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Old 11-30-2012, 10:43 PM   #1
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Default Supplying power -- 3-prong range outlet?

So, I've been doing a lot of research and figuring out what all I need to buy to get started on my Kal/theelectricbrewery.com clone. I am at the point of figuring out how to supply power to the rig.

The issue is, my only 240V outlet is an old 3-prong, 50amp Range outlet which is usually plugged into my stove/oven. The way I understand it, the 3 lines in that receptacle are hot/hot/neutral, no separate ground. I am renting, so it's really not an option to route new outlets, new breakers in the main panel, etc.

So the actual questions here:

1) Is GFCI protection even an option from this outlet? I was planning (if it is possible/safe) to buy a spa panel and hook it up between the outlet and my control panel.

2) How do I deal with the no-ground issue? Could I run a 3+ground wire from my control panel, to the spa panel, then to the 3-prong receptacle? Would it be safe, useful, and/or "legit" to connect the ground and neutral at the range plug (and only there)?

3) I really don't have any desire to run back to back batches or both elements at the same time, would it be ok to run a 10gauge/30amp feed from the wall and have a 30 amp slow-blow fuse (or fast acting?) wired up at my power input in the control panel? I'm going to be somewhat far from the outlet, so would love to not have to buy a massive amount of 6ga wire..

Thanks in advance for your help. And thanks to the community for the massive amount of information already out there!

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Old 11-30-2012, 11:10 PM   #2
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If you cannot run a ground wire (or rewire completely with 4 wires), your best bet is to get the spa panel GFCI, and you can wire it to make it functional as a GFCI with 4 wires out to your control panel. What you CANNOT do safely, is use one of the hot legs and the neutral for 120V power in the control panel, so you should make your control panel 240V only. You would have to draw 120V from a separate circuit, and that would need its own GFCI.

Some people bring a 120V feed from a separate circuit into the control panel as well as the 240V. That is feasible, but always bear in mind that you need to disconnect two power inputs to completely de-energize the panel.

Good luck with it.

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Old 12-01-2012, 12:03 AM   #3
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Thanks for the input! Good to know that I am at least not dead in the water. Running a separate 120V circuit could be doable, I suppose. I have a GFCI'd 120V plug just next to the stove anyway, it's just another extension cord and adding extra terminal blocks for the 120V circuit, i suppose.

Just for my curiosity's sake though, what is unsafe about using the hot and neutral for 120V? From some more reading I've been doing, the impression I get is that the developed ground is legitimate, or just as much so as the pre-1995 3-pronged outlet is?

Also, I'm still a bit stumped on the best way to deal with the 50amp 240V supply and 30amp cable/control panel. Would it be OK to run 10gauge wire for everything and just have a 30amp fuse on the 240v circuit?

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Old 12-01-2012, 01:25 AM   #4
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Originally Posted by jeffmeh View Post
If you cannot run a ground wire (or rewire completely with 4 wires), your best bet is to get the spa panel GFCI, and you can wire it to make it functional as a GFCI with 4 wires out to your control panel. What you CANNOT do safely, is use one of the hot legs and the neutral for 120V power in the control panel, so you should make your control panel 240V only. You would have to draw 120V from a separate circuit, and that would need its own GFCI.


Good luck with it.
I dont believe this is correct. PJ has been showing that you can bring 4 wires into your control panel and still be able to use 120v pumps. Im not the expert but i suggest we try to find the real answer to this.
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Old 12-01-2012, 01:33 AM   #5
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Yeah, it's no problem, and a damn good idea to put in the GFCI spa panel, and there is no problem I know of drawing 120V from hot to neutral. That's the whole point of having the neutral...to have 120/240V. If there was no intent to derive 120V there would be two hots and ground instead of two hots and neutral.

That said, the part about three wires into the spa panel and four wires out has me in a bit of a concern. Not that I think it's any less safe, but currently I'm of the opinion that it's not within Code to "make" ground out of neutral in this case. It's false advertising if you will.

Anyone with a code reference to justify that I'd appreciate the reference to examine it and admit wrong if that's the case.

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Old 12-01-2012, 01:38 AM   #6
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Also, I'm still a bit stumped on the best way to deal with the 50amp 240V supply and 30amp cable/control panel. Would it be OK to run 10gauge wire for everything and just have a 30amp fuse on the 240v circuit?
That's a good question. Certainly I plug things into 15A or 20A circuits that don't have 14ga or 12ga power cords. Whether or not that changes with what might be considered a dedicated circuit I don't know. Probably another one of those Code deals that is why there are Master electricians.
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Old 12-01-2012, 02:43 AM   #7
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What you CANNOT do safely, is use one of the hot legs and the neutral for 120V power in the control panel, so you should make your control panel 240V only. You would have to draw 120V from a separate circuit, and that would need its own GFCI.
This is incorrect - you can safely us a hot leg and the neutral for 120V. How do you think your stove is powering its 120V oven light?

The ONLY difference between 3 wire & 4 wire is with 4 wire, a separate gound is run from the panel (the 4th wire). If you were to chase the wires all the way back to the main incoming panel you would find that both are tied together by the sheet metal of the box. With 3 wire, the white wire or shield serves as both neutral and ground.
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Old 12-01-2012, 02:57 AM   #8
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If you want your GFCI to work, your pot (and other exposed metal) cannot be connected to the neutral wire. It must be connected to a earth safety ground.

A GFCI won't detect a short in your pot if the pot is grounded to the neutral.

But, if you don't have a safety ground (green wire), you still need to tie the neutral to any exposed metal, like your pot. At least you have a chance that if there is a dead short in your pot the breaker might trip in your pot; but, it might not. If it doesn't, you'll be the first to know about it.

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Old 12-01-2012, 03:02 AM   #9
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This is incorrect - you can safely us a hot leg and the neutral for 120V. How do you think your stove is powering its 120V oven light?

The ONLY difference between 3 wire & 4 wire is with 4 wire, a separate gound is run from the panel (the 4th wire). If you were to chase the wires all the way back to the main incoming panel you would find that both are tied together by the sheet metal of the box. With 3 wire, the white wire or shield serves as both neutral and ground.
The neutral goes through the GFCI, the ground does not. This is VERY important to understand if you expect the GFCI to work.
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Old 12-01-2012, 03:12 AM   #10
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The neutral goes through the GFCI, the ground does not. This is VERY important to understand if you expect the GFCI to work.
I understand but the discussion was about a 3 wire range circuit & it's ground, not a GFI protected ground. The statement was made that you can't safely use neutral and one of the hot legs of a 3 wire range circuit for 120V and this is not true.
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