My house was built in 1960, before gound wires were run. I’m putting a new branch line in my garage, comming from and old 30AMP 220 appliance circuit. That line came though a 3/4″ flex conduit, but didn’t have a ground wire. I know that the flex jacket is supposed to be the ground, but I would like something better.
Since this is in the garage, I’ve got some flexibility with technique. How do I make a new ground for this setup? I know I could run a new ground wire through the flex to this new breaker box, but I’d like to stay out of my old box as long as possible (until I upgrade and replace it entirely with new).
I do have access to copper pipes going into the slab, if that is the best way to do this. Are there any downsides to this method? Is there a way of putting down a new rod – or embedding something in the slab?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Replies
It sounds as if you have the equipment grounding conductor confused with the grounding electrode conductor. EGC versus the GEC. Green wire versus the big bare copper wire going to your ground rod.
The flex should be good as a ground for 6'. Then hopefully you will have metal pipes to your panel. That's the easiest approach. But you have an advantage in that you do have conduit/flex run to you panel so it will be easy to pull an insulated green wire in [using one of the original conductors to pull with]. You could pull a bare copper wire in but I don't like the idea of naked wires dancing around inside a panel.
~Peter
Regardless of what RW says, Bush did not cause the Seattle-Tacoma earthquake.
Not to highjack the thread but----- your tag line cracked me up.
You always have a seattle based point to be made.
What's the connection ---- old home town or somethin?
I have never been to poor, fated, doomed Seattle nor Tacoma. For a full explanation, select the area below with your mouse:
Every night, I listen to the Art Bell show. Last Dec. he had a guest named Ed Dames who practices what he calls "remote viewing". This enables him to see the futre, find bin Laden, discover why airplanes crashed and so on. Art asked him for a prediction and he said that there will be a terrible earthquake in the Seattle-Tacoma area sometie during the first six months of this year. Art asked him how bad and he said the Space Needle was [will be] tilted.
If he is wrong, then don't believe in fortune-tellers, mystics, clairvoyants nor remote views. If there is an earthquake [big], then I told you so.
~Peter
I did not have anything to do with the Seattle-Tacoma earthquake.
Um, well -- The space needle ain't gonna pull a Pisa on us. Structurally, I really doubt that it could tilt enough to be visible without going so far that it falls. ;-)
-- J.S.
OK then, I would like to put in an additional GEC in or around my garage.
Just so everyone is clear here, at the moment I don't think I have ANY ground connections coming out of my main box. When I redid my kitchen, I ran the grounds for the GCFIs to the cold copper plumbing into the slab. Any new wiring I did I connected back to that ground. Any EGCs are connected via a halfassed backbone ground I created awhile back and keep adding onto that kitchen ground. There was one 14ga. bare wire that I found that might go back to the main panel... but I'd not want to run every circuit ground off that wire!
Like I said originaly, I'd like to not have to dig around in the main panel if I can avoid it. I can if I have too... but why would I have to?
So back to the original question, how can i install an effective GEC? Is connecting to a cold pipe going into the slab effective, or should there be a rod embeded into the concrete, or should I pound a rod into the ground?Rebuilding my home in Cypress, CA
Also a CRX fanatic!
? Is connecting to a cold pipe going into the slab effective, or should there be a rod embeded into the concrete, or should I pound a rod into the ground?
No.No.No.
What you need is a solid connection back to your panel. The way it works is, if you have a fault, the current flows through the ground wire back to the panel where it is connected to the neutral. All the little electrons see this as their opportunity for a "great escape" and they all jump at the chance. So you suddenly get 100s of amps worth of electrons flowing through the breaker. The breaker detects this and trips instantly.
With your ground rod, those little electrons do ok getting to the rod alright but then they have to fight their way through the muck and hardpan until under your house until they reach the ground rod that is hopefully attached to your panel. The resistance of earth is fairly large and often not enough amps get through to trip the breaker. But enough to kill you if you get in the way.
You could use a ground fault interrupter. Required for garages anyhow. Cliff is right about trusting your senses. When you start feeling 60 hertz, something is wrong.
~Peter
Bush did, however, cause the Space Needle to topple. Maybe he was re-acting to the SH-60B victory.
