Sorry for the barrage of electrical questions, need to learn enough stuff before I do my projects.
Question: If there is a broken wire somewhere, lets say in a conduit or coil (MC) that touches the walls of it, is that enough to trigger a REGULAR (non-gfci/afci) breaker as a short circuit? Where would the electricity go?
Thanks!
If conduit is grounded then yes the current will go to ground in a direct short, and that should be enough to trip breaker,
If conduit is not grounded then the current will have no path, and voltage will be on conduit until it finds a path to ground,… like through who ever happens to touch it.
Wire inside armored cable or conduit almost never fails. Think about it. The wire is just a hunk of metal, surrounded and cushioned by insulation, inside a protective metal shell. It’s not going to be damaged by the elements, unless you somehow get water inside the conduit, and the metal on the outside will protect the wire from critters and other types of physical damage (although I have heard of someone managing to drive a screw through the sheathing of armored cable and creating a short, but stuff like that is very rare).
The common failure points are on the ends, where the wire connects to something else. This is why the National Electric Code doesn’t want you covering up junction boxes and the like. That’s where the failures will be, so they need to be accessible.
If it is installed properly, the sheathing or conduit should be electrically grounded, so if you somehow do manage to short something out, it will generally trip the breaker and any electricity that flows will go harmlessly to earth. It is possible, if you have a small enough point of contact in thee short, for the failure to not quite draw enough current to trip the breaker, but that’s pretty rare. Small, intermittent points of contact like that tend to arc a bit, so installing an AFCI will generally protect you from that sort of thing.
Regular old fashioned breakers were designed to prevent major faults like shorts from causing fires. That’s their main purpose in life. While they don’t catch every possible fault, they do a pretty good job with most of them.
In my three decades of work as an electrical engineer, I’ve never seen wire in a conduit or inside armored cable just fail for no reason. The only failures I’ve seen have been from physical damage or from water or chemicals getting into conduit (I mostly work in industrial settings where nasty chemicals can be present).
The above posters nailed it.
If there’s a short circuit somewhere in the circuit, a standard breaker will trip. This is done to protect the wiring from overheating and causing the insulation to melt/burn.
It doesn’t “go” anywhere. If there is a load connected anywhere in the circuit, there will be current. Current always travels in a loop. The circuit breaker simply senses the over-current situation and trips.
Wow! It astounds me how much you guys know. Thats awesome. I guess I was just paranoid that if I was pulling cable (MC) I could damage the internal wires somehow. Story behind this: I’m thinking of putting in a half bath in the garage, sink and toilet and I just don’t want to you know, worry if the cable or conduit is touching the pipes and one day I turn the faucet on and get zapped.
I actually had an experience like this in a cottage in Wisconsin (ex-gf’s family), bare and uncapped wires just barely touching a pipe (the plumbing was haphazardly done too) in the closet with the water pump. I found this out of course after I went to shower and got a crippling jolt before slipping out. Never want that again.
Speaking of which, doesn’t the insulation decay or break down over years even inside the Metal Clad cabling even if indoors/not near elements? I thought I read that somewhere.
Thanks again guys for being so informative!
You’re going to want to make sure that the cable or conduit isn’t touching the pipes, since you’ll have different metals touching which can set up a galvanic reaction and eat away at the metal. You’ll eventually end up with a pinhole leak in your water pipe.
If everything is installed to code, both the cable sheathing / conduit and the metal water pipes should be grounded, so there’s no shock risk.
Way back when, homes were required to ground their electrical systems through the cold water pipe, since pretty much all homes had a cold water pipe and it was a convenient hunk of metal to ground to. When PVC pipe started becoming popular, the electrical rules were changed, and homes now require grounding through copper rods instead. However, all metal pipes in the home are required to be electrically grounded so that there’s never a risk of accidental electrocution from something shorting out to the water pipes.
Given your OCD bordering on phobic attitude to all things electrical as demonstrated in several threads and umpteen posts, my advice is to not treat anything electrical as a DIY project.
You lack the context to worry about the right things. So you’re worrying about the wrong things and as a result you’re developing a very lopsided knowledge base. Which will cause you to triple overcompensate on something that doesn’t matter while leaving some glaring defect unnoticed.
Doing rehab or improvements on existing installations takes extra skill to know not only what current practice is, but what current practice was in your locale when the house was built and or modified down the years. The older the house the larger the knowledge base needed to perform work safely and successfully.
Last of all, your insurance is exactly as good as your permits and inspections. Doing unpermitted and uninspected work, even if it’s done technically correctly, will void most insurance policies. If you want something to trigger your OCD, start repeating the mantra “My fire insurance won’t pay. My fire insurance won’t pay.” Seriously: don’t go there.
Once you’re going to the trouble to A) learn to do the job right, and B) do the paperwork correctly, the incremental cost to have a pro do the whole thing approaches zero.
How many dollars is peace of mind worth to you?
The chance of a broken wire inside AC is almost none, as people have said.
And the chance of that causing a short circuit, and thus tripping the breaker is even less – only about 1/3 of ‘almost none’. There are 3 wires inside, only one of them is hot – the other two are a neutral & a ground – both of those are already tied to the same electrical ground as the outside of the AC cable. So for 2 of the 3 wires, a broken wire touching the outside of the cable does not involve any electrical flow at all.
Man, electrical engineers have thought of everything! Thanks for the tips guys.
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T-Bonham** Thanks for the info, still putting in GFCI’s obviously, if anything for the sake of updating!
Engineer_Comp_geek Yeah, that cottage must have been a DIY gone horribly awry if I got shocked. Good to know.
LSLGUY, None of this is OCD related, that was temporary I suppose, I was under a lot of stress at that time and hence made me worry about EVERYTHING lol. I checked with the insurance agent, they will cover all DIY projects given it was examine by a licensed inspector afterwards, and that is pretty cheap. So not worried about that at all. I enjoy doing DIY stuff, makes me feel whole.
Shorting neutral to ground will cause current to flow through the ground if a load is connected to the circuit, which will trip a gfi breaker.
If you’re pulling on the cable when you’re pulling cable, you are doing it wrong,
If the cable or conduit is touching the pipes, you’re doing it wrong.
I don’t say you have to be gentle with the wire /all/ the time, but you should be gentle /most/ of the time, and when you aren’t, you shouldn’t be rough. It’s not designed to handle being pulled on.
Sometimes you have to cross pipes. Metal should not touch metal when you do that. Apart from that, you don’t run wire with pipes. Your wiring code will have the seperation distances.