I have an older (around here 1960s is older) house with a 100-amp service. Whenever the washing machine is on, all of the incandescent lights in the house start to pulsate in time with the washing machine agitator. What could be causing this?
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I have seen a bad ground at the panel cause that. Or a loose neutral. I'm betting on the bad ground, sometimes they were connected to iron water pipes that are now cut loose, and there is no ground rod.
The system grounding conductors (grounding electrode conductors, i.e., wires to ground rod and/or underground metal water pipe) are designed to pass high energy pulses (from lightning strikes or a high voltage power line cross to the secondary distribution lines or the service drop), to ground.
The GEC shouldn't carry any current if the neutral in the service drop (or underground service lateral) is intact. If the service neutral is compromised or open, some of the return current will attempt to get back to the stepdown transformer via a ground path. Or, to many a plumbers suprise, via the metal water piping between the house with the bad neutral and adjacent houses with good neutrals...and back to the transformer via the other houses neutrals.
What the OP describes sounds like a loose neutral, which may be in the house panel, the service point (meter base), the service drop-service entrance conductor connection, or the utility drop connection. If it's a loose neutral at the transformer, neighbors will also see some lights dim and others brighten when a large 120v appliance is turned on (I use the garbage disposal to check this, and a 2-channel recording voltmeter).
Some utilities are better than others about responding to a complaint of "lights dim and brighten". A loose neutral causes the poles or legs of the 240V service to divide unequally, so, for instance, you can get 60 volts on some circuits and and 180V on others. And that'll fry a lot of electronics--every appliance has a microchip now, not just home electronics. I've had a big Nor Cal utility blow people off for weeks, claiming it's not their problem, and when I show up with the Fluke 123, they suddenly get serious and find a bad neutral splice in the URD system...The utility paid for a lot of new appliances and electronics.
Cliff
In retrofitting an old house for ground, in the case where the outlets have no existing ground wire- I have seen where a ground wire is run from the outlet and connected to the cold water iron pipe with a clamp.Doesn't this "electrify" the cold water when there is a short in the outlet? For example, let's say the neutral becomes loose at the outlet, so now, the juice bypasses the neutral wire, and goes to the ground wire, which then carries the current to the cold water iron pipe, which then electrifies the cold water. You could be taking a shower and be electrocuted.I have never heard of this happening though.
If installed correctly the ground connection at the receptacle is isolated from the neutral.The only time that there would be any current in the ground is if there is leakage in the device connected to that receptacle or if there is a fault (short) between the hot and parts that are grounded such as the metal case..
William the Geezer, the sequel to Billy the Kid - Shoe
In a perfect world there is no current on the ground but the world is far from perfect. In fact if the utility is using "wye" distribution on the primary (one hot wire on the pole plus the common grounded conductor) there may be a couple amps on everyone's ground electrode system. There is no way to stop it.
Current takes all paths and the earth is always going to be one of them on a grounded wye.
A 3 block primary with a couple dozen transformers is going to see voltage drop on the grounded conductor. That gets expressed on everyone's neutral and sunk into their ground electrode, even with the main breaker off.
The ground electrode, of it is effective, is what makes the whole house go up with the voltage gradient that gets imposed on your service neutral. My swimming pool is probably the ground electrode for my whole end of the street. I see 2a on my neutral with the breaker off and a similar number on the pole ground at the curb. The meter stops so it is not from my side.
Yes, in the situation you describe it does "electrify" the water pipe and water. But if the pipe is continuous out into the earth the resistance is so small that the entire length of pipe is for all practical purposes the same voltage as the earth and therefore can be said to have zero voltage. At the short in the outlet the connection where the shorted hot wire touches the ground would be a very poor contact and you'd have almost the entire voltage drop from 110 to 0 at the point of contact.
If someone were to break the continuity of the pipe to the ground between where the clamp was attached and where the pipe enters the earth, by, say, installing a section of plastic pipe, then some voltage could build up on the pipe inside the house. That's why when plastic pipe became available some decades ago the practice of grounding to a water line was discouraged. Under current code it would not be allowed for a new installation.
Wayne,
Hmmm, what current code does not allow connecting the grounding electrode conductor (GEC) to an underground metal water pipe (one that is in the earth at least 10 feet)?
The National Electrical Code says you have to use all of the following grounding electrodes, if they are present:
--Ufer (rebar or AWG 4 solid copper wire in a concrete footing)
--underground metal water pipe. The GEC must be connected to the pipe within 5 feet of where it enters the structure. This is to minimize the chance of losing the ground path due to a repair with non-metallic pipe.
--metal frame of building or structure
-- ground rod, ring, or plate.
--a few other things, not pertinent to residential work.
See Sec 250.52 of the 2008 NEC. The requirements have been that way for many years.
