Need some help please w/ elec cord & digital multimeter (long post, Sorry!)

[Mike Manning]

Disclaimer:
It will be quickly evident that I know nothing about electrical wiring. For that reason, I've never attempted to add outlets or lighting to my own home. I thought this little project might be different. With that, off we go...

Background:
My shop is our third car garage. I have one 115V outlet and one 230V outlet (which doesn't get used). Woodworking machines which I use with some regularity are Delta 14" band saw, Delta floor drill press, Delta 6" jointer, Delta 10" contractor's table saw, 10" Unisaw, Craftsman grinder, Makita angle grinder, California Air Tools air compressor and a Dewalt DW735 planer. I use a vacuum and occasionally extra lighting. I use the supplied outlet in the shop for this. I am generally only using one machine at a time and most of the time there isn't anything beyond the radio using that 115V outlet. All my machines are mobile and get wheeled out when needed and put back in place when finished.

The project:
It gets tiring constantly moving my extension cord from one end of the shop to the other or out in the driveway depending upon what tool I'm using. I saw this "Extension cord from hell" and thought that could be useful in my shop. I took a 12G 50' extension cord and cut the plug off at 10'. I put together these three metal boxes (don't know the official name) with four outlets facing up on each box. That initial length at 10', 9' to the next box, last section at 10' and then the female end of the original extension cord. Each box has an upstream cable and a downstream cable on either end of the box. The two double electrical outlets are wired with appx 6" 12G wire as follows:
- white jumper wire connected via silver screws from double plug "A" to double plug "B",
- black jumper wire connected via gold screws from double plug "A" to double plug "B",
- upstream cable white wire connected to nearest double plug "A" and silver screw,
- upstream cable black wire connected to double plug "A" and gold screw,
- downstream cable white wire connected to double plug "B" and silver screw,
- downstream cable black wire connected to double plug "B" and gold screw,
- upstream cable green connected to green ground screw on double plug "A" along with one end of green jumper,
- downstream cable green wire connected to green ground screw on double plug "B" along with other end of green jumper

Why I need help:
I suspect that ought to be about as clear as mud if you're still reading. I've finished two of the three 4-way outlets. As I get close to finishing I'm thinking about testing it prior to plugging it in. I didn't read the entire article to make this "extension cord from hell" because if I had I would have seen that it really skimps at the point of telling you how to test the connections using a digital multimeter. I have an older Sperry CM-350A (see pic). I've never used it. I really need help to test the connections before I plug it in. I've read the manual and that was less helpful than reading the project article. The guys basically says "check for shorts between the conductors on the cable. Neutral to ground, neutral to hot, and hot to ground. If you find any shorts fix and recheck." He then says "Check that the metal boxes are connected ONLY to the ground conductor! YOUR SAFETY DEPENDS ON THIS CHECK!" Sounds like he should have mentioned this first but what do I know. So at this point I don't know how to do any of these checks with my Sperry digital multimeter and I'm hoping someone can help me to do that.

If anyone made it this far all I can say is thank you. I appreciate any help anyone can provide. I'll be happy to provide any pics or answer any questions.

Thanks!
Mike
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[Marc Jeske]

Mike - this is wayyy simpler than you think.

First off, put away your meter.

ALL Ground wires in any box need to come to a common point in a correctly sized wirenut.

NOT jumping daisy chain style as you have it.

Also, from that wirenut, you run w a "pigtail" to each of your receptacle ground terminals, AND a pigtail to a screw on back of box in the 10/24 threaded hole.

So in the box you show you have 2 wires from the two cables, and three pigtails.. total of 5 conductors in the wirenut.

So now the Grounding is done.

On the hots and neutrals, I recommend doing them in the same manner.

You CAN daisy chain those, but a overall better job is done as I have explained the ground.

Also, the style of cover you have chosen is not the best choice because the receptacle is only supported by one single screw, definately not the best especially for frequent plug in plug out uses.

Sending PM, glad to help.

Marc

[Mike Manning]

Mike - this is wayyy simpler than you think.

First off, put away your meter.

ALL Ground wires in any box need to come to a common point in a correctly sized wirenut.

NOT jumping daisy chain style as you have it.

Also, from that wirenut, you run w a "pigtail" to each of your receptacle ground terminals, AND a pigtail to a screw on back of box in the 10/24 threaded hole.

So in the box you show you have 2 wires from the two cables, and three pigtails.. total of 5 conductors in the wirenut.

So now the Grounding is done.

On the hots and neutrals, I recommend doing them in the same manner.

You CAN daisy chain those, but a overall better job is done as I have explained the ground.

Also, the style of cover you have chosen is not the best choice because the receptacle is only supported by one single screw, definately not the best especially for frequent plug in plug out uses.

Sending PM, glad to help.

Marc

Marc,
I appreciate the reply. Basically, it sounds like you're trying to simplify this for me and beyond that I don't read or speak Russian. Or maybe that was electric you were speaking. :-)

I'm not following you on the comment about the style of cover...there are two screws on opposite corners.