Thanks for that info - more in the next reply...Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Paul,
If what your talking about is a new branch circuit, the only way to do it is to run an equipment grounding conductor (ground) from the supply panel, and make sure it is connected to the grounding bar.
If you're not comfortable in the panel, trust that instinct. There's a lot of ways to run into big trouble in an old panel, some obvious (like getting burned by an arc flash, or getting electrocuted), and some not (like making the wrong connections; sometimes the wrong connections will work, but create a very unsafe condition).
Cliff
Exactly. That old panel had a few different people working in it over the last 46 years, and judging the workmanship that's been done to this house everywhere else I'll bet there is a surprise or two lurking in there as well.
Is there a problem creating a new ground in the system instead of trying to go back to the old one?Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Paul,
There are two "grounds" in a typical residential electrical system. They serve very different purposes, you need both, and it can be death to confuse the two.
One is the system ground. It's there to protect the house against an overvoltage condition on the supply lines (the overhead drop or the underground service lateral). An overvoltage condition can come from lightning striking the lines or near 'em (even miles up or down the lines), from a high voltage (many kV) line falling across the secondary lines carrying 240/120 that connect to the drop or lateral, from transformer failure, or even from high voltage switching causing transients on the primary grid that jump the transformer to the secondary. This stuff really happens, and the goal of the system grouding system is to keep that energy from setting your house on fire.
The system ground for your house is the grounding electrode system. That is, an underground metal water pipe, concrete-encased electrode, driven ground rods, or other piece of metal in good contact with the earth. The grounding electrode conductor runs from the electrode(s) to the grounding bar in your main panel or service panel. In an overvoltage condition, the idea is that the energy will arc over to the grounded panel can (housing), travel through the GEC, and dissipate in the earth, before it lights up every wire in the walls of the house. It's not designed to protect all the sensitive electronic appliances in your house from having their chips blown out. You need surge protectors for that.
The critical role of the grounding electrode is why the latest version of the NEC requires a concrete-encased electrode (called a Ufer, after the guy who invented it to protect bomb storage buildings) if there's footings or foundation being poured.
The other kind of ground is the equipment grounding conductor, or EGC. It's the bare wire in romex or the green-insulated wire, or the EMT or other metal conduit (except flex conduit, as someone mentioned). It's job is to make sure that all metal objects that might accidentally become energized will stay at zero volts, that is, ground or earth potential. The GEC does this by carrying the current back to the overcurrent protection device (breaker) where it originated. This creates a short circuit, and will trip the breaker if the ground fault is bad enough. If the ground fault is not enough to trip the breaker, the EGC will at least drain off the voltage to minimize the chance of someone being shocked or electrocuted. This is, if all the connections are good and tight.
Drain the voltage off of what, you ask? Well, the metal case of a drill or other tool, the metal base of a table lamp, the housing of a washing machine or a dryer, the housing of a breaker panel, or metal conduit, metal water piping, metal gas piping, basically anything conductive that might become accidentally energized. In fact, the NEC requires all of this stuff to be electrically connected and connected to the system ground, and this connecting is called "bonding". Double-insluated tools and appliances--those with a two-prong plug--don't count, they are build to present essentially zero chance that any metal you could touch might become energized.
So, for your branch circuit, you want a equipment grounding conductor, one that provides a low impedance path back to the breaker panel feeding the branch circuit. Just hooking up to a separate ground rod will not do this. The soil resistance will not pass enough current back to the source (breaker panel) to trip the breaker.
What you've done at your house is to use the water piping as an EGC bus, and that used to be allowed. Not anymore--it's way too common for the metal pipng to be interrupted with a patch of PVC.
There are other considerations--the pathway may not have low impedance, so dangerous voltage could build up in case of a ground fault. There are cases where the soldered joins in copper pipe have come undone due to heat from current flow from serious ground faults. This is more an issue with commercial situations, but the point is, to use a metal water pipe as part of the EGC now is not smart, not safe, and im my opinion, it's worse than no ground at all. It's not practical to deal with all the installations where a ground has been grabbed off of a water pipe, and yea, those may be just fine. But keep in mind that the little outlet polarity tester may show "good ground" when in fact the impedance of the EGC is high enough to cause a danger in some ground fault situations.
