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Old 01-10-2008, 05:43 PM   #1
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30 amp question


Hi, I recently replaced our single wall oven for a new double unit. I pulled new 8g wire and installed a new 40 amp breaker for it. Now my question begins... I have the old 10g wire pulled back into my wood working shop. I was wondering what my options are for using this to power some of my larger machinery. Is there any way for this 10/3 wire to provide power to a series of outlets for my larger tools? The only option I can think of is not use red wire and replace breaker with a 20 amp then im fine to run regular 20 amp receptacles. any other options? thanks alot hope that was clear. douglas

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Old 01-10-2008, 06:04 PM   #2
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What "larger" tools do you want to run and what are their voltage and amperage requirements?

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Old 01-10-2008, 06:20 PM   #3
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Run it into a large enough recep box and branch off with 2-20 amp circuits. No reason to cap the red.
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Old 01-10-2008, 07:14 PM   #4
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You can do two things with that cable.
1. Install a small sub panel and leave it on the double 30 amp breaker. Install 15 or 20 breakers in the sub panel.
2. Change the double 30 to a double 20amp and use the circuit as a multiwire. It will provide two 20 amp circuits with a common neutral.
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Old 01-11-2008, 08:30 AM   #5
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Thanks guys! I think it sounds like Switiching to a double 20 amp breaker then having multiple recepticles run from that sounds like a plan. I will be running a grinder,dust collector buffing motor, vibratory magnetic and tumbler finishers, ultrasonic finisher and steam cleaner. Any other spisifics I should take into account. thanks again erik
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Old 01-11-2008, 11:43 AM   #6
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Doug

Sounds like you are chosing Joeds 2nd choice. Since you have the 10/3 put in a junction box and split the circuit into two 20 amp branch circuits. You will have a double pole 20 amp breaker in the main panel as joe stated. It will look like this only you don't necessarily need to gfci protect the split circuit as shown. You can add more receptacles than shown of course.
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30 amp question-split-multiwire-2.jpg  

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Old 01-11-2008, 02:45 PM   #7
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Doug

Sounds like you are chosing Joeds 2nd choice. Since you have the 10/3 put in a junction box and split the circuit into two 20 amp branch circuits. You will have a double pole 20 amp breaker in the main panel as joe stated. It will look like this only you don't necessarily need to gfci protect the split circuit as shown. You can add more receptacles than shown of course.
I thought I heard from somewhere that GFCI or AFCI receptacles could not be used on multiwire circuits
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Old 01-11-2008, 03:11 PM   #8
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I thought I heard from somewhere that GFCI or AFCI receptacles could not be used on multiwire circuits
The GFCIs are used downstream from the mulitwire portion of the circuit. It's fine in this case.
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Old 01-11-2008, 03:26 PM   #9
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These are the other 2 ways gfci's are most commonly used on multiwires......
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Old 01-11-2008, 04:11 PM   #10
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WoW. thanks for all the help the diagrams really help. My only question is what does the box with "load line" represent? thanks erik
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Old 01-11-2008, 04:32 PM   #11
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WoW. thanks for all the help the diagrams really help. My only question is what does the box with "load line" represent? thanks erik
That represents the gfci receptacle. Any rececptacles downstream of the gfci outlet that you want protected will be connected to the load terminals. Line side is connected to the power source.

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Old 01-11-2008, 04:43 PM   #12
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Any rececptacles downstream of the gfci outlet that you want protected will be connected to the load terminals. Line side is connected to the power source.
There are no recepticles down stream of the gfics in the wiring diagram.
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Old 01-11-2008, 04:45 PM   #13
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There are no recepticles down stream of the gfics in the wiring diagram.
I think he was asking about the first diagram.
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Old 01-11-2008, 04:45 PM   #14
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Also note that the last receptacle will be fed with 2 wire with ground cable instead of 3 wire with ground as the other leg of the multiwire is not needed and will not be carried to the last device.

As Jerry said a gfci has line and load connections. If you want downstream receptacles to also have gfci protection you will connect the cable going to them to the load terminals of the gfci. If you just want the single gfci to protect itself and not the downstream receptacles then only line connections should be made.

BIG Mike.... there actually is no upstream or downstream it is just a figure of speech in electrical terms. In geographical terms traveling towards the source is always upstream... traveling away from it is downstream.


Last edited by Stubbie; 01-11-2008 at 04:53 PM.
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