I want to run a circuit to the opposite side of an unfinished basement. The run would go perpendicular to the joists. Can I run NM along the upper side of a beam? If so, do I need to put it in EMT? Or do I have to drill through 20 to 30 joists?
I’ve drilled through joists for all of my smaller runs, and changed to EMT when moving down the foundation walls. The beam is perfectly placed to go from the junction box to where I want to install outlets. But since doing so deviates from what I’ve researched/checked/rechecked/etc. in the past, I thought it prudent to ask. Plus, the existing wiring (house was built in 2003) seems to do both, but I don’t know if the previous owners installed either or if both were done by the builder. Here a 12 gauge NM cable is stapled to the side of the beam near the top. I’d like to add my line right next to it (with my own staples, of course). On the other hand, over by the boiler the cable comes down from the joists and into EMT.
So, what’s the right/best way of doing this from a safety/code point of view? Drill through all the joists? Put it in EMT? Or staple it close to the existing run?
It should be fine to run NM cable along a beam as long as it’s stapled or secured in a reasonable way. EMT is really only necessary in situations where it would be difficult to properly secure the cable or if it would be subject to stress or being knocked around.
Whatever you do, don’t run the NM cable through conduit. You have to use loose THHN wires for that.
In my house, built at about the same time, all the wiring seems to run along joists and make turns under them only on the edges, where it’s recessed over the basement wall. However, I had 50A service run to the garage, and the cable for that is simply stapled across the joists, about six inches from the adjacent wall. That job was professionally done and permitted, so I’ll assume it’s a proper procedure.
ETA: You basically never want to drill through joists if you can avoid it.
Thanks. So it seems like I can feel safe using the first picture as a basic model.
I used EMT to come down the basement walls, and switched over to THHN wires inside junction boxes. I had gotten mixed advice on that front; some sources said it was okay to put one cable in for short runs. I opened up some of the original boxes in the basement (original as in builder-installed) and there was NM inside. That said, I figured the relatively minimal cost in materials and time was worth it in a just-in-case sort of way.
I’ve come to understand that stapling across/underneath joists was problematic. My best take on it was that it invited things hanging from or catching on the wires or that if ultimately finished, being placed on the surface like that invited disaster when someone goes to hang a picture. There is space at the end of the joists, between them and the foundation, but how/what would I secure the wire to?
Why not drill the joists? Over here that is the standard approved method and considered safer than any other way. The cable is properly supported and ventilated, with little risk of accidental damage. The holes should be in the centre of the joist and large enough to allow the cable to be free. Cable inside conduit may have to be heavier because it is not ventilated and can heat up. Sharp bends are to be avoided.
Drilling through is my default. I made a little template based on existing work and use that to ensure all the holes are aligned horizontally and vertically, so it goes fairly smoothly. But there’s a good number of joists to go through. It’s not that much work, but aligning, moving around insulation, working around existing wires, etc. is a non-trivial task. So it would be preferable if there’s an acceptable and **safe **way to run down the beam—because the junction box is right next to it and it’s a straight shot to the destination wall, it would be much less labour-intensive. (But again, only if it can be done safely.)
I had always heard that it’s a code violation to run NM cable through conduit due to heat-dissipation concerns. But upon googling it appears that may be an old myth.
However, pulling NM cable through conduit can be rather difficult because it’s bulky. I helped a friend of mine dismantle a bunch of conduit with NM cable in it which he wanted to reuse for something else and it was a bear to get it all out of there.
Conduit, being enclosed, doesn’t allow water to evaporate very easily. Any moisture from condensation or anything else will tend to collect in the conduit and will stay there for a long time. The insulation on NM cable isn’t rated for moisture.
The NEC does allow you to run NM cable in conduit if it’s not in what the NEC calls a wet or damp location. Local codes may vary.
It’s a common belief (but not in the NEC) that running NM through conduit could cause the wire to overheat under high current loads since NM cable expects to be able to dissipate heat to the open air. Personally, I’m not sure about the validity of that one. It seems to me that the insulation on NM cable already provides pretty good thermal insulation and I doubt that the conduit around that would make much difference. That’s the reason that a lot of folks will tell you, though.
(ETA - friedo’s post wasn’t there when I started typing)
Part of the reason for asking was that by running along the side of the beam near the top, I’m also running directly underneath the joists. I can run along the middle of the beam, but that seems off too, particularly because there is already a cable near the top of it.
I read the whole thread before looking at the pictures and was assuming a steel beam. Steal beams do carry some issues. Wooden beams do not.
It’s perfectly permissible to staple NM along that beam. That’s how it is done in new construction. You can run along the beam or sill. What you can’t do is run wire under the joists to joists in an unfinished area.
Do not drill through your joists. Home owners like to do that a lot for some reason, it always looks unprofessional. Electricians normally only drill joists if they have to, which is rare as most our wire can be routed to where we need it without doing so. Joists are only rated for so many holes so we leave them open so the plumbers are the only guilty party when they are made into swiss cheese.
Its fine under the joists as long as it’s flat against the beam. Part of the reason for the restriction on stapling to the bottom of joists is it creates a convenient span for people to put coat hangers on, it created many issues in the past.
I almost always staple 2 wires per staple to keep things tight and neat looking. In your case those are uninsulated staples holding the existing NM. I’d pull those stack those wires on one another and re-staple them with the right staples. Then you can put your new wire right where the white one was.
When you have a bunch of wires that need to run along beams you use these which are good for 8-12 wires rather than 4-6 staples.
We regularly run NM through R-19 insulation, you’d think that would overheat quicker than conduit.
The downside of stapling the wire to the underside of those beams is that if you ever wanted to hang drywall on the ceiling, you’ll have to drill holes and re-string the wire. Try to avoid drilling the holes in the beams out in the middle of the span, keep them close to the bearing walls, or best right over the top of the bearing wall.
I’m very slow on exposed romex, maybe it’s perfectly safe but it creeps me out. EMT ain’t that expensive and it will give you some margin of safety when you’re swinging that axe …
I’m echoing what typerama (#12) said about drilling holes in joists, i.e., avoid it. In your case the joists are conventional lumber and it is not such a big deal. My home uses manufactured (OSB) joists throughout. Drilling holes in manufactured joists is discouraged by the manufacturer. When necessary there are specific “rules” to follow about number and size. Not a factor with your application but others should be aware of it.
I don’t see anything wrong with the pictures from a code point of view.
From a practical point of view I might be afraid of a ladder being leaned on it. If I were doing it I’d probably run it along the beam and then nail a 1X2 below it.
When finishing a basement electrical and mechanical tucked neatly against a beam makes my job a lot easier. I want to make as clean and tidy a ceiling as possible and bulkheads are time consuming. Keeping mechanical close to beams utilizes precious headroom in a basement.
Drilling through joists is not a problem if done properly. Modern TJI’s even have knockouts for the purpose though it is unlikely the knockouts will be aligned.
What I do not like to see are holes drilled too close to the bottom of the joist. Keep them as close to center as possible especially with dimensional lumber joists. The top and bottom of the joist is doing most of the work so do not mess with those areas. You should always be 2.5" minimum from framing surface to avoid drywall screws and finishing fasteners anyway. Also try to stay 6’ away from bearing points, especially on longer spans.