I live in a very old Victorian condo building. All units still have fuse boxes, not circuit breakers. My range died and I need to replace it. All modern ranges require a minimum of 40 amps, but the fuse box only has 30 amps (x 2) going to the range. So, I need to upgrade to a circuit breaker, right? HOWEVER, there are 15 units in this building, and everyone has an oven and everyone only has 30 amps maximum. How is this possible? Thank you.
It's possible because a range has it's electrical requirements calculated based on a certain usage pattern that might not be realistic. They might require 40A, because if you turn on the oven and all the elements, it's going to draw 40A. But, no one really does that. You might use the oven and one element, or no oven and two elements...
That's the answer of "how is it possible that my neighbors are doing this". The range will work. Heck, if you only use one thing at a time then I bet you could make it work on a 20A circuit. The circuit breaker or fuse protects the wiring in the walls, so if you use more than 30A, the fuse should blow, and there should be no danger. The problem is, that's a lot of shoulds and you're working with very old wiring.
So, as with most electrical "rules", it comes down to safety and liability. Sure, you can install a 40A range and it will probably work fine - right up until it doesn't. If a fire starts in the condo walls, is it your fault because you installed the wrong range? Will insurance cover the damage if it was an improperly installed appliance? Would someone die? At the very least, it would void the warranty of the new range.
The point is that you can do a lot of "illegal" stuff with wiring, and it will work just fine. It might never cause a problem and work great forever, but there are edge cases that he electrical codes guard against. The codes tell you how to be as safe as possible.
To sum up, and answer your question, I think that using a 40A range on a 30A circuit is low risk with normal range usage, but all bets are off if you have people over and they start turning on more burners than normal. You should upgrade the wiring to be safe. Or... just repair the old range.
Now you're cooking with gas
Lots of people make 30A cooktops. And lots of people make 20A or 30A ovens. Neither one is a problem to acquire.
So one possible answer is to pull a gas line to the location, and then go with separates: use the existing 30A for the oven, and the new gas for the range. This gives you the best of both worlds: an oven that doesn't add humidity, and a range that responds when you turn the knob.
You said "dual" 30A, if you mean four total fuses, that means you are already set to handle dual electric separates.
There is no way to get a 40A circuit out of that panel
Here's the rub: even if you were able to run a new circuit with 8/3 of any description, you still couldn't get 40A out of that circuit unless you changed the panel. Why? The old-style "edison base" plug fuses are limited to 30A at 120V, unlike cartridge-type fuses, which can handle higher currents.
Your old ranges were less than 8¾kW, so your new range must follow the same rules
A 240VAC/30A circuit maxes out at 7.2kW of resistive load. If you back-run the numbers from Table 220.55, Column B, for the largest range that'll fit on a 30A circuit using the rules for that column, you find yourself looking at something around 9kW, which is more than the limit for that column. So, this means two things, given that the Table 220.55 demand factored range load is the branch circuit load for a range, as per the last paragraph of NEC 422.10(A):
Branch circuits and branch-circuit conductors for household ranges and cooking appliances shall be permitted to be in accordance with Table 220.55 and shall be sized in accordance with 210.19(A)(3).
and 210.19(A)(3) (modulo exceptions, as neither apply here):
(3) Household Ranges and Cooking Appliances. Branch- circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8¾ kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
- The existing range was less than 8¾ kW in order to fit on a 30A circuit
- The new range must also be less than 8¾ kW as well
Obviously, repairing the existing range should be an option; coiltop electric ranges generally follow the same basic design, and it hasn't changed much over the years (save for more sophisticated oven controls being a thing), so finding parts should not be a major issue. However, if a replacement is called for, that 8¾ kW limit does pose a challenge, as you have discovered. The most available range I have found that's in that size class, if you will, is the Frigidaire FFEH2422U(S/W). It's an apartment-sized range at 24" wide, has a 7.5kW specification (nameplate) power rating, and is reasonably priced. You'll want to use a dryer cord for this application, by the way, as you're putting it on a 30A circuit with a 30A receptacle (range and dryer cords both use SRD cordage, just in different wire gauges and fitted with different plugs, so a 30A range uses a dryer cord, not a range cord).
