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manhattan42 07-01-2006 06:46 PM

Electric Range Wiring
 
Folks:

I am remodeling a kitchen and am replacing a gas range with an electric range.

Because this is a new installation I ran a 6-3 NM-B for the dedicated cable directly from the loadcenter.

The range manufacturer allows for either a 40 or 50 amp installation.

When I asked for a cord for the appliance I was sold a 40amp cord.

I had already installed a 50 amp receptacle and anticipated installing a 50 amp breaker at the panel.

Now I am thinking that I must:

1)install only a 40 amp breaker because of the 40 amp appliance cord.
2)replace the 40 amp cord with a 50 amp cord
3)could be completely wrong on all counts

At this point it would be simplest to just use a 40 amp breaker and I'm inclined to think that 1) is the proper thing to do.

Can anyone confirm this or correct and direct me to the proper installation method?:confused:

Thanking you in advance.

manhattan

Sparky Joe 07-01-2006 09:16 PM

#1 is what I would do. Perhaps someone else in here knows of a code rule that says you could use the 50 amp breaker.

Speedy Petey 07-02-2006 07:03 AM

There is NO such thing as a 40 amp cord and plug.

40 and 50 amp breaker/circuit are basically interchangable. You can use either for a 50 amp receptacle. What is critical is what the load requires.
99% of residential ranges require only a 40 amp circuit.

What exactly were you given?

manhattan42 07-03-2006 06:44 AM

Speedy pete asked:

Quote:

"What exactly were you given?"
I think you are asking me what type of cord I was given. If so it is a 4 prong cord that was labled as 40 amp. That is what confused me although I have seen these also refered to as "universal" range cords.

It (the 40 amp) does fit into a 50amp receptacle, and because of this, it made me think everything was ok.

Just wasn't sure about how large a breaker I should then use. (I have a 50...I could easily just get a 40.)

Couldn't find a kVA rating plate on the range to run some quick load calcs...but that was late Saturday and I was in a hurry to get home from this job. Will look again today.

Thanks Speedy Pete for the reply.

Just want to make sure I didn't or don't overload the wiring, etc...

Let you know what I find.

Looks like I was 'thinking' about this too much.

IvoryRing 07-03-2006 08:01 AM

I'm interesting in knowing the answer on this too... specifically, I'm considering going 6/3wg NM, with a 50A recept on a 40A breaker... as I understand it, this should be pretty dang safe (capacity wise - the wire should be able to handle 60A), but I would love to hear confirmation of this from the pros. Confusingly enough, HD seems to carry a bunch of 120/240V 30/50A outlets...

manhattan42 07-03-2006 09:34 PM

Electric Code
 
Spoke to an NEC and IRC certifed electrical inspector today and he verified that using either a 40 or 50 amp breaker would serve in this case, and that the 40 amp labled cord does not matter. The following is his reasoning:

Quote:

"The NEC treats cords differently than they treat branch circuit wiring. Cords are found in a chapter just for cords. There are two cord lengths found in the NEC: 6' max length for normal use and 2' for small appliances in the kitchen. These cord lengths greatly lessen the heating due to the shortness of those cords allowed. The NEC in the cord chapter of the NEC greatly increases ampacity of 6' and 2' cords over branch circuit wiring found in walls. You will find that a 6 awg copper wire acceptable to install as high as 60 amp on that range. Reason is finding the 60 degree column in the tables is 55 amps. Then a second rule found in 210 allows ampacity to increase to next larger normal amp size breaker found in 240.6. This means the 55 ampacity of 6 awg copper would be allowed on 60 amp breaker per NEC rules. Since the manufacturer limits it to 50 amps then 50 amps then becomes maximum due to 110.3.B manufacturer's installation instructions must be followed.

To further refute your thoughts look inside the range and you will find 12 and 14 awg wire connected to the other side of that terminal connection for your cord inside the range. This is normal also due to rules for within appliances differently designed due to closeness of loads inside the appliances and short lengths.

You are fine with 40, 50 amp for your certain range due to manufacturer's installation instructions. You could even use 60 amps per NEC rules except for your installation instructions overrules NEC in this case. Cords have a much higher ampacity rating due to the 6' or shorter lengths. If you want verification check the chapter for cords in the NEC and there is a chart that will confirm what I am saying. "


If I'm understanding correctly it has less to do with the cord rating and more to do with the rating of the cable and the breaker.

Cords, because of their short lengths, can carry greater amperages.

In my case, a 40, 50 or even a 60amp breaker can be used with 6-3 wire and a cord labled as "40 amps", because the cord is actually rated to carry much more than that.

This is why range cords can be considered "universal"

So the moral of the story appears to be, as long as the cable is sized properly for the amperage of the breaker, the cord labeling does not matter.

Sparky Joe 07-04-2006 12:37 AM

Thanks for the lesson. #6 wire is rated for 60 amps per table 310.16 in the 75C column #8 is good for 50 amps. The rating of wire is based on its insulation, that's why you'll find #12 inside your range. I've installed ceramic insulated #12 wire that was good for 150C. Also note that the entire range with everything on will draw 50 amps, while the individual burners may only draw 10 amps individually. The cords fall under a 'tap rule' for cord and plug connected devices which can allow much smaller wire than the branch cicuit wiring due to the fact that when you plug something in it is going to serve that appliance only and will not be tapped further to supply any number of other devices through the original cord and plug connected device.

Speedy Petey 07-04-2006 06:42 AM

Joe, problem is we cannot use 75c for NM cable. This limits us to 40a for #8 and 60a for #6.
Also, the temp rating of the wire has less to do with it's ampacity and more to do with it's environment. The ampacity charts only go up to 90c, and even then we can basically never even use that column for actual ampacity.

After all this I am still curious as to what the OP has. There is no such thing as a 40a plug. So what does he have? I assume it has a 50 amp plug configuration on it.

frenchelectrican 07-04-2006 08:31 PM

Most stove plugs have 50 amp plug conferation [ set up ] and i did double check with my catalog book for the repectailes and they are listed at 50 amp max so you can use either 40 or 50 amp breaker depending on the wire size

becarefull with both copper and Alum verison it get tricky here.

and all the repectales device are rated at 75 C but i know older device did used to rated at 60 but they change some time back i am not sure what code cycle it did change


Merci , Marc

manhattan42 07-05-2006 03:24 PM

Quote:

Originally Posted by Speedy Petey
Joe, problem is we cannot use 75c for NM cable. This limits us to 40a for #8 and 60a for #6.
Also, the temp rating of the wire has less to do with it's ampacity and more to do with it's environment. The ampacity charts only go up to 90c, and even then we can basically never even use that column for actual ampacity.

After all this I am still curious as to what the OP has. There is no such thing as a 40a plug. So what does he have? I assume it has a 50 amp plug configuration on it.

Speedy,

The cord is labeled at 40amps but it does have the 50amp standard range plug configuration .

manhattan42

Speedy Petey 07-05-2006 03:34 PM

Ahhh. New one to me.
I just get "range cords". All are rated for 50 amps if I am not mistaken.

manhattan42 07-05-2006 05:03 PM

New one to me also, Speedy.

Thanks to all for your input.


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