My suggestion--hire an electrician to replace the panel and run the new circuit. Clean up the kludged work you've done, piece by piece. Run new NM cable, stuff with an EGC. Side benefit--you'll learn to do drywall patching!
Oh, yea, about confusing the two--system ground and EGC. Here in Sacto where I live, an unqualified, unlicensed contractor installed standards and light fixtures for a self-serve car wash, and instead of pulling an EGC, he drove a ground rod at each light pole. Everything worked fine for a few years and then a ground fault developed in one of the standards. With no EGC back to the source to carry the fault current and trip the breaker, the pole became energized, but the light continued to work fine. A little girl touched the pole while standing in a puddle and was electrocuted.
Keep in mind that if you're going to work on electrical systems, you really need to know the whole story, or you could hook it up, it might work, but if something goes wrong, it might injure or kill someone.
Cliff
Thank you very much - both of you - for providing the information, and the explination, that you did. You both provided me with exactly the information that I needed to know, thank you very much. I guess I was missing the direct connection between the Hot and the Ground, and how they work together to trip the breaker. Yes, I do have GCFI on every circuit in the kitchen and the garage... though what ground they are actually connected to is up for grabs.
OK, it looks like I'll be going back to that main box. whee.
On the plus side, I'll at last have actual grounding though all the work that I've done after I get through.
I'm curious, could you push a fish tape through a 3/4" ID flex tube that had 3 10ga conductors already in it? I've never tried so I don't know.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
I gather your garage is attached to the house, and you want to have a 220v recept. in the garage, rather than just 110s?
Actually, a 220 outlet is very low on my priorities - I haven't yet found a need for it.
But having to walk around my house to reset the breaker when I run my tablesaw and vacume at the same time gets old pretty quick. I also want to isolate the garage circuits from the house, so work in one area doesn't make the other go dark. I've also gat a couple of electric radient heaters on the porch that each need and independent 20 amp line.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
You didn't say how long the 3/4" conduit is, but it is unlikely that you could push a fish tape through it.
I would attach 2 new wires to one of the wires that is already in the conduit and pull the 2 new wires through. One of the wires would be a circuit wire to replace the one you use for pulling and the other would be the new insulated grounding wire.
D'OH! That was plainly obvious - why didn't i think of that? Thanks!
That flex is about 40 feet long, BTW.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
> Yes, I do have GCFI on every circuit in the kitchen and the garage... though what ground they are actually connected to is up for grabs.
One big advantage of GFCI is that it doesn't need to be connected to a third wire for ground. What GFCI does is it compares the current in the hot and neutral, which should be equal and opposite in direction. If electrons leak into or out of the wires anywhere past the GFCI, it detects the difference and pops. Nicked insulation on buried UF romex will trip a GFCI. It could be on the neutral or a switch leg, it doesn't have to be the hot. Think of it as drawing an envelope around everything downstream of the GFCI. If electrons pass thru that envelope, the GFCI trips.
That's what makes GFCI an easy way to substantially improve the safety of old two wire circuits.
-- J.S.
> One is the system ground. It's there to protect the house against an overvoltage condition on the supply lines ....
Actually that's one of two reasons for ground rods. The other is that since the earth is conductive, we want to ensure that it stays at the same voltage as the exposed metal parts of our electrical system. Theoretically, you could let the whole thing float relative to true earth, like a car on rubber tires. But in practical systems, the danger is that somewhere a hot will come in contact with the dirt. Without ground rods, you'd have 120 volts between the dirt everywhere and the boxes and conduit.
With ground rods, you get a voltage gradient instead. The ground rods and pipes, etc., are much bigger than a nick on a wire, so the resistance to hot is a lot more than to ground/neutral, which keeps the region of dangerous voltage in the dirt relatively small.
In the example of the little girl, evidently a hot came in contact with the metal pole. If the pole was bonded to its local ground rod, the "hot" rod was trying to pull the surrounding puddle to the same potential as the pole. But that one rod lost out to whatever other grounding electrodes there were that were at the correct voltage. Your ground rod is directly connected to all your neighbors' ground rods on the same transformer, and the utility's rod at their pole. Electrons really don't care who owns what, they take the path of least resistance.
-- J.S.