E-mail Sherry Listgarten About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving a... (More) About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving and how they want to respond, and will feel comfortable asking questions and exchanging comments on the topic. It is important that we develop a shared understanding of the basic science and impacts of climate change, to make sense of our actions and policy options going forward. My background is not in climate science, and I'm not even particularly green; my hope is that helps to make this blog more relatable. I studied math and neurobiology on the east coast before moving out here in 1987 for grad school in computer science. After working in the tech industry for about 25 years, I retired a few years ago to better align my time with my priorities. I love spending time outdoors, and feel deeply our responsibility to this incredible planet that we call home. (Hide)
View all posts from Sherry Listgarten 100 Amp Breaker
Excellert summary! Only one comment, it is possible that a “full" panel has one or more breakers that are no longer feeding any appliances in the home, particularly if there has been previous remodels. I have an orphan 20A breaker that controls nothing and a 220v circuit in the garage that once fed a dryer. That task is now serviced by a circuit in a subpanel, but if I did not know that I might assume the panel was already full.
Excellent article/blog and one that most readers can comprehend easily. Sometimes your other posts with all of the charts and statistics is a bit too much for simpletons like me to process.
Great Article. Not mentioned are considerations for a homeowner wanting to add solar panels or battery storage which probably merits a separate blog. The rules for adding a solar breaker are different than those that apply to load breakers, since solar (and battery storage) supply power to the home, rather than consume it. In my experience as a solar installer I've found that adding solar to home which has an electrical panel rated 100A (or less) can limit the size of the solar installation. Many households are being told to upgrade their service to 200A or higher to support a larger solar installation. This can be expensive, especially if the home has underground service. I'd like to point out that upgrading the service wiring isn't always necessary. There are new electrical panels that are made to connect solar, for example a panel with a 125A main breaker and a 225A rated bus bar can support a larger solar installation without the need for the Utility to upgrade the service wiring to the home. If your existing panel has insufficient bus bar rating for a PV system larger than 5kW and you can use more space for breakers, talk to a qualified electrician to find out what options are available to you besides a service upgrade.
Good article. It's worth noting that optional method 220.87 cannot be used if a house has solar power (or other renewables).
These comments are great, thank you! @Eric, thank you, I will add that note to the post. @Marc, thank you for letting me/readers know about that new type of panel, it makes a lot of sense. @Eeyore, great point. Ideally an electrician would disconnect and label orphaned circuits, at least the ones that have no outlet or equivalent. When I was writing this post I discovered that my parents have two (big) breakers on separate panels labeled "range". A new range replaced an old one but the electrician never disabled the old circuit or changed the label. Yikes. @Lyle, I am glad that you liked the post! Generally speaking, it is hard for me to know what level of detail readers appreciate. As you noticed, I tend to include data (esp visuals) because I think it's important that people be able to see the facts/data behind the words. And sometimes it's fun to look at pictures even if you don't entirely understand them. But in the end I can never tell which posts will be popular. I wrote one once called "Pipelines, power lines, and eminent domain", which I thought would get almost no readers (with a title like that??) and I was completely wrong. My daughter was teasing me that "Your electric panel" is also an awful title. Well, at least it was readable! Thanks for the comment :)
@ Eric, Thanks for pointing out that new prohibition in the latest code cycle. I see that new exception prohibiting solar customers from using section 220.87 for determining panel adequacy for new planned devices was just added in the recent code cycle. By outright prohibiting the use of the 220.87 method for solar customers it seems to overconstrain the issue since it could just say that 80% of the rating of the solar feed-in breaker will be added to the 125% of historic loads and that would get the panel loading to reflect worst case conditions allowed by the code. e.g. Someone with a 100A panel and a 4 kW AC output inverter and a 8 kW historic highest 15 minute (net) load would be allowed to add 10 kW of new attached device nameplate load. (24 - 4 - 10) (24 kW panel capacity - 4 kW inverter max output - 8 kW highest load X 1.25 factor) To solve climate change we need to make doing the right things easy.
Thanks very much for this series and previous posts like the heat pump water heater installation. It's good to see real-world examples and learn about important but rarely-mentioned issues such as the calculations for determining simultaneous load on a panel.
@Mondoman: I'm so glad it's helpful! I've been using this info to fill out my HPWH permit. It's been strangely fun to look at electric panels. BTW, a lot of the credit for this goes to Menlo Park's Tom Kabat, who has been leading the charge to point out the surprising flexibility and capacity of our electric panels.
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