uninsulated overhead grounded conductor

[iwire]

Re: uninsulated overhead grounded conductor

Originally posted by rattus:
when I say "grounded", I mean properly grounded.

Properly grounded or not the structure side of a broken grounded conductor will be at a dangerous potential to ground if one or more of the ungrounded conductors is intact.

The only way this might not be true is as Don mentioned the building has a metal water main interconnected with the neighbors bonded metal water main.

Think of a house fed from a well or a plastic water main, it has a uffer and a ground rods, break just the neutral from the utility.

There will now be dangerous potential between any bonded surfaces and the 'earth'.

You would get blasted standing on damp ground while touching the meter socket or an outside faucet.

The grounding electrodes can not eliminate this difference of potential.

 

[rattus]

Re: uninsulated overhead grounded conductor

Iwire, yes, with a poor ground you could get a potential between earth and neutral. The earth itself would be at a potential which decreases as you walk toward the pole. Now if you climb a metal ladder barefooted and touch the neutral first on one side of the break, and then on the other, you would get zapped twice. Even so, I see no great advantage in insulating the neutral. The power companies and the NEC do not see this advantage either.

This brings up the question, "What is the resistance of a good ground?" In some locales, you have only a thin layer of topsoil over the kaliche, and you must depend on the water system for a decent ground. That works well here because we keep our lawns watered, but there is no guarantee that low resistance is provided at the junction to the water main. We do however have something akin to a 100 ft. ground rod in damp soil.

 

[don_resqcapt19]

Re: uninsulated overhead grounded conductor

rattus,
If there is not a direct metal connection back to the source, there is a hazard. The earth will never prevent a shock no matter how good the grounding electrode system is. The only reason a common metal water pipe system provides additional safety is because it it bonded to the electrical system at multiple points...not because it is a better grounding electrode.

Now if you climb a metal ladder barefooted and touch the neutral first on one side of the break, and then on the other, you would get zapped twice.

It is unlikely that you would get zapped by the line side neutral in this case.(assuming there is a grounding electrode at the pole and it is connected to the utility grounded conductor)
Don

[ December 13, 2004, 01:33 PM: Message edited by: don_resqcapt19 ]

 

[bgisborn]

Re: uninsulated overhead grounded conductor

Some excellent observations and comments have been made but please let me offer the following without direct evidence, at this time. To address some of the comments: A grounded conductor can electrocute you. Take that to the bank. If there is a load on the circuit from any source and you break the circuit at the grounded conductor and you complete that circuit with your electrolyte filled body you could die. As for those who believe the body resistance will protect you, understand that more than 90 percent of the electrical resistance is at the skin contact. If that breaks down, 50 volts is more than enough to kill you.
When a conductor is insulated it presents far less probability of contact if it is broken.
When dealing with large number installations we must think in terms of probabilities.
Improbable on a single case can mean a few probable instances over a large number of cases.
Every single safety rule in the NEC is considered statistically: deaths of fires/number of installations/years.

 

[bgisborn]

Re: uninsulated overhead grounded conductor

Bob, in Mass. Throw away those open delta transformers you guys are still using and do me a favor. Go to Google and do a search with the words "220 volt service".
A General Electrical Administrator is something you need in your State.

Bob

 

[roger]

Re: uninsulated overhead grounded conductor

Bgisborn, the fact is that 220 volts is not a voltage system used in the NEC, see 220.3(A)
and the tables in 430.

Roger

 

[bgisborn]

Re: uninsulated overhead grounded conductor

Roger, indeed it's not. The NEC voltage is a NOMINAL voltage meant to represent the many different transformer connections one would run across in the field. 240 volts would be the highest(for a residence) and usually indicates wye wye connected transformers. The actual RMS voltage is almost always somewhat less. The 220 volt service designation is used internationally. It is a nominal field designation. I never met an electrician who talked "NEC talk" in the field. We call the grounded conductor the "neutral", though the neutral may or not be grounded. The 220 volt designation came about when the usual residential service was 110-115 volts. In fact when I started in the field-some 52 years ago-we refered to the household voltage as simply "110".
The term "220 volt service" is still widely used in the US and in most of the world (By the way, in the "civilized" world a grounded conductor is not used at all-but don't get me started on the stupidity of using one).
Now, a technical point that is applicable here. The meter you are using to measure voltage is a RMS meter rated for 60 cycles. The actual voltage that electrocutes someone, from a 120 volt NOMINAL line, is in the order of 170 volts. The human heart feels peak, not RMS voltage.


Bob

 

[iwire]

Re: uninsulated overhead grounded conductor

Originally posted by bgisborn:
Bob, in Mass. Throw away those open delta transformers you guys are still using and do me a favor. Go to Google and do a search with the words "220 volt service".
A General Electrical Administrator is something you need in your State.

