Somewhere between the electrical assessment and the first trench, every commercial EV charging project settles a handful of decisions about service equipment: what switchgear to install, what voltage to take service at, and how the utility will meter you. These choices happen quietly, inside a one-line diagram most owners never read closely, and they are among the most expensive to get wrong. A switchboard ordered to the wrong rating, a metering section the utility will not accept, or a service that exceeds the utility's size cap can each restart the design and add months to the schedule.
You do not need to design this yourself. A licensed engineer or commercial electrician owns the detail, and the utility has the final say on much of it. The goal of this article is narrower and more useful: to make you a fluent client who can read a proposal, ask the right questions early, and recognize the traps before they are poured into concrete.
What "service equipment" actually is
Strip away the jargon and the electrical service is a path. Power leaves the utility's transformer, passes through a metering point, hits a main disconnect, lands on a large piece of distribution gear, and fans out to the chargers. The "service equipment" is the gear at the front of that path: the main disconnect and the distribution section that everything downstream depends on.
Three pieces of equipment get used loosely as if they were the same thing. They are not, and the difference shows up in price, footprint, and lead time.
| Equipment | What it is | Typical use | Listing |
|---|
| Panelboard | The familiar wall-mounted "panel" of branch breakers | Feeding a cluster of chargers downstream | UL 67 (commonly up to 1,200A) |
| Switchboard | A floor-standing dead-front lineup of breakers in sections | The service and main distribution for most commercial EV sites | UL 891 (up to roughly 6,000A) |
| Switchgear | Heavier gear with compartmentalized, draw-out breakers | Large, critical, or utility-grade installations | UL 1558 |
In everyday conversation, and in this article's title, "switchgear" is shorthand for the service and distribution gear as a whole. For most commercial Level 2 and mid-size DC fast charging sites, that gear is a UL 891 switchboard, not true UL 1558 switchgear. The distinction matters when you read a quote: true switchgear costs more and takes longer to build, so make sure you are comparing equipment of the same class across bids.
Decision 1: What voltage your service should be
Commercial buildings typically run on one of two service voltages, and EV charging often forces the question.
- 208Y/120V is common in smaller commercial buildings and is fine for a modest number of Level 2 ports.
- 277/480V (a four-wire wye) is the workhorse for larger Level 2 counts and for DC fast charging.
The reason to care is current. Power is voltage times current, so the same kilowatts at 480V draw a bit under half the amps they would at 208V (the current scales with the voltage ratio, 208 over 480, or roughly 43%). Lower current means smaller conductors, smaller breakers, and more headroom before you hit the utility's size limits. A site that would need a 4,000A service at 208V might need roughly 1,700A to 2,000A at 480V for the same load. For anything with DC fast chargers, 480V is effectively mandatory; the chargers are built for it.
The trade-off: a 480V service usually needs a step-down transformer to serve ordinary 120V building loads, and the equipment and labor are priced differently. If your building is already 208V and the EV load is small, converting to 480V purely for the chargers is rarely worth it. If the EV load is large or includes fast charging, the voltage decision is usually made for you. Your electrical infrastructure assessment is where this gets pinned down against your actual load.
Decision 2: How the utility will meter you
How the utility measures your usage sounds like a billing detail. It is actually an equipment decision, because the metering method dictates hardware that has to be designed in from the start and approved by the utility.
There are three methods, and the size of your service usually decides which one applies.
| Method | How it works | Roughly when it applies |
|---|
| Self-contained | A standard meter plugs into a socket and carries the full current | Smaller services, often up to about 400A |
| CT metering | Current transformers measure the load indirectly through a CT cabinet | Larger services, commonly above 400A |
| Primary metering | The utility meters on the high-voltage side; you own the transformer | The largest loads, or by customer election |
The self-contained-to-CT crossover varies more than people expect. Lincoln Electric System, for example, allows self-contained metering up to 400A and requires CT metering above it. Other utilities require current transformers above 200A, and a few allow self-contained meters as high as 600A. The practical point: a larger EV service will almost certainly be CT-metered, which means a CT cabinet has to be located and coordinated with the utility, and that section often has to come from the utility's list of accepted metering equipment. Designing the gear and then discovering the metering section is not accepted is a common, avoidable delay.
