Electricity question

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August 24th, 2015 at 1:48:29 AM permalink
Pacomartin
Member since: Oct 24, 2012
Threads: 1068
Posts: 12569
I have to talk to electric company in about 8 hours, and I thought that I would run my thoughts by somebody.

We have a dead end series of utility poles that runs for about 1000' and uses 7 poles. There are three tees off this main line (one with 3 utility poles, 2 utility poles, and 1 utility pole). All four terminus electricity poles have a pole mounted transformer which feeds home voltage to up to three homes apiece.

The neighborhood is heavily wooded with trees over 60' tall, and they play constant havoc with the wires after a storm. The one last week was caused by a fire as the high voltage lines touched the tree.

While the two T's with 2 and 3 utility poles are fairly long, the one T with a single utility pole is only about 145' and it runs into heavy old growth. From this terminus there is a transformer which feeds four homes at roughly 110', 120' and 150'. The fourth home is about 300' away so the insulated wire follows the utility poles back underneath the high voltage 7 kV wires.

My feeling is that it is insane to run 7kV wires down this 145' T. They are bound to rub against trees or come into contact with branches that are constantly falling after storms. Wouldn't it be much safer to put the pole mounted transformer on the main line, and send the lower voltage insulated wires through the trees and on to the houses?

Am I missing something?
August 24th, 2015 at 2:01:00 AM permalink
Fleastiff
Member since: Oct 27, 2012
Threads: 62
Posts: 7831
the word "drop" is missing.

aside from a step down transformer, what voltage drops do we get as a result of distance?

the cost of cutting trees is equal if you have 7kv or 110volts. the risk of animal contact on transformers (squirrels, etc) is equal.

If its 145 feet I would say you are correct.
August 24th, 2015 at 7:29:28 AM permalink
Pacomartin
Member since: Oct 24, 2012
Threads: 1068
Posts: 12569
Quote: Fleastiff
If its 145 feet I would say you are correct.


Tree when exposed to un-insulated high voltage line


Let's see if I can persuade them. To run high voltage 145' and in one case of four to simply run the 110 Volt insulated back down the same two poles seems stupid.
August 24th, 2015 at 8:11:10 AM permalink
kenarman
Member since: Oct 24, 2012
Threads: 14
Posts: 4470
Quote: Pacomartin
I have to talk to electric company in about 8 hours, and I thought that I would run my thoughts by somebody.

We have a dead end series of utility poles that runs for about 1000' and uses 7 poles. There are three tees off this main line (one with 3 utility poles, 2 utility poles, and 1 utility pole). All four terminus electricity poles have a pole mounted transformer which feeds home voltage to up to three homes apiece.

The neighborhood is heavily wooded with trees over 60' tall, and they play constant havoc with the wires after a storm. The one last week was caused by a fire as the high voltage lines touched the tree.

While the two T's with 2 and 3 utility poles are fairly long, the one T with a single utility pole is only about 145' and it runs into heavy old growth. From this terminus there is a transformer which feeds four homes at roughly 110', 120' and 150'. The fourth home is about 300' away so the insulated wire follows the utility poles back underneath the high voltage 7 kV wires.

My feeling is that it is insane to run 7kV wires down this 145' T. They are bound to rub against trees or come into contact with branches that are constantly falling after storms. Wouldn't it be much safer to put the pole mounted transformer on the main line, and send the lower voltage insulated wires through the trees and on to the houses?

Am I missing something?


What you have described is typical electrical company standards. They usually don't want to have a secondary (120/240 volt) line to house more than about 150' because of voltage drop. To run secondary (household voltage) in to serve 4 homes would take very large secondary distribution wires on the poles to overcome the voltage drop. If you have deep pockets Paco and offered to pay for it they might rework it for you.
"but if you make yourselves sheep, the wolves will eat you." Benjamin Franklin
August 24th, 2015 at 10:39:32 AM permalink
Pacomartin
Member since: Oct 24, 2012
Threads: 1068
Posts: 12569
Quote: kenarman
What you have described is typical electrical company standards. They usually don't want to have a secondary (120/240 volt) line to house more than about 150' because of voltage drop. To run secondary (household voltage) in to serve 4 homes would take very large secondary distribution wires on the poles to overcome the voltage drop. If you have deep pockets Paco and offered to pay for it they might rework it for you.


The situation right now is the 110V lines are 110', 120', 150' and 300' off a single pole transformer. Ideally, I would like to see them at least pull the 300' drop and put it on it's own transformer. I've read that a lot of transformers are overloaded. One blogger said depending on the model, they should really only be serving a single house with 200 Amp service instead of four homes.

I get tired of this attitude of call me back when there is a fire. I tried several times to tell them that one of their poles was split down the middle and was leaning over at a dangerous angle. They said they couldn't do anything as long as everyone had power. Last week the pole blew over in a windstorm, started a fire, and three homes lost power. So they had to come at 2 in the morning to cut away branches.
August 24th, 2015 at 11:03:58 AM permalink
kenarman
Member since: Oct 24, 2012
Threads: 14
Posts: 4470
Quote: Pacomartin
The situation right now is the 110V lines are 110', 120', 150' and 300' off a single pole transformer. Ideally, I would like to see them at least pull the 300' drop and put it on it's own transformer. I've read that a lot of transformers are overloaded. One blogger said depending on the model, they should really only be serving a single house with 200 Amp service instead of four homes.

