Electricity question

Quote: petroglyph

Every place has their own little peculiarity's, if it's working and no one is getting shocked off of the water pipes or fridge, it is somebody's standard? All power company's are sensitive to complaints however, and I have seen more than once where a "squeaky" wheel will be the one that is greased. Often times there are words they key into, such as sparks or smoke coming from the trees. just sayin

The only standards I can find online are for "Maximum Length of Service Drop".


(1) The EU has a utility pole with high voltage wire about 50' from this customer's service drop. But instead of putting a pole mounted transformer to reduce voltage to his house, they run the wire for 300' through heavy trees to share the transformer with two other houses and a garage. That seems like a false economy.

Quote: Maximum Length of Service Drop:

The customer, where necessary, provides space on customer's property for PPL EU to install its pole, transformer structure or substation at such location so that the length of PPL EU's overhead service drop does not exceed the following approximate lengths:
Service Drop Maximum
#4 Triplex Aluminum 150 feet
#1/0 Triplex Aluminum 125 feet
#4/0 Triplex Aluminum and #2/0 or #4/0 Quadruplex Aluminum 100 feet
Open 3 wire, #4/0 or 350 kcmil Copper and 350 kcmil or 500 kcmil Aluminum 60 feet
Open 3 wire, 500 kcmil or larger Copper and 750 kcmil Aluminum 60 feet
Open 4 wire, #4/0 or larger Copper and 350 kcmil or larger Aluminum 60 feet

(2) It seems unusual to use the "neutral" as a strength member to partially support insulated line going to a house.

Quote: Pacomartin

The only standards I can find online are for "Maximum Length of Service Drop".

Did you try "high voltage specifications"? Or, even your own utility will probably send you a copy of their "specs" upon request?

Quote:

That seems like a false economy.

Per region or utility, each has there standard construction drawings. Each unique service isn't designed uniquely. Typically someone from engineering will look at the site, customers needs, and distances involved and send out the build instructions to the crews, who have standards that are utility wide. It is pretty simple, I hate to admit. Dangerous and heavy sure, but simple.

Length of span is directed by the manufacturer. There is a range at how taught the conductors can be pulled [sag]. The apparent aluminum in the center, has a steel core, and is called acsr, Or aluminum conductor, steel reinforced. The insulated conductors wrapped around it are just laying on it and they are not nearly as strong comparatively. The neutral or bare wire, if looked at it safety wise is the most important of the 3 or 4. Without the neutral, wild voltages can happen and electric shock.

Quote: kenarman

The blogger doesn't know what he is talking about Paco. Transformers come in a variety of sizes depending on the connected load. The KVA(kinda of like KW) of the transformer is usually the largest number painted on the transformer. You can do your own math and divide that by 240 Volts (not 120v) to get the number of amps the transformer is rated for.

OK, I see that the transformer connected to one home is 13 kVA, while the transformer in question connected to 3 homes and a garage is 50 kVA. So I stand humbly corrected that the overload is not an issue.

I don't know the voltage of the wire. I read 7.2 kV or 12 kV or possibly something else. But I still don't understand that it is necessary to run a single 140' line with high voltage into a stand of trees, just to run at least one secondary line for the service drop back out on the same poles. It seems like an unnecessary fire hazard. But the repairman came early this morning without consulting with me, and just repaired the line as is.

I still have questions on the neutral line. A tree is laying right on it in one section, and a few yards over a secondary electrical line is wrapped for about 50 yards around the neutral. In other places the secondary line is independent of the neutral.

Quote: Pacomartin

OK, I see that the transformer connected to one home is 13 kVA, while the transformer in question connected to 3 homes and a garage is 50 kVA. So I stand humbly corrected that the overload is not an issue.

I don't know the voltage of the wire. I read 7.2 kV or 12 kV or possibly something else. But I still don't understand that it is necessary to run a single 140' line with high voltage into a stand of trees, just to run at least one secondary line for the service drop back out on the same poles. It seems like an unnecessary fire hazard. But the repairman came early this morning without consulting with me, and just repaired the line as is.

I still have questions on the neutral line. A tree is laying right on it in one section, and a few yards over a secondary electrical line is wrapped for about 50 yards around the neutral. In other places the secondary line is independent of the neutral.

A tree should not be on the neutral line. In normal conditions it doesn't create an immediate problem because the neutral should be at or close to the same potential as ground (I actually like the English term better which is Earth Potential). There are however all kinds of possible fault conditions where the neutral can become energized and then the tree on the neutral could be a danger to life or property. I have never seen a situation like your describing with a secondary conductor wrapped around a neutral, that sounds really hokey. Just a thought but you are sure it is not the telephone line. If they are on the poles they will be the bottom conductors but are likely underground.

Quote: kenarman

I have never seen a situation like your describing with a secondary conductor wrapped around a neutral, that sounds really hokey. Just a thought but you are sure it is not the telephone line. If they are on the poles they will be the bottom conductors but are likely underground.

It is not the telephone line. Of the 13 utility poles there are four cases where the secondary conductor goes from one pole to another. In only 1 out 4 cases is it wrapped around the neutral. In the other three cases they are separate lines.

My initial guess is that someone was lazy. As I understand it the neutral line can function as a lightning rod, and should not have a current circling it.

