By Alexandru Goncear, Owner and CEO, ElectON Enterprise. Washington electrical contractor license ELECTEL765MN. Kent office at 1609 Central Ave S Suite E.
The pattern is consistent enough that we now bring it up unprompted. One EV shows up in a Kent driveway, we install a charger, everyone is happy. Two or three years later the second car in the household turns over, it is also electric, and we get a call asking how much to add a charger on the other side of the garage.
The answer depends almost entirely on a decision that was made at the first install, usually without anyone discussing it. If the run was sized for one charger and nothing else, the second charger means opening the same wall, pulling new conduit down the same path, and in a fair number of East Hill houses, upgrading the service that could carry one charger but cannot carry two.
If somebody thought about it the first time, the second charger is a breaker, a short piece of wire and an afternoon.
What you actually pay twice for
Not the charger. Hardware is the predictable part and prices roughly what it prices.
You pay twice for the path. Conduit through a finished wall, a run around the outside of the house, a trench across the yard to a detached garage, drywall repair, and the labor hours that go with all of it. On the line-item breakdown of what a Kent charger install costs, that middle row is the one that moves, and it is exactly the row you repeat if the first job was scoped for one unit.
You can also pay twice for the service. A 100 amp service that squeaked through a load calculation with one charger on it will not clear the second one. Under the 2023 NEC, which is what Washington inspects to, section 220.57 requires each EVSE to be counted in the dwelling load calculation at 7,200 VA minimum or its nameplate rating, whichever is larger. Two chargers means two of those numbers in the calculation. That is often the difference between a house that needs no service work and a house that needs a full upgrade.
So the question is not really “how do I add a second charger.” It is “what do I do now so the second charger is cheap later.”
Four ways to get two chargers
Two separate dedicated circuits. The straightforward version. Each charger gets its own breaker, its own conductors, its own everything. Both cars charge at full speed at the same time, forever, with nothing clever going on. It also demands the most capacity: two 48 amp chargers means two 60 amp circuits under the 125 percent continuous rule in NEC 625.41, and a 100 amp service is not going to accommodate that alongside a heat pump. This is the right answer for a house with 200 amp service and headroom to spare.
One circuit, two chargers, power sharing. The 2023 NEC changed the picture here. Previously an EVSE over 16 amps needed its own individual branch circuit, full stop. Section 625.40 now carries an exception: multiple chargers can share a circuit when they are managed by an energy management system under 625.42(A), or when the equipment has adjustable settings with restricted access under 625.42(B). In practice, the pair of chargers talks to each other and splits a fixed allocation, so the total never exceeds what the circuit is rated for.
Both cars still charge overnight. Neither charges at full speed while the other is plugged in. For a household doing normal Kent commuting distances, that is a distinction you will never notice at seven in the morning.
The catch is brand lock-in. Tesla’s Group Power Management, for example, handles up to six Gen 3 Wall Connectors on a single circuit, and Tesla is explicit that the feature only works between Gen 3 Wall Connectors. It will not manage a unit from another manufacturer. Their Wall Connector power management documentation spells out what each of their three modes does. Other manufacturers offer comparable load sharing within their own product lines, with the same limitation. If one household member is driving a Tesla and the other a Rivian, power sharing between the two units is generally off the table and you are looking at option one or option three.
A subpanel in the garage. One feeder runs from the main panel to a small panel mounted in the garage, and both charger circuits come off it. This is the option worth taking seriously if the panel is a long way from the parking, and it is what we recommend most often for detached garages. You pay for the expensive run once. Adding the second circuit later means opening a panel that is already ten feet from where the charger goes. A garage subpanel and feeder typically runs $400 to $900 above the cost of a single charger circuit, and it usually pays for itself the first time you add anything out there, whether that is a second charger, a welder, a compressor or a heat pump for the shop. It falls under the same dedicated circuit work we do for hot tubs and workshops.
Install one now, pre-wire for the second. The cheapest thing on this list, and the most overlooked. Details in the next section.
The pre-wire nobody asks for
If you are installing your first charger today and there is any chance of a second EV in the next five years, this is the conversation to have while the estimator is standing in your garage.
Run the conduit one trade size up. The incremental cost of larger conduit is small. The cost of pulling a second run through a finished wall three years from now is not. Leave a pull string in it while you are at it.
If we are trenching to a detached garage, put the second set of conductors in the trench now, or at minimum a second conduit. The trench is the expensive part. Digging it twice is the single most avoidable waste of money in this entire category of work.
Size the feeder for two. If you are putting in a garage subpanel anyway, sizing the feeder and the panel for two charger circuits rather than one costs very little at install time and saves the whole feeder job later.
Decide where the second charger goes before the drywall closes. Charge port locations differ by manufacturer, and a cable that reaches comfortably on a driver-side port will not necessarily reach a car parked nose-in on the other side of a two car garage. Walk both bays with both cars in mind.
