[FlyingSparks]

Okay, here is the scenario my instructor laid out in a recent question on a test we had. I've been doubting my work ever since I took the test for some reason.

You have a 120/240v 6kw cooktop and a 120/240v 8kw oven, determine the amount of branch circuits needed, conductor sizes, ocpds, and the load in volt amperes for each circuit.

Okay so,
I remembered that somewhere in the NEC it allows you to combine both on to one circuit -- I think, so here's what I calculated:
8 kW + 6kW = 14 kW
14 - 12 = 2 kW
2 * 5% = 10%
8 * 1.1 = 8.8 kW

So I said one branch circuit, 8awg wire, with an OCPD @ 40amps. Load is 8800va.

Anyone see a problem with the answer I gave? It's been bothering me like crazy.

 

[FlyingSparks]

Anyone?

 

[aftershockews]

1- 6/3 w/ ground circuit on a 50 amp breaker.

 

[bkmichael65]

8kW+(8kW*.10)=8.8kW/240=36.66 amps. #8cu and 40amp cb. Looks good to me

 

[Dennis Alwon]

T. 220.55 note 4 is your reference and you are correct. 40 amp cir.

 

[aftershockews]

Anyone?

Glad to have helped get someone to answer your question.

 

[Dennis Alwon]

I have said this before but it always amazes me that you can have a 9 kw range or a 16 kw range and they would both calculate out to 40 amps. 16 kw would be 8kw plus 5% for every kw over 12kw. 16kw is 4kw over 12 kw so .05x4= .2
1.2*8 kw= 9.6kw or 9600. Divide by 240 and you get 40 amps

 

[Dennis Alwon]

Glad to have helped get someone to answer your question.

You are the man....:thumbsup: :laughing:

 

[FlyingSparks]

You guys have made my night, I was searching for that reference, forgot it was a note under the table.

What is the rationale behind that Dennis? I still struggle to understand this whole oven load calculating wizardry haha

 

[aftershockews]

I am not a code guru. I have always calculated an electric stove or oven, range top at 125% of the namplate wattage. I mean, hell, we have to do it for a water heater and an oven is going to be fired up longer than a water heater especially on Thanksgiving.

 

[Dennis Alwon]

You guys have made my night, I was searching for that reference, forgot it was a note under the table.

What is the rationale behind that Dennis? I still struggle to understand this whole oven load calculating wizardry haha

It has to do with the fact that the oven is thermostatically controlled and will not be on constantly. The range eyes are also on a T-stat but I think the NEC guys figured you won't be using every eye on high and the oven at the same time. Even if you do the t-stats will regulate it somewhat so that they wont all come on at the same time