The cable guy pointed out that I had about 5.5 amps of current going through the grounding rod outside my home.
Wondering if this was connected to the flickering light problem I had I called the electric company (who I must say got right on it in 3 hours).
The wires from the pole coming to the house were rubbing against the tree in the front yard. The neutral from the pole was virtually cut.
The current in my ground wire as I understand it resulted from the current going through either of the two hot legs of the 220 to the neutral in the circuit box that is attached to the neutral coming in from the pole. As this was cut, the current instead flowed to the ground rod outside (the box is also grounded to the plumbing system).
My question is: I guess neutral and ground are joined on the neutral bar in the circuit box. Why goes not the current always flow to ground? WHat am I forgetting from my ancient BSEE degree?
Also does this mean when I was checking the ground wire of the cable system (were it is lugged to the ground wire on the way to the ground rod) could I have fried myself?
Hopefully, they replaced this "neutral from the pole" as it's usually also the guy wire supporting the 2 hots.
What you are forgetting is that ground is for safety, in this case a redundant backup in the event something just like this happens.
You're also forgetting, utilities don't deal with "neutrals" in the sense that inside wiremen do - for a utility system there is no "neutral," they call that conductor just ground. It only becomes a neutral after it has joined with your ground rod in your main panel.
The current doesn't normally just go to ground (from your panel's neutral buss bar to your grounding rod and/or water main) because it's easier, and usually a shorter trip, to get back to exactly where it came from (the utility's transformer, where their "neutral," - the center tap) via the guy wire. That's supposed to be the path of least resistance. Without it, all of your home's unbalanced load would have to flow through your ground rod, into the ground and make either a b-line toward the transformer's ground rod (If it's present and maintained) or, to the next home's ground rod, into their panel's neutral buss and back through their intact guy wire.
Or then again, since you can't tell which way the AC is flowing on your 5.5 amp reading, perhaps it's your neighbor who has a bad neutral...
You could have, if that was the path taken by your, or someone else's unbalanced load.
Taking the terms in the standards literally, it's the reverse of that. Neutrals are effectively the "centre reference" of a multiple wire circuit. Ie: three phase. Ie: the neutral of the 220 split phase circuit that's your house feed.
Technically, for example, a 120V circuit cannot have a neutral because it's not a multi-wire circuit.
Once the neutral comes to your panel, it becomes the "grounded conductor" because it's connected to ground. As contrasted with the "grounding conductor" (safety ground).
The electrical codes (both NEC and CEC) very specifically uses the "grounded conductor" term instead of "neutral" for the white wiring in your house.
However, the home building trade uses the word neutral. So do most others, despite the fact that the terminology isn't technically accurate.
[There's a longer explanation in the electrical wiring FAQ which specifically uses "neutral" to be consistent with the majority of usage, and make it very difficult to confuse it with "grounding conductor"]
"shorter trip", being short form for "lowest resistance".
Most people tend to think that grounding rods and the like have very low resistance (as in zero). They do not. The grounding-rod to dirt resistance can be surprisingly high. For example, a NEC-satisfactory grounding system can have _more_ than 25 ohms to dirt. A dead-short to dirt could only push 5A or so at 120V. Not even enough to trip the breaker.
Grounding systems aren't supposed to carry current. They're really only a secondary way to keep the power from drifting too far away from a dirt reference. Neutral current (the imbalance between the currents of the two hot wires) is _supposed_ to go down the real neutral wire back to the transformer.
Trying to make the dirt be a conductor can lead to all sorts of problems - highly variable voltage (especially under variable loads), electrical shocks from standing on the dirt, setting the grass on fire. Etc.
If you see appreciable current flow in the grounding conductor, it almost always means that there's something wrong with the neutral. Which implies the "loose neutral" syndrome, where you can get wild voltage swings on 120V circuits. Including up to 220V...
Unlikely. The range is relatively short, and you're only getting "side effects" of a situation which'd be _far_ worse in the neighbor's. Ie: exploding TV sets. Ie: high voltages on grounded appliance cases or plumbing.
I believe the NEC recommends driving a second ground rod, if the first measures more that 25 ohms. I can't remember if you are supposed to do anything else if you still have over 25 ohms.
In telephony-land, cell sites usually are required to have 5 ohms or less. Of course,they come with 100 ft+ lightning rod, known as the cell tower. :-)
I can... It doesn't say that you have to do _anything_.
The rule can be paraphrased as "If under 25 ohms, add a rod. Don't bother measuring again, we don't care what the resistance is anymore".
This remark is made in some of the NEC guides.
Canadian practise treats this a bit differently. The base code essentially gives you "standard installation" practises (eg: rods vs well casings vs UFers etc), but final authority is vested in the municipality to state the minimums. As I understand it, the CEC recognizes that soil (and other) conditions can vary a lot, and rely on the local inspectors to specify a minimum requirement on an installation-by-installation basis. That being said, the majority of installations end up with similar requirements.
The machine that we run the FAQ posting stuff on has lost access all but a very small number of Usenet groups. None of which are in common with the groups the FAQ was posting to, hence it wasn't working for quite a long time.
H'm, maybe it does work. Stay tuned.
If not, google for "Electrical Wiring FAQ". There are links _everywhere_.
Tony Are you lost, just quarrelsome or both. Have you ever actually measured a ground loop current in access of one amp. Natural ground gradients never produce currents of 5.5 amperes. Ground loops occur from voltage gradients that are measured in millivolts. The only hazard a naturally occurring ground loop causes is to electronic signal quality between digital equipment connected to grounds with differing potentials.
250.4 General Requirements for Grounding and Bonding.
The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
The actual grounding of electric systems is not done for electrical safety but rather for limiting damage to the system from "lightning, line surges, or unintentional contact with higher-voltage lines."
The conductors that actually provide a safe level of touch potential on the exposed non current carrying metallic parts of the wiring system are called Equipment Grounding Conductors because they connect the exposed metallic parts to the Grounding Electrode Conductor. The connection that actually clears any fault is the main bonding jumper. That conducts the stray current back to the neutral of the service and to the Xo of the transformer. If the fault that is allowing the current to get into the exposed metallic parts in the first place is of a low enough impedance sufficient current flows to trip the Over Current Protective Device. If the fault impedance is too high for this then the low impedance pathway provided by the EGCs keeps the touch potential below dangerous levels.
1) Ground loops cause the flow of continuous current from one place to another, usually including one or more "sub-optimal" connections. Ie: buried/wet. Which can lead to galvanic corrosion and connection failure. Even if the current flow is very low...
2) It's not just "natural" ground gradients you need to worry about.
Doesn't Kirchoff's Law have something to do with this even if the "neutral" is good? On a 3 wire service the ground rods and the earth will form a parallel path with the neutral and there will be a small amount of current flowing through the rods. I know livestock operations had some problems with transient voltage with
3 wire hookups. Four wire hookups are recommended now for things like milking barns etc.
Absolutely true. But consider: ground rod connectivity isn't that good usually.
Do the calculations - if the ground rod to dirt resistance is, say, 25 ohms [permissible in the NEC], and the neutral wire resistance is, say, .1 ohms (which is probably much higher than it should be), what would the neutral wire current be for the ground rod current to be 5.5A? Secondly, what would the voltage on the grounding system (eg: your plumbing, appliance cases etc) be relative to dirt?
Something on the order of 1400A (the service wires will melt) and 120V (danger! danger! don't touch that pipe!) respectively.
Measureable current through ground over a few milliamps means there's a problem. High current guarantees there's something VERY wrong with the neutral or something else major.
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