The size cap that catches large projects
Here is the trap most owners never see coming: every utility sets a largest standard service it will provide, and a big charging site can run straight into it.
San Diego Gas and Electric makes a clean worked example because its rules are public and specific. SDG&E's standard service equipment is rated from about 800A up to 4,000A. A single secondary service, the 277/480V wye that large EV sites lean on, is generally built to that ceiling. When a site's load would push a single service past roughly 4,000A, you have two paths:
- Add another service. SDG&E grants a second service only under specific conditions, such as locating it close to the first or a set distance apart. There is a limit to how many services and paralleled main sections a utility will allow, and it is set by the utility, not by your designer.
- Step up to primary service. You take power at the utility's higher distribution voltage and own the transformer yourself. SDG&E addresses that path in its service guide's primary-metering provisions (section SG 012), and it also runs an EV-specific pathway, Rule 45, in which the utility designs, installs, owns, and maintains the equipment between its system and your meter for separately metered charging sites.
Pull your utility's service guide on day one of design, not after you have a one-line diagram. Every utility publishes one. PG&E and others call it a greenbook; some call it electric service requirements or a service standards and guide. The numbers differ from SDG&E's, but the pattern is identical: there is a largest standard service they will set, and beyond it you either parallel services or go primary. That single number quietly caps how much charging one service can support.
The lesson generalizes well beyond California. Before anyone sizes a switchboard, find your utility's maximum standard service amperage and the point at which it forces a second service or primary metering. If your charging plan crowds that ceiling, the design conversation changes completely, and it is far cheaper to learn that now than during the interconnection review.
Decision 3: Primary metering, the option past the cap
Primary metering deserves its own look, because it is both the way past the size cap and a long-term commitment.
In the ordinary arrangement, secondary metering, the utility owns the transformer that steps its distribution voltage down to your 480V or 208V service, and it meters you on your side of that transformer. With primary metering, the utility meters you on its high-voltage side, and you own, operate, maintain, and eventually replace the transformer and the gear behind it.
What you get in return is a lower rate. Utilities bill primary-voltage customers less per kilowatt-hour, and you stop paying for the energy lost as heat in the utility's transformer. What you take on is real: the transformer is expensive, it sits on a pad or in a vault you provide, and the maintenance and replacement are yours. The rate difference is the only financial upside, so primary metering tends to pencil out only for large sites with steady, heavy load, the kind of profile a busy fast-charging plaza or a fleet depot can have, and rarely for a modest Level 2 installation. Run the rate difference against the transformer's lifetime cost before you commit; the math, not the size cap alone, should make the call. The way your rate is structured matters here too, which is why it helps to first understand how to read your commercial EV tariff sheet.
Sizing for the build you will want later
Service equipment is one of the few parts of the project that is genuinely hard to enlarge after the fact. Two habits prevent the common regret.
Size the bus and leave room for sections. The horizontal bus rating and the number of spare breaker positions or future sections are cheap to add at the order stage and costly to retrofit. EV programs grow. Building the switchboard to today's exact port count, with no spare capacity, is how a successful pilot turns into a second mobilization and a second trench a year later. The companion to this is future-proofing your installation.
Respect the continuous-load math and the clearances. Under the National Electrical Code, EV charging is a continuous load, so circuits and the equipment feeding them are sized at 125% of the charger's rated current (NEC Article 625). That inflates the service size faster than owners expect. Equipment also needs code-required working space around it (NEC 110.26), and that clear area cannot be used for parking, storage, or anything else. A switchboard squeezed into a closet that fails the clearance rule is a failed inspection, so the footprint has to be planned, not found.
Choosing a manufacturer without ranking brands
Owners often ask which switchgear brand is best. That is the wrong question, and any honest answer would go stale quickly. The better question is whether a given manufacturer's equipment clears the requirements your project actually has. Evaluate on criteria, not on a name.