Alternatively, you can use one of the ~8kW Avanti 20" or 24" ranges (ERU(200/240)(P0W/P1B/P3S)) instead of the aforementioned Frigidaire here. Note that these ranges will run without a neutral connection (as they use 240V for their controls and their oven light), which is advantageous from a safety perspective, as it allows them to run on a 3-wire connection with the bond strap pulled and the third wire used solely as an equipment safety ground. The downside is that the 20" Avanti in particular is rather bare-bones, lacking something even as basic as an oven timer, and they also use a somewhat odd control scheme for their broiler element.
Or, you could go with separates
Your other option here would be to build a cabinet up in place of the range and fit a separate cooktop and oven into that cabinet. Two-burner electric cooktops in the 3-4kW range are available, and so are single electric ovens (which generally draw roughly 3-4kW of power as well), so you don't really have to sacrifice much to get this. Note that the idea of using a multi-mode (convection/microwave) oven (as xeeka's post suggests) requires a separate neutral and ground to be available, as most all of the built-in multi-mode ovens made for the North American market use a 20 or 30A, 120V circuit. (They're in the 1.5-2kW range, mostly.)
One way to avoid high loads is to replace the normal range with a combined microwave oven (MW + grill + oven) and separate induction plates.
It has important advantages.
In Europe, most domestic fires start in the kitchens. Pets and non-pet animals, sleep walkers, confused people or with memory leakage, small children, a long emotional telephone call - normal ovens and plates have a certain risk.
A MW oven can only operate if the door is closed, and the time is automatically limited. Induction plates do only operate if a pot or pan is put on the plate, and the time is limited, too. The plates do not get hot directly, but only indirectly by the contact with the pot - the temperature will be much lower compared to ceramic or convection plates.
Less Power - Saving Energy, Money and Time
Both devices are available for standard outlets, since the wattage is low enough (f.e. 16A @ 230V).
An induction plate is much faster then other electric plates and can be even faster then a gas plate.
But it is important to have a fine temperature adjustment control - a lot of induction plates have steps of only 20 degree Celsius. And the cooling fans for the power electronics can be very noisy - fine temperature adjustments and low noise levels are important features.
The low temperature of the plate is saving time and energy in multiple ways - f.e. the danger of burning-ins in the plates or their surrounding from over-boilings is much less saving again energy/chemical detergents and time.
The volume of a MW is smaller needing less energy for 1 or 2 pizza, and it allows a mixture of hot air plus microwave, which gives an excellent result. No asymmetric heating (front raw, backside burnt) since the pizza will be rotating on the plate.
And of course, it is more environment-friendly by less power consumption to get the same results. And by less consumption of chemicals and water/energy to clean over-boiled and burnt-in residuals on the plates. Even baking paper can be put on the plates avoiding any contact with spilling/over-boiling food.
Another advantage is the easy exact leveling of the plate. House settings, underground movements, traffic etc. can have an influence on the angle of the cooktops/plates. The oil would accumulate at one place.
With a separate induction unit, the level incl. pan can be easily adjusted to zero degree via wedges, thus saving oil resp. equalizing the oil/heat level all over the pan. This seems to be a minor issue, but helps to minimize the oil/fat consumption and to minimize partly overheated/burnt food.
Edit: 2 Photos
Here is an example of a 50 year old small 8m2 kitchen, where the old kitchen board with openings for the range plates and fridge was replaced with a simple one without any hole.
Thanks to the flat induction plates, a big board area is now available if the plates are hooked up. And if somebody wants to cook on the terrace or balcony - or needs just plates to keep the food warm, it is very easy with those mobile plates.
The old huge oven space can now serve as storage area for bottles, food, big pots etc. Or it can serve for a 2nd dish washer, which will be used in interleave mode. That way, some storage for the dishes will be saved and the time to put the clean dishes into the cupboards.
The multi-mode MW has 4 wooden sticks beneath in order to clamp a tray which is convenient for (dis-) charging and brushing/cleaning the MW (3rd hand).