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Old 02-04-2013, 09:57 AM   #1
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Wall Oven Wiring


I am installing a new electric wall oven (Long Island, NY). The oven has an armored cable connected to it with 16ga stranded wires. I plan to run a new dedicated circuit from the main panel box to the oven. The distance is 75' (ouch).

The installation instructions are as follows:

"Can consume up to 4000w at 240vac. Use a circuit breaker of 30amp and wire gauge #8 awg.

A 3-wire or 4-wire single phase 120/240 or 120/208 volt electrical supply is required on a separate circuit fused on both sides of the line (time delay fuse or circuit breaker is recommended). Do NOT fuse neutral. The fuse size must not exceed the circuit rating of the appliance specified on the nameplate.

The appliance should be connected to the fused disconnect (or circuit breaker) box through flexible armored or non-metallic sheathed cable.

A suitable strain relief must be provided to attach the flexible armored cable to the junction box

Note: the armored cable leads supplied w/the appliance are UL recognized for connection to larger gauge household wiring. The current carrying capacity of the conductor is governed by the temperature rating of the insulation around the wire, rather than the wire gauge alone."

I plan to run 8/3 romex (plus ground) to a 30-amp double-pole breaker.

My questions are:

1. Do I really need #8 wire? I know everyone will say to "follow the OEM instructions", and I certainly intend to. Regardless of the responses, the incremental cost is minimal compared to the risk if it is not done right. I am really trying to understand the technical justification for the specification. Seems odd to me to connect #8 wire to #16 stranded.

2. Based on the description above, is Romex acceptable? I believe yes, based on the comment "non-metallic sheathed cable". I just want to confirm.

3. What is required to "fuse at both ends"? Do I need to run the feed to a separate fuse box/disconnect and then to the oven, even if it is on a dedicated circuit?

Thanks in advance,
B

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Old 02-04-2013, 10:18 AM   #2
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Wall Oven Wiring


Full disclosure: I'm not a pro. I don't understand the requirement for #8 wire. For a 30 amp breaker, #10 should suffice. Don't know what "fuse at both ends" means either. My wall oven isn't so configured. From the tables I looked at, the ampacity of #16 individual conductors is 18 amps. At 240 volts, that's well above 4,000 watts

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Old 02-04-2013, 10:26 AM   #3
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Quote:
Originally Posted by Burnside View Post
I am installing a new electric wall oven...
I plan to run 8/3 romex (plus ground) to a 30-amp double-pole breaker.

1. Do I really need #8 wire?
No. But the *house* needs the #8 because most wall ovens use
more power than you say this oven does... and that common need means more ampacity has to be provided for.

btw you could probably use a 20A breaker on 4000W @240V

2. Romex is a brand name for "non-metallic sheathed cable"

3. What is required to "fuse at both ends"?
Where do you see that? I saw fused on both sides of the line.
(which means use a circuit breaker)

You're on the right track.

Last edited by TarheelTerp; 02-04-2013 at 10:29 AM.
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Old 02-04-2013, 10:32 AM   #4
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You are correct. I was interpreting "both sides" to mean "both ends". Apparently both sides means that it should be both hot legs, which makes perfect sense (not sure how you would do it otherwise). Thansk for clarifying this for me.

Any idea why it would specify #8 wire?
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Old 02-04-2013, 10:45 AM   #5
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Quote:
Originally Posted by Burnside View Post
You are correct. I was interpreting "both sides" to mean "both ends". Apparently both sides means that it should be both hot legs, which makes perfect sense (not sure how you would do it otherwise). Thansk for clarifying this for me.

Any idea why it would specify #8 wire?
I'd like to see the information off the nameplate, however these are the installation instructions. Based on 4000 W at 240 volts not considering a blower or the 120 volt loads (which it does have)... 4000/240 = 17 amps , then for continuos load that's 1.25x17 = 21 amps or 22 if you want to round up. so there are some 120 volt loads which would or might get you up to 25 amps at most. So 30 amp breaker seems reasonable from the supplied information. 8 awg copper seems large and might be a miss statement by the specifications writer, hard to say. I would say that 10 awg likely would suffice but without nameplate information to verify the instructions you don't have an argument. It is also possible that wiring run length is addressed and for example it might say for runs over 50 feet use 8 awg.....etc.
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Old 02-04-2013, 10:49 AM   #6
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yet another "I do not know"
Yes, you need proper wiring to that outlet.

