Load Calculation
We read actual draw on your main feeders with a clamp meter, check the main breaker size, and confirm your service can carry the added load. You get the numbers in writing before we quote the job.
Licensed
Licensed & Bonded
Fully Insured
Insured & Bonded
24/7 Emergency
Same-Day Response
Professional Electrical Services
Quality-Focused Service in San Mateo
What's Included in a Subpanel Install
Every subpanel job we quote includes the panel, the feeder, the breakers, the permit, and the inspection. If you want a trenched run to a detached building or a generator interlock added on, we price that separately so you can see exactly what you are paying for.
Panel and Breakers
We supply a UL listed enclosure from Square D, Eaton, or Siemens, sized to your load. Breakers are matched to the panel brand, and we install AFCI or GFCI protection where the NEC code compliance requires it.
Feeder and Grounding
Copper feeder conductors sized to the subpanel ampacity, run through conduit or fished through the wall. We land the grounding wire and neutral bar correctly and torque every lug to the manufacturer spec.
Permit and Inspection
We pull the local building permits through San Mateo County, schedule the inspection, and meet the inspector on site. If a correction is needed, we handle it and re-inspect at no extra charge.
Labeling and Walkthrough
Every breaker gets a printed label and a directory taped inside the panel door. We walk you through what each breaker controls and show you how to reset the subpanel main if it ever trips.
What Subpanel Installation San Mateo CA Actually Involves
Subpanel installation San Mateo CA is the work of adding a second, smaller electrical panel fed from your main service so you can run more circuits without overloading the original box. We mount the enclosure, run the feeder conductors, land the neutral and grounding bars, and torque every lug to spec. You get a dedicated breaker for the garage, the ADU, or the hot tub instead of daisy-chaining off a circuit that was never sized for it.
Most San Mateo homes we open up were built between 1940 and 1975, and the original 100-amp service is already carrying more than it was designed for. Add an EV charger, a mini-split, or a backyard ADU and the main breaker starts tripping. That is when an electrical subpanel upgrade San Mateo makes sense. We check the existing load first, then tell you honestly whether a subpanel solves it or whether you need a full service change.
How Our Subpanel Installation Process Works
You get a written scope, a fixed price, and a clean job site. Most subpanel jobs finish in one day, and we tell you up front if yours needs two.
01
Schedule
Call or book online — a real human picks up and confirms a 2-hour arrival window.
02
Diagnose
Licensed tech inspects on-site, then walks you through the cause and your options.
03
Fix
The job is completed to code and done right the first time — no shortcuts, no surprises.
04
Project Completion
Every job backed by a written workmanship warranty — and we stand behind it.
Tools and Methods We Use
Tools & Equipment
Clamp Meter
We clamp the main feeders to read actual amp draw during the load calculation. That tells us whether your service has headroom for a subpanel or whether you need a full upgrade first.
Torque Screwdriver
Every lug on the subpanel and main breaker gets torqued to the manufacturer spec. Loose lugs are the number one cause of warm panels and arcing, and a torque screwdriver removes the guesswork.
Panel Knockout Punch
We punch clean, round holes in the enclosure for conduit and feeder entries. A proper knockout keeps the panel UL listed and passes inspection without a fight.
Fish Tape and Cable Ripper
For feeders run inside finished walls, we use fish tape to pull conductors without tearing out drywall. The cable ripper strips the jacket cleanly so the conductors land without nicks.
Circuit Breaker Finder
After the install, we map every breaker to its outlets and lights so the panel directory is accurate. No more guessing which breaker kills the bedroom outlet.
Multimeter and Voltage Tester
We verify voltage and continuity on every circuit before we close the panel. The voltage tester confirms the main is dead before we touch a conductor, every time.
Methods & Standards
NEC Load Calculation
We follow the NEC optional method to calculate existing and new load in amps, then size the subpanel and feeder to match. This is the same math the county inspector uses, so the plan holds up on the first review.
UL Listed Equipment Only
Every enclosure, breaker, and lug we install carries a UL listing. That matters for insurance claims and for the inspection. We do not install gray-market panels or mismatched breakers.
