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Questions from a newbie

Posted by eleena (My Page) on
Thu, Sep 27, 12 at 12:55

This has been probably answered many times but I don't know what to search for. I have read the FAQs and have tried reading the first few pages and couldn't find answers to my situation.

I had an electrician come over and give me a "consultation" (which I paid for, of course) but his answers were quite vague (as I now understand), so I am still confused.

I was told I had a 16 amp circuit where the old wall oven had been. I thought they came only as 15 amp and 20 amp? Was it a miscommunication or there is something I don't know?

If I am going to install two 24" ovens reach requiring 240 V 15 amp each, do I need two 15 amp circuits or one circuit with higher amps? The answer to one of the FAQs seems to indicate the latter. Is there a considerable price difference between running two lines with lower amps vs. one with higher amps?

I have three free breakers on the panel located inside the house. However, the only 240 V (15 or 16 amp) circuit we have is connected to the breaker on an outside wall of the house. Is there a reason why it couldn't have or shouldn't have an inside breaker?

I was told I could use the available circuits on the inside panel for 240 V 15 amp circuits but not 50 amp one, that one has to go to the outside wall. What about everything in-between, like 20 amp, 30 amp, or 40 amp?

TIA!


Follow-Up Postings:

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RE: Questions from a newbie

Either get a clarification or ask for your money back.

While it's technically possible to build a 16 Amp circuit breaker, no one does. The most common breakers for household circuits are 15 and 20 Amp at 120 volts, and 30,40, and 50 Amps at 240 volts. These 240 volt breakers are double-pole, meaning they take up two adjacent slots in your panel.

It's also unlikely that a wall oven only requires 15 Amps at 240 volts. Most wall ovens require considerably more power. Let us know the make and model, and we can probably help find the right information.

If these two ovens are actually a single unit, it may be possible that a single circuit will suffice. That will depend on the manufacturer's installation instructions. Yes, it is more expensive to install a circuit with larger capacity, primarily because the wire itself costs more. The labor is about the same. YMMV.

An outside disconnect, say for an air conditioning unit, may or may not contain a current limiting device like a fuse or a circuit breaker. However, the inside end of that circuit (the supply end in the circuit breaker box) will definitely have a circuit breaker to protect the wiring.

I don't know how to answer the inside/outside question without some additional information. If the "outside" box is actually an electrical panel, your electrician may be talking about available slots for new breakers. Your inside panel (with only 3 available slots) won't be able to handle two new 240V circuits. Can you take a picture of both the inside and outside panels (with the doors open so we can see the circuit breakers)?


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RE: Questions from a newbie

Cannot ask for money back as you pay for them just to come in. It was not the only thing they told me wrong. I know, I should not have called this company. :-(

Will take pix and post tomorrow or on Saturday (as I have to learn how to do it).

Here is one of the ovens I want to buy (floor models, not full price, LOL). IDK how to upload an PDF file, so you have to click on the file to open.

It says:

208/220-240V / 60Hz
Total Amps: 16

Does it mean I need a 20 amps circuit?

Here is a link that might be useful: Steam oven


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Here is another

This is the second oven:

Total rating: 3.7 kW
208/220-240V / 60Hz
Total Amps: 16

Can they be run from one 20 amps circuit?

Here is a link that might be useful: Wall oven


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RE: Questions from a newbie

Forgot to copy:

The steam oven has Total rating 2.9 kW.


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RE: Questions from a newbie

He probably 'meant' to say it was a 60 amp, 240 volt circuit. Many range circuits are.
If you look in your circuit breaker (or fuse) panel, you should find a label for 'range' with the amperage for that circuit clearly visible.


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RE: Questions from a newbie

Interestingly, the online installation instructions aren't precise in the wiring requirements. However, it appears that each oven will draw approximately 16 Amps at 240 volts. Without any information to the contrary, you therefore will need two circuits, each 20A at 240 volts.

Those circuits will each require two adjacent slots available in your circuit breaker panel.

I'm assuming you are not thinking about replacing your regular oven(s) with these specialty devices, so there won't be any possibility of reuse of an existing circuit.


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RE: Questions from a newbie

I went outside to take a look. There are three "double-breakers". IDK the proper name, it looks like the ones on the left on the FAQ "This is a test. This is only a test" picture. It looks like two slots connected by a handle.

Two seemed to be in "On" position and one in "Off" which would make sense as they turned it OFF when the old oven malfunctioned and was removed.

So, the OFF one has "50" and "50" written on each side of the "handle". It also says "Use 65/75 (degree sign) C dual wire" as well as AWG 8. FYI: the old oven was a single GE oven.

BTW, the other two (in ON position) have 125/125 and 60/60.
Does this make sense to you?