But how in the world they ship a oven with 16 gage wire and it works is beyond me.

When a real electrician drops by, would hope they can explain.
In my case, was a kitchen remodel, was a wall oven and some hold up on the cabinet. The electrician had already done his trim out, we can set the oven when cabinet is ready.

Was first time I seen a oven with silly little 16 awg wire .... how can this possibly work?
I know it does work, just is confusing to me.
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Old 02-04-2013, 10:58 AM   #7
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I checked the plate inside the oven. It's hard to see (because the oven is in the garage with a ton of s*#! blocking it. Not much information on it that I could see based on my viewing angle - power consumption was shown as 4000W, but little/no electrical information beyond that.
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Old 02-04-2013, 11:03 AM   #8
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It's not so much the gauge of wire but the insulation covering it.
Do not try this but you could take a smaller bare wire, say #12, and run 60amps maybe more through it without damaging the wire. (copper melts at ~ 2000 degrees)
The insulation on the wire is what really determines the ampacity, this is how they can use #16 for larger loads from manufactures, the insulation rating is higher.
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Old 02-04-2013, 11:04 AM   #9
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Originally Posted by funfool View Post
yet another "I do not know"
Yes, you need proper wiring to that outlet.

But how in the world they ship a oven with 16 gage wire and it works is beyond me.

When a real electrician drops by, would hope they can explain.
In my case, was a kitchen remodel, was a wall oven and some hold up on the cabinet. The electrician had already done his trim out, we can set the oven when cabinet is ready.

Was first time I seen a oven with silly little 16 awg wire .... how can this possibly work?
I know it does work, just is confusing to me.
Manufacturers use wire insulation that allows them to run more amperage through a smaller wire without compromising the insulation. They also use lots of tap conductors that carry less amperage to each load they are operating vs supply voltage and total amperage of all loads. The power cord of the cooktop however will be smaller awg even though the supply wiring from the house panel will be much larger. Appliance manufacturers are not required to follow the same rules as the NEC. The NEC requirements end at the outlet/receptacle/junction box where the appliance gets its source power. After that they have their rules for appliances ...
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Old 02-04-2013, 11:11 AM   #10
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Did they by chance list the 8 gage because of distance?
I have seen the correct wire size at 50', but once you went past, the manufacturer up sized the wire for the extra length.
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Old 02-04-2013, 11:20 AM   #11
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The installation instructions are boiler plate, and the manufacturer has no idea how far the panel is from the appliance.
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Old 02-04-2013, 11:55 AM   #12
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Quote:
Originally Posted by Burnside View Post
The installation instructions are boiler plate, and the manufacturer has no idea how far the panel is from the appliance.
What JBFAN is saying is what I was addressing in post #5 ... if in the installation instructions it would say something like use 8 awg for branch circuit wiring runs over 50 feet. You see this quite often ... but the point here is that the NEC requires branch circuit conductors be sized according to the manufacturer instructions or be sized by nameplate information as to electrical requirements.
You should have a technical questions phone number that you can call and they may be able to clear up any confusion. Aside from that you are required to install the cooktop with 8 awg copper branch circuit conductors.

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Old 02-04-2013, 12:04 PM   #13
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Originally Posted by stubie View Post
...but the point here is that the NEC requires branch circuit conductors be sized according to the manufacturer instructions or be sized by nameplate information as to electrical requirements.
...and in the absence of that nameplate data or when a manufacturer is selling a product that they know is rated less than what is commonly installed for the job (as is the case here) they have determined -perhaps with aid of their attorney- that if you tell people to run a new circuit that you should tell them to do that the way an electrician would otherwise do for the *general* application:
#6 for a range or #8 for wall oven

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Old 02-04-2013, 02:22 PM   #14
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Wall Oven Wiring


I am not an electrician but I think the 8awg suggestion is so that when this oven is removed and replaced with a standard oven that the owner then does not just replace the breaker with a 40 amp breaker and wire up the new one. The wiring will be good for any replacement oven.
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Old 02-04-2013, 04:23 PM   #15
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Google SRML wire. It is used in high temperature enviornments and #16 SRML is rated for use between 30 and 35 amps. There is no voltage drop issue as you are not running SRML all the way from the Service, but voltage drop is why they want you to use #8 construction grade (NM-b or THWN) wire from the main panel.

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