220.55 and 40A range circuit

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hillbilly

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The other day I saw a 16KW range (240V) on a 40A circuit.
#8/3 NMB, 40A breaker.
I did the calculation according to 220.55 Note 1, and the installation seems to be code compliant.
8KW + (20% of 8KW) = 9.6 KW = 40.0A @ 240V
Is this correct?
It seemed strange to me, but apparently it's allowed by code.
Is my math correct?
thanks
steve
 
It does not work for me.

In no case can a branch circuit supply a load rated higher than the branch circuit.

We had a marathon thread about this, I will try to find it.
 
Steve, your math and method is correct. The reality is that it would be rare that the range would ever be operated at full capacity.

Roger
 
I?m not sure if this question has been debated already, but let me present an alternate view.

First of all, the only thing covered in article 220 is the calculation of loads. It does not address the sizing of branch circuits. Rather, it only covers the determination of how much load must be included, when sizing the branch circuits, feeders, and services.

I see a possible conflict between Part II of Article 220 and Part II of Article 210.

210.19(A)(1) says that the rating of the branch circuit (i.e., the rating of the OCPD) must be no lower than ?the maximum load to be served.? It does not say ?the load for that branch circuit, as calculated in 220.? It says ?maximum load.? The range can draw a maximum of 16 KW. It is calculated at 9.6 KW, but the maximum is still 16. I see this as requiring a 70 amp circuit.

I realize that in practice a 40 amp circuit is more likely to be installed than a 70 amp circuit. I also do not know what the manufacturers of such equipment typically call out as the recommended circuit size.

But what do you think about the word ?maximum,? as used in 210.19(A)(1)?
 
OK, I was typing when Bob and Roger were posting. So perhaps this has been debated already.
 
220.14(B) explicitly provides that branch circuit load calculations for household electric cooking appliances shall be permitted to be calculated as specified in 220.55.

220.55 Electric Ranges and Other Cooking Appliances - Dwelling Units.

"The LOAD for household electric ranges, wall-mounted ovens, . . . shall be permitted to be calculated in accordance with Table 220.55."

That is the table that permits the range load to be calculated at 8kW + 0.4 kW for each kW by which the nameplate rating exceeds 12 kW.

The load is the calculated value based on the larger nameplate rating, and it is the calculated load for which the circuit is required to be designed.

Therefore, there is no conflict within the code.

As has been pointed out many times, the code is the minimum. It is not uncommon to put in larger wires and larger breakers.
 
Bob NH said:
"The LOAD for household electric ranges, wall-mounted ovens, . . . shall be permitted to be calculated in accordance with Table 220.55."
Click to expand...

I disagree that 210.19(A)(1) is referring to a calculated load.

IMO that section is based on the name plate.
 
So what does a guy do when wiring a new house and has no idea what the KW of the range will be? Around here, a 40A, 8-3 circuit is the norm.
 
iwire said:
I disagree that 210.19(A)(1) is referring to a calculated load.

IMO that section is based on the name plate.
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210.19(A)(3) Exception No. 2 acknowledges the application of Table 220.55 when it permits reduction in size of the neutral conductor for a range of 8 3/4 kW or more rating for which the demand has been calculated in accordance with Table 220.55.

I can't imagine that they intended to require conductor ampacity per nameplate rating in 210.19(A)(1), and recognized in 210.19(A)(3) that conductor sizes could be based on calculations per Table 220.55.
 
That exception lets us get away with a smaller neutral. But the branch circuit rating is based on the OCPD, and the neutral is not a player in that determination.

What happens when the owner turns on the oven and all four burners? OK, it doesn?t happen often. But it does happen. Are we allowed to install something that we know will trip the breaker? I think not.

210.19(A)(3) echoes the word ?maximum? from the more general statement in 210.19(A)(1). I can?t get myself past the maximum load being 16 KW here.
 
