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Old 09-12-2010, 07:49 PM   #1
lustrum
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Default Need 240v Wiring Confirmation

So I had been planning all along to use the 240v outlet at my dryer to power my electric setup. Two 5500w 240v elements controlled by a PWM. The PWM wants a 12vdc input so it can send a signal to the SSR.

Well... I pulled the 4-prong dryer outlet apart today and realize that it had 10/2 wire run to it, so there is only hot, hot and ground. Besides wondering what is going on with the fourth prong on my dryer, since it is obviously going nowhere, i now have no power source for my PWM circuit.

My question then is, do i have to run 10/3 so i can run this circuit (it is powered by a 115v walwart) or is there some mystical way of doing it with a 10/2 240v feed? Or possible alternative that doesn't cost $100 (10/3 = expensive).

Thanks



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Old 09-12-2010, 10:41 PM   #2
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We need more info on your setup. Looks like you need a neutral (fourth) wire for the 120v circuit. Do you plan on running both heating elements at 240V? If so, that 30A dryer outlet is not enough. Two 5500W elements at 240V = 45A. 10 ga wire is only good for 30A. I imagine the breaker feeding the outlet is also 30A based on the wire size.



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Old 09-12-2010, 11:33 PM   #3
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You are correct. The breaker is 30a and the outlet is a nema 14-30. I am only planning on energizing one element at a time, so I will not exceed 30a, according to my calculations.

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Old 09-13-2010, 12:35 AM   #4
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If I were to guess - Which I'm about to - Your dryer came with a 4-wire plug, and the house had a 3 wire outlet. So the last guy installed a 4-wire plug with only 3 wires. This works great, as long as there aren't any 120 volt components in the dryer feeding off of the neutral. IOW - Even if the dryer had a 4-wire plug, it's only using 3. (Obviously, since I'm assuming your dryer works )

As for your wall wart - Power it with a separate 120v circuit. The big 220v to drive your elements, and a 120v for the little stuff like pumps and electronics. It might suck to have to use 2 cords to power your rig, but it's a hell of a lot easier than re-wiring for proper 220v.

And you may already know this, but remember that you can't even run both elements at 25%. It's one element at a time period, due to how a PID controls duty cycle - Even if both are set for 10% power, they can both fire at 100% at the same time.
EDIT: Just re-read - You've only got one PWM = 1 element at a time

I'm feeling quick tonight...

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Old 09-13-2010, 04:03 AM   #5
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why don't you just get a euro 12VDC wall wart, and use your two hots with it to get your 12VDC? Should only be a couple bucks from one of the hong kong Internet sites like dealextreme.com - http://www.dealextreme.com/details.dx/sku.15989 - and as long as you don't need 120VAC for anything else, it ought to work.

If you do need 120VAC, there are other options, though I'm sure they're grossly against code (use the ground wire to the panel as a neutral - the neutrals and ground are tied together on the chassis of the panel, after all), and for the ground, run a fresh 10 gauge wire to a nearby copper water pipe and ground clamp, for example.) Like I said - probably grossly against code, and possibly unsafe (I don't see how it would be, but I'm not an electrician...) but it should work - even with a GFCI breaker.

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Old 09-13-2010, 12:54 PM   #6
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Quote:
Originally Posted by SweetSounds View Post
If I were to guess - Which I'm about to - Your dryer came with a 4-wire plug, and the house had a 3 wire outlet. So the last guy installed a 4-wire plug with only 3 wires. This works great, as long as there aren't any 120 volt components in the dryer feeding off of the neutral. IOW - Even if the dryer had a 4-wire plug, it's only using 3. (Obviously, since I'm assuming your dryer works )
Good guess. Probably the plumber who was not licensed in the first place to do the wiring. Either something is run off of 110v in the dryer or there is something else (the chassis?) that should be grounded that is not (for the time being). I think you are right that the easiest solution for my purposes would be to run another 110v line. Long term, I'll have to run 10/3 since that is code i guess.

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why don't you just get a euro 12VDC wall wart, and use your two hots with it to get your 12VDC?
I didn't think about this. Good idea! I might try this.

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Like I said - probably grossly against code, and possibly unsafe (I don't see how it would be, but I'm not an electrician...) but it should work - even with a GFCI breaker.
Yup. Definitely against code.


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