Circuits for electric ranges

[czarstoo]

The 2002 NEC Article 422.10(A) last sentence states that"the branch circuitsof householdcooking appliances shallbe permitted to be in accordance with Table 220.19. Recently I have had a number of clients compaining about range circuit breakers frequently tripping. In most cases the ranges were in 12 kW to 13.5 kW sizes and were powered from 40 circuits. This appears to be OK with article 422.10 and Table 220.19.

Actual measured curent for each of the client's typical cooking situations was frequently in the 50 ampere range. No wonder the breakers were tripping. So much for derating.

Upgrading the circuits to 50 amperes would likely resolve the problems, but I can't understand why the NEC would permit 40 ampere circuits to be installed when normal range usage could result in current draws in excess of 50 amperes.

Can anyone shed some light on the "problem"??

 

[pierre]

Re: Circuits for electric ranges

"210.19 Conductors ? Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum
branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load."


"(3) Household Ranges and Cooking Appliances. Branchcircuit 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 83⁄4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes."

Notice this says MINIMUM. If the load is larger, then as per 210.19(A)(1), the branch circuit will be required to be larger.

 

[haskindm]

Re: Circuits for electric ranges

Remember that the code is not a design specification and the only thing that the code is supposed to address is safety. If a range overloads a circuit and the breaker trips, is that a safety issue, or a design issue? Remember the code says in 90.1 that even though you follow the code you may not have an installation that is "convenient or adequate" however it will be safe; no one should get electrocuted and there should be no fires. The NEC is a MINIMUM and you will often need to exceed the MINIMUM in order to have a good installation.

 

[kevinware]

Re: Circuits for electric ranges

Pierre:

I am trying to understand. So if I have a range with a name plate rating of 14KW then the math should be done as follows: (2005 NEC)

14KW
x1.25
--------
17500KW (210.19(A)(1)) My new rating.

Applying 220.55 and table 220.55 for one range rated over 12KW:

8000 (table 220.55 Column "C")
+ 30% (Note 1 table 220.55)
-------------
10400KW / 240V = 43.33Amps

So my OCPD would be a 50 Amp breaker (240.4 (B))

Please correct me as you see fit..........

 

[czarstoo]

Re: Circuits for electric ranges

Let me see if I have this straight. If I have a 13 kW range at 240 V that's a 54A maximum load. If the range is to be on for 3 or more hours (continuous load) I would multiply the 54 A by 1.25, but I don't think that's real. Anyway, since the maximum load is 54 A I will have to use #6 Cu conductors and a 2 pole 60 ampere breaker (per 240.4(B)). Doing so will result in both a safe and a usable situation.

By the way, just because a circuit breaker is in a circuit to protect against overloads does not necessary make everything safe. I have had at least 2 clients that have had circuit breakers burn, melt or come apart as a result of 15% or 20% overloads and they were not FPEs either.

 

[volt101]

Re: Circuits for electric ranges

I do not see were the load is actually running for 3 hours continuously, the thermostats provided in the oven enable the load to be cycled on and off.
That why the indicating lights on older stoves turn on and off during the use of the stove.

14kw stove
that's 2 above 12 2 x 5%
that's 10% plus 100% of the 8kw
8000w x 1.1 = 8800w or 8.8kw
or 36.67 amps

[ June 23, 2005, 04:23 PM: Message edited by: volt101 ]

 

[czarstoo]

Re: Circuits for electric ranges

The point that I am trying to make is that, even though 422.10 (A) says that it is permissible to use Table 220.19, article 210.19 (A)(3) clearly states that "branch circuit conductors shall have a ampacity not less that the rating of the branch circuit and not less than the maximum load to be served". In my example of a 13 kW range, the maximum load to be served is 13 kW. Therefore the branch circuit must be sized to handle 13 kW. I do not believe that the proper circuit installation for a single 13 kW range would be in accordance with the derating guidelines provided in Table 220.19 which would result in a 35 ampere breaker and #8 copper conductors to serve a 13 kW range.

 

[mdshunk]

Re: Circuits for electric ranges

I just wanted to make the observation that the original poster must have done some work for a few gourmets. It takes some serouis cooking to get the range to draw near it's full kilowatt rating. Holy cow, and he said several clients.... I've never gone out to troubleshoot a tripping range breaker where there wasn't a bonafide problem with the range. Maybe I've just been lucky.

 

[molotov27]

Re: Circuits for electric ranges

This is definitely a design issue....40A minimum.....period...but you can go up in rating. Most of the "standard" household ranges, for the typical household will do OK with a 40A circuit because of the cooking habits of the owners, unless there is a special ocasion where they have the oven and the top going on at the same time. As a rule of thumb I always specify a 50A breaker unless the range requires more than 50A, just for the fact that the range comes with a standard 50A plug & cord, plus very few ranges draw the 40A, most are closer to 50A

 

[jwelectric]

Re: Circuits for electric ranges

Originally posted by czarstoo:
The point that I am trying to make is that, even though 422.10 (A) says that it is permissible to use Table 220.19, article 210.19 (A)(3) clearly states that "branch circuit conductors shall have a ampacity not less that the rating of the branch circuit and not less than the maximum load to be served". In my example of a 13 kW range, the maximum load to be served is 13 kW. Therefore the branch circuit must be sized to handle 13 kW. I do not believe that the proper circuit installation for a single 13 kW range would be in accordance with the derating guidelines provided in Table 220.19 which would result in a 35 ampere breaker and #8 copper conductors to serve a 13 kW range.

Well I wonder why did they put that part in the code for.

volt101
I do not see were the load is actually running for 3 hours continuously, the thermostats provided in the oven enable the load to be cycled on and off.
That why the indicating lights on older stoves turn on and off during the use of the stove.

14kw stove
that's 2 above 12 2 x 5%
that's 10% plus 100% of the 8kw
8000w x 1.1 = 8800w or 8.8kw
or 36.67 amps

This is absolutely correct.

 

[kiloamp7]

Re: Circuits for electric ranges

Generally speaking, for conventional household type range unless its little-bitty or extra large, use 40A minimum or 50A maximum branch circuit.

The standard range cord has a 50A male plug (cord cap).

IMO, to think of a household range as continuous duty is almost ludicrous. Read the NEC definition of continuous duty. You set the heating elements, whether oven or on cooktop to desired temperature. The heating elements cycle on & off to maintain appx. that temperature.

Now if you turn all elements on to maximum temperature & try to use it to heat the dwelling unit, you may experience bkr. tripping.