So, is it your local or State electrical code that doesn't allow (much less require) use of an underground metal water pipe as part of the grounding electrode system?
Cliff
I've been away from it for a while. Thanks for the added information.
>>....Ufer....underground metal water pipe - connected within 5 feet of where it enters the structure......metal frame of building or structure.... ground rod, ring, or plate.<<
We connect all of those here.
If water piping in the house is metallic, we also install jumpers around the water meter and between the hot and cold piping at the hot water heater.
We also bond any metallic gas piping either underground or in the house.
Jim Never underestimate the value of a sharp pencil or good light.
Actually for the water pipe if it qualifies as a ground electrode then it MUST be used, but it is not allowed to be the sole electrode.And if it does not qualify, but the interior piping is metal then it must be bonded..
William the Geezer, the sequel to Billy the Kid - Shoe
Well said, Sir Bill. (Suprise!--I put in the good word for you and you're now a Knight of the Ancient and Honorable Order of Light and Power...)
Grounding and bonding are not the easiest conecpts and practices to master. I've had clueless inspectors require bonding of PEX interior water piping, and running a grounding electrode conductor to plastic (ploy butylene?) water service piping...
duh-o!
I have a question, to satisfy an idle curiosity:
Does anyone have an AHJ that'll accept the branch circuit equipment grounding conductor of a gas appliance (usually the furnace) as the gas piping bond? Code allows it, but no AHJ I've ever worked with will accept it.
Not that I wouldn't run a separate gas pipe bonding conductor; I like a belt-and-suspenders approach. Well, sometimes--I think taping wire nuts is a waste, except on motor lead splices.
Cliff
>>Does anyone have an AHJ that'll accept the branch circuit equipment grounding conductor of a gas appliance (usually the furnace) as the gas piping bond? Code allows it, but no AHJ I've ever worked with will accept it.<<
That will not fly here, New Castle County, DE.
Jim Never underestimate the value of a sharp pencil or good light.
Yep, those are the rules we play by here.
JimNever underestimate the value of a sharp pencil or good light.
"But if the pipe is continuous out into the earth the resistance is so small that the entire length of pipe is for all practical purposes the same voltage as the earth and therefore can be said to have zero voltage. "I am just trying to wrap my mind around this concept. Once the ground and then the cold water supply become electrified, the water coming out of the shower head does not have current because the electricity is following the path of least resistance, and that path is into the earth?
Exactly.
There would be two paths to earth for the electricity. One would be through the pipe, the other through the water, through you, through the water you're standing in, through the water and/or drain pipe, to the earth. Since the supply pipe is large and metal and the path through you and the water are very much higher resistance in comparison, the electricity will flow through the pipe and not through you.
Thanks, I finally understand this.
Pure water is a virtual non-conductor.
Drinking water is a very poor conductor, about 1.2 billion times poorer than copper.
Even sea water is a poor conductor, about 12 million times poorer than copper.http://en.wikipedia.org/wiki/Electrical_conductivity#Classification_of_materials_by_conductivityTo zap you, your poorly conducting shower water must deliver relatively high amperage current AND there must be a good connection from you to ground; metal drain pipes all the way to the ground for instance.BruceT
120022.13 in reply to 120022.11 "Pure water is a virtual non-conductor.
Drinking water is a very poor conductor, about 1.2 billion times poorer than copper.
Even sea water is a poor conductor, about 12 million times poorer than copper"This is a horrible analogy.To get a 60w bulb to light you need 500MA to travel 30-40 miles through the wire, to kill you you need 100ma to travel .0001" through the water between you and the drain cover you are standing on.
Just a little gee whiz info. If you put water in a plastic bucket with 2 12" probes 8" apart in series with the cord, that 60w light bulb will light with a surprisingly small amount of salt in the water.
My well water cruises in the .8PPT range and it will light the bulb dimly.
I guess I will have to make up that test rig again with amp and volt meters to show what happens with different amounts of salt and make a video.
Sounds like a subject for Myth Busters. Yojimbo was asking about getting zapped by his shower water, so that current has to travel probably 12" through a spray of poor conducting potable water, not a 12" deep bucket with electrodes immersed 8" apart. I don't think it happens.BruceT
I agree you are probably not going to get shocked from the spray but the water in the PVC pipe might be able to get tingling current into the shower fixture if there was a gradient.
On vacation in Ecuador and was in a hotel. The hot water was heated through a device that attached in the shower. Turn on the water and stepped in the shower. Tickled me pretty good. Asked for another room.
Looking back, I don't know why I even trusted one of those things in the second room. At least Darwin didn't come knocking at my door.
An electrician I knew said they had a job where the husband and/or wife was getting a tingle in the nether regions when using the john. They traced it to a wire connected to a pipe in finished basement by an errant fastener IIRC.
You are absolutely correct.