But if it is a 50 amp circuit, why did they tell me I couldn't use it for a 40 amp induction cooktop?

Anyway, if it is a 50 amp one, what can I run on it?
For example, can I use it for a 16 amp cooktop and 30 amp oven?

I don't think I can take a good picture of the indoor breaker box, it is sort of in the corner and there isn't enough light there. All but two small breakers in it say 120/240V and they all have 15 or 20 written on the handle, except for the one for the dryer that says 30.

So, if I need a circuit for a 16 amp oven, do I need to use 2 slots or one?

Thank you!


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RE: Questions from a newbie

Kurto,

I don't have an oven, it broke 5 years ago. :-(

As I was under the impression that it was using only a 15 (or 16 amp) circuit, I was going to reuse it for a 15 amp induction cooktop that would be placed just inches away from where the oven was. The fridge will be going to where the oven was and these two ovens are to go where the fringe is.

If I can re-use one 50 amp circuit for two 16 amp ovens, it shouldn't be a problem to run another 20 amp circuit to the location of the cooktop, right? I have an attic above the kitchen, not living quarters.


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RE: Questions from a newbie

"So, if I need a circuit for a 16 amp oven, do I need to use 2 slots or one? "

If you need 240 V you need a double pole breaker (2 slots) no matter what the current.

A double pole breaker provides access to 240 V.
It can be any current from 15A up to the max current breaker allowed in the box.

If you have two ovens it is very unlikely you will get away with a single circuit for them.

While load sharing is allowed on multiple range circuits, it is over multiple apartments.
Not everyone will be cooking at the exact same time.

Two ovens in a single kitchen are far more likely to be operating at the same time, and need full power to preheat (many now use both the broiler element AND the oven bottom element to speed up preheating.

No single piece on a branch circuit is allowed to be over 80% of the capacity.
A 16 A load is 80% of a 20 amp circuit.

Two ovens will require two separate 240 V, 20 amp circuits.
Oven manufacturers get some relief in establishing ht branch circuit requirements for their ovens since they are NOT 100% loads indefinitely.

The heating elements may pull even more than 16 amps for a very short time until they heat up (seconds to minutes).

Even at the highest temperature the heating element is NOT going to be on 100% of the time.
The oven thermostat will cycle it off and on to hold the setting.


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RE: Questions from a newbie

Thank you for the explanation!

Could you answer this question:

Can re-use one 50 amp circuit for two 16 amp ovens?


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Multiple receptacles

Here is a quote from this Forum's FAQ page (see link below).

"The National Electrical Code, in article 210.21 (B) 1, 2, and 3, describes the requirements of single and multiple receptacles on a circuit. The use of multiple 15 amp receptacles on a 20 amp circuit is permitted in part 3. A duplex receptacle is considered as multiple receptacles and is therefore permissible to use as the single, or one of several, multiple type receptacles on the circuit."

I am curious if it different from running two 20 amp ovens on a 50 amp circuit?

Here is a link that might be useful: Multiple receptacles


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RE: Questions from a newbie

To answer your question, no, you cannot reuse a single 50 amp circuit for two 16 amp ovens. Even though this single circuit would supply enough power for both, that installation would not be compliant with the electrical code.

The problem is that if one of the ovens developed a fault that caused a 30 amp flow of current (more than enough to start a fire within the oven), the circuit breaker wouldn't trip, because it is rated for 50 amps.

For two ovens, you need two properly rated circuits.


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RE: Questions from a newbie

"Can re-use one 50 amp circuit for two 16 amp ovens?"

No.

You could save some money by replacing the 50 amp two pole with a 20 amp, and use the larger conductors for one of the circuits.
This is likely to cause an issue with connecting the larger wires if a receptacle is used.

Hardwired connections may require split bolts instead of wire nuts, or other connection means to the smaller conductors for the final connection to the stove.


" that installation would not be compliant with the electrical code. "

Or the installation instructions, and they carry the more weight than the NEC.

The NEC requires the manufacturer's installation instructions to be followed since they may supersede the NEC.

If the manufacturer "requires" a particular circuit size and type, that takes precedence over the more general rules of the NEC.

While using an oversize circuit (like 50 amps when a 20 is called out) may not seem like a problem, the internal wiring of the device must be able to sustain enough current without IT becoming a fuse to trip the breaker, without causing additional damage, or even starting a fire.

While the breaker is really there to only protect the branch circuit wiring, permanently connected equipment often is NOT rated for use on significantly larger circuits.


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RE: Questions from a newbie

Oh, I see.

Thank you VERY much!

I now understand my particular situation but puzzled with this sentence:

"The use of multiple 15 amp receptacles on a 20 amp circuit is permitted in part 3."

