Why could he do it and I can't?

eleenaOctober 1, 2012

Here is what someone asked here a few months ago (see link below):

"There is a single 240V stove connector at the bottom of one wall where I had my stove unit, including electrical cooktop, plugged in. I want to replace that stove with a seperate drop in electrical cooktop range and a seperate in-wall oven, both 240v.

Question: Can I run another cable run from the original 240v outlet and use it to connect my in-wall oven? So that I would use the original for the drop in cook top,and the new one for the wall oven."

And the answer was "Yes".

I have seemingly the same situation: 240 V 50 amp outlet that is a square metal box (don't know the name for it, searched for Google images but couldn't find).

I need to plug two 16 amp ovens. You "guys" have told me I needed a separate breaker for each of them and I understood the reasoning.

But I do not understand the difference between his case and mine. Would you indulge me with an explanation?

I really want those ovens and really cannot afford $$$ to run another line to the outside electrical panel that is more than 50' away, especially counting that the wire has to go up the wall into the attic and then down to the panel.

Please?

TIA!

Here is a link that might be useful: An old post

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kurto

There are some exceptions to the rule, but from the information you have provided, yours is not one of these exceptions. If you read to the end of the thread you provided, you'll see that the OP wound up installing two circuits for his situation as well.

    Bookmark   October 1, 2012 at 6:09PM
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Ron Natalie

There's an exemption in the NEC to allow the cooktop and the oven to be tapped of a 50A range circuit. The bigger issue is that by the time you get around to running two ovens AND the cooktop you're going to need more than the aggregate 50A.

    Bookmark   October 1, 2012 at 8:17PM
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hendricus

I've been following this thread and wonder if you can put a 2 or 4 breaker sub panel at the end of the 50 amp run and take 2 20 amp circuits off that.

    Bookmark   October 1, 2012 at 9:53PM
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bus_driver

"2 or 4 breaker sub panel". Given the rules of today about panel access and working space, that will be difficult to do and the customer be pleased with the appearance. But it is technically feasible.

    Bookmark   October 1, 2012 at 10:01PM
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eleena

But I am NOT going to run two ovens AND a cooktop, just two small ovens each requiring 16 amp (so even less than 20 amp). I want to move the cable to a different wall (which is slightly closer to the breaker than its current location).

And fwiw, I will hardly ever use both ovens at once. If necessary, I can wait till one is pre-heated before turning the second one on.

Still no?

    Bookmark   October 1, 2012 at 10:03PM
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Ron Natalie

In that case, as long a your taps are at least rated for 20A you can do it.

Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance.

    Bookmark   October 2, 2012 at 5:23AM
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eleena

Yay!

Thank you so much!

BTW, Ronnatalie, did you cut and paste from an electronic version of NEC or some other place?

Could you tell me which page or section or, if from another (hopefully, more accessible) site, post the link?

I can read the code online but it does not allow searching.

Thanks again!!!

    Bookmark   October 2, 2012 at 9:53AM
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eleena

Two more questions.

Could someone clarify why

"Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of NOT LESS than 20 amperes"? I.e., why 15 amps are not permitted?

Can I use a 20 amp branch circuit for an appliance rated for 15 amp?

I know that the circuits also come in 15 amps, but wouldn't using the 80% rule imply that 20 amp might be better?

    Bookmark   October 4, 2012 at 4:43PM
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Ron Natalie

It means that the conductors (after the tap) have to be sized for at least 20A (regardless of how small the load is). That's typically #12 copper. The reason (not that it matters) is that they assume that as long as they are sized at least that big, the risk of having a 50A breaker protecting that circuit is an acceptable risk.

The answer to the question "Can I use a 20 Amp branch circuit for a 15A appliance" is yes. However, it's also immaterial the question at hand. You do not have a 20 Amp branch circuit here.

The 80% rule doesn't really enter into this.
And besides, you said each oven requires 16A. You couldn't put those an a 15A circuit anyway.

    Bookmark   October 4, 2012 at 5:09PM
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eleena

Oh, the 15 amp question was related to something else.

I was considering paring another 20 amp oven (that our local appliance store has for a good price) with a 2-burner 15 amp induction cooktop, so that I don't have to move the outlet.

If I could do it, I would get only one of the two 16 amp ovens and run a 20 amp line from the indoor breaker for it.

In the previous scenario (with two ovens on one wall), I would have to give up the induction all together and I really want to have induction.

Would the correct question then be:

Can a 15 amp appliance and a 20 amp appliance used with the two 20 amp tap conductors from the 50 amp outlet?

TX!!!

