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Is it safe to adapt a 20amp 240volt appliance to a 30amp 240volt outlet?

Is it safe to adapt a 20amp 240volt appliance to a 30amp 240volt outlet?

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  #1  
Old 04-02-14, 06:13 PM
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Is it safe to adapt a 20amp 240volt appliance to a 30amp 240volt outlet?

Hi there, I am John, and I like to make beer, straight from the barley itself (and I live in Canada). Through a complex evolving story, I find myself trying to adapt to garage-residing brewing system with a portable induction cooktop. This cooktop is 3500watts and has a 3 prong plug (ground, two blades that orient 90 degrees from each other, a 20amp 240volt plug). My circuit breaker box is huge, modern, but full. My laundry room is directly next to the garage. My dryer is has a 4 prong outlet (1 ground, 2 flat blades, 1 bent blade, a 30amp 240volt plug). Tracing this back to the circuit breaker shows a green-toggled 30amp double-busbar breaker installed on this circuit.

So, my question is: Can a person safely adapt a 20amp 240volt plug to a 30amp 240volt outlet? Ideally I would like to simply make a heavy gauge extension cord with an appropriate 4 prong plug for the wall-outlet, and an appropriate 3 prong outlet for the cooktop to plug into (of course with meticulous attention to ensure all wires are properly allocated and installed). But I am getting ahead of myself there. The first question should be: Can such an extension cord be safely made?

I would greatly appreciate any responses to this. Of course, if someone wants to further expound on how I could do this, I would appreciate that to the ends of the earth and back. Hey, if you are close to my house, come on over for a beer when I have the system up and running again!

Thanks a million

John (Alberta)
 
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  #2  
Old 04-02-14, 06:39 PM
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Welcome to the forums!

Yes, you could make a 30 amp, 240 volt extension cord, using the proper materials, and make it as safe as any other extension cord. (temporary use only ) We can tell you how to do this, but first i want to ask, why?

By hooking up your cook top to a 30 amp circuit, it will not change how the cook top runs. You posted it is 3500 watts. 3500/240 volts is 14.5 amps. No matter what circuit you connect it to, as long as it is 240 volts, it will only draw 14.5 amps.

Now if this cook top can do more than 3500 watts, as with multiple burners, then that is a different story.
 
  #3  
Old 04-02-14, 07:07 PM
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Well, the medium (not too long) story is: I started off with a 1800w cooktop, but it just would not get 30 litres of water to a boil. So, as I was contemplating how to get a work-around on that cooktop, the wife gave it away thinking I wasn't able to use it. So, I figured, "I might as well go for the most powerful, reasonably priced cooktop I can get", so that just so happens to be this 3500w single "burner" cooktop. I bought it online, while sitting at work, and noticed the 20amp 240volt service it needed. But, having installed a garage heater in a previous house (for which I was able to research and install the proper 240volt 20amp breaker and circuit, myself), I figured I could do this myself. Only when I got home, I realized that recent renovations to the house (with a lot of fancy electrician-installed electronic subsystems) had used up all the remaining spots on the power panel. So....while wife-authorized renovations warrant electrician fees, husband-initiated projects had better stay under the DIY budget line LOL. Instead of thinking about getting subpanels installed, I had better come up with a simpler and cheaper solution. The simple elegance of this plan is...the dryer has adequate voltage and amperage, would need to be unplugged from the circuit during brewing session and this brewing system could never be left plugged in after use, because I would have to unplug it, put it away and re-plug in the dryer before the wife realized that dryer-operation was any more difficult than a push-of-a-button...otherwise any 3 hour brewing session would be followed by 4 hours of "hearing about it"...LOL. So, I am not hoping to get any type of special functionality from the cooktop by plugging it in where the dryer was, I am simply trying to find a circuit that won't be overloaded by the appliance, and luck has it that the dryer is sitting right there with 240v and 30amps....and hey...Tolyn, thanks for the quick response, its wednesday here, and if all goes well....maybe I can contemplate a brew session by the weekend; all because of quick responses. Cheers, John
 
  #4  
Old 04-02-14, 07:28 PM
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Ah, it is all making sense now.

So, what you would need is a male cord plug that fits the dryer receptacle (30A 125/250V, 4 wire), a female cord receptacle that fits your cook top (20A 250V, 3 wire) and a length of SO cord. I suggest SO rather than SJ as it is extra hard usage.

The SO cord should be at least #12 wire as the cook top will not exceed 14.5 amps. However, if you ever think you might even go bigger, then get #10 cord. The cord will either be 12/3, or 10/3.

When you wire this up, you will color the white wire with black marker showing it is a hot wire. On the 4 wire Dryer plug you will not connect anything to the silver (neutral) screw. Otherwise green to ground, hot to hot, and other hot to other hot.

Note: I see you are in Canada so some of the terminology might be different. I know that your non metallic cable is called NM90 and 240 volt cables have black, red, and no white. I'm not sure if SO cord is the same or not. You will need to find that out in the store.
 
  #5  
Old 04-02-14, 07:32 PM
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I beg to differ. Yes, you can make an adapter or extension cord as described above to do what you stated but it is not considered safe. Electrical equipment is rated only for use on circuits of a certain maximum number of amperes. This maximum is documented somewhere such as on a name plate on the appliance, or is implied by the power plug. This cooktop is rated for 20 amps.

The cooktop will work correctly assuming it has no defects but if a defect should suddenly occur, say, as a result of parts biodegrading inside or its falling on the floor, there could be fault current or overheating that might cause a hazard but not trip a 30 amp breaker.

There is something else you could do. Make up a portable subpanel with a 20 amp (double) breaker protecting a 20 amp (240 volt) receptacle, the aforementioned components could be mounted on a piece of plywood. A cord with plug as described previously can be made up to connect this to the 30 amp receptacle..
 
  #6  
Old 04-02-14, 07:49 PM
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Wow, that's great. I have most of those supplies already (I was hoping it was going to be that easy, but wanted to be certain). Thanks a grand!

As a late response to Allan...I was wondering if a 30 amp circuit could give the appliance "enough rope to hang itself". Basically, I think you are suggesting an extension cord with an integrated 20 amp breaker in it? I was wondering if such a solution might get suggested. But, as a novice, I wasn't going to venture that idea without someone with more experience also suggesting it. I was afraid that my own novice creativity could creat some type of unreasonable danger. Thanks to you as well, Allan.
 
  #7  
Old 04-02-14, 08:05 PM
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Originally Posted by AllanJ
There is something else you could do. Make up a portable subpanel with a 20 amp (double) breaker protecting a 20 amp (240 volt) receptacle, the aforementioned components could be mounted on a piece of plywood. A cord with plug as described previously can be made up to connect this to the 30 amp receptacle..
Eh, you are working with water, and electricity.

I would suggest replacing the cook top plug with a 20 amp 240v GFCI power PLUG.
They make them for air conditioners, they're available for under $20 on ebay.

Then go with the 30 amp to 20 amp adapter cord.
 
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