150 amp panel with 100 amp breaker feeding

150 amp panel with 100 amp breaker feeding full#

Fire up a heater and those loads get big fast. 125% of that is 59A, so 60A would be bare minimum there, but even that overlooks lighting and other routine potential loads. In the example above, the higher leg was 47A. In fact, it should be at least 125% of the maximum routine load you ordinarily expect. You want to size that large enough that it won't cause nuisance tripping from peak loads. What matters is the size of the feeder breaker inside the main panel. A 'plenty of spaces' subpanel will probably have a main breaker bigger than 100A. It depends on you being in a commercial application where AFCI and GFCI breakers are not required. Some panels specify x spaces and y circuits (a larger number). Whereas avoiding this problem (with a big panel) will set you back a few latté's. That creates an expensive, high-labor problem when you add things in the future, like a 240V table saw, a better welder, a water heater, electric car charger etc. The size of your panel in terms of number of spaces is very important to not running out of spaces. Its size doesn't matter - it's not even required! What is required is a shutoff switch, and the cheapest way to get a shutoff switch in a subpanel is to use a panel that features a main breaker. Now, at the subpanel in your outbuilding, there is also a main breaker in the subpanel. One is at the main service panel, and that has a very important job - protecting the wire run to the subpanel, and protecting the subpanel itself if the subpanel doesn't have its own main breaker. I get 1.95% at 4 AWG Aluminum wire, as the minimum needed to carry practical current in this example. Take the average of that - 41A - and put that into the voltage drop calculator. The two 240V loads put 23+12A=35A on both legs, and the 12A dust collector adds 12A to one leg so your two legs are 35A and 47A. If the number is pushing 5%, then change it to 4% and see what it says.įor instance let's say you have a '30A' 240V compressor that draws 23A, a '20A' 240V table saw that actually pulls 12A, and a 12A/120V dust collector. How much do you actually intend to load up this panel? (remembering that 120V loads only accrue to one leg or the other).Ĭalculate voltage drop based on that, and use 5%+ for your voltage drop number, because otherwise the calculator might find the standard wire is 3.06% and make you bump a size over 0.06% - that's ridiculous. They're not much cheaper than actual breakers though, so if the cost is within 20% just use a proper breaker.You have two separate questions to think about. Otherwise they make 'sub feed lug kits' which snap in like a breaker, but are just lugs (have no overcurrent capability). And in that case, if your main panel has feed-through lugs on the bottom, you can tap off those. Yes, you can put a 100A subpanel off a 100A main panel.

150 amp panel with 100 amp breaker feeding full#

3 AWG copper / 1 AWG aluminum allows a full 100A.6 AWG copper / 4 AWG aluminum can be breakered as large as 60A.If the cable were a larger size, you could run a larger breaker. The ground wire being #10 instead of #8 is allowed. I gather downbreakering to 40A will be an inconvenience, but so will owing a mortgage on a burned out house because insurance denied the claim. This is due to the 8 AWG cable connecting the two panels.

You are already overbreakered and you need to fix that. Given the facts you have provided, your maximum safe breaker size is 40 amps.