The short answer
You need 200-amp service when a load calculation says your existing service cannot carry what you have plus what you are adding. That is the whole answer, and it is deliberately unsatisfying, because the useful version is specific to your house. The code provides two ways to do the arithmetic for a dwelling: the standard method in Article 220 Part III, which adds loads category by category with defined demand factors, and the optional method in 220.82, which is a simplified route treating the first 10 kVA at full value and the remainder at 40 percent with separate handling for heating and cooling. California adopts both through the CEC. They can give different answers on the same house, which is one reason a real calculation beats a confident guess.
What that means practically: if somebody tells you a 100-amp service is inadequate without having done the arithmetic, they are guessing. Plenty of Santa Cruz homes run comfortably on 100 amps and will keep doing so. The question is never whether 100 sounds small — it is whether 100 covers your actual list.
What actually pushes a house past 100 amps
In practice, almost nobody outgrows a service gradually. They add something. Five loads account for nearly every upgrade we do:
- An EV charger — a Level 2 unit is a substantial continuous load, and continuous loads are counted at 125 percent
- A heat pump for heating and cooling, replacing gas heat
- A heat-pump water heater, replacing gas
- An induction range, replacing gas
- Solar with battery backup, which changes the service arrangement as well as the load
One of those on its own often fits. Two at once is what most commonly turns a maybe into a definitely — which is why the sequencing question matters, and why it is worth having the calculation done for everything you intend to do rather than just the next thing.
Signs worth paying attention to
None of these is conclusive on its own, and none replaces a calculation. But any of them is a reasonable prompt to have one done.
- No spare spaces in the panel, with tandem breakers doubled into positions to make room
- Lights dipping noticeably whenever a large appliance starts
- The MAIN breaker tripping — which is a different and more significant event than a branch breaker tripping
- You are planning any of the five loads above
- An insurance carrier, home inspector or solar installer has raised it
Worth separating two things that get conflated here. Capacity and condition are different questions. A panel can be perfectly adequate in amperage and still need replacing because of its brand or its condition — and a large service with a failing connection is no safer than a small one. If the panel is a Federal Pacific or a Zinsco, that is a separate conversation from this one, and we have guides on both.
What the work actually involves here
This is where local practice matters, because quotes sometimes describe a smaller job than the one that has to happen. Every main panel job we do — a 100 to 200 amp upsize OR a like-for-like replacement at the same amperage — is a full electrical service rebuild. The service entrance conductors, the combination meter main, and the grounding and bonding all come up to current code, not just the box on the wall. We do not quote a panel-only version of a main panel, because on a main panel there is not really one.
On an OVERHEAD service the chain is weatherhead, mast, service entrance conductors, combination meter main, grounding. On an UNDERGROUND service there is no mast or weatherhead at all — the utility conductors come to a service point and terminate inside the combination meter main. One thing that surprises people: an underground like-for-like still needs PG&E to disconnect and reconnect at the splice point, so it is not the smaller job it sounds like. And worth knowing that there is no separate meter base in California residential work — it is inside the combination meter main, so anyone itemising one is describing something that does not exist here.
On an underground UPSIZE, the largest single cost variable is the conduit. If the existing conduit is 2 inches or larger and in reusable condition, the job is straightforward. If it is not, new conduit has to be trenched, and that is a materially different piece of work. We assess the visible conduit when quoting; PG&E verifies it after contract; and if they require new conduit we requote rather than absorb it quietly or spring it on you mid-job.
Most of these are a single day. PG&E disconnects, we rebuild, the AHJ inspects, PG&E reconnects. You are without power for the working portion of the day — worth planning around if someone works from home or there is medical equipment in the house. The panel we install is Siemens. Other brands are available if you ask for one, and breakers always match whichever panel goes in, because mixing them voids the UL listing of the assembly regardless of whether another maker's breaker physically clips onto the bus.
Permits and who issues them
A service change always needs a permit and an inspection. Which authority issues it depends on your address, and this catches people out more than it should: the City of Santa Cruz, Capitola, Scotts Valley and Watsonville each run their own, and everything unincorporated goes through County Planning. Live Oak, Pleasure Point, Soquel, Aptos and Felton are all unincorporated county despite what the mailing address suggests. We pull the permit and coordinate the inspection either way.