i have a 150a panel, i have plenty of space left in it, but my question is about total capacity, obviously the main breaker will trip if more than 150a gets pulled, but ive been trying to get a better understanding how you determine what the limit is for how many total amps in breaker size you can add. for instance, in this 150a panel, can i have 200a total breakers? 400?, etc...
Thanks!
I'm glad you have gathered that panels are like checkbooks (having a lot of checks doesn't mean having a lot of money). I like to order plenty of checks, and I like to have plenty of breaker spaces.
Figuring out how much ampacity you're actually using is a tricky but well-solved problem. The numbers on the breaker trips are useless; for instance if you have 40A breaker on an air conditioner and 50A on electric heat, does that count as 90 or only 50? How about a 15A breaker to a 1A refrigerator?
This is solved by a gold-standard way (couple of them) of doing a Load Calculation, relying on nameplate data and standard formulas. On residential:
What spits out is a number (expressed in VA, similar to watts) which says how big your service needs to be - say 18400 VA. You divide that by 240V and that gives you the service amps you need.
Keep in mind, the emerging tech of "smart panels". They monitor your current, and have the physical ability to interrupt loads under software command - like tanked water heater, dryer, EV charging and the like. So you can put a controller and some smart breakers in, and say "stay under 150A" - that removes the need for a service heavy-up. I'm speaking entirely of self-directed demand-side manamagement.
Of course this creates a business opportunity with the power company for cooperative demand-side management. So far, that's being implemented in very klutzy, ham-handed ways... but there are much better ways to do that, and we think they'll come around quickly to that.
If you are in an area where the utility company records the peak summer and winter demand. You might be able to get that information from them. Peak demand is the highest KW usage that ran for 15 minutes or more. You can usually call them from the phone number on your utility bill.
The only other method is to run a power analysis. Unfortunately, This is usually cost prohibitive for a residence.
The only other solution is to purchase a personal power monitoring meter which can give you that type information.
Both of these last methods will require you to monitor your system for a period of time in order to average out you usage and peak times and should be installed by a professional.
Good luck
To answer your question simply: the panel manufacturer will specify the maximum number of circuits allowed in the panel.
They will also specify what kinds of breakers you can put in the panel.
Finally, they will specify the maximum amperage for the panel — 99% of the time, the panel will come with a main breaker that is rated for the maximum amperage. So if you bought a 150A panel with a 150A main breaker, the maximum sized main breaker is also 150A. If you bought a panel that can have its main breaker replaced with a larger amperage main breaker, then it will say so in the panel data sheet and should be printed on the panel somewhere.
In terms of whether or not the total number of amps of the breakers can mathematically add up to more than the total amperage of the main breaker, the answer is yes. This is where the load calculation comes in. If the load calculation comes out to, say, 100A on a 150A panel, that’s fine even if the simple addition of all the face values of all the breakers is over 150A. And that’s definitely possible if for some reason you have lots of circuits with small loads on them or a small number of non-continuous larger loads like in a house with a basement suite that has a kitchen and a laundry.
