The dangers on the pole..EVERYONE read, please.

[jneutron]

The telephone pole, that is..

I was walking around town with my sweetheart a couple of nights ago, when I spotted a problem with the AC feed to a building..(yes, I'm a geek...I can't help it..)

On Long Island, the power feed to buildings is this:

1. High voltage three phase wires at the top of the poles..the neutral wire for that set is lower on the pole.

2. Whenever required, a one bushing transformer is put on the pole...one of the 3 phases is connected to with a jumper, and it goes down to the high voltage bushing.

3. The neutral wire for the 3 phase set up above, is also the neutral for the single bushing transformer...that is why it is called single bushing...there is only one wire to it that is hot with respect to the case of the transformer. In reality, it should be called an auto-transformer, as that is how it is electrically configured.. And, every couple of poles, that neutral is fed down the pole, sometimes covered with a protective shield, to a long earth ground rod.

4. Out of the xfmr comes the two 120 volt hots, 240 total as they are opposite polarity..and the neutral connection, which is xfmr case, house center neutral, and return for the hv feed from the top of the pole. If the power company plays their cards correctly, there will be a net zero current on that neutral overall, but at each location, it will carry the current of the xfmr(s) that it is feeding.

5. The house wires will connect to the three wires. Typically, the neutral wire to the house will be the wire that supports the two hot wires...it will be anchored to the house, it will be bare, and the hots will twist around it.

6. For 3 phase building feeds, there will be 3 xfmrs, and 3 hots wrapped around the neutral.

7. For all residential installs in my area, the 3 wires go first to a meter pan, then down into the house breaker panel. By code, there will be a solid conductor, bare copper wire, that goes from the service panel, to the water pipe where it enters the building.

8. Within the house panel, all neutrals and grounds from the housefeeds are bonded together, to the ground wire, and to the neutral feed from the street.

My apologies to those who already knew this...

Now......the problem...

The neutral wire to the building was broken up where it connects to the pole wires...the hots were still connected, but there is no neutral connection.

So, how does a 120 volt appliance in the building work???

Simple..because the neutral to the pole is broken, all 120 volt appliances will have their return current go through the copper wire that is attached to the water pipe..

The problem? That wire is not sized for a real steady state load..it is sized only to clear a momentary fault..

And, it is in a location that is by design, begs for corrosion to break the continuity.

And the electrical continuity of the plumbing system may be compromised by either a dielectric isolation device (to prevent galvanic corrosion), or by one of those plastic whole house filters, an extreme electrocution hazard will be created..

Worst case scenario? The water pipe connection goes away...any single leg load will be able to raise the potential of the neutral and ground wires within the entire house to 120 volts.

Several appliances connected to the plumbing also have electrical ground connections...electric water heater comes to mind...So, it is possible that one of the appliances connects the entire building's plumbing to 120 volts..

Except of course, for the drains...

Imagine taking a shower, wet, standing in water, on a metal tub that is earthed via large copper drainpipe...and at some moment in time, a 1 KW space heater thermostat connects, finally popping the horribly corroded water pipe ground connection, making the pipe that feeds the shower head that is spraying you rise to 120 volts.

Nuff said.

If anyone ever, EVER sees this situation....do not hesitate to inform the people in the building that the situation warrants immediate attention by the electric company....this is, in fact, the second time I have seen this..

To all:

1. Check your external feed connection and make sure you have a good neutral feed...if not....immediately (and I really mean it) contact your electrical provider so that they can fix it..

2. Check your ground wire integrity...it is a failsafe device that is not just there to satisfy some arcane whim....as I point out, it can mean life or death worst case.

3. Make sure any device that breaks the plumbing ground integrity is doing what it is intended to do while not compromising the safety of the building.

For any questions of this nature, get the advice of a registered, licensed electrician in your area...do not ask me....do not ask anyone on a forum...do so with someone in your area who is qualified..

Cheers, John

 

[Francious70]

What?? Non-home electrical guru speak please.

Paul

 

[jneutron]

What?? Non-home electrical guru speak please.

Paul

My apologies...I am trying to find a picture that will explain...by the time I get home tonight, it will be too dark to take one..I'll look on the web for a good one..

Bottom line...there are three wires going from the pole to your house. One is bare, the other two are insulated...

If the stranded one is broken, that is dangerous...very very dangerous...it is time to call in someone who knows how to fix it..

If it is broken, your electrical stuff in the house may still work fine, but that does not mean it's safe..

Cheers, John

 

[Rip Van Woofer]

Oh, great. I finally get over my fear of showers from seeing the original "Psycho" at a tender age...and now THIS!!

 

[jneutron]

Oh, great. I finally get over my fear of showers from seeing the original "Psycho" at a tender age...and now THIS!!

Hey, just figured I'd scare ya....

Actually, it's real...not a figment of my imagination..it's not possible to stress the safety of home dist. enough..

Paul: here's two pics...they have been copied from:
http://www.photovault.com/Link/Technology/Power/Distribution/TPDVolume01.html

In the first, the top 3 wires are the high voltage ones..very high voltage.
The transformers on the right pole take that hv, and turn it into the voltage we use in our house..this pic is actually for 3 phase wiring which is usually just for large business power users...I couldn't find a good one for house use.
the lower batch of thicker wires is the group of wires that go to the building. Sometimes, the connection from the house goes to a pole where it connects to those lower ones...sometimes, if the house is close to the street, the connection will be made right in the middle of those dangling wires...the house I live in is connected that way, and the business I spoke of also is connected in the middle.

Below the house power wires will be the cable and phone runs, which are entirely different from what I speak of.

You know? These are pics of the same poles, just a slightly different angle...

