Range/Oven Breaker Amps Too High?

Specific Inspection Topics Electrical Inspections
1

I am really trying hard to understand all the principles I need to know in order to properly inspect an electrical panel. I am having a bit of trouble so please bear with me. My instructors offered little guidance so I am self taught. I am over preparing to take the National test again. I missed it by 5% the first time I took it. Some because I needed more knowledge and preparation, I was nervous and some because there are questions on the test that don’t have anything to do with the Standards of Practice I passed the state test, no problem

I am looking at an electric range/ oven that has a maximum wattage usage of 10095 watts if everything is on at the same time, according to the label. 240 volt appliance. which for me makes it pull 52 1/2 amps at it’s worse pull. So Watts 10095 / 240=42.0265 x 1.25 is 52.578 amps…There are two 50 amp breakers for this device in the service panel. Would this mean that these breakers would never trip if the appliance overheats because you have 100 amps on the breakers? Is this overkill or do I have a problem here. If not can you please explain why?
Thanks
Sue

2

Electric ovens and ranges are not continuous loads so you do not need to use a 125% factor in your calculation but you’re also missing another important component which is the demand factor. Demand factors are in T220.55 of the NEC. In general a 12kw oven or range can be used on a 40 amp branch circuit.

3

Besides the factors Robert has mentioned, I would not concern myself with matching the oven with the breaker as much as I would concern myself with making sure the wire size and breaker are correct for each other. I have seen several times where a breaker has been installed one size to big for the wire. This is common when someone buys a larger stove and fires that big boy up on Thanksgiving and, pop goes the breaker. They look into the stove they bought and find it needs a 50amp breaker instead of 40amp, then it is off to Home Depot. You get the rest of the story. Very easy to change stoves.

4

Yes, the conductor size must be equal to or greater than the size of the OCPD. You may notice that the single receptacle in many cases will be larger than the conductor and OCPD because many ranges/ovens use 40 amp branch circuits with 50 amp receptacles which is permitted.

5

Ok, I am good with matching breaker and wire sizes. I have memorized all the tables and know what to look for in that case. Thank you for reminding me of this. Also I forgot about the continuous load table so good to remember that one. I guess what I am stuck on is that if the breaker is too big for the load it will never trip. Is this correct? maybe I read this wrong. Why would they put 100 amps worth of breakers on a non continuous load that will never pull more than 42 amps even on Thanksgiving? Is this a safety problem in the fact that the breakers will not trip on an over current because they are waiting for 100 amps of over current before they trip?

6

Since it is a 240v appliance, they would have used a double pole, 50 amp breaker that is tied together. Those would not be individual 50 amp, single pole breakers.

7

Good point it sounds like it’s a 2-pole, 50 amp circuit breaker which is OK if the conductors are the proper size.

8

You do not add the breaker handles together . It is a 50 amp breaker, not a 100.

9

You’re getting a little bit out there on this thing.

I see I got an electric range in the house; it works and has an anti-tilt device.

When I’m at the electrical panel, I look at all my breakers. My range breaker and wire size should match … There will be a double breaker with a tie. The double breaker looks about right for the size range present.

Thats about it. Trying to find the data plate, multiply or divide watts, volts, amps … NO … Way out there.

Don’t feel bad on the test its got at least a 47% failure rate.

10

Double pole 50amp breaker =240v * 50 = 12,000 watts (2 handles tied together). If it were a single pole breaker it would be 120v (120v * 50 = 6,000 watts). A 50 amp double pole breaker is the appropriate capacity and voltage for your example range. Btw: I always check the breaker size. With new construction, the electrician installs the breaker before the oven is on site,so they are frequently oversized and on occasion undersized.

Good luck on the exam retake. Give me shout if you need local help.

11

Agreed…As a home inspector I would not subscribe to the concept that you are going to be doing calculations on your inspections. Determine the conductor size, determine the OCPD size and do as expressed here and do not get into the math. Home Inspectors do not need to get into those weeds.

12

Thank you everyone for your reply. Still a bit confused that you don’t add them together. I am doing this for the test mostly. Once I pass the test most of these calculations won’t really be necessary. Wire sizes to breakers very important for sure in an inspection. There are questions on the test that make you do calculations so I am only learning this for that. Chuck in Stagecoach, thank you for your offer of help! have been in Stagecoach a lot lately. I am looking for land to build a house. If you need an apprentice or someone to carry your tools, I would love to tag along on a couple of inspections. I know I can’t officially participate. I will probably be posting more questions before this is all over with for sure.
Best Regards to All,
Sue

13

OK since you’re trying to learn this for an exam a few questions: Do you understand the difference between 120 and 240 volts? Difference between single pole and two pole circuit breakers? Do you own or have access to a NEC book?

14

hmmm…now how far is Cypress from McKinney TX. I could probably sit down over a cup of coffee at the local starbucks and tell all your care to hear about electrical things…lol…but then again…who wants to hear all those things anyway.

I agree with Robert. You have to firmly establish you know what the difference is between 120V and 240V Nominal and as stated the difference in a single pole versus double pole OCPD. Do you know what OCPD is the acronym for?

Have you taken the online Electrical Training Module and successfully passed? As basic as it is it still provides good information.

If we assume you are referring to a 50 AMP Double Pole or Two Pole Circuit Breaker then you have 50 amps as the rating. You do not add single poles together and assume 100 amps.

Single-Pole Breaker gives you two wires that are 120V apart: a hot (Black) wire and a white (Neutral) wire. For simplicity sake the current on both wires is the rated ampacity of the breaker.

Double-Pole Breaker gives you two wires that are 240V apart. The two wires are typically (for this example) red and black. Again for simplicity sake the amount of current passing through any point in the circuit is limited by the rated ampacity of the breaker.

Lets say you have a single pole 20 amps circuit breaker you have the ability to load to 20 amps (non-continuously) but only at 120V. Now, install another single pole 20 amp circuit breaker right beside the first one…you happen to tie them together…nothing changes…you still have 20 amps of load ability (Non-Continuously) per phase, leg or line…how ever you choose to learn it.

This also still applies to the double pole circuit breaker…It still connects to each leg separately yet in a single device with regards to an AC system (single phase mind you for simplicity).

So with regards to calculating the loads…the NEC permits you to use section 220.55 and Table 220.55 as well. Notice that Note 4 is also applicable for use with branch circuit applications.

Here is my suggestion to you…go on Google and Type Charles Miller Range Calculations and you will get a very detailed series on all the calculations you would every want to know. Here you go…I will help you get started…http://www.ecmag.com/section/your-business/article-220-cooking-equipment-calculations-part-vi

OH…I also wanted to add something. Do not fall for the ole trick of giving you different values and then asking you what the minimum branch-circuit rating is for a 8 3/4 kW or more range.

210.19(A)(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 8 3∕4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

15

Paul! Thank you for finally explaining this to me…McKinney is far away…LOL…but…I PASSED, I PASSED, I PASSED…today. I’m numb and my whole body feels like a marshmallow.Now it’s time to get to work. Somebody pinch me please, I can’t believe it and I am so relieved.

16

Congrats!