contactor installation to control oven?

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  #1  
Old 10-27-10, 10:39 AM
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contactor installation to control oven?

I would like to install a timer to control my oven so that it is preheated by the time I wake up. My oven is a very simple model with all manual controls and is connected to a 3 wire NEMA 10-50R receptacle which is in turn connected to a 40A or 50A breaker (I am not home at the moment to check). Based on the research I've done, I will need a DPST contactor relay that is controlled by 110V. I still have a few questions though:

What amperage rating will the contactor need to be?

I will probably be installing the contactor in my attic, would a NEMA1 enclosure be appropriate? Normal junction box?

Would Romex 14/2 be appropriate to use? If not, what should I be using?

Thanks,

Jeff from CA
 
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  #2  
Old 10-27-10, 10:56 AM
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Just from a safety stand point (I am biased since that is my profession), I don't find what you are wanting to be the safe and I would discourage any of our members from telling you how to do it. I'm willing to bet the manufacturers instructions state not to leave a oven unattended while on. What were to happen if this thing caught fire while you slept or if you were gone?
 
  #3  
Old 10-27-10, 11:06 AM
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Thanks for the concern and that is a valid point. However, what I do now is wake up to preheat the oven and go back to sleep or go for a run. Maybe that is a bad habit anyways, but at least this way my sleep will not be interrupted.
 
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Old 10-27-10, 11:28 AM
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Really not a good idea...though they do have timers on ovens so they will start and cook unattended. Even older manual control ovens had settings for stop and start as I remember.

I won't try and advise as to how to do it...but I would have to ask why? Any interruptions in the main supply will throw off your clock and possibly other settings and may not allow the unit to function anyway.

Exactly what model do you have?
 
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Old 10-27-10, 11:45 AM
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My thoughts exactly, I figure that if they make ovens that can turn on at a certain time, it must not be a completely bad idea. I have a Whirlpool RF111PXSQ and it is a very basic model. There is no clock on it or anything that would be adversely affected by cutting the power. The controls are completely manual.
 
  #6  
Old 10-27-10, 11:59 AM
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A safe design will incorporate a DP 50a contactor like: DP Compact Contactor, 24VAC, 40A, Open, 2P - Magnetic Contactors - Starters and Contactors - Electrical : Grainger Industrial Supply

The contactor goes into a
Nema 1 box (or better) like: Enclosure, NEMA 1 - Motor Starter Enclosures - Starters and Contactors - Electrical : Grainger Industrial Supply

A 120 volt plug in timer could work for the coil control. If the above 24v coil contactor is used, then you will need a small, 24v control transformer.

Do not even consider making this into the home wiring, and should be put in the proximity of the oven, between the oven and the wall recept. as a plug in device between the two.

If you don't understand how the wiring would go, get a EE involved for the design, one that has done factory automation, controls, etc. If the run to the main panel is short, I strongly advise to run a new 4 wire branch, and change out the recept and cordset. In industry, this carry-over 3 wires doing the job of 4 does not fly. (L1,L2, N, G) is much safer.
 
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Old 10-27-10, 12:14 PM
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Once again....why? Please tell me you aren't using it for heat!? What is so important that it can't wait about 20 min? If it's taking longer than that to reach the setpoint...I'd suspect another issue.
 
  #8  
Old 10-27-10, 12:17 PM
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I have been baking a lot of bread recently and use a baking stone. The stone takes 45 minutes to an hour to get up to temperature.
 
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Old 10-27-10, 12:42 PM
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Ahhh...clearer now..thx. That clarifies...but I still think the expense and complexity may not be worth it.

I'll step out now....
 
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Old 10-27-10, 12:55 PM
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I'm guessing it'll be pretty close to break-even on assembling all the right parts, wire and devices together vs. just buying a basic model oven with a timer function built-in.

There's also the technical code issue that if you modify the existing three-wire range circuit it loses its grandfathered status and must be upgraded to four-wire (#8 copper w/ 14-50R).
 