For a residential feed, there may only be one hv wire up top, with one transformer, and the lower runs will be only 3 wires instead of the 4 shown here. My house is like that....only one wire way up there, and the strong neutral with two hots bundled with it.

I'll try in the next few days, to have a digital camera with me to get a good pic.

John..

 

[jneutron]

OK guys, heres the pics.

The first pic is the transformer on the pole.
The single thin wire going up is the high voltage feed to the one bushing transformer. It connects to the middle high voltage wire from the power company three phase system.
The three thick wires from the top right of the xfmr come down, then to the batch of wires that are below it. They are the neutral wire, and both the hots needed for 240 volt house use. They connect to the thick wires with those big boxlike splice things, they are about 2 inches cube. the slightly fuzzy twisted wires going to the left of the "mess" is a feed to a building on my left. If you look veeeryy closely, you will see that there is a thick copper wire stapled to the pole to the left of the streetlamp feed (we have some nice looking old style streetlamps here that look like the old gas lamps..) That wire goes to the base of the pole, and is connected to a very long, very thick grounding rod to earth. That is what is done every two or three poles.

The second pic is the building feed. Notice the wire that is twisted around the insulator thing attached to the house..That wire is the neutral, the center tap of the 240 volt feed. Also note that it has a connector, and it is fed into the pipe that goes down to the load panel in the basement. If one thing in the house is turned on, like a light or hairdryer, the current will go in one of the hot wires here, and it will go out on that neutral wire..for 240 volt things, like a central ac...the current will go in one hot, and out the other. leaving the neutral relatively unforced..

The third picture is the same building I was talking about feed, where it attaches to the wires between telephone poles. The two bottom splice connectors are to the two hot wires needed for 240...the wire that is broken is the neutral wire. It supports the two hots physically to the house, and should be attached to that wide connector at the top of this picture.

The fourth picture is the in pipe ground connection in my house. It looks to be either a #8 or a #6 wire. This is the wire that all the 120 volt current will go through if the neutral wire to the transformer outside is not connected..

This connection is the only thing in that other building that is keeping the neutral and grounds at all the outlets in the building from going to 120 volts. Remember that copper wire on the pole that went to the earth ground? that is how the current is getting back to the transformer in that building. If the water pipe wire corrodes enough to disconnect, then any neutral or grounded surface in the building will be able to make that return current go through you... Is this something you should rely on for your life??

It is a safety connection...it is exactly like an emergency brake..If your regular brake system fails...you certainly can stop your car with the E-brake...you could drive around town all day with the E-brake...but if the E-brake fails, the only recourse you have is yabba dabba dooo...hope ya got an airbag...

Spoke to the store owner again...he said a friend of his told him that this is not a problem...

I guess he believes that I have nothing better to do than bother a complete stranger with some fairytale of a safety thing..

I pray he is not in the running for a Darwin award..

Cheers, John

PS...I called the LIPA company..they are responsible for all electricity distribution here...The girl on the phone was very pleasant, and absolutely confirmed that this is indeed a safety issue and that I'm not just nuts..(well, maybe that's an exaggeration). Unfortunately, I didn't know the building number, so I gotta write that down tonight and call back.

 

[RaT]

What you say is quite accurate except that in many places, mine included, the plumbing system is not our ground anymore for the very reasons you pointed out like dielectric unions as well as plastic piping. The best method is a ufer (20' length of #4 rebar) ground embedded in the bottom 3 inches of a concrete footing (thats where the lowest resistance is) grounding the entire system. That typically ties to the main panel with a minimum of #6 solid copper which can carry 200 amps for a short duration tripping a 200 amp main or the fuses on the transformer. We still ground the plumbing, the plumbing is not grounding the system, same with the gas line. If you do not have a ufer ground, a 5/8" 8' long copper coated steel rod driven straight down is acceptable in many locals. Problem is, it must be in moist soil in order to keep resistance low. Locating it near a downspout is an option. It's not an issue back East, but out West, something to consider. You are correct though, a bad neutral is a problem. Lights that flicker excessively especially with high loads on the home circuit can tell you somethings up. Call your utility company, they can easily check.

 

[jneutron]

Lights that flicker excessively especially with high loads on the home circuit can tell you somethings up. Call your utility company, they can easily check.

Total agreement..

I note you are in California...

Just got back from San Fran, with a coupla days in Napa...

I noted that the xfmrs on the poles out there were two bushing types, so the hv neutral is independent of the house neutrals...So, you are not tied intimately to earth as we are here.

If you lose a neutral over there, while neutral and ground may float off center, I don't think it will cause them to rise with respect to earth, but just toast some electronics...Here on LI, it can do that..

The Mike Holt site has some good stuff on this..

Cheers, John

 

[Shinerman]

Dang, I thought were you going to post on the dangers of "Stripper Poles".

But seriously, back in my stripper days I had many close calls. I still have nightmares. Yeh, that's right, you are all looking at my Avatar right now and wondering why I ever quit.

Shinerman

 

[RaT]

Typical utility setup is to ground the transformer neutral at the pole with what they call a butt wrap. The pole is wrapped with the grounding wire before setting it in the ground. It is pretty amazing to see all the configurations out there. When I see some of the shows like This Old House I sometimes see the differences in East style utility configurations vs West Coast.

Total agreement..

I note you are in California...

Just got back from San Fran, with a coupla days in Napa...

I noted that the xfmrs on the poles out there were two bushing types, so the hv neutral is independent of the house neutrals...So, you are not tied intimately to earth as we are here.

If you lose a neutral over there, while neutral and ground may float off center, I don't think it will cause them to rise with respect to earth, but just toast some electronics...Here on LI, it can do that..

The Mike Holt site has some good stuff on this..

Cheers, John