The oven (and in many cases the burners too) cycle on/off via a t-stat in the appliance. Rarely will the circuit see all of the possible load. As someone who has done residential troubleshooting for north of 30years I can say that I have never seen a tripped 40 or 50 amp range c/b because of the normal operation of the appliance. I know this is purely annecdotal evidence but but experience does sometimes tell us things.
 
bkludecke said:
. . . I can say that I have never seen a tripped 40 or 50 amp range c/b because of the normal operation of the appliance. I know this is purely annecdotal evidence but but experience does sometimes tell us things.
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Well this time it is telling us something that is not at all surprising, for three reasons:

First, if the oven did trip, the homeowner would probably just reset the breaker, turn one of the burners down, and never call for assistance.

Secondly, how often do you see oven/range units over 12KW?

Third, you are right (as are several others who have said the same thing), it is not often that all heating elements would be on full at the same time.

All of that said, what is the maximum load that would be seen in a branch circuit that supplies a 16 KW unit?
 
I know this has been discussed before, it was a long heated discussion.

That said I have searched for it and can not find it.
 
charlie b said:

Well this time it is telling us something that is not at all surprising, for three reasons:

First, if the oven did trip, the homeowner would probably just reset the breaker, turn one of the burners down, and never call for assistance.

Secondly, how often do you see oven/range units over 12KW?

Third, you are right (as are several others who have said the same thing), it is not often that all heating elements would be on full at the same time.

All of that said, what is the maximum load that would be seen in a branch circuit that supplies a 16 KW unit?
Click to expand...
Well you would think that most homeowners would just reset the c/b but where I am in this resort town most of the houses are rented on the weekends and I spend a good deal of time resetting c/bs and telling people how to do it by phone (good point though). I have seen VERY few residential ranges over 12kw (another good point). Max load on 16kw range is approx 66.72amps which should work just fine on a Zinsco 2pole 20amp c/b LMAO.
I do agree that the circuit should match the load but this one is still a bit grey to me. When we rough-in for an electric range we always run 6/3 nmb and so far have not seen a range requiring a larger circuit.
 
OK I found it for those that have some time to kill.

I think every angle was covered and I still believe that the circuit must be based on the full nameplate rating.

Range Wire Sizing

A strange side note, the forums search function could not find it.

I Googled for it and found it easily.:roll:
 
Branch circuits are designed for the LOAD.

The LOAD for cooking appliances is permitted to be based on Table 220.55.

That LOAD calculation based on Table 220.55 is stated or acknowledged in several places, including 210.19(A)(3) Exception 2 which says in part, "where the demand of a range of 8 3/4 kW or more rating has been calculated according to Column C of Table 220.55, . . ."

220.14 Other Loads - All Occupancies says in 220.14(B) that "Load calculations shall be permitted as specified . . . in 220.55 for electric ranges and other cooking appliances." Exactly what does that mean if not that the circuit LOAD used for the branch circuit design is to be based on Table 220.55?

Can any of those who believe otherwise cite any place in the code that contradicts the plain English of 220.14(B), 220.55, and Table 220.55?

What part of LOAD do I fail to understand, and what section of the code contradicts the code that I have cited?
 
Here is an interesting post from Don that he posted in the other thread.

don_resqcapt19 said:
Mike,
I see your point and the words in the NEC support your point. However where there are conflicting rules, and I think that is what we have in this section, I just choose to ignore the less stringent rule. It appears that CMP 2 agrees with me. Proposal 2-209 in the 95ROP suggested the following wording: "For ranges rated between 8 3/4 kW and 11.9 kW, the minimum branch circuit rating shall be 40 amperes. For ranges rated 12 kW and higher the minimum branch circuit rating shall be 50 amperes." The substantiation said that larger ranges need larger branch circuits. The proposal was rejected with a panel statement that said: This section still requires that the branch circuit conductors have a rating not less than the maximum load to be served". It appears that the last sentence in this section has no use, and it should have been removed by the CMP in response to this proposal.
Don
Click to expand...
 
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