  #11  
Old 10-27-10, 01:17 PM
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It is beginning to sound like it will be more trouble than it is worth. The oven was new and came with the house when I bought it. I will definitely look for this feature when it is time to upgrade my oven (which might be sooner than later given how much my wife and I enjoy cooking).
 
  #12  
Old 10-28-10, 12:24 AM
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By time you spend the money and time to rig this up it will be justifyable to just get new oven for your purpose and they will have modern feature to set the time to turn on to preheat your baking stone.

I rather just get new oven with the features you are looking for and they just cost little more than convetal oven is.

Look around there are few diffrent verison of ovens you may find to suit your needs.

And this is a wall oven or a standard stove ?? that part may clear up the question.

Merci.
Marc
 
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Old 10-28-10, 01:45 AM
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Originally Posted by french277V View Post
By time you spend the money and time to rig this up it will be justifyable to just get new oven for your purpose and they will have modern feature to set the time to turn on to preheat your baking stone.

I rather just get new oven with the features you are looking for and they just cost little more than convetal oven is.

Look around there are few diffrent verison of ovens you may find to suit your needs.

And this is a wall oven or a standard stove ?? that part may clear up the question.

Merci.
Marc
free standing Freestanding Ranges RF111PXSQ from Whirlpool Home Appliances
 
  #14  
Old 10-28-10, 06:33 AM
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You could buy a bread machine cheaper than what you are proposing and with far less hassle.
 
  #15  
Old 10-28-10, 11:37 AM
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You are talking to someone who bakes on a stone. I HIGHLY doubt they are interested in a bread machine.
 
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Old 10-28-10, 03:00 PM
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I did own a bread machine a few years ago, but yes, I have moved on =).

Originally Posted by JerseyMatt View Post
You are talking to someone who bakes on a stone. I HIGHLY doubt they are interested in a bread machine.
 
  #17  
Old 10-28-10, 03:38 PM
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You could easily do this with a relay and a timer. Run your 14/2 to the relay, which would in turn provide contacts for the 240 vac wires to the oven. Those wires would need to be very beefy to go from the oven to the attic and back. You're into at least $350 to do the job.

I've seen some used or donated-new ovens (and other incredible deals!) at the local recycle/reuse centers for around the same price.

A question for you: As a baker, wouldn't you prefer a gas oven? I've heard that gas ovens hold their temps more consistently, and the convection is more evenly distributed.
 
  #18  
Old 10-28-10, 04:01 PM
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Originally Posted by Rick Johnston View Post
wouldn't you prefer a gas oven? I've heard that gas ovens hold their temps more consistently, and the convection is more evenly distributed.
The big problem with gas ovens is the extra water vapor added by the burning gas. A dry oven (electric, wood fired) is best for anything that's supposed to come out with a crunchy crust.
 
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Old 10-28-10, 04:14 PM
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Gas ovens are definitely more temp stable, but the water vapor produced by the burner is not ideal for bread. Gas deck ovens get around this by heating the rock on the bottom of a sealed compartment. The burner is not in or open to the cooking compartment like a residential oven is.

I was also thinking along your lines, but why not install the contactor at the panel. Saves on having to run a set of #6 to the attic, then the 120v 14/3 (need neutral for a timer) control line can be run to the kitchen. Using a 3 way (SPDT) switch, the contactor can be set to on or timer from the kitchen. I don't see any problem with this codewise, except for the fact that it 'technically' would be required to be upgraded to a 4 wire circuit. But since this is a non-standard setup, you would remove it before selling the house anyway and an inspector would be none the wiser.
 
  #20  
Old 10-28-10, 08:15 PM
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I just had a thought.. Assuming you have your regular routine that probably wouldn't require much changing of the timer, you could install that at the panel also, and it would allow you to run 14/2 instead of 14/3, and use a standard on/off switch. You could also use a switch with a pilot light if you wish (would require 14/3) to let you know the range is receiving power. I would also advise using a digital timer with battery backup to ensure a power failure doesn't cause it to start at an unintended time.

 

Last edited by JerseyMatt; 10-28-10 at 08:35 PM.
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