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Author Topic: 240VAC passing thru 120VAC outlets..  (Read 3953 times)
W9FIB
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Posts: 2502




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« Reply #15 on: February 28, 2019, 12:26:14 PM »

conduit is not recognized as a protection ground in a life-safety environment. corrosion and loose connections break it.

Reread the NEC code book. Or site the code that has changed. To my knowledge general electrical construction with EMT when properly installed and bonded is acceptable for ground. Also outlets in a basement unless specifically designed for certain types of special equipment are nothing special.

And btw, a green ground wire can corrode and/or loosen over time, or be physically damaged as well. Same is true for any wires in the circuits.
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73, Stan
Wisdom is knowledge you gain after you know it all.
K3GM
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Posts: 2549




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« Reply #16 on: March 01, 2019, 11:08:57 AM »

Update:  My local big box home store had 20A GFCI  outlets for $18.00, and a std 20A breaker for $4.50.  A GFCI/AFCI 20A breaker was nearly $50.00, so I went with the simple GFCI outlet and 20A breaker.  Thanks all for your inputs.  I'll begin pulling wire shortly.
« Last Edit: March 01, 2019, 11:12:04 AM by K3GM » Logged
N9TGR
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Posts: 10




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« Reply #17 on: March 03, 2019, 09:41:52 AM »

You are going the right way about it, use #12 thhn and a separate ground wire bonded to your 4x4 box ,there is a 10/24 screw hole in each box for the ground, Splice and pigtail a ground for each outlet . The 240v line will use the same ground wire ,, on my install I used a DP and single pole toggle switch to power down everything when I am finished operating, You could leave one duplex outlet unswitched along the chain if you want to leave your PC running. Switch the hot wires only and never the neutral.
Nice to see people doing it the right way.

Andy N9TGR
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KB2WIG
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Posts: 630




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« Reply #18 on: March 03, 2019, 10:10:49 AM »




You could reall walk tall if you ran #10 AWG in your 20 A ckt.

KLC
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W9FIB
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Posts: 2502




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« Reply #19 on: March 04, 2019, 02:56:50 AM »

You could reall walk tall if you ran #10 AWG in your 20 A ckt.
KLC

Waste of money and conduit fill space on such a short run. Its like using LDF50 hardline instead of RG-8 for a 10-15' run on HF.

Plus installing #10 AWG THHN on 20A devices is a pain in the rear. So why go through the aggravation for no gain?

Remember also in NEC code, #12 AWG is already down rated from actual physical ampicity.
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73, Stan
Wisdom is knowledge you gain after you know it all.
KB2WIG
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Posts: 630




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« Reply #20 on: March 05, 2019, 05:54:07 PM »


"  So why go through the aggravation for no gain?  "

Cause it builds character.... ..     Stan, you're probably right, but I've been know to do things the hard way.

From the photo, it looks like an easy job. One can use stranded THHN if it makes things easier. Just make sure whatever you decide will fit onto the terminal screws.

Jim Brown has a nifty website which deals with a lot of noise and RFI issues.This is where the idea of the 10 AWG replacing 12 AWG came from. (Although I did wire my wheel grinder in the garage with 10/2)

http://www.audiosystemsgroup.com/publish.htm

The following may be of interest.
http://www.audiosystemsgroup.com/GroundingAndAudio.pdf

http://www.audiosystemsgroup.com/InfoComm-Grounding2012.pdf

I'll go to places like the homely despot or lowleys for wire or boxes. For breakers, recepticles etc., go to a electrical supply house. You are less likely to be sold crap, although the prices are going to be higher, as the guy behind the counter knows you are not going to spend a few $K every mounth or so. Just don't ask for outlets, as the counter person will secretly hate you.

klc

If I had some LDF50 hardline, I'd be using it......
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W9FIB
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« Reply #21 on: March 05, 2019, 07:38:29 PM »


"  So why go through the aggravation for no gain?  "

Cause it builds character.... ..     Stan, you're probably right, but I've been know to do things the hard way.

From the photo, it looks like an easy job. One can use stranded THHN if it makes things easier. Just make sure whatever you decide will fit onto the terminal screws.