Quote: Pacomartin

It is not the telephone line. Of the 13 utility poles there are four cases where the secondary conductor goes from one pole to another. In only 1 out 4 cases is it wrapped around the neutral. In the other three cases they are separate lines.

What you describe is not "standard", sounds like a repair not an initial install. Or hokey. As was the picture you posted of the xfmr.

Quote:

My initial guess is that someone was lazy.

That was probably one of those coffee drinking, donut eating, cab lizard cousin dating lineman? This is where the term "hero to asshole in 60 seconds" comes from. Lets face it, everybody loves 'em when the power is out, but when the lights come back on, would anyone really want a lineman dating their sister?

Quote:

As I understand it the neutral line can function as a lightning rod, and should not have a current circling it.

The neutral is the return to source in an AC system where the voltage originates. It attracts lighting like flame to a moth, as does everything else. Lightning is funny stuff. It often is earth originated and actually flows from the earth to the clouds.

Lighting is also DC current, it is no part of an ac system, it does "pick" on the tallest best grounded objects in the sky.

Bonus fun factoid: Do you know that most electric clocks account time by the frequency from their electric source, at a frequency of 60 cycles per, [in the US]? Stand alone systems on generation, the locals know when the generator is running slow, because their electric clocks lose time.

So when the crew arrives to find the lights out and discover the service is underground, they call the supervisor and say, hey supe, we forgot our shovels. The supe says, "that's ok, you guys can lean on each other till I get 'em out there". lol

Quote: kenarman

You can do your own math and divide that by 240 Volts (not 120v) to get the number of amps the transformer is rated for. Although the size of the main breaker on a house can relate to the load it often doesn't. Many homes have oversized services either because the home owner was of the "bigger is better" mentality or the electrical contractor sold him an unnecessary upgrade. The electrical code recognizes this by allowing what is called 'demand factors'. This means that the more residences that are connected to a service the smaller amount each additional residence adds to the size of the main service. In a typical apartment/condo unit after allowing for the first few residences at 100% of the main breaker size you quickly get down to the point where each service only adds 25% to the main service size. The electrical utility goes through this same process when sizing transformers and conductors.

In three cases there are single homes hooked to single isolated transformers. In two cases the transformer is 15 kVA and in the third case it is 25 kVa.

15KVa <=> 125amps
25KVa <=> 208amps

I think these value represent average over a certain amount of time. So 15KVa is more than enough transformer to run one house.

Quote: Pacomartin

In three cases there are single homes hooked to single isolated transformers. In two cases the transformer is 15 kVA and in the third case it is 25 kVa.

15KVa <=> 125amps
25KVa <=> 208amps

I think these value represent average over a certain amount of time. So 15KVa is more than enough transformer to run one house.

You are still dividing by 120 volts not 240 volts Paco.

I will try and give you a quick lesson on a transformer works and in particular the pole top transformers you have been looking at. You can even look at the transformers and see how the connections work to some extent.

The transformer has relatively small high voltage wires and larger low voltage wires wrapped around a magnetic core. The ratio of these wraps is the ratio of the two voltages. On the pole top Xformers you are looking at the ratio is set up to output 240V on the low voltage side. In order to supply the 120 volt that much of your equipment and lights require they also take a 3rd wire from the center of the low voltage conductor. The KVA rating on the transformer is based on this 240V output.

To relate this to the overhead wiring running into your house you likely have what is called triplex. This consists of 2 black insulated and 1 bare neutral. This neutral is constructed the same as the ACSR discussed earlier in the thread and has a steel core for the structural strength required for the cable. The voltage between the insulated cables is 240V and the voltage between EITHER of the insulated conductors and the neutral is 120V.

End of Professor Mode hope it makes sense.

Quote: kenarman

The transformer has relatively small high voltage wires and larger low voltage wires wrapped around a magnetic core. The ratio of these wraps is the ratio of the two voltages. On the pole top Xformers you are looking at the ratio is set up to output 240V on the low voltage side.

So the transformer has a turns ratio of 7200:240 = 30:1.

But these online tutorials are very confusing. One say "A 200 amp service for a home can consume 48,000 VA (E*I) or 48 KVA". While I realize that most homes never get close to 200 Amps, it still seems like a 15 kVA transformer is rather small (15,000 Volts/240 Volta/Amp = 62.5 amps) . It seems like the 200 Amp home wiring is ridiculous overkill.


This video helps.

As I mentioned in an early post it is usually total overkill. If you do not have electric heat you would seldom need to install a 200 Amp service. A residence seldom draws over 10 amps @ 240 volts unless the oven, dryer or hot water tank are on. Take your electric bill and divide the KWH for the month by the number of hours in the month and you can calculate what the average amperage draw is.

To illustrate this I at one time provided service to a trailer park which had 14 mobile homes on a 200 Amp service. Each of these homes had an electric range, electric dryer and an electric hot water tank and was about 1000 ft sq. in size. In the winter when people would start plugging in electric space heaters, heat tapes and the block heaters in their vehicles the park would blow the 200 Amp fuse about once a month. That particular park was built under an older code and was eventually upgraded to a 400 Amp service and had no more issues.

I also once installed a 100 amp service in a new house. Over time the owner added a standalone garage, a shop, a swimming poll, a sauna, a hot tub. When he was done counting the sub panels in all the outbuildings he had used 132 breaker spaces. The 100 Amp main breaker never tripped in the 10 years I serviced the building.