- Listing match. The equipment should carry the right UL listing for what it is (UL 891 for a switchboard, UL 1558 for true switchgear, UL 67 for panelboards). Confirm the listing covers the full assembly, including the metering section.
- Utility acceptance. Many utilities publish a list of accepted service and metering equipment. If the manufacturer's metering section is not on it, the utility can reject it, regardless of how good the gear is. Check this before you order.
- Local inspector and AHJ acceptance. The authority having jurisdiction has to pass it. Equipment that is unusual in your area can draw extra scrutiny and slow the inspection.
- Lead time and availability. Switchboards and switchgear have long, volatile lead times, and the gear is frequently on the project's critical path. A brand that is two months faster can matter more than one that is slightly cheaper. See realistic timelines and delays for how this ripples through the schedule.
- Serviceability and local support. Breakers fail and need replacing. Equipment with a local representative, available parts, and electricians who know it will cost less to live with than a cheaper unit with no support within a day's drive.
- Room to grow. Favor a lineup you can add sections or breakers to later over one that is fully built out on day one.
The anti-patterns are the mirror image: buying on price alone, accepting a metering section the utility has not approved, ignoring lead time until it becomes the bottleneck, and choosing equipment no local electrician stocks parts for. None of these show up in a side-by-side price comparison, which is exactly why they bite later.
The pitfalls that restart designs
These are the failures that send a project back to the drawing board rather than costing a few extra dollars. Walk the list before the gear is ordered.
- The service is sized past the utility's single-service cap, forcing a redesign to parallel services or primary metering.
- The metering section is not on the utility's accepted list and gets rejected after the gear is built.
- The CT cabinet location was never coordinated with the utility, so the meter cannot be set.
- The voltage decision (208V vs 480V) was made late, after conductors and equipment were already specified for the wrong one.
- Working clearance per NEC 110.26 was not reserved, and the install fails inspection.
- Primary metering was chosen for the rate without budgeting the transformer's ownership and replacement.
- The switchboard was ordered before the utility's service planning was final, so it no longer matches what the utility will actually set.
- The continuous-load 125% factor was missed, leaving the service undersized for the rated charger load.
Questions to ask early
A short, well-timed set of questions prevents most of the above. Ask the utility and your engineer before the design is locked, not after.
Ask your utility's service planner:
- What is the largest standard service you will set at our voltage, and at what point do we need a second service or primary metering?
- At what service size does metering move from self-contained to CT, and is there an accepted-equipment list for the metering section?
- Do you offer an EV-specific make-ready or new-service pathway, and what does it cover?
- What is your current timeline for service planning, design, and energization for a load like ours?
Ask your engineer or electrical contractor:
- Is the service equipment a UL 891 switchboard or UL 1558 switchgear, and why is that the right class for this site?
- What bus rating and spare capacity are you building in for future ports?
- How does the 125% continuous-load factor change the service size we need?
- Where does the equipment sit, and does the layout meet NEC 110.26 working clearances?
Where this sits in the project
Service equipment selection is the bridge between knowing your site's electrical reality and starting construction. It comes after the electrical infrastructure assessment has told you what your service can carry, and it has to be settled before procurement, because the switchboard is a long-lead item that everything downstream waits on. Get the voltage, the metering method, and the size right against your utility's specific rules, and the rest of the build has a stable foundation. Get them wrong, and you discover it at the most expensive possible moment, in the field. For the full picture of how this fits the wider job, see what commercial installation actually involves.
Last factually verified: 2026-06-19 against the SDG&E Electric Service Standards and Guide (2025) and SDG&E EV Infrastructure Rule 45 and EVSE standards material (4,000A standard service ceiling, primary service under SG 012, EV make-ready pathway), the Lincoln Electric System Meter Services Specification Guide and comparable utility metering specifications (self-contained vs CT metering thresholds), UL 67, UL 891, and UL 1558 equipment listing scopes, and NEC Articles 230, 408, 110.26, and 625 reference material (services, switchboard and panelboard construction, working clearances, and EV continuous-load sizing).