Electrical Range Calculation

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I also agree with Haskindm and Roger.

A range is never a continuous load.

A breaker should hold when run at it's rating.

If you take a look at trip curves you will find a 40 amp breaker might hold 50 amps forever and it would still be within specification.

I would never plan for that to happen but it can, the typical modeled case breakers we use are fairly crude and inaccurate devices.
 
iwire said:
I also agree with Haskindm and Roger.

A range is never a continuous load.

A breaker should hold when run at it's rating.

If you take a look at trip curves you will find a 40 amp breaker might hold 50 amps forever and it would still be within specification.

I would never plan for that to happen but it can, the typical modeled case breakers we use are fairly crude and inaccurate devices.
Click to expand...

To expand on IWire's idea, that 40A breaker run at 50A is gonna be HOTTT! and will not last as long as a 60A breaker running at 50A. Every 10 degrees celcius over ambient that a electrical device operates at cuts that components life in half. I typically see breakers running at or over their capacity 20 degrees celcius over ambient temperature. Sure it may not trip out, but that dosn't mean it was designed to serve this application. Over time, the 50A on the 40A brkr will fail. The heating then cooling causes the expanding and contrasting of contacts, and can cause loose connections between the brkr line side and the panel bus and then arcing. Breakers can also fail internally by that heating and cooling. You can hear buzzing noises internal to a failing breaker that signal there is internal arcing going on from the expansion and contraction of contacts.

In office buildings, the biggest culprit of breaker failure in an office enviorment is copiers and printers. Often offices are designed by someone who likes to put all the copiers and printers from one panel, and the desks and computers from another. Well, if you have a 100A 3phase 120y/208 main circuit breaker and you feed all printers and copiers, even if you calculate the loads to be less than the main, that main will fail quick. From 8am to 5pm every day, that panel main will see a continuous fluctuating load of 30-80 amps, will run hotter than if it was a steady load of 110A and can trip out and fail because of the fluctuating load for the same reasons as described above.
 
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Okay....I sat and thought about it for a while. I just couldn't get over the notion of the oven being turned on continuously. However, I see that while the knob may say it's on, the heating elements aren't all on continuously, or even all at the same time. So I can see now why it is non-continuous and doesn't have to do the whole 80% thing.

But I still say the range manufacturer is being dishonest if he advertises a product at a power rating it simply can never deliver given his own recommendations.
 
bcorbin, The heating elements can be on as long as the dial is set on. With that said, the four top burners and the oven coils combined on at the same time will draw more than 45 amps through the Breaker and line conductors. This is where the NEC minimums do not take degradation of the disconnect and line insulation into consideration as mentioned by bondjumper. The OP questioned his calculations per the NEC without offering any applied conditions. This is where getting confused is understandable when using empirical values. If this was a remodel upgrade without original breaker and cable changeout, then using a 40 amp breaker and line capacity would send up a red flag. Your concerns are well taken.
 
Coulda, woulda, shoulda. The code tries to deal in reality. Yes it would be POSSIBLE to come up with a scenario in which a 12.9KW range COULD draw more than 35-amps as jw properly calculated the load using article 220. It is also possible that a multi-family dwelling COULD exceed the load calculated using the demand factors in article 220. It is also possible that a dwelling COULD exceed the general lighting load of 3-VA per square foot as estimated using article 220. The fact is that any of these would be unusual (maybe even abnormal) conditions. The code is a MINIMUM standard, it is acceptable, allowable, and in some cases perhaps even required that the MINIMUM standard of the code be exceeded - see article 90.1. The standards of the code have been shown to usually work and provide a reasonable degree of safety. In a normal installation the demand factors that are allowed by the code will provide an acceptable level of performance and safety at a reasonable cost. If you feel that a derating factor is too generous, submit your justification to the code making panel and perhaps it will be changed. In the meantime it says what it says. Follow it or exceed it as you see fit. Just do not do LESS than the code requires. When taking an exam, if a demand factor or load reduction is ALLOWED it must be taken to find the correct answer. In the field, not using a demad factor or reduction will cost you money, but is certainly acceptable and may result in a better installation for your customer.
 
I must correct my earlier post from a perspective of reading a range load demand factor calculation determining branch circuit mimimums [220.55] without including the conductor minimum rating [210.19] for the range load 'being served' requirement. The NEC minimums are taken into consideration when using the proper Article requirements for the related application. Like apples and oranges so goes the difference of calculations[220] and branch circuits [210].
bcorbin, Your concerns are correct if loads being served were questioned.
 
gndrod said:
Like apples and oranges so goes the difference of calculations[220] and branch circuits [210].
Click to expand...

Which is why there are such threads as receptacles-per-circuit and light-circuits-per-house.
 
Thanks for the link, 1793. At the very least, it made me realize I'm not alone in my thought process. ;)
 
It is admirable that you stood your ground. It sure makes us all think a little harder and appreciate the different individual views from experience.
 
bonding jumper said:
To expand on IWire's idea, that 40A breaker run at 50A is gonna be HOTTT! and will not last as long as a 60A breaker running at 50A. Every 10 degrees celcius over ambient that a electrical device operates at cuts that components life in half. I typically see breakers running at or over their capacity 20 degrees celcius over ambient temperature. Sure it may not trip out, but that dosn't mean it was designed to serve this application. Over time, the 50A on the 40A brkr will fail. The heating then cooling causes the expanding and contrasting of contacts, and can cause loose connections between the brkr line side and the panel bus and then arcing. Breakers can also fail internally by that heating and cooling. You can hear buzzing noises internal to a failing breaker that signal there is internal arcing going on from the expansion and contraction of contacts.

In office buildings, the biggest culprit of breaker failure in an office enviorment is copiers and printers. Often offices are designed by someone who likes to put all the copiers and printers from one panel, and the desks and computers from another. Well, if you have a 100A 3phase 120y/208 main circuit breaker and you feed all printers and copiers, even if you calculate the loads to be less than the main, that main will fail quick. From 8am to 5pm every day, that panel main will see a continuous fluctuating load of 30-80 amps, will run hotter than if it was a steady load of 110A and can trip out and fail because of the fluctuating load for the same reasons as described above.
Click to expand...
bonding jumper,
Every 10 degrees celcius over ambient that a electrical device operates at cuts that components life in half. I typically see breakers running at or over their capacity 20 degrees celcius over ambient temperature.
Click to expand...
I don't think that rule applies to things like breakers. It is for motors and transformers.
 
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