Jim Brown has a nifty website which deals with a lot of noise and RFI issues.This is where the idea of the 10 AWG replacing 12 AWG came from. (Although I did wire my wheel grinder in the garage with 10/2)

http://www.audiosystemsgroup.com/publish.htm

The following may be of interest.
http://www.audiosystemsgroup.com/GroundingAndAudio.pdf

http://www.audiosystemsgroup.com/InfoComm-Grounding2012.pdf

I'll go to places like the homely despot or lowleys for wire or boxes. For breakers, recepticles etc., go to a electrical supply house. You are less likely to be sold crap, although the prices are going to be higher, as the guy behind the counter knows you are not going to spend a few $K every mounth or so. Just don't ask for outlets, as the counter person will secretly hate you.

klc

If I had some LDF50 hardline, I'd be using it......

If I would apply that philosophy to my designs/installs...I would lose money with a low bid, or not get the contract as those who would do it right could bid lower if I wanted to actually make money. Both from a material cost and a labor cost.

But if your happy wasting time and money, go for it. NEC codes are to make things safe. Going beyond what is needed is up to you and your expense.

Just make sure that #10 wire is securely tucked under those tiny screws or it will fail inspection. And I have seen a lot of sloppy work get tagged.
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73, Stan
Wisdom is knowledge you gain after you know it all.
K3GM
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Posts: 2549




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« Reply #22 on: March 05, 2019, 08:53:33 PM »

For the record, I'm pulling #12 THHN wire.  The most power hungry thing in my shack is an HF amp which runs at 240V, 9A max.
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WB4SPT
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Posts: 777




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« Reply #23 on: March 10, 2019, 01:36:12 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.

IF you do run a bonding/grounding conductor, it must be attached to each box.   You can't run green or bare wire thru a box and not attach it, EVEN if you use EMT.  I always run a green conductor within EMT.  I don't trust the mickymouse conduit grounding provisions.   
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N8FVJ
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« Reply #24 on: March 16, 2019, 04:05:23 AM »

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.


Technically, you need grounding bushings at each conduit connector and having a ground wire to connect to each electrical box grounding bushings. Cheaper to run the ground wire.
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W9FIB
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Posts: 2502




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« Reply #25 on: March 16, 2019, 07:13:01 AM »

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.


Technically, you need grounding bushings at each conduit connector and having a ground wire to connect to each electrical box grounding bushings. Cheaper to run the ground wire.

No you don't. And its not cheaper because in a branch circuit, the EMT fitting nuts bond the conduit to the box. Bonding bushings are required only if the EMT is interrupted by a non conducting material and a green wire run to compensate. And with todays copper prices, adding unneeded wire only adds to the expense with no real purpose other than to look good for those who do not know or understand the NEC code requirements.

Service entrance metal conduit needs to be bonded with bonding bushings. But that's a whole different set of rules than branch circuits.
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73, Stan
Wisdom is knowledge you gain after you know it all.
KD6VXI
Member

Posts: 177




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« Reply #26 on: March 22, 2019, 08:50:55 PM »

conduit is not recognized as a protection ground in a life-safety environment. corrosion and loose connections break it.

Reread the NEC code book. Or site the code that has changed. To my knowledge general electrical construction with EMT when properly installed and bonded is acceptable for ground. Also outlets in a basement unless specifically designed for certain types of special equipment are nothing special.

And btw, a green ground wire can corrode and/or loosen over time, or be physically damaged as well. Same is true for any wires in the circuits.

In California, you are NOT allowed to use the 'sheath' as ground, except in cases EXPLICITLY allowed.  Like MCH style cable.  That is isolated ground mc cable.

He's right, you are wrong.  At least in California. 

No, I'm not going to go to the truck and get my code book out to cite the code.  You're more than welcome to Google it.  I inky have to prove an I spector wrong, and then they have the AHJ clause to fall back on, 'as interpreted'.


THAT BEING SAID!  Yes, years ago it WAS within code to use the pipe / sheath as ground.  Problem was, oxidation.  Doesn't take much oxidation to have a voltage potential in a fault condition.  Doesn't take many volts to kill you, either.



As to the question of grounding conductors being shared.  This is done all the time.  Code states that you must use wire with an insulation breakdown greater than the highest voltage in the pipe.  You also must use a grounding conductor bug enough to carry the fault current of the largest conductor in the system.  IE, if you have a 240 / 30A plug, you must use a ground wire big enough for the 30A plug, even if you have 3 other 15A circuits in the pipe.

