Adding an outlet in a concrete floor.

NCGrimbo

NCGrimbo
Corporate Member
I've been thinking about adding an outlet in the floor of my garage workshop's concrete floor so that I can get the table saw's power cord out of the way. i know that there will be a need to cut a channel through the concrete to give access to run the cable and conduit from the wall. So here are my questions:

1) Do I need to make the channel myself or is this something the electrician will do?
2) After the electrician is done, will he patch the channel or do I need to do that?
3) Has anyone done this?

Thanks.

-NCGrimbo
 

tri4sale

Daniel
Corporate Member
1) Do I need to make the channel myself or is this something the electrician will do? - Typically yes, but you might find an electrician to do it
2) After the electrician is done, will he patch the channel or do I need to do that? - Typically no, you'd have to patch
3) Has anyone done this? -

Thanks.

-NCGrimbo
 

FlyingRon

Board of Directors, Webmaster
Ron
Staff member
Corporate Member
Daniel is correct. Many electricians will cut the trench but some won't. You'll need to ask.
Electricians almost never fix the surface when they're done, be it the floor or the wall or ceiling.
I've not cut trenches in, but I've had to chip out concrete around boxes that were either set at the wrong height or the wrong size.
 

nn4jw

New User
Jim
Have you thought about the actual outlet box for this application? A standard floor outlet may not be what you want for this because of sawdust and dirt. I'm assuming you'll be wanting to keep the saw plugged in so the type of floor box that seals when nothing is plugged in might be risky as well as a fire hazzard. How about water protection?
 
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Brantnative

Jeff
Corporate Member
Talk to a licensed electrician before you go further. Outlets in the floor have different requirements than ones in the wall or ceiling. A line in concrete then sealed over is probably going to be considered as in a wet location and also requires different code. The suggestion of a drop down line is far easier and less complicated.
 

JimD

Jim
Senior User
I have not done this either but I moved drain lines under the slab in my last house. It had a walk out basement and I was finishing a bathroom down there. I paid a plumber to put in the waste lines before the slab was poured but they were way off. So I rented a jack hammer and took out enough slab to move the drains. Then I mixed up enough concrete to patch the hole I made. It was a lot of work but wasn't terribly expensive. You could also rent a concrete saw, I've done that too, but I think I would go the jackhammer route for what you describe. It will take out more concrete but if you saw cut the concrete you will still probably want the jackhammer to remove what you cut. The ragged edges of a jackhammered trench would help keep the patch in position.

A garage already needs a ground fault circuit to meet current code. Wire to be buried is different, however. I wouldn't actually put the outlet in the floor for the reasons already mentioned. I would have it come up to a little box above the floor next to the table saw. I've seen little metal boxes for this, they must sell them.

An electrician is an expensive trade to bust up concrete. You might find one who would do it but I would think it would save a bunch to do it yourself, if you can handle a jackhammer, or hire a laborer for this. Running wire in an existing building almost always involves some demo and reconstruction. Moving concrete out of the way isn't easy but I don't love removing, replacing and retaping drywall either.
 

Skymaster

Jack
Senior User
most likely you will have to run conduit,seperate conductors, romex is NOT allowed in conduit. Retractable ceiling drop way cheaper,easier
 

Strom

Strom
Senior User
I did something similar when I remodeled my den. All advice above is good. I had a skilsaw and fibre blades it was the biggest mess you've ever seen. You will need to cover everything and have some mighty good respirators. I ran underground wire into a duplex receptacle in a weather tight box. House is still standing 35 years later but who knows. Forget paying an electrician. You could repour the slab for what they would charge here.
Get some wire and conduit and do some clever thinking you'll figure it out I bet.
 

Phil S

Board of Directors, President
Phil Soper
Staff member
Corporate Member
I do this often on commercial sites. I use pro concrete cutters but you can DIY, just rent a diamond blade slab cutter with water cooling - no dust, just some concrete slurry that will need to be cleaned up. Remove the concrete and add plastic pipe and a good floor box.
 

FlyingRon

Board of Directors, Webmaster
Ron
Staff member
Corporate Member
There are all kinds of floor boxes you may want to look into.

Indeed embedded in a slab that is in direct contact with the earth is a wet location (I assume we're not talking floors like my house that are poured over a subfloor). You'll need a wiring method that is both approved for such embedding plus rated for wet locations.
 

Oka

Casey
Corporate Member
Being a licensed Electrical, Mechanical, Plumbing contractor in the past ( and now managing for one), I recommend against floor plugs ............ unless they are in specific conditions (like hospitals and labs). They are more expensive to install , have more concerns not just safety, but like others have stated keeping them clean, dry... Not really worth it. You could put a ceiling track/trolley and install a mechanic/tech retractable system for about 300-400 bucks and it would be 12 ga 20 amp rated. More convenient, safer and much easier to install.

