I'm looking to add a subpanel for a basement kitchenette. Here are the power requirements and intended new circuits.

 Appliance  Voltage  Amps       Slot    Circuit Amps 

 Oven/Range 220      28.0       1/2     40 

 Macerator  110      4.5        3       15  

 disposal   110      4.0        4       20    
 Range Hood 110      2.0        4    
 Microwave  110      9.1        4    

 dishwasher 110.     15.0       5       15 

 Fridge     110      6.0        future? 10

screenshot of sizing

What size sub-panel breaker do I need and what size cable is required (indoor 30 ft away)?

  • FYI, nominal voltages (since at least the 1960s) are 120 and 240. – isherwood Feb 17 '20 at 19:20
  • The answer is that a 60A panel will do fine, and it's really a matter of your prerogative how much overhead (for future-proofing) you want to build in. Unless this is an extremely locked-down, space limited installation, never leave yourself without 1) several extra breaker slots, and 2) substantial extra current capacity. I'd do 100A. – isherwood Feb 17 '20 at 19:21
  • Thanks! I always go back and forth between writing 110/120 and 220/240. Obviously, I'm not an electrician. – gte037p Feb 17 '20 at 19:22
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    In US/Canada (which I assume based on 120/240), typical minimum breaker is 15A - so 15A for refrigerator circuit, not 10A. Also will most likely need (code requirement for a regular kitchen and likely applies here too) 2 countertop circuits, 20A each. – manassehkatz-Moving 2 Codidact Feb 17 '20 at 19:35
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    So that's a 6 space panel. "Circuit" is a useless number anymore, and is basically a marketing lie at this point. That leaves you 1 space. I don't know how full your main panel is, but we deal with LOTS of "My panel is full, what do I do?" questions. Spaces are cheap, so it's very cheap to assure you never have that problem... so we really bang the drum hard for fitting LARGE panels. Large. Really. Large. – Harper - Reinstate Monica Feb 19 '20 at 2:38

Currentwise, I think a 60A supply breaker will suffice. You use #6 copper or #4 aluminum wire for this. There's a case to be made for either one. Copper can be spliced in smaller boxes, but it's stupid expensive and it invites a dissimilar metal issue on the panel lugs (which are typically zinc plated aluminum). If you run this cable in conduit, and you use THHN/THWN-2 wire, then you might as well use a 70A breaker since the #6Cu/#4Al 60A wire is good for 70A when it's in THHN.

Panel-wise, we need to have a conversation. The most difficult problems we see here (the ratio between simplicity of project vs cost to do it) is "Panel Full" situations. "My panel is full, how do I add a circuit?" often means a $1000+ panel replacement for a simple circuit add. In practicality, that means the on-demand heater, table saw, or EV charger simply does not happen.

So, you have to size up your own house. If you've got a 40 space panel that's half empty, this may not be much help. But not knowing all those details, our default reco would be for something on the order of an 18-space panel - that would give you a lot of expansion room for future circuits. For instance if you needed room in the main panel, nearby circuits could be rerouted here. The cost differential is not that large, and the protection it gives you is considerable.

The subpanel does not need a main breaker, and the bus rating is just a rating, like the 130 mph rating on your car's tires. So there's nothing wrong with feeding a 125A or 200A panel from a 60A breaker for instance.

  • And for the advantages of #4Al: much cheaper and you are free to buy a spool of all black wire and re-mark the wires with tape, which is not allowed with wire sizes below #4. – Nate S. Mar 16 at 16:06

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