-game redesign significantly.

How Vault Placement Affects Grading

A vault lid at finish grade sounds simple. It's not.

The vault lid elevation is fixed by the utility. It's a precast structure, and the utility sets the lid elevation relative to their primary conduit depth, which is typically 30–42 inches below finish grade for distribution voltage (typically 12 kV to 21 kV in PG&E territory). That means the lid elevation is essentially determined by the street or sidewalk grade at the conduit entry point.

If your site grading calls for fill in the vault area — say, you're raising the pad 18 inches above street grade — you'll need a modified vault riser section to bring the lid up. That's a cost and lead-time item. If you're cutting, you need to make sure the vault drainage (most vaults have a sump and drain) still works.

Vault lids also create a flat spot in your grading scheme. A 10 × 16-foot concrete lid at a single elevation will conflict with any grade break or swale you were planning through that zone. We've redesigned drainage patterns on at least a dozen projects specifically to route sheet flow around vault lids that couldn't be relocated. It's manageable, but it takes time and it needs to happen before the grading plan is finaled.

PG&E vs. Municipal Utility: Where the Requirements Differ

If your project is in PG&E territory — most of Northern and Central California — you're working under PG&E Rule 16 (Service Planning) and their Electric Distribution Standards. Key things to know:

Municipal utilities — SMUD in Sacramento, Roseville Electric, Alameda Municipal Power, and others — have their own standards that vary considerably. Some are stricter on clearances; some are more flexible on vault sizing alternatives. The common thread is that they all have design standards documents, and you need to have them in hand before you start laying out the site. We keep a working library of the standards for the utilities we see most often in our site planning practice.

Costs That Surprise Developers

Most developers budget for "underground utilities" as a line item without understanding what's in it. Here's where vaults add cost that nobody warned them about:

The Civil Engineer's Coordination Role

The civil engineer isn't the one designing the vault — that's the utility's job. But the civil is the one who has to make everything else work around it. That means:

On projects where the civil doesn't drive this coordination, it tends to fall through the cracks until construction — and that's when it gets expensive.

Start the Coordination Before You Lock in the Site Plan

Electrical vaults aren't a detail. They're a site planning constraint that needs to be treated the same as a building setback or a fire access lane. Get the utility's preliminary service layout before you finalize your site plan, confirm the vault footprint and lid elevation before you finish grading, and protect the easement area before your landscape architect fills it with bioretention.

If you're early in a project and need help working through the utility coordination alongside the civil design, give us a call. We do this on every project we touch, and it's a lot less painful when it's built into the process from the start.

Learn more about our dry utility consulting services or see how we integrate utility coordination into site planning.