NEMA Standards Compliance
We match the enclosure rating to the location. A garage or outdoor subpanel gets a NEMA 3R enclosure rated for rain and dust. An interior subpanel gets a NEMA 1 enclosure mounted at the correct working height.
OSHA Safety Standards
We lock out the main, verify dead with a voltage tester, and wear the right PPE on every job. No live work on a panel unless there is no other option, and never without a second person on site.
When San Mateo Homeowners Add a Subpanel
01
You are adding a detached ADU in the backyard and the main panel has no room for the new circuits.
What we do: We run a trenched feeder from the main panel to a 125-amp subpanel inside the ADU, then wire the kitchen, mini-split, and bathroom circuits off it. We coordinate the trench inspection and the final electrical sign-off with San Mateo County.
→ The ADU gets its own breaker panel, the main house stays on its existing circuits, and the county signs off on the ADU permit.
02
You bought a Level 2 EV charger and your 100-amp main panel is already full.
What we do: We run a load calculation, confirm the service can handle the added 40 to 48 amps, and install a subpanel with a dedicated 240-volt breaker for the charger. If the service cannot carry it, we quote a 200-amp upgrade instead.
→ You charge overnight at full speed without tripping the main breaker, and the install is permitted and inspected.
03
Your garage workshop keeps tripping the one circuit that feeds the whole space.
What we do: We install a 100-amp subpanel in the garage, move the existing garage circuits onto it, and add dedicated breakers for the table saw, compressor, and dust collector. Every tool gets its own circuit.
→ You run two tools at once without tripping anything, and the main panel stops carrying the shop load.
04
You are remodeling the kitchen and adding a wall oven, induction cooktop, and dishwasher.
What we do: We add a subpanel near the kitchen, run dedicated 240-volt and 120-volt circuits to each appliance, and install GFCI protection where the code requires it. The main panel keeps the rest of the house on its original circuits.
→ The kitchen runs on dedicated breakers, the remodel passes inspection, and you have spare spaces for future additions.
How Subpanel Work Runs in San Mateo
San Mateo sits between the bay and the hills, and that shows up in the housing stock. The flats near downtown and Hayward Park are full of 1920s to 1950s bungalows with 60-amp or 100-amp service and cloth-wrapped wiring. Up in the Highlands and around Beresford Park, you get 1960s tracts with aluminum branch circuits and panels that were undersized from day one. Add the fog belt and the salt air coming off the bay, and we see more corroded panel connections here than inland crews do. When we quote electrical subpanel upgrade San Mateo work, we plan for that: new lugs, anti-oxidant compound on aluminum, and NEMA 3R enclosures for anything mounted outside. If you are searching for an electrical subpanel upgrade San Mateo open now on a weekend, call us. We keep Saturday slots for tripping breakers and dead panels. Permits go through San Mateo County, and we meet the inspector on site so you are not chasing paperwork.
Neighborhoods We Serve
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Beresford Park
Mostly 1940s and 1950s homes with original 60-amp or 100-amp service. Subpanels here usually feed garage workshops and kitchen remodels.
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San Mateo Highlands
Larger lots with detached garages and ADUs. We run trenched feeders out back and set NEMA 3R subpanels for exterior mounting.
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Hayward Park
Mix of older bungalows and newer infill. Many panels here are full, so subpanels are the cleanest path for EV chargers.
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Downtown San Mateo
Older multi-unit buildings where each unit may need its own subpanel fed from a house panel. We coordinate with property managers on access.
Local Conditions We Plan For
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Salt air and fog belt corrosion
Panel lugs and bus bars corrode faster near the bay. We inspect for corrosion on every call and use anti-oxidant compound on aluminum terminations to slow it down.
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Aging 100-amp service in older tracts
Many homes cannot carry a modern load without an upgrade. We run the load calculation first and tell you honestly whether a subpanel is enough or whether the service needs replacing.
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San Mateo County permit and inspection timelines
Permits typically clear in a few business days, and inspections are scheduled within a week. We build that timeline into your quote so you know when the job actually finishes.
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Detached garages and backyard ADUs
Feeder runs to detached structures need trenching and separate inspection. We handle the trench, the conduit, and the inspection in one coordinated job.