Bob

Sorry I have not run across a "220" service in 20 years of working in MA.

I still ask what it is you do?

 

[iwire]

Re: uninsulated overhead grounded conductor

Originally posted by bgisborn:
To address some of the comments: A grounded conductor can electrocute you. Take that to the bank.

Bob I did not see anyone say that it could not.

Originally posted by bgisborn:
If there is a load on the circuit from any source and you break the circuit at the grounded conductor and you complete that circuit with your electrolyte filled body you could die. As for those who believe the body resistance will protect you, understand that more than 90 percent of the electrical resistance is at the skin contact.

I would also say most all of us agree with that also.

Originally posted by bgisborn:
When a conductor is insulated it presents far less probability of contact if it is broken.
When dealing with large number installations we must think in terms of probabilities.

Can't argue with that either.

Here is a question for you.

Would you have us insulate all the metal surfaces that we must bond the grounded conductor to?

Staying with a 240 volt house service, break the neutral, now all the metal piping in the house is as dangerous as the bare conductor outside.

If you want to propose a change to the NEC on this you will need to offer some evidence.

Simply saying that the number of installations warrants the change is not going to do it.

 

[don_resqcapt19]

Re: uninsulated overhead grounded conductor

Bob,

240 volts would be the highest(for a residence) and usually indicates wye wye connected transformers.

240 leg to leg on a wye?? I don't think so.
Don

 

[roger]

Re: uninsulated overhead grounded conductor

Bgisborn,

240 volts would be the highest(for a residence) and usually indicates wye wye connected transformers.

as Don says, no, this is not the case. A Delta/Delta (center tapped kicker) connected transformer can supply a 120/240v residential service as well as a single winding center tapped transformer can, (most common) but a wye to wye? This is probably the most unstable system there is, and unless a specially built transformer were supplied, a wye would not supply 240 v.

The actual RMS voltage is almost always somewhat less.

It is always less when refering to "effective" AC voltage verses DC equivilant.

The 220 volt service designation is used internationally.

That's because 220v is a true source in some countries.

I never met an electrician who talked "NEC talk" in the field.

You might be surprised if you were actually in the field today.

I started in the field-some 52 years ago-we refered to the household voltage as simply "110".

I take my hat off to you, even if you started at 15 you are an inspiration to me, not that I'll be working, but that I'll be actively fishing.

(By the way, in the "civilized" world a grounded conductor is not used at all-but don't get me started on the stupidity of using one).

We have drug this through the coals before also, mostly in agreement.

Now, a technical point that is applicable here. The meter you are using to measure voltage is a RMS meter rated for 60 cycles.

Surely not, you mean my meters are not accurate. (That was pure sarcasm, I appologize, just couldn't help myself)

The human heart feels peak, not RMS voltage.

Well as stated earlier, the heart muscle will feel and can be electrocuted at a much lower voltage than peak or .707 of peak, actually even as low as 10 volts

Now, I will also ask you, what is it that you actually do?

Roger

[ December 14, 2004, 07:57 PM: Message edited by: roger ]

 

[bgisborn]

Re: uninsulated overhead grounded conductor

Please, please, go to your favorite search engine and type in "220 volt electrical service". From the zillion hits, select as you will. Or, nice guy that I am, I will give you a link to an official document from a public utilty where you can read "220 volt service" The public utility is a New York based one. New York-where it all started and my home town- at one time had only 208 volt service and still does in some areas.
This is a pdf-as you can see:
http://www3.dps.state.ny.us/pscweb/WebFileRoom.nsf/0/042DA8F9661A146985256DEC0067EB4B/$File/doc6871.pdf?OpenElement

220 volts is the European standard and has been since old man Siemans was alive. But French brain washing may have something to do with the wide use of the term "220 volt service" and all those thousands of 220 volt labels we see on water heaters and stoves.

How can you guys doubt a guy from New York?

Bob

 

[iwire]

Re: uninsulated overhead grounded conductor

Originally posted by bgisborn:
220 volts is the European standard and has been since old man Siemans was alive. But French brain washing may have something to do with the wide use of the term "220 volt service" and all those thousands of 220 volt labels we see on water heaters and stoves.

Ah this is America we do not use European standards, we are very independent.

They also use 50 cycles in some foreign countries but what has that got to do with anything?

I have never seen a water heater, stove, dryer etc rated 220.

208 and / or 240 volts will be the ratings.

Here are some examples

I usually find a 240 service measures 235 to 245.

 

[charlie]

Re: uninsulated overhead grounded conductor

Bgisborn, I am having trouble with your concept of 110/220 volts. The public service commission is not made up of electrical professionals, they are political appointees. Why would they know the difference?

