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Determining Electrical Service Capacity

maine_tyler | Posted in General Questions on

I’m trying my hand at determining what electrical service capacity I need, in anticipation of a new heat-pump.

Using this great article by John: https://www.greenbuildingadvisor.com/article/does-your-electrification-project-require-a-service-upgrade#0

2 questions:
1) I have a GE Cafe induction range. When I look at it’s specs (can’t easily get to it’s nameplate right now) it says “KW rating at 240 volts: 13.6”
https://www.cafeappliances.com/appliance/Cafe-30-Smart-Slide-In-Front-Control-Induction-and-Convection-Range-with-Warming-Drawer-CHS900P2MS1

That seems crazy high. It dwarfs everything else in my calc, including any proposed heat pump. Am I missing something? I have heard that induction stoves can draw a lot of power, but 13.6 kW would be more than the breaker is even sized for…

2) I am likely installing a 6k btu Mitsubishi or similar heat pump. Does anyone have a rough VA rating handy for such a unit? I’m not seeing it in the documentation.

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    I think that "13.6kw" number is a bit optimistic, and represents something unachievable in reality. The reason I say this is that the same specs list the amp draw at 240 volts as "40 amps", and a 40 amp, 240 volt single phase circuit can only deliver a maximum of 9.6kw under perfect conditions. Regardless of what the other specs say, if that range is fed with a 40A, 240V circuit, the circuit breaker will see to it that you're under 10kw with that range.

    You probably won't always be running every burner and the oven too, which means you'll typically be quite a bit less than maximum. I know in my own home, it's unusual to run more than 2 or 3 burners at the same time on the cooktop. You're not really supposed to use demand factors when you only have one range though, so you should assume maximum amp load from the circuit here.

    6k BTU is about a half ton. I would guess around maybe 1kw or so to run that, 1.5-2kw max. I'd really try to find a datasheet for it though -- it should specify it's electrical load while operating.

    If this is new construction though, you're almost sure to be safe with a 200A service and I wouldn't recommend installing anything less. There isn't a huge cost difference between 100A and 200A service in most cases when you're doing a new build. The only time you're likely to need anything over 200A is if you have several electric cars that you want to charge at the same time, or if you have a very large solar system due to some codes dealing with how those tie into panels (and there are some ways to get around that too).

    BTW, if you're expecting a heavy electrical load, try to get a breaker panel using copper buss instead of aluminum. In the case of Siemens panels (which is what I usually design with), there is almost no cost difference between the two.

    I recommend ordering your materials well before you need them too. A lot of electrical switchgear has been in short supply as of late. Siemens, for example, missed ship dates for me multiple times last year on several commercial projects, and none of the other manufacturers is doing any better. Make sure to allow extra time for your materials to arrive so that you don't have unexpected project delays.

    Bill

  2. Matteus_Olmedo | | #2

    If you add up the individual wattage you get 14500 when you use all 4 burners and the broiler so not sure why they wrote 13.6k. I’m sure the manufacturer has built in logic to limit power to the burners if all burners are in use on high so the breaker doesn’t trip. This will never happen though. You only use that amount of power to boil water and nobody boils 4 pots of water. Those are not abnormal wattages for an induction though and with a heat pump water heater, heat pump dryer, and plenty of insulation, the induction SHOULD dwarf all other loads in an all electric house. In my experience anything over 40 amps for EV charging is unnecessary because you usually have all night to charge so I would say even with multiple EVs and all electric if you are using modern appliances you will have absolutely no problem with 200. As far as the heat pump goes a 6k is pretty insignificant for any decent brand. If you can’t find the nameplate you can get a rough idea from HSPF or SEER rating since that is BTUs in winter (or summer for SEER) divided by kWh in winter ( or summer).

    1. maine_tyler | | #4

      "I’m sure the manufacturer has built in logic to limit power to the burners if all burners are in use on high so the breaker doesn’t trip."

      I do recall reading that individual burners will reduce their output as more come online.

    2. charlie_sullivan | | #12

      Regarding EV charging, the option to put in load management is now pretty easy to implement, with the Wallbox Pulsar Plus offering a load management system that senses the current at the main feeders, and adjusts the charging rate to keep the overall load within your service capacity. Basically that means it will charge slowly while you are cooking dinner on the induction stove, charge fast when you sit down the eat, back off to a medium speed while you are doing the dishes and using hot water, and then ramp up to full speed overnight.

