table 220.55 madness

[smoke stack lightning]

Can anyone help me? I am studying for my test and I can not destinguish the difference of when to use the name plate rating of a range or goto column A or B? If a range is rated at 7kw do you use collumn B or the name plate rating. How do you know what method to use? This diffucituty is driving me mad.

 

[Dennis Alwon]

Table 220.55 is for household ranges. Table 250.56 is for other than dwelling units. For 1 cooking unit you would use the nameplate rating for non dwelling. For household on a 7kw range you would use column B if it is a dwelling unit. Also see note 5 in Table 220.55

 

[celtic]

Smoke,
you may find this page of interest:

220.55 Electric Ranges and Other Cooking Appliances—Dwelling Unit

Here is a brief glimpse:

While household cooking equipment can be added to a feeder or service load calculation at 100 percent of the equipment’s rating, it is not required. It is permissible to reduce the rating by applying the demand factors or by using the maximum demand loads in Table 220.55. For example, a 12-kW electric range will be installed in a one-family dwelling. This range can be added to the service load calculation at 12 kW (12,000 watts), or instead of the full rating, this range can be added to the calculation at a reduced load as specified by Table 220.55. Look in the left column of Table 220.55 for the number of appliances. This example has only one range; therefore, drop to “1,” and follow the row across to the appropriate column. Column A is used where the rating of the appliance is less than 3? kW. Column B is used where the rating of the appliances is 3? kW through 8? kW. Column C is the only column applicable for a 12-kW range. In accordance with Column C, a 12-kW range has a maximum demand of 8 kW (see Figure 1).

​

...

Thanks to Charles R. Miller​

 

[smoke stack lightning]

Thanks guys for responding. Sorry for being so dence on the subject but I need alittle more clairification. For example, if the question was "what is the branch circuit calculated load (in amps) for one 7 kVA ?" My confusion is do I go to collumn B in table 220.55 or the name plate rating as per note #4? In other words, when do you use either collumn A or B or chose to use the name plate rating. In my practice exam questions when I use the name plate rating I should have used column A or B and when I use column A or B I should have used name plate rating. None of my exam guides clearly defines the difference. Thanks again for your time

 

[haskindm]

I may be over simplifying, but you would always use table 220.55 to calculate the service load on a cooking appliance NOT nameplate (as long as you are using a standard article 220 part III calculation). On an exam, if you are allowed to derate an appliance you must do so. If you are using the optional dwelling calculation (part IV), you would then use nameplate. This is all for calculating the load on the service.
Note 4 makes it clear that you ALSO use table 220.55 to determine the load on the branch circuit UNLESS it is a wall mounted oven or cook-top, then you use the NAMEPLATE to calculate the load on the BRANCH CIRCUIT.
Make sure whether the question is asking fro service load or branch circuit load. Also make sure what type of appliance they are asking you about. It is a 7 KW single wall oven or a 7 KW "range"? Every word is important because a single word changes your answer.

 

[barone]

haskindm is correct, you need to pay close attention to detail on these kind of questions. I just found out the hard way that an 8.8kW (42.3amps @ 208V 1PH.)range can be supplied from a 40Amp branch circuit and a 40Amp cord. In article 420.10 the very last line states that the branch circuit for a range shall be in accordance with table 220.55. We had designed it with a 50Amp branch circuit, by using nameplate, and when the range manufacturer shipped the ranges with 40Amp cord and plug sets, we now have to change all of the branch circuit breakers to 40Amp. I suggested changing the cord to 50amp, due to a much cheaper install cost, and the inspector will not have it. He wants 40Amp branch circuits. If you ask me either case will meet code but hey I'm not the authority.
If you are taking the code test, I suggest skipping all the service calculation questions and go back to them at the end. They take up a lot of time and energy during the test and count the same as the very simple questions like, how often must you support EMT. Save them for last then go back and waste your time with as many as you can answer. Odds are you will not get those calculation questions right anyway. That's not to say it is not important to know how to do calcs as a contractor, by all means you should learn the right way, but for the test, do not waste your time and energy.