Does it refer to receptacles for plugging in devices that will not be used at the same time?

Please don't laugh as it has been awhile since I took Physics 101 and I wasn't good at it either, LOL. Plus, they did not teach Electrical Wiring 101 and I have no idea why an appliance would suddenly develop a higher current. :-(


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RE: Questions from a newbie

I am not an electrical code genius so I could be off. I do really welcome correction and further information. The discussion that you linked had to do with using 15 amp devices (outlets/receptacles) on 20-amp circuit. It is kind of out of context in this thread.

That "said", this seems to be the root of what is confusing you. To me, there seems to be a major difference between convenience outlet circuits (low power) and circuits for higher power appliances. The latter always seem to be dedicated, meaning that multiple outlets are not allowed. I can only speculate about what the logic or underlying safety reasons are, what exceptions there might be, and where the break point is (Are multiple outlets allowed on 15- or 20-amp 208/240 circuits, for example?).

An appliance might suddenly develop a higher current because it is broken (short circuit). This could be why branches are not allowed on higher power circuits. (Here I go stepping off over the speculation abyss.) The manufacturers may depend on the fusing to protect against exploding devicee (stoves, dryers, etc.). I doubt it though. I think that the wiring in appliances is supposed to be pretty well enclosed so that it can not cause an external fire though the results of an internal short can be pretty impressive.

OTOH, the dichotomy might be simply due to the higher power of the circuits running through your walls and through power cords/pigtails, more power = more heat (bigger explosion) if there is a fault. Look at it this way, if your oven has a cord capable of 20A and the cable leading to the plug and the breaker both handle 50, what could happen to that cord if it suddenly get 50 and up amps for a few minutes? That is physics 101, it has some mass to it and it will get pretty hot.


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RE: Questions from a newbie

The exception that you mention is for using 15amp receptacles on a single 20amp 120Volt circuit. This is a narrow exception and doesn't apply in your case where you need multiple 240V/20A circuits.

That exception is designed for "convenience" receptacles, saying that on a 20A circuit, you can use 15A receptacles instead of 20A receptacles, as long as there are more than one receptacle on the circuit.


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RE: Questions from a newbie

And how was I supposed to know that? LOL.

Thanks for the lesson in EW 101. :-)


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RE: Questions from a newbie

"And how was I supposed to know that?"

The NEC is not intended to teach you, just set the minimum rules for a safe installation.

To apply it in many cases rquires you t undersand ALL the sections that apply to a particular installation.

You have to know enough of the code to determine what applies.

The inspector will surely know.

You happened to pick a very special exception for the use of 15 amp, 120 V receptacles on a 20 amp circuit.

There are further restrictions, like a 15 A receptacle cannot be the ONLY outlet on the circuit, and it ONLY applies to 120 V branch circuits.

Actual fault currents form a short circuit can be VERY large.
Thousands of amps for a very brief time.

There are a couple place sin the NEC minimum wire sizes are called out, and other things (like getting a UL listing) and NEMA (National Electrical Manufacturers Code) place further restrictions (and provide 'guidance').

There are NEC 'handbooks' that provide further explanations of many of the code requirements.

Below is a link to a popular one.

Here is a link that might be useful: National Electrical Code 2011 Handbook


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RE: Questions from a newbie

Yes, the Handbook can be read online for free and I started reading it yesterday. But it requires a lot of time and I might have to re-take Physics 101 as well as take Electrical 101, which is not going to happen on time for remodel. LOL.

That is why I had to ask you. :-)

But I took my time and read all the FAQs.

"You happened to pick a very special exception for the use of 15 amp, 120 V receptacles on a 20 amp circuit."

That exception came from this forum's FAQs, I'd have never thought of it myself, obviously. :-)

I used to rely on contractors for this stuff. But with all the flakiness going around and remembering what happened in my friends' VERY expensive remodel, I do not trust anyone where we live, not anymore. Sigh.

I really REALLY appreciate that you took time to explain!

Perhaps, it should be added to FAQs?


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RE: Questions from a newbie

Eleena: It's always good to learn some of this stuff, even if we're not the ones doing the major work. I dug my hands into my house's electrical system for the first time last week (two outlets had reversed polarity, and the work was so badly done that I started mucking around in other outlets/switches to figure out what was there, and finally mapped every outlet/light/switch to the circuit breaker. I knew *nothing* about wiring or the kinds of information about amps/volts that's being discussed here before last week, but I'll likely need to have some electrical work done professionally (hoping to add a dishwasher and an outside light) and at least I'll now have SOME sense of what's being said/done... and some basis to tell if the professional knows what he/she is doing, because whoever wired the living room definitely didn't know!


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