Mike

[Jim Becker]

Marc is correct regarding the grounding and the covers.

Firstly, you don't have the boxes grounded at all...it's required with metal boxes. So there needs to be a connection added from the grounds that connect the outlets back to the box, itself and it is a very important safety issue that needs to be fixed. That's normally done by bringing all the grounds that enter the box together and then connecting individual wires to each outlet as well as to the box. (those individual wires are generally called "pigtails") Wire nuts are usually used for the connection where all those ground wires are twisted together. In this case, you'd need a wire nut sized appropriately to handle five pieces of wire of the gage you have for your setup. The connections for the hot and neutral are also daisy-chained and well...not really how I would do that, either.

As to his comment about the box and cover type, there's nothing that supports the outlets other than the single screw in the middle of the outlet that passed through the front of the cover. While not "horrible", that single screw is taking the entire load each time you plug and unplug something from the outlet. In normal wall boxes, the outlet is supported at the two ends by screws that physically attach it to the box and the center screw merely holds a simple cover in front of the outlet. There's no stress at all applied to that single screw.

Lastly, I'd like to mention that although I don't know the details of the NEC, etc., to any large degree, I've never seen outlets wired with the crimp-on connectors like that for side-wiring. I'm not sure if it's legal or not. I suspect you did this because cord-stock like you used is very often stranded wire. I'm sure the "resident sparkies" can help out with this concern I have.

[Malcolm McLeod]

... because the receptacle is only supported by one single screw...


... there's nothing that supports the outlets other than the single screw in the middle of the outlet that passed through the front of the cover. ...

I can't say I've used these particular boxes & covers, but it sure looks like in Mike's 2nd pic, the receptacle has 2 screws thru the cover and into the receptacle...?? If so, this should be mechanically bulletproof.

Marc, I think this is what you are trying to describe - - (sorry about the crudity; it's best I can do w/ MS Paint on short notice.) Red 'hats' are wire nuts, the light blue 'wires' represent your white neutrals.
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One thing to note, this may distribute your connections all around the shop, but it will still only give you 15 or 20 AMPS total - cuz' that's probably what the wall plug's CB is rated. No clue about related code (so hide it when the building / home inspectors are creeping about!)

Adder: You can make the pigtails out of 14ga wire, which will be a little easier to handle. But even so, with 5 wires (2@12ga, 3@14ga) these will need to be some *honkin'* wire nuts! (*Sorry, lapsed into electric-speak again...?;))

[Marc Jeske]

My kneejerk comment on the cover was based on the "Old" style covers w the single center screw, I did not notice OP had the new style that has bolt/nut for the device straps.

Mike and I have talked and he's on track now re pigtailing for grounding.

I advised removal of the stakons due to fact he has upgrade side wired outlets w integral clamps.

He will still use Stakons on the ground pigtails to box and to individual outlets, rather than struggle w stranded hooked around screwhead.

We also discussed importance of GFCI protection.



Marc

[Mike Manning]

Marc,
Thanks for talking me through all the electric stuff involved with my extension cord from hell and my shop's potential issue with GFCI. I'll hopefully get it redone tomorrow and get back to you.

Jim, Malcolm,
Thanks for your input as well. With Malcolm's diagram I see what i think Jim was referring to when he said he didn't particularly like that I was still daisy chaining. I see and think I understand what you're suggesting. Given that my expert, thank you Marc!, didn't mention it I'm going to stick with his advice for now. And Malcolm I do understand this doesn't increase the electricity to my shop. It does allow me to stop moving the extension cord and unplugging and re-plugging machines in though.

Mike

[Marc Jeske]

Mike has good quality "spec grade" receptacles w nice wire clamping, so to simplify it I told him to go that route rather than pigtailing everything.

He will not be using stakon terms on his Hots or neutrals, only on the dead end ground pigtails.

Marc

[Jim Becker]

I can't say I've used these particular boxes & covers, but it sure looks like in Mike's 2nd pic, the receptacle has 2 screws thru the cover and into the receptacle...?? If so, this should be mechanically bulletproof.

Yes, I looked again carefully and you are correct. My bad for not looking closely enough previously.

And your diagram is what I also feebly described in words. Good!

--

Marc, thanks for talking him through things!

[Marc Jeske]

Malcolm's and Jim's posts are both 100% correct.

Although "daisy chain" can be acceptable IF all done correctly, Malcolm's drawing is the best method.

Grounding conductors are never daisy chained, but always tied at a common point and bonded to the enclosure.

Marc

[Dave Chatham]

One thing, get in the habit from the start of un- plugging this homemade "wiring system" every time you are done in the shop. Lots of connections that will get knocked around a lot. Nothing will ruin your day more than a shop fire.

[Matt Marsh]

Just a little Nit here. We can get by with these types of assemblies at home, but technically speaking the use of these types of boxes, raised covers, and Romex connectors for this cordset violates their listings. These devices are not listed for use as portable equipment. Any place where OSHA has jurisdiction, the owner would be subject to a fine.