  3. Expert Member
    AKOS TOTH | | #3

    When it comes to demand calculations, you don't use the actual rating of the range. There is a demand factor you need to apply, so under our code, a 12kW range has only a 6kW demand. Doesn't matter what the plug or breaker size is, the demand is only 6kW.

    For the heat pump, the data sheet has max power rating which is what you use. If there is a heat strip, you also have to add that on at 100% factor.

    1. maine_tyler | | #5

      Akos, can you elaborate on the demand factor? I understand you are in Ontario? Perhaps there is a different method being described?

      I am going by the method described in Jon Harrod's linked article, which uses NEC 220.83.
      It says to use 'name plate' rating in VA of fixed appliances. Later in the process, load beyond 8,000 VA gets discounted to 40% of the sum. Is that what you are referring to?

      This is not for sizing a new service, by the way, but rather an existing 100 amp service. What's funny is that I probably should have worried more when I upgraded to an induction range and not so much now with a 6k btu heat pump...

      1. Expert Member
        AKOS TOTH | | #7

        I took a quick look and the NEC load calculation is different than the CEC. There are some online calculators that you can look at that will do all the math for you. I think in your case the base load also includes water heater, dryer, dishwasher and EV charger, so the the discount is applied to a much larger total number.

        Demand factor in our case discounts from peak load to account for the fact that most devices never run at 100% capacity. Sounds like similar to your 40% number.

        I have power meters on a number of all electric units and I can tell your that real world peak load is nowhere near the demand calculation. Even if your demand calculation is close to your existing service size, I would not sweat it.

  4. Expert Member
    MALCOLM TAYLOR | | #6

    How much more juice do induction ranges use over the old resistance burner ones? Are they less efficient, or is the high demand just due to their much quicker response time?

    1. maine_tyler | | #8

      I had heard induction was higher draw, presumably due to faster boils (i.e. less total energy but greater power). But I just checked the comparable GE radiant electric range and it actually lists 13.8 kW for 240V. Well there goes that assumption. I guess I just never realized how much power a range could (theoretically) draw.

      That said, I definitively had to upgrade the breaker and circuit feed when I swapped stoves (from an older electric). I have a feeling newer ranges—whether induction or radiant—have higher power ratings. Depending on specific models obviously.

      It's looking like I'm a-ok for my service capacity given there's few large loads in my case (water heater is indirect off boiler).

  5. walta100 | | #9

    If you want to be code compliant you will need to follow the manufactures directions and install the 40 amp 208-240 volt circuit they have listed.

    POWER / RATINGS
    Broiler Wattage 4000W
    Amp Rating at 240V 40
    Bake Wattage 2850W
    Convection Wattage 2500W
    Amp Rating at 208V 40
    KW Rating at 208V 11.3
    KW Rating at 240V 13.6

    I could see how someone using the broiler 3 burners and the warming drawer could push the limits of a 40 amp breaker.

    My GE cook top called for 50 amps seems silly but I paid up for the wire.

    Note the total of the individual breakers is allowed to exceed the capacity of your main breaker. I just add up all the breakers in one of my 2 200 amp panels it = 1025 amps I have never tripped the main.

    Walta

    1. Expert Member
      BILL WICHERS | | #10

      It's probably worth mentioning two things:
      1 - A "200A" panel has two 120v legs, each 200A. If you were to add up all the single pole breakers, lets say you got 600A (30 x 20A breakers, for example). That would be 300A per leg, since they should be pretty close to evenly distributed between legs. Double pole breakers "count" double if you do this, since they apply to both legs. Not that any of that really matters though.

      2 - Just because a breaker says "20A" on the toggle doesn't mean that's the load it presents to the panel. The rating of the breaker is what it is rated to pass without tripping. so it sets a sort of maximum that can be drawn by that circuit. Actual average load is typical lower, usually much lower, than the rating on any of the breakers in a panel. Think about that for a moment -- even that 40A breaker feeding the range is probably usually only drawing maybe 0.02A or something like that, to run the clock. Most of the time you're not going to be running any burners at all.