100-Amp Subpanel for a Garage Shop
Problems a Subpanel Fixes for San Mateo Homes
Most subpanel calls start with the same complaints: breakers tripping, lights flickering, or a panel that is simply out of spaces. Here is what we see and how we fix it.
Problem
Breakers trip when two big appliances run together
You reset the breaker, it trips again, and eventually someone leaves a penny in the fuse box or upsizes the breaker, which is how fires start.
Our Fix
We move the heavy loads onto their own breakers in a new subpanel, sized to the actual draw. The main panel stops carrying the combined load, and each appliance gets the circuit it needs.
Problem
No spare breaker spaces for an EV charger
You buy a Level 2 charger, then find out the main panel is full and the install quote jumps by thousands because the whole service needs replacing.
Our Fix
If the load calculation supports it, we add a subpanel with dedicated 240-volt breaker spaces for the charger. That keeps the project in the low four figures instead of a full service change.
Problem
Warm electrical panel and flickering lights
A warm panel usually means a loose lug or a corroded connection. Left alone, it arcs, damages the bus bar, and can take the whole service down.
Our Fix
We open the panel, inspect the lugs and bus bar with a multimeter, and repair or replace what is failing. If the panel is beyond saving, we install a new subpanel or replace the main service.
Problem
Outdated 100 amp service cannot carry an ADU
Adding a detached ADU with a kitchen and mini-split pushes a 100-amp service past its limit, and the county will not sign off on the ADU permit without an electrical plan.
Our Fix
We run the load calculation, then either add a subpanel fed from an upgraded main or upgrade the service to 200 amps and feed the ADU from a new subpanel. Either way, you get a permitted, inspected install.
Why San Mateo Homeowners Add a Subpanel
A subpanel is not a luxury add-on. It is how you keep a modern house running on older service without tripping breakers every evening. Here is what a properly sized subpanel gets you.
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Stop Tripping Breakers
When the dryer, microwave, and space heater share one circuit, the breaker does its job and shuts everything down. A subpanel gives each heavy load its own breaker. Most homes we rewire stop nuisance trips the same day, and you can run the appliances you already own without thinking about it.
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Room for EV and ADU Loads
A Level 2 EV charger pulls 40 to 48 amps continuous. An ADU with a kitchen and mini-split adds another 60 to 100 amps. If your main panel is full, a subpanel for garage or ADU San Mateo California is the cleanest path. We calculate the load and size the feeder so you have spare breaker spaces left over.
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Code-Correct and Permitted
Every subpanel we install meets NEC code compliance, uses UL listed equipment, and gets inspected by San Mateo County. We pull the local building permits, schedule the inspection, and correct anything the inspector flags. That paperwork matters when you sell the house or file an insurance claim after a surge.
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Safer Than a Fuse Box Workaround
We still find overloaded fuse boxes with pennies behind the fuses and warm electrical panels that never got addressed. A subpanel with modern circuit breakers, a proper neutral bar, and correct grounding wire removes that risk. You get arc-fault and ground-fault protection where the code now requires it.
Licensed, Insured, and Inspected
Licensed & Certified
- California C-10 Electrical Contractor License — issued by California State License Board
- NEC Code Compliance — issued by National Fire Protection Association
- UL Listed Equipment Standards — issued by Underwriters Laboratories
- OSHA Safety Standards — issued by Occupational Safety and Health Administration
- San Mateo County Building Permits — issued by San Mateo County Planning and Building
Verified Reviews
Google ★★★★★4.9
They did a load calculation before quoting, which no one else did. The subpanel went in clean, the county passed it first try, and the price matched the invoice. Highly recommend for anyone in San Mateo needing a subpanel.
Yelp ★★★★★5.0
Called about a warm panel and flickering lights. They came out same day, found a loose lug, and installed a subpanel to take the load off the main. Professional, tidy, and they explained everything without talking down to me.
BBB ★★★★★4.8
We used them for an ADU subpanel in the Highlands. They handled the trench, the permit, and the inspection. The crew showed up when they said they would and cleaned up the site better than they found it.
