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Nonmetallic Sheathed Cable

Throughout the vast majority of the U.S.A., nonmetallic sheathed cable (NM cable) has been the most common type of residential wiring system since about the early 1950’s.  And it’s had a pretty good track record of success.  It consists or two or more insulated wires along with a bare ground wire, wrapped in paper and then contained inside a thermoplastic outer sheathing.  It’s often called Romex®, but that’s a brand name and not all NM cable is Romex®.  It comes in large spools of different wire sizes, it’s easy to install, it’s easy to cut to length, and it goes up pretty quickly.

Despite its long history of successful usage throughout most of the country, in much of the Chicagoland area this type of wiring isn’t allowed.  Chicago and many of the surrounding suburbs require that wires be pulled through some type of raceway, which usually is electrical metallic tubing (EMT) and normally called “conduit”.

So when you see NM cable in a part of Chicagoland where it’s not allowed, what should you think?  And what should you do?

The first thing to note is that if this issue is coming up when you’re buying a house then it’s likely to come up again when you sell.  So keep that in mind.

The biggest problem with NM cable in Chicagoland is that it’s often installed not by a good qualified electrician but by a handyman or homeowner.  In this case it’s not the material that’s in question but the installation methods.  When it’s exposed, NM cable needs to be run closely along the surfaces of the building finish to provide support and protection.  It needs to be supported at least every 4.5 feet and secured within 12 inches of its ends.  Where the cable enters any type of panel enclosure or junction box it needs to be clamped to the box.  These are very common defects when NM cable is installed by an amateur.

This house is in Chicago so there shouldn’t be any NM cable. Still, this is run closely along the building surfaces, it’s supported properly, and it’s clamped into this junction box for the light. It’s installed well.

This cable isn’t clamped to the box. Not done by a licensed electrician.

NM cable can only be used inside.  It can’t be used outside or exposed to sunlight.  It can’t be buried underground (there’s a special kind of cable for that) or encased in concrete or plaster.

NM cable shouldn’t be used outside. No self-respecting electrician did this.

NM can’t be used with a plug, making it into an extension cord.  It isn’t designed to be bent back and forth many times like an extension cord is.

A double whammy — NM cable run through a concrete wall and used with a plug as a glorified extension cord. Not done by a good electrician.

In an attic NM cable needs to be protected from physical damage.  Often times the cable is just run across the tops of the framing members, right where you want to step.  NM cable needs to be protected within six feet of any attic access opening, and if the attic has a permanent ladder or stairs then it needs protection throughout the attic up to a height of seven feet.

When NM cable is run in an unfinished basement along the bottoms of floor joists it needs to be attached to a running board (usually a 1×4 board fastened to the bottoms of the joists).  Or it can be installed through holes bored in the middle of each floor joist.

Cable that’s run along the bottoms of floor joists is susceptible to physical damage. First a 1×4 running board should be installed, and then the cable is attached to that.

NM cable is much more susceptible to damage from nails than is conduit.  So when NM cable is run through a wall stud hole that’s less than 1-1/4 inch from the front edge it needs to be protected with a steel strike plate to stop an errant nail from piercing the wire.

And dealing with the equipment grounding conductor (the ground wire) is quite a bit different with NM cable than with conduit, so that has to be taken into account.

So if the NM cable in your house is installed well then it’s likely to not pose a hazard, even though it wasn’t installed under a building permit like it should have been.  But if it has any of these defects described above then the risk of problems rises greatly.  And that can lead to shock, electrocution, fire, or other problems.  Electrical wiring is not the place you want to see amateur workmanship in your

Decks built sideways

Decks are one of the most common do-it-yourself projects.  Unfortunately many deck builders fall into the category of shouldn’t-do-it-themselves.

It’s easy to hammer a few boards together, but it’s a lot harder to do with the best techniques, tools, equipment, and devices so that the deck has the best chance of safely lasting many decades.  Almost every deck that I see has some problem, and many are built so poorly that I advise my client to just tear it down and rebuild.

A deck has many details to inspect, but there’s one deck problem in particular that drives me crazy.  And it seriously weakens the deck structure so it’s worth looking at more closely.

Here’s the typical way to build a standard deck:

A ledger board is securely attached to the house, with bolts staggered up and down and spaced no more than about every 8 inches.  Then the floor joists are installed perpendicular to the house and ledger board, and they’re attached to the ledger using joist hangers.  At the far end the floor joists sit on a beam that’s supported on both ends by posts that sit on concrete footings.

Now let’s take a look at the load path takes to the ground.  When you’re standing on the deck, your weight is shared among several joists (but we’ll look at just one joist in this example), and that load (green lines) moves horizontally out to the beam and in to the ledger board.  When that load hits the ledger board it only has to move a very short distance horizontally before it hits the very secure connection of the ledger board to the house structure.  At least we hope that connection is secure, but that’s a topic for another day.

When your load hits the beam it then might have to move quite a long distance horizontally before it gets to the posts and into the ground.  Because the load might have to move a long distance horizontally the beam needs to be doubled – it needs to be made up of 2 pieces of 2x lumber.

Everything’s fine with this design.

But here’s how some decks are built.

 

There’s a ledger against the house, but then there are boards at both ends of the ledger coming out perpendicular to the house.  These boards are usually not attached very well to the ledger board — that’s the problem.

But now all the floor joists are attached to these side boards.  Now let’s take a look at the load path.  When you stand on the deck the load is shared among several joists, transferred horizontally through the joists over to the side board, and then horizontally again over to the ledger at the house and over to the post at the corner of the deck.  But because the load is moving a long way horizontally these side boards should be doubled – they should each be made up of 2 pieces of 2x lumber.  Otherwise they’re not strong enough to carry all that load.  (Remember that the several floor joists share the load so they’re OK as single pieces of lumber.)

But when the load gets to the ledger board, the only thing holding this deck up is the single connection between the side board and the ledger (red oval in the figure).  Often times this connection is only a bunch of nails.  Now think about this.  About half of the entire load on this deck – and that might be a whole deck-full of people if you’re having a party – is supported only by this bunch of nails.  And then suppose that this deck is 10 or 20 years old, and it’s been subject to rain, sun, hot, cold, over and over and over.  So that connection isn’t nearly as strong as it was when originally built.

This connection just isn’t strong enough, and this is the wrong way to build a deck.