I currently have electric appliance, and I want to replace them with newer units.
These are the ratings of newer units I am considering:
Adding both together (assuming 240V): 21.2kW
How do I find out what breaker size is required? This will help me know what wire size to install as well
Considering that most folks don't run every element and burner on a range or oven/cooktop pairing at full blast at the same time, all the time (your house would get rather toasty if you did!), the NEC has special rules for cooking appliance loads, given in 220.55 and it's associated Table, that apply to your situation. In particular, we would normally start by applying Note 4 in Table 220.55 to your situation:
- Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.
However, NEC 110.3(B) drags the manufacturer instructions into the picture, given that your oven is a listed appliance:
(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
Given that the installation instructions for your oven require the use of a dedicated circuit, as follows:
- Models rated from 7.3 to 9.6 kW at 240 volts (5.5 to 7.2 kW at 208 volts) require a separate 40-amp circuit. Models rated at 7.2 kW and below at 240 volts (5.4 kW and below at 208 volts) require a separate 30-amp circuit.
this means that your best bet is to pull two circuits, a 50A circuit for the cooktop by itself and a 40A circuit for the oven by itself.
The good news here is that we can fit all this into the same conduit, as a 1" ENT provides 215mm² of usable fill, and the wires for both circuits (2 6AWG stranded THHN wires for the cooktop circuit, 2 8AWG stranded THHN wires for the oven circuit's hots, an 8AWG white stranded THHN wire for the oven circuit's neutral, and a 10AWG green stranded THHN wire to ground the lot take up a mere 149.86mm² of space. Given that 1" ENT (smurf tube) is widely available, and not much harder to run than a couple of fat NM cables, this is definitely the recommended approach; it also makes changing out wires in the future trivial, in case someone down the road needs a bigger circuit for a bigger double oven or the likes.
I'm not sure about the Viking cooktop. The installation instructions repeat the specs but don't specify a breaker size. It sounds like a 50A should do it, though 48A continuous would actually need a 60A breaker. You may want to check with Viking on that.
The Kitchenaid oven is very clear in the specs:
Models rated from 7.3 to 9.6 kW at 240 volts (5.5 to 7.2 kW at 208 volts) require a separate 40-amp circuit. Models rated at 7.2 kW and below at 240 volts (5.4 kW and below at 208 volts) require a separate 30-amp circuit.
so a 40A circuit is called for.
You definitely do not want to run those together on one circuit - turn on 3 burners and the oven at the same time and you will overload the circuit.
Both of those on a 100A subpanel is fine, with the key question being: What else is on the subpanel? If it is a few lights, no big deal. But if you have your kitchen countertop circuits (2 @ 20A and easily could pull 15A each at the same time), fan, refrigerator, etc. you might be overloading that at 100A.