    Bookmark   October 4, 2012 at 10:54PM
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Ron Natalie

Is the induction cooktop connected with a plug. In that case, the reason is small applicance circuits in the kitchen are required to be 20A. That's just the way it is. But, then the answer is YES, you can plug in 15A loads to a 20A circuit.

    Bookmark   October 5, 2012 at 2:45AM
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eleena

I have finally found the right manual for the cooktop. I was going by the specs before. For some reason, the installation manual had only the instructions for the mechanical part (cut-out, etc.) but not electrical.

Here is what the "right" manual says:

"Cooktop electrical characteristics are:
Operating voltage240 V~ 60 Hz
Maximum power output 3600 W , 15 A
Connect to 240 V, 60 Hz, 20 A minimum supply,
(3 conductors #12 AWG)

This unit comes equipped with three connection
wires in a metal 180 cm flexible conduit.
The conduit must be routed and properly
connected to an approved, owner-supplied,
electrical, wall junction-box. An approved
connector must be used for connecting the
conduit to the junction box. A three wire, 2 poles,
240 V, 60 Hz service with minimum 20 A
circuit protector must be provided. The red
and the black wire from the unit are to be
connected to the service ("hot") wires, and the
green wire is to be connected to the ground
conductor.

The circuit protector for the unit should be properly
marked inside electric panel and anybody
using the unit, or technician servicing the unit,
should be advised of circuit protector�s location,
so that the power to the unit can be disconnected
when necessary."

So, it is not a 15 amp but a 20 amp appliance then.

If the oven truly requires 20 amp, they can both be run from the 50 amp outlet, using tap conductors, right?

What if the oven requires a 30 amp breaker, even though it has maximum output XXXX W 20 amp?

    Bookmark   October 5, 2012 at 3:14AM
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Ron Natalie

I think you need to find a good electrician. You seem not to be able to grasp the simplest of concepts in order to explain them.

Without wasting time trying to educate you, yes, you can probably put this cooktop on the tap'd 50A circuit, with 12g (20A) wiring.

    Bookmark   October 5, 2012 at 1:05PM
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brickeyee

"Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance. "

That does NOT give permission for multiple taps of the same circuit.

It defines what the taps to ANY load on the circuit must be.

I would really doubt that your equipment is allowed on a 50 amp circuit.

PERIOD.

In the event of a short circuit, the internal wiring may cause a fire before the 50 amp breakers trips.

And if you had a 40 amp fault it would sit there cooking.

Trying to find a narrow exception to 'get around' correct wiring is a fools errand at best.

Make sure your fire insurance is up to date and paid for.

    Bookmark   October 6, 2012 at 12:51PM
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pharkus

I've always liked the "stick a subpanel there" solution. Results in a panel in a funny place sometimes, but a lot safer than the (allowed, sometimes) tap "solution."

    Bookmark   October 20, 2012 at 11:29PM
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sung

A question for brickeyee. What you say makes sense (about the appliance's internal wiring burning up because it is not suitable for 50A). But why is that the manufacturers always list minimum breaker size but never the maximum size? Okay, I can see that is like a pharmaceutical company not providing too much information with the drugs they sell. A legal issue. But even in NEC, I cannot find any article that requires maximum breaker size. However, NEC imposes minimum breaker sizes (210.19 & 215.3) just like the manufacturers. As far as what I can understand the code, all it requires me to do is to make sure that my conductors are protected by the breaker, but nothing about protecting the load, like the appliance internal wiring. Do you know of any NEC article (other than the small conductor rule of 240.4) that requires maximum breaker size? Thanks.

    Bookmark   October 21, 2012 at 9:39PM
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brickeyee

The listing by a recognized lab of the equipment is when the device suitability for the breaker size is checked.

The NEMA has some standards, but even it does not cover everything.

If you want to get a listing by a lab you better make sure that the internal wiring is suitable for the breaker size your equipment requires to operate.

The fusing current of wires is surprisingly high, and represents an upper limit to fault current capacity.

Since the equipment is not operated near this value, insulation has little impact.

The fusing current for a #14 wire is around 166 amps, and a #10 around 333.

As long as the fusing current is large enough to allow the breaker into the magnetic trip mode (usually around 20 times the rated current) the breaker will open in less than one 60 Hz cycle.
This greatly limits the power that can be delivered into a solid short circuit.

"As far as what I can understand the code, all it requires me to do is to make sure that my conductors are protected by the breaker, but nothing about protecting the load, like the appliance internal wiring."

The NEC is all about the permanent wiring.
The requirement for listing is how minimum conductor sizes for equipment get required.

Notice there IS a minimum size for light fixture wires (#18) providing around 88 amps of fusing current.

    Bookmark   October 22, 2012 at 4:59PM
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