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Author Topic: 240VAC passing thru 120VAC outlets..  (Read 4281 times)
K3GM
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Posts: 2556




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« on: February 25, 2019, 01:11:04 PM »

I'm wiring my shack in a home we moved into recently.  I've got ten surface mounted duplex outlets in a line along a concrete basement wall.  #1 is closest to the panel and #10 is farthest away from the panel.  I'm using 1/2" EMT, outlets are spaced about 16" apart.

Question: If outlet #8 is designated for 240VAC, and both voltages are in the same conduit, can I pass the 240V THHN wires behind each outlet until I get to outlet #8?
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W9FIB
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« Reply #1 on: February 26, 2019, 02:41:19 AM »

Sure with 2 comments...

All wire must be rated at 300V. Most THHN in the big box stores is rated at 600V.

And as long as the conduit does not have too many wires in it. There is a maximum fill allowed by NEC. Here is a link to a handy fill chart:

http://www.elliottelectric.com/StaticPages/ElectricalReferences/ElectricalTables/Conduit_Fill_Table.aspx
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73, Stan
Wisdom is knowledge you gain after you know it all.
K3GM
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« Reply #2 on: February 26, 2019, 08:00:08 AM »

Thanks, Stan.  I am under the max. allowable conductors in the EMT.  Ok, here's another question:  I am assuming (perhaps in correctly) that I can share the same 12awg, green ground wire in both the 120 and 240 outlets provided the wire guage meets the  current requirements?
« Last Edit: February 26, 2019, 08:02:13 AM by K3GM » Logged
KX4QP
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« Reply #3 on: February 26, 2019, 08:18:04 AM »

Thanks, Stan.  I am under the max. allowable conductors in the EMT.  Ok, here's another question:  I am assuming (perhaps in correctly) that I can share the same 12awg, green ground wire in both the 120 and 240 outlets provided the wire guage meets the  current requirements?


Code requirements aside, I'd be cautious doing this -- at the least, I'd check that the ground those are connected to is actually a good ground with low resistance.  If you should get a crossover on the 240V, and have a high resistance in the ground (bad connection at the stake, dry clay around the stake, etc.), you'd wind up with 240V on the chassis of everything grounded to any of the 120V outlets.  Use of GFCI on all the outlets would help here, in that a ground crossover would be instantly cut off at the outlet with the problem.
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K3GM
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« Reply #4 on: February 26, 2019, 11:01:06 AM »

I can run a separate ground wire for the 240VAC outlet, but both grounds would be essentially connected back at the panel.  While not wired yet, the plan is to use either a GFCI breaker (this is a new dedicated circuit) or a GFCI outlet at the beginning of the chain of plugs.
Here's a shot of the work.
« Last Edit: February 26, 2019, 11:06:28 AM by K3GM » Logged
AA4PB
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« Reply #5 on: February 26, 2019, 12:06:42 PM »

Most of the outlets I've seen have the green ground screw tied to the metal mounting tabs. When you mount them in a metal box, the box gets connected to the grounding conductor. Since you are using metal conduit, all the boxes are electrically connected via the conduit. That means that even if you use separate grounding conductors for 120V and 240V outlets, both types of outlets have their grounds tied together via the conduit anyway. I don't see any issue with using a single grounding conductor.

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Bob  AA4PB
Garrisonville, VA
KX4QP
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Posts: 404




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« Reply #6 on: February 26, 2019, 01:45:19 PM »

I can run a separate ground wire for the 240VAC outlet, but both grounds would be essentially connected back at the panel.  While not wired yet, the plan is to use either a GFCI breaker (this is a new dedicated circuit) or a GFCI outlet at the beginning of the chain of plugs.

The GFCI outlets I've seen protect only loads connected on their own sockets; to protect the whole string you'd need either all the outlets to have GFCI or you'd need a GFCI breaker.
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KB2WIG
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« Reply #7 on: February 26, 2019, 03:08:51 PM »



You can use a GFI breaker, or one GFI receptacle. The GFI receptacle will protect receptacles 'past' it on the same ckt, if you wire it correctly.

Check this out.

https://www.do-it-yourself-help.com/gfci-outlet-wiring-diagrams.html


Be careful accepting information online; how do you know I'm not a wazoo when I tell you things?