Also ..........since we are in this subject ....... a quick electrical tutorial. There are a number of ratings in electrical components, the wire rating that is best for a shop is THHN rated and the IC rated connections or outlets should always have the same temperature rating as the wire 90 Deg C (194 F).
As you can see below, the NM-B (this is romex) is a 140 deg rated wire. Using our power tools like a planer the draw is long and constant which means over time the wire can heat up, posing more risk.

Finally, as a rule of thumb never max you demand to the max of the breaker. The standard rule is 57-80% max per rating. So, if you have a 13 amp motor, better use a 20 amp circuit, particularly if it is a lathe or planer, or table saw (in use a long period of time) vs saw skil saw used for a couple of minutes.

Better stop there, this is getting in to the weeds. IF you any specific questions feel free to pm me.




Wire Gauge Size60°C (140°F)
NM-B, UF-B
75°C (167°F)
THW, THWN,
SE, USE, XHHW
90°C (194°F)
THWN-2, THHN,
XHHW-2, USE-2
14152025
12202530
10303540
8405055
6556575
 

Rwe2156

DrBob
Senior User
Are you running a duct to your saw? If so you can follow a circuit along that.

I mounted an outlet box directly on the machine stand. I don’t know if that “code” but it works for me,
 

Willemjm

Willem
Corporate Member
I have all my major 240V machines with floor outlets, using floor boxes in the concrete. The wires run in conduit.

If you use the right floor box, they are sealed, dust cannot get in.

Running cables from above is always a hassle, when long boards are processed the cables seem to always get in the way.
 

Dreuxgrad

Ed
Senior User
I did a new subpanel and outlets for this garage which had only a couple of 110 GFCI. outlets.
Did a drop from ceiling for the 220 at the end of the TS. So much easier going through
the attic and haven't had any encumbrances with any cutting (yet)
My inspectors and permit office was always willing to offer advice.
Permit was only $45 and insurance is still enforce.
Ed
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
romex is NOT allowed in conduit
I remember spending a fair bit of time trying to get to the bottom of that statement when I was running electric in my basement shop. If you start looking into this, you'll find it is a great big debate, even on the contractor message boards.

This is the conclusion that I reached at the end of my research. I'd be interested to see what @Oka has to say about it.
-- Running romex in conduit is not strictly forbidden
------ Romex is not allowed to be taken out of the outer jacket. That is where all the labeling is and romex is tested/sold/qualified as a "cable assembly" not as individual wires.
------ Romex is not allowed to be inside conduit in "damp" locations
 

Oka

Casey
Corporate Member
In many municipalities do not allow romex in conduit, so check local code. I know the west coast states do not allow romex in conduit even if you up size the conduit. Reason being, it increases heat loading on the wire But ,more to the point kind defeats the purpose of the conduit, if you run conduit then run bare wire, it is better assembly, the wire will dissipate heat better from the wire. But, if you are tying into romex, then, just terminate the romex in a 4 square box with a romex connector and the then go from there in conduit. That is most common. If the change to conduit and it is less than twenty feet, you could just strip the white/yellow outer plastic carefully cut out the paper insulation wrap and tension pull paper cords away and feed the now separate 3 wires into the conduit alleviating the connection wire nuts in the 4sq box. If you go this route, remember to leave about 8-10 inch service loop in the box, in case you have to replace the conduit side wire or to need extra slack from the loop. I do this a bit but usually, on runs that are fairly short less the 10 feet. My conditions are different, we are under contract so for us time is money.

The other thing, code requires in basements, garages and out buildings the wire be protected if it is in the wall lower than .......I believe it is 80" like the door height. This can be accomplished by sheetrocking or plywood the wall so the romex is not visible (or just that stud bay). Often, in these conditions, we will go to MC cable (Metal clad) it has 3-12 ga wires- black, green and white. It is a roughly double the cost of romex typically, 140-180.00 per 250 ft roll. It is a useful alternative, but takes getting used to and you really need a roto-zip hand tool (mini cable cutter) to do it efficiently. Just mentioning so you know what it is and knows it exists. We use this method usually by running in the make-up boxes (4-sq)that feed power from the panel and pre-make the down the wall whips in MC with the outlet boxes attached all done in the shop.

Out here in Hawaii, I am currently working with an electrical inspector from North Carolina, I ll ask for you his thoughts. His electrical code knowledge is excellent..... not all inspectors usually this good. But, like me and so many of us old-scool boys we came up with tools in our hands. Now, so many inspectors and new managers are coming from college without that experience .......... cest' la vie
 
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NCGrimbo

NCGrimbo
Corporate Member
Thanks for all the responses. Sounds like putting the outlet in the ceiling may be a better option even if the wire will be hanging down.
 

JimD

Jim
Senior User
I don't think it's better. It might be easier but I don't think going through the floor is that bad, especially if the run is short. It's unfortunate the code varies from place to place but if you get a permit and talk to a local inspector you will quickly find out what is allowable in your area. Then you just buy what the local authorities have decided is allowed.
 

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