 

[George Stolz]

Re: uninsulated overhead grounded conductor

iwire originally wrote:
Sorry I have not run across a "220" service in 20 years of working in MA.

I still ask what it is you do?

At the risk of displaying how uncool I really am, with mathematical genius that courses from my being, I'm quite often heard saying "120/220", because two-forrrty doesn't seem to roll off the tongue. Not to say I use the two numbers as a phrase as listed above. But in the field we aren't carrying our codebooks and meters everywhere we go...

Call it George Voltage.

 

[Ed MacLaren]

Re: uninsulated overhead grounded conductor

bgisborn,

The only people around these parts (Eastern Canada) that I hear using the terms "110 volts" or "220 volts" are folks that are not involved in the industry.

This rule has been in our Code as far back as the 1970s -

"8-100 Current Calculations -
When calculating currents which will result from loads expressed in watts or volt-amps to be supplied from a low-voltage system, the voltage divisors to be used shall be 120, 208, 240, 277, 347, 416, 480, or 600 as applicable"

Ed

 

[bgisborn]

Re: uninsulated overhead grounded conductor

This is getting away from the safety issue I brought up but let me clarify. First there were two small errors I made. The example I gave first said 220 volts. I realized this and immediately corrected myself. It should have read 120-from a true 240 volt service. Secondly the wye wye is used in New York for the 208 volt service not the 240 volt as I mentioned. I won't get into the harmonic issue with this type of transformer. I'll save that for power quality. None of this had anything to do with the strength of my example.
However, you guys are dead wrong on the field use of the term "220 volt service". I gave you a source for thousands of examples and supplied you with an example from a New York utility report. As for appliances with ratings of 240 volts-of course there are. There are also appliances rated at 220 volts. Now we can return to safety. Applience manufacturers must manufacture for the general market. For years, many areas had 208 volt service and later 240 nominal residential service came into practice. Now it is not a safe practice to operate an electrical device with less than 90% of its voltage rating. That is exactly what you would be doing if you wired a 240 rated appliance to a 208 volt service. That's why, one sees the 220 volt rating on some motors and appliances. They are generally applicable to 208 and 240. Another factor that touches on safety and this issue is that you have one devil of a good transformer if you can run rated voltage under load.
There is more and more a tendancy to use NEC terminology in the field. Motor connections are now being called terminations, neutrals are designated grounded conductors, if they are. Pretty soon I'll hear lights being called-what's the NEC word? Luminair? Nothing wrong with this.

 

[wirenut1980]

Re: uninsulated overhead grounded conductor

I believe that 110 V, 115 V, 220 V, and 230 V, etc ratings have nothing to do with RMS, but rather are utilization voltages found on equipment. I always thought that these slightly lower voltages (than those recognized by the NEC) were included in equipment ratings in case there was voltage drop to the point where the equipment actually only sees 110 V, 115 V, etc. I also agree that people who use these voltages are not involved in the electrical industry, because they are often talking about service voltage. Just my 2 cents.

 

[bgisborn]

Re: uninsulated overhead grounded conductor

David, this is an example from an electrical contractor.
http://www.guldenelectric.com/Residential/residential.html
I could give you thousands of examples where the generic term "220 volt service" is used.
My reference to peak vltage as opposed to RMS had to do with electrical shock. It is a material condsideration for an electrician when he puts a capacitor in a system. They have to be rated at peak voltage, usually,though, it can be ignored. Actually, engineers who design insulation have to consider peak to peak voltages which are 2x peak, but this is rarely a concern of an electrician who would not encounter a 180 degree phase difference from a single source.Single phase transformers can reverse phase by 180 degrees so I can imagine such a situation with two services supplied by different transformers-pretty unlikely.


Bob

 

[bgisborn]

Re: uninsulated overhead grounded conductor

Just to finish this off, here's a link for all the condensor fan motors (vertical mount) for residential air conditioners made in America. not a single one is rated 240 volts single phase. You can wire them to a nominal 240 line but that's not their name plate rating. I have rarely seen any motor simply rated 240 single phase but many rated 220/240 (50/60) or 200-240. It's a silly point, but it was a silly point about the use of the term "220 volt service" you guys brought up. It is a designation that has been in common use by both professionals and non-professionals. 2x4's are not really 2x4 and 1 inch pipe water pipe is not really one inch and a 220 volt service is not-in America-really 220.
http://shop.emotorstore.com/estore/dept.asp?dept%5Fid=1194&tab%5Fdept%5Fid

This has not a thing to do with my initial observation about the uninsulated gounded conductor. I've sufficiently substantiated my case on that.

Bob