Check this out,

https://www.mikeholt.com/instructor2/img/product/pdf/1292432628sample.pdf


klc
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EXTRALight  1/3 less WPM than a Real EXTRA
W9FIB
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Posts: 2531




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« Reply #8 on: February 26, 2019, 07:41:47 PM »

Most of the outlets I've seen have the green ground screw tied to the metal mounting tabs. When you mount them in a metal box, the box gets connected to the grounding conductor. Since you are using metal conduit, all the boxes are electrically connected via the conduit. That means that even if you use separate grounding conductors for 120V and 240V outlets, both types of outlets have their grounds tied together via the conduit anyway. I don't see any issue with using a single grounding conductor.

AA4PB is correct. The EMT bonds the boxes together for the ground provided that it is EMT properly installed from the breaker panel to the last box on the end. Green grounding wires with the green screw are used to tie the ground terminal on the device to the box itself. The cover holding the device being attached with screws to the box is not considered a proper ground per NEC requirements. The big box stores sell these ground wires in a package. Low cost and time saving compared to making your own and buying the green screws.

Per recent code revisions, Arc Fault Circuit Interrupters (AFCI) may be required for most new wiring installations. You would need to verify this with your local building inspector for this application. In my jurisdiction as of 2015 it was not required for my new office/shack at that time. However other parts of my house were required to have them in 2015. But this requirement has been changing with each new NEC code book update. It is worth a phone call. Otherwise GFCI is a good item to use. Info here for those who want to know more: https://www.ecmweb.com/content/arc-fault-detection-your-questions-answered

BTW Nice looking install based on your pic.
« Last Edit: February 26, 2019, 07:45:30 PM by W9FIB » Logged

73, Stan
Wisdom is knowledge you gain after you know it all.
K3GM
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Posts: 2556




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« Reply #9 on: February 26, 2019, 08:12:32 PM »

Good info.  Thanks, Stan and everyone.
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KX4QP
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Posts: 404




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« Reply #10 on: February 27, 2019, 08:37:58 AM »

From what I read in the provided link, an AFCI doesn't replace a GFCI -- you really need both for safety.  GFCI protects against hot wire contact (shuts off if as much as 10 mA flows outside the protected load circuit), while an AFCI protects against an entirely different kind of fault at much higher characteristic currents.  Then there's the PFCI, which seemingly can only be installed in the receptacle -- but it looks complicated to get AFCI, GFCI, and PFCI protections all on the same receptacle.  You seemingly have to choose which two you'll install (either AFCI or GFCI at the box, and either GFCI or PFCI at the outlet).

This looks like it's heading toward another case of codes wanting to make us so safe we can't do anything.  If code requires all of AFCI, GFCI, and PFCI, there'll be no place you can plug anything in (at least until they start selling receptacles, likely for $100 each, that combine the functions of GFCI and PFCI).
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K6JH
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Posts: 526




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« Reply #11 on: February 27, 2019, 03:35:06 PM »

PFCI? I can't seem to find that one. Can you clue me in?
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73
Jim K6JH
W9FIB
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« Reply #12 on: February 27, 2019, 04:04:27 PM »

PFCI? I can't seem to find that one. Can you clue me in?
Power Fault Circuit Interruper
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73, Stan
Wisdom is knowledge you gain after you know it all.
K6JH
Member

Posts: 526




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« Reply #13 on: February 27, 2019, 04:52:49 PM »

PFCI? I can't seem to find that one. Can you clue me in?
Power Fault Circuit Interruper

Oh, so they are basically looking at the voltage drop to find high resistance in the wiring. Doesn't look like they are generally available yet, or required.

They're gonna take all the fun out of playing with electricity... ;-)
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73
Jim K6JH
KD0REQ
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« Reply #14 on: February 28, 2019, 12:06:54 PM »

conduit is not recognized as a protection ground in a life-safety environment. corrosion and loose connections break it. as a personal note, you can always exceed the code requirements. what I'd do is pass a over-rated ground wire and use that for all the protection grounds. thus, no ground loops, no differential currents.

the AFCI also has GFI capabilities, and that's now the NEC code standard for all liveable spaces, so don't chain them. you'll have false trips till Hell freezes over.
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