      It's only the loads that are likely to run simultaneously that matter here. and those loads are set by the equipment using the power, not the breakers on the circuits feeding those loads. A lot of the "400A" service stuff is an upsell for buildings -- very, very few homes are likely to ever come close to that. I know of one home in my area that has a "400A" service that is fed by a dedicated transformer by the utility, and it's a 25 KVA transformer. A 25 KVA transformer is only good for about 104A at 240V, so you can see that the utility doesn't think much of "400A" services either.

      Most codes are pretty conservative, and for good reason. Do you want to save $50-100 on an electrical install and then burn your house down some day? Or even just have issue with the main breaker tripping? Granted, it's probably more than just a few hundred bucks difference between 100A and 200A services, but it's usually a good idea to just go with 200A service and be done with it if you're planning for any decent amount of electrical appliances. Since people reading GBA are probably a whole lot more likely to be thinking about electric car chargers (BIG loads), and all-electric kitchen stuff (big loads), GBA readers on average are probably more likely to have a real need for something more than the 100A minimum residential service allowed by code. If you go with 200A service, you're pretty safe. If you will have several electric cars, or some massive 8,000 square foot home, then something more than 200A service might be a good idea.

      BTW, if anyone reading this is planning a massive house with lots of square feet, I would NOT recommend putting two 200A panels next to each other for that "400A" service. Put in a seperate disconnect switch and feed 4 wire cable to at least one of the 200A panels, then mount that second panel at the opposite end of the house. This will cut down on a lot of the branch circuit wire run lengths, which will save money and reduce volt drop on those circuits. It will likely be cheaper to run the 4/0 four wire aluminum service cable to that distant second panel than it will be to bring all the many branch circuits back to the same spot as the first panel.

      Bill

  6. richmass62 | | #11

    Using a single burner induction cooker, it is rarely necessary to go over 1600 watts. It would be a good idea if someone came out with an "eco mode" induction range that kept the individual burners below 2000 watts, or maybe below 1500 watts when the oven is in use, so that people wouldn't have to worry about oversizing their breakers.

    1. Expert Member
      BILL WICHERS | | #13

      When you size breakers for appliances, you have to size based on the required overcurrent protection. You cannot "oversize" the breaker -- you have to use what is specified. If the appliance specifies a 40A load, you use a 40A breaker and at least 8 gauge wire. You can't just put some "oversized" breaker on an appliance.

      Regarding the load calculations for an entire structure, that is more complex, but it has to do with what combination of devices is likely to run at any given time more than it does with how much load each particular device draws. This pretty much means that the only way any special operating mode of an appliance could help you with overal service sizing is with some kind of "smart" system where the appliances could talk to each other to keep their TOTAL load under some defined limit. As far as I know, there aren't systems like this for the residential world (there are systems capable of doing this in the commercial world). At the current time, it's likely to be cheaper to just upside the service a bit compared to what it would cost to "smart-ify" all the appliances.

      For a typical home, I generally recommend a 200A service regardless of what loads you might have. For VERY large homes, or homes with special setups (multiple EV chargers, really big solar arrays, etc.), 400A services *might* be advantageous, but most of the time 400A services are just an upcharge from a builder with little benefit to the homeowner. I'm not a fan of the usual "400A" service that has two meters tapped off of a 320A meter can, either. If you need a big service, you're better off going with a commercial-style setup where the meter feeds a switchboard (a big panel that has big breakers, and only big breakers), and have that switchboard feed multiple subpanels around the home. This allows for a lot more flexibility, and any particularly large loads can be fed from the main switchboard to keep the subpanel loads in check. This is essentially how pretty much how every large commercial building's electrical sytem is designed.

      Bill

  7. Expert Member
    PETER G ENGLE PE | | #14

    FWIW, there are "smart" panels available that limit total loads based on your programmed settings for each of the circuits' priority. The intent is that they can respond to time-of-day charges and/or the capacities of battery or generator backup systems. The loads are scheduled in order of importance, so that any loads can operate on their own, but if a lot of stuff is running the system might start shutting down the lower priority equipment. This is still just on/off though, so if your induction range was set at a lower priority you wouldn't be cooking anything when everything else is running. I doubt that you would want to use one of these to undersize the service though. It could cause mayhem with your living style, and the cost upgrade for the smart panel is probably greater than just going up to a larger service. But they look like da bomb for houses that already have solar and batteries, or where utilities are giving discounts for off-peak operation.

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