In my jurisdictions, we also MUST ground tail each metal box.  This means a seperate ground wire from the small screw hole in the back of the box tied in to the ground system.  This is SPECIFICALLY because we aren't allowed to use the emt / sheath as ground. Then a ground wire also to each plugs ground screw tied in with the same wires.  As you can see, ground is a big deal.

If you use stranded wire in the pipe you may not use that to each plug.  The connection to the plugs should be in hard drawn copper.  Some jurisdictions also require each plug to have pigtails for each conductor as well.  That provides a point of disconnect so you can work on a single plug without taking the whole system down.

Since your residential, that means you must have 120 volt wire.  We have split phase 120 to make 240 here in residential USA.  In commercial (and I guess limited residences, I have 3 phase in my garage and some places like Arizona also have 3 phase for AC units) you can have 120/208 circuits.

Almost all wire sold in spools is either THHN/THHN-2 or THWN/THWN-2.  In Los Angeles, I have to use the THWN-2 rated wire.

Otherwise, you look good.  I'd use a seperate gfi on each plug.  Then use an AFCI breaker in the panel.  This will help with nuisance trips.  If you plan on high power, go with the AFCI breakers that have the yellow button.  They are RF hardened.

You can use turns through ferrite to quench RF getting into the AFCI as well.  I would NOT recommend using disc caps, as those can break your gfci protection.  And as they age, they can and do cause leakage current that again will nuisance trip the gfi system.

Hope this helps / clarifies.

--Shane
KD6VXI


information given based on 2017 NEC / CEC. 
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KD6VXI
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Posts: 177




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« Reply #27 on: March 22, 2019, 08:52:28 PM »

On bonding bushings, you also must use them on a concentric knockout.  That way the pipe is still at ground potential if the concentric breaks free.

Again, it's the whole not being able to use the pipe / sheath as a ground thing.  The code is pretty freaking clear about it.

--Shane
KD6VXI
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W9FIB
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Posts: 2502




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« Reply #28 on: March 23, 2019, 01:57:53 AM »

information given based on 2017 NEC / CEC. 

We are not talking MC cable sheath here. But rather rigid EMT conduit. A whole different class of electrical construction.

Citation please.

I do not find this information being applicable to EMT in my copy of the NEC. With that said, local areas can go beyond the national standard. So a citation of where you got this information would be helpful to teach others new things that have been recently changed by the NFPA.
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73, Stan
Wisdom is knowledge you gain after you know it all.
W9FIB
Member

Posts: 2502




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« Reply #29 on: March 23, 2019, 02:39:53 AM »

On bonding bushings, you also must use them on a concentric knockout.  That way the pipe is still at ground potential if the concentric breaks free.

Again, it's the whole not being able to use the pipe / sheath as a ground thing.  The code is pretty freaking clear about it.

--Shane
KD6VXI

Correct. Which is why areas that commonly use concentric knockouts are most common around service entry equipment and do fall under different construction methods. I even mentioned that earlier. The reason being that the cable size coming into the service entrance equipment can vary in size based on the service rating. So it stands to reason that the entrance piping can vary in size to accommodate the various size service entrance conductors. Flexibility at the expensive service entry equipment is vital.

Another reason for various service entry pipe sizes has to do with the bending radius of the conductors. Using too small a pipe could mean using LBs, elbows, etc. that provide too small of a bending radius for the conductor and must be upsized to accommodate a proper radius. So again flexibility at the expensive service entry equipment is vital.

However, I rarely see outlet boxes have this type of knockout anymore. They come with standard sized holes for direct mounting of EMT fittings. Therefore there are no rings to break so the bond does not break. And if more room is needed, the conduit is upsized and the proper sized boxes are then used that accommodate the correctly sized conduit.

However, you would be correct if you did use such a type of box in place of standard hole size knockout boxes. I avoid them. That way I do not have an added expense by using materials not specifically suited for the job at hand, or extra materials and labor to compensate for using the wrong boxes for common outlets.
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73, Stan
Wisdom is knowledge you gain after you know it all.
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