[Mike Manning]

Just a little Nit here. We can get by with these types of assemblies at home, but technically speaking the use of these types of boxes, raised covers, and Romex connectors for this cordset violates their listings. These devices are not listed for use as portable equipment. Any place where OSHA has jurisdiction, the owner would be subject to a fine.

What is Romex connectors? I thought Romex is the cable used to wire homes. Just so you know, the extension cord I'm using is a brand new 12ga extension cord made in the USA by Anderson Industries for Costco.

[Malcolm McLeod]

What is Romex connectors? ...

I think he's referring to the cable clamps. I can't tell from the pic if they are specifically for Romex, but they are probably not approved for this 'portable' usage - by manufacturer/UL/NEC, etc.. You would need a strain relief designed (and rated) for SO-cord, I believe. Or, stash it if/when the inspector is inspecting.

[Mike Manning]

I think he's referring to the cable clamps. I can't tell from the pic if they are specifically for Romex, but they are probably not approved for this 'portable' usage - by manufacturer/UL/NEC, etc.. You would need a strain relief designed (and rated) for SO-cord, I believe. Or, stash it if/when the inspector is inspecting.

So what kind of cable clamps should I have used exactly? I wasn't really happy with these but it was pretty much all I saw (or very similar) at those big box stores. If there's something better I'd like to use that.

[Malcolm McLeod]

So what kind of cable clamps should I have used exactly? I wasn't really happy with these but it was pretty much all I saw (or very similar) at those big box stores. If there's something better I'd like to use that.


This is simple style (https://www.homedepot.com/p/1-2-in-Strain-Relief-Cord-Connectors-2-Pack-21692/100207234) (not sure if it will fit your specific cord diameter). This is a bit more (https://www.grainger.com/category/strain-relief-grips/cable-support-wireways-and-protection/wire-cable-and-carrier-systems/electrical/ecatalog/N-qqh) ($$ and function).

Edit: I've used these before, too (https://www.alliedelec.com/hubbell-wiring-device-kellems-hj1015bpk25/70116171/). On control panel penetrations, they work well - - not sure how they would last on a rig like yours, as they might get tossed around???

[Marc Jeske]

Even though Malcolm is technically correct, I am quite sure 99% of the guys on this forum would do it w the components Mike purchased... as would most any typical Electrician making one for home shop or even to carry in his truck

OSHA Industrial or heavy everyday rough use Commercial application are different, but far from the need here.

My opinion anyway.

Marc

[Matt Marsh]

That’s why i said we can get away with it at home, .... but.

I’ve seen this same setup fail so many times. The new raised covers are indeed better now that the receptacle is held at each end, rather than just the center 6-32, but because the receptacle sits proud of the cover, it often breaks, when the cord is tossed around during use. Another problem with these, is the equipment ground connection to the box. Because the ground screw protrudes through to the outside of the box, it often loosens up over time. This setup gives you one additional receptacle, with an option for another duplex if a double duplex raised cover is used. A cord splitter such as the one at the link below is UL listed for portable use, and is a much better choice.

https://www.amazon.com/Yellow-Jacket-Extension-Heavy-Duty-Contractor/dp/B000BQU576/ref=sr_1_13?ie=UTF8&qid=1518046716&sr=8-13&keywords=Cord+splitter


Even better, is a cord with a splitter AND an in-line GFCI protector like this one.

https://www.amazon.com/Outdoor-Lighted-Extension-Watts-Wire/dp/B071QX752S/ref=sr_1_1_sspa?s=hi&ie=UTF8&qid=1518046987&sr=1-1-spons&keywords=GFCI+Cord+splitter&psc=1

[Matt Marsh]

378568A Romex connector is what you have there, it is not listed for use with cord. The connector pictured above is a commonly used type, and is listed for use with cord. It is usually referred to as a "CGB". The type with the "Chinese finger" strain relief is really only needed when a cord is used as a pendant.

[Mike Manning]

Just to update everyone, I finished my extension cord from hell on Wed and it's working very well. Thanks to everyone for their feedback but especially to Marc for talking me through what I need to do to build this safely.

Marc,
I know I've still got some homework to do on the GFCI. Will try to do it today or this weekend and let you know! Thanks a ton!

Mike

[Matt Marsh]

Because electrical safety has been a large part of my life since I started in the trade almost 42 years ago, I feel compelled to follow up on this. This particular assembly is one of the most common OSHA violations. It is an illegal assembly for good reasons, because it has proven itself to be unsafe. I realize that yes, some of you have been using this setup for years without any problems, but OSHA deals with numbers, and the numbers prove why it’s not a safe assembly.

For those interested, here is a link to OSHA’s site that outlines their rules for these homemade portable power cords. Pay particular attention to the numbered section toward the bottom of the page, especially sub-section 2.

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=20579