Google ★★★★★4.9
Needed a subpanel for a Level 2 EV charger. They told me honestly that a full service upgrade was not needed and saved me thousands. Install was fast, labeled well, and permitted through the county.
Local Experience With San Mateo Electrical Systems
Our electricians hold California C-10 licenses and work to NEC code compliance on every job. We have opened panels in hundreds of San Mateo County homes, from 1920s bungalows near Central Park to 1960s tracts in the Highlands. That means we know the wiring quirks: aluminum branch circuits, cloth-wrapped feeders, and the fuse boxes that predate grounded outlets. We carry Square D, Eaton, and Siemens panels on the truck so we are not waiting on a supply house when your job is scheduled.
- California C-10 licensed electricians on every subpanel job
- NEC code compliance and UL listed equipment on all installs
- Load calculations done with a clamp meter, not guesswork
- Permits pulled through San Mateo County on every project
- Square D, Eaton, Siemens, and Leviton panels stocked locally
Frequently Asked Questions About Subpanels
Real answers to the questions we hear most often from local homeowners and property managers.
How much does subpanel installation cost in San Mateo CA?
Most subpanel jobs in San Mateo run $1,200 to $3,500 in 2026, depending on panel size, feeder distance, and whether the wall needs opening. A simple 100-amp subpanel in a garage sits near the low end. A 125-amp subpanel feeding a detached ADU with a trenched feeder lands at the high end. The price includes the permit, the panel, breakers, and the inspection.
Do I need a subpanel in San Mateo California?
You need one if your main panel has no spare breaker spaces, if breakers trip when two large appliances run together, or if you are adding an EV charger, ADU, or workshop. A load calculation tells you for sure. If your 100-amp service is already near capacity, a subpanel will not fix it and you need a 200-amp upgrade instead.
Who installs electrical subpanels near me in San Mateo?
We do. San Mateo Panel Pros is a licensed C-10 electrical contractor working out of San Mateo and serving San Mateo County, including ZIP codes 94401, 94402, 94403, and 94404. We pull the permit, install the subpanel, and meet the inspector on site. Call +1 (650) 372-5030 to schedule a load calculation.
How long does a subpanel upgrade take in San Mateo CA?
A typical subpanel install takes four to six hours on site, plus a county inspection a few days later. If we need to run a feeder through a finished wall or trench to a detached ADU, plan on a full day or two. We give you a realistic window when we quote the job, not a best-case guess.
Related Electrical Services
Electrical Panel Replacement
When your main panel is corroded, undersized, or a recalled brand, a subpanel alone will not solve it. We replace the main service panel and add a subpanel in the same visit so your whole system is code-correct and properly grounded.
View Electrical Panel ReplacementElectrical Panel Repair
A warm electrical panel, flickering lights, or a breaker that will not reset often points to a loose lug or a failing bus bar. We diagnose the fault with a multimeter and clamp meter, repair what is fixable, and tell you when replacement is the cheaper long-term call.
View Electrical Panel Repair200 Amp Panel Upgrade
If your load calculation shows a subpanel will not buy you enough headroom, a 200-amp panel upgrade is the right move. We handle the service change, the meter base coordination with PG&E, and the county inspection, then add a subpanel for your garage or ADU.
View 200 Amp Panel UpgradeFuse Box Replacement
Older San Mateo homes still running fuse boxes cannot support modern loads or AFCI protection. We replace the fuse box with a breaker panel, then add a subpanel where you need extra circuits for an EV charger, shop tools, or a kitchen remodel.
View Fuse Box ReplacementCall San Mateo Panel Pros
Call (650) 372-5030 or email info@sanmateopanelpros.com and we will get you on the schedule. We answer the phone Monday through Friday, 8am to 6pm, and we run emergency panel calls 24/7. Same-day estimates are standard. If your panel is warm or a breaker will not reset, call now rather than waiting.
San Mateo Panel Pros
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Phone
+16503725030 -
Address
7 37th Ave, San Mateo, CA 94403, USA
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Hours
Mon–Fri: 7AM – 7PM
Sat: 8AM – 4PM
Sun: Emergency Only
24/7 Emergency Available