Altogether, that pre-wire usually adds something in the $150 to $400 range to a first install. Compare that against repeating a wall run or a trench.
Which of these fits your Kent house
The housing stock decides more than personal preference does.
Post-2000 homes around Panther Lake and the newer plats. Usually 200 amp service, panel in or near the garage, open slots. Two dedicated circuits are typically fine, and often no service work is needed at all. This is the easy version and it is worth confirming with a load calculation rather than assuming.
East Hill split levels and ramblers from the 1970s and 1980s. This is where power sharing earns its keep. A 100 amp service that accepted one charger will fail the calculation with two. Sharing a single managed circuit between two units, or running both at reduced settings under 625.42(B), can keep a household on its existing service instead of paying for a 200 amp upgrade. Not every house qualifies. Some genuinely do need the panel and service upgrade, and we will tell you when the numbers say so. We walked through how to read your own panel before calling anyone, using a Federal Way house as the example, and the method works the same here.
Detached garages and shops, common toward Soos Creek and on the older Scenic Hill lots. Subpanel, every time. The feeder and the trench are the cost, so build the far end to carry more than you need today.
Houses with an ADU, or one going in. Two dwellings and two chargers is a different load calculation entirely, and it needs to be worked out at the plan stage rather than discovered later. That sits alongside our ADU and new construction wiring.
The code details that decide the design
Worth knowing, because they explain why quotes differ.
Each charger is a continuous load, so the circuit is sized at 125 percent of the nameplate rating under NEC 625.41. A 48 amp charger needs a 60 amp circuit whether or not the car is ever plugged in.
In the dwelling load calculation, section 220.57 counts each EVSE at 7,200 VA or nameplate, whichever is greater. This is why the second charger can push a service over the line even though your monthly electricity use barely changes.
Above 60 amps, NEC 625.43 requires a disconnecting means in sight of the equipment. Two 60 amp chargers on a shared circuit can put you into that territory depending on the design, which is a detail worth having an electrician resolve before you buy hardware rather than after.
Any new 240 volt circuit needs a permit. The City of Kent does not run its own electrical inspection program, so permits and inspections here go through the Washington State Department of Labor and Industries out of the Tukwila office. Doing both circuits as one job means one permit, one inspection, and one crew mobilization instead of two of each. That saving alone is usually worth more than people expect.
Common questions
Can two EV chargers really run on one circuit? Yes, under the 2023 NEC, provided the chargers are managed by an energy management system or set to restricted adjustable ratings under 625.42. Both cars charge at once, just at a shared allocation rather than full speed each.
Will power sharing slow my charging down noticeably? For most households, no. A Level 2 charger at a reduced allocation still adds far more range overnight than a typical Kent commute uses. If one of you regularly drives long distances and needs a full battery every morning, say so at the estimate, because that is a real reason to choose two separate circuits.
Can I mix charger brands and still share a circuit? Generally no. Load sharing features work within a manufacturer’s own product line. Two different brands usually means two circuits, or a third party energy management device sized for the job.
I already have one charger. Did I miss my chance? Not necessarily. It depends what got installed. If there is a subpanel in the garage, or the conduit has room, or the existing circuit was sized generously, adding the second unit can still be inexpensive. Send us a photo of the panel and the existing charger and we will tell you which situation you are in before anyone drives out.
How much does the second charger add if we do both at once? When both units go in on the same visit and the path is already open, the second one is usually a few hundred dollars of additional wire, breaker and labor on top of the hardware, rather than a repeat of the whole job. The gap between doing it together and doing it three years apart is the entire point of this post.
Do I need a bigger service for two chargers? Sometimes. It comes down to the load calculation, your service size, and whether you have electric heat and an electric range. Two chargers on a 200 amp service is often fine. Two chargers on 100 amp service usually is not, unless load management is in the design.
Getting the design right the first time
We are a licensed residential electrical contractor with an office at 1609 Central Ave S Suite E in Kent, minutes off the SR-167 interchange. We cover East Hill, West Hill and Riverview, Panther Lake, Meridian and Lake Meridian, Scenic Hill, Midway, Star Lake, downtown and the Kent Valley, across zip codes 98030, 98031, 98032, 98035, 98042, 98064 and 98089, plus Auburn, Renton, Covington, Des Moines, SeaTac, Tukwila, Maple Valley and Federal Way.
Alex walks the garage and opens the panel before quoting, and if you tell him a second EV is likely, the design will account for it. That costs you very little now and saves a repeat of the expensive part later. More detail on our EV charger installation work, and on what we do generally as electricians in Kent, WA, is on those pages.
Call (253) 508-7529 or request a free estimate. Mention both cars, even if the second one is hypothetical.
ElectON Enterprise, 1609 Central Ave S Suite E, Kent, WA 98032. Phone (253) 508-7529. Washington electrical contractor license ELECTEL765MN. Licensed, bonded and insured. Monday to Friday 8:00 AM to 5:00 PM, emergency calls answered 24/7.