I get tired of this attitude of call me back when there is a fire. I tried several times to tell them that one of their poles was split down the middle and was leaning over at a dangerous angle. They said they couldn't do anything as long as everyone had power. Last week the pole blew over in a windstorm, started a fire, and three homes lost power. So they had to come at 2 in the morning to cut away branches.


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. 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.

If it is only one high voltage span that is the main problem you could suggest to your utility that they put a separate fuse on that line. It won't do anything for the fire hazard but at least only that residence will lose power.
"but if you make yourselves sheep, the wolves will eat you." Benjamin Franklin
August 24th, 2015 at 12:45:18 PM permalink
petroglyph
Member since: Aug 3, 2014
Threads: 25
Posts: 6227
Quote: Pacomartin
The situation right now is the 110V lines are 110', 120', 150' and 300' off a single pole transformer. Ideally, I would like to see them at least pull the 300' drop and put it on it's own transformer. I've read that a lot of transformers are overloaded. One blogger said depending on the model, they should really only be serving a single house with 200 Amp service instead of four homes.

I get tired of this attitude of call me back when there is a fire. I tried several times to tell them that one of their poles was split down the middle and was leaning over at a dangerous angle. They said they couldn't do anything as long as everyone had power. Last week the pole blew over in a windstorm, started a fire, and three homes lost power. So they had to come at 2 in the morning to cut away branches.


Ahhh, a sidewalk supervisor, glad to meet you. You are not the first to think the power company should change their system to better facilitate your way of thinking. lol

Like Kman said look up, you can probably see the # on the xfmr, chances are its a 50 or maybe a 25KVA, as Kman knows that stands for 25 thousand or 50 thousand volt amps which is the amount of watts the xfmr is rated at. So the formula is Volts x Amps = watts, 50kva is 50 thousand watts rated. I say rated because PGE used to like to run their xfmr's at around 150% of nameplate, but in the day, they did have heavier windings.

A loose way to figure the xfmr sizing is appx 6kw per residence for average size homes, that mostly use 200 amp service's. So 200 amps x 240 volts is 4800 watts with a bit of safety thrown in, +/- for peak shockload etc. A lot of transformers are overloaded for efficiency. Which will cause them to burn out faster, it's all $$ thinking.

There is a voltage drop [as Kman mentioned], that differs for amount of voltage, size of load, length of line, heat, type of wire, and temperature. Hot weather and large loads cause the wire to stretch [overhead] and the sag [parabolic curve] to drop actually thinning the conductor increasing the resistance, which increases the temperature which lowers its capacity and increases voltage drop. Whatever it is, it has all been done before.

I'm guessing with your description of the split pole that your power company is privately held, they tend to do less maintenance and will at times wait for storms to repair their facilities. Way back in the day, it was easy to tell during storms when PGE had met their million dollar deductible on their insurance, we would then work round the clock.

I think what you described would add the 140 feet to the 300 foot service and increase that customers line drop to below accepted limits. I was surprised to learn that, the power company only has to get your voltage within 10% of what they claim which IIANM is 115 volts? So, they can sell you 105 volts and be withing parameters. It does shorten the life span of a lot of electric devices however by increasing their internal heat.

I also think you are suggesting they string that same length of primar cabling [2x] that distance. Their are costs for everything. You are talking thousands of dollars for what is suggested? Underground can be 10x. SOP these days, isn't like the old rea/rus days, they often expect the customer to pay for any changes. But pocketbook willing , there isn't much that money can't fix.
The last official act of any government is to loot the treasury. GW
August 24th, 2015 at 5:46:44 PM permalink
Pacomartin
Member since: Oct 24, 2012
Threads: 1068
Posts: 12569
Quote: petroglyph
I think what you described would add the 140 feet to the 300 foot service and increase that customers line drop to below accepted limits. I was surprised to learn that, the power company only has to get your voltage within 10% of what they claim which IIANM is 115 volts? So, they can sell you 105 volts and be withing parameters. It does shorten the life span of a lot of electric devices however by increasing their internal heat.


I must not be describing it correctly. The high voltage line runs off a T for 140'. The 300' customer has his 110V line retrace the 140' T and then run another 160' back to his house. So I want to reduce his service drop by 140' (not add to it) by moving the pole transformer (pr adding another transformer)..

Unfortunately that would add 140' to the other two houses which are currently 110 and 120'. It would also add 140' to the existing 150' to a garage which only runs tools, lights and garage doors (maximum 150 kWh in a month over the last 5 years).

The advantage to moving the pole transformer is that there would be no need for 140' high voltage run, which goes right into a stand of very tall trees. If the trees catch on fire they could fall on nearby home roofs.

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The existing pole transformer has a 50 on the side, so it is presumably good for 50,000/240=208 Amps. Now there are three houses with 200 Amp service and a garage with 100 Amp service. I don't know what kind of safety factors are used here. The smartmeter registered 12000 watts once (which I assumed meant 100 Amps).

A quick survey of the neighborhood grid does not identify more than two homes per transformer for any other transformer. I count 12 homes and 7 transformers. Three homes have their own transformer, three transformers have two homes, and the last transformer that I am writing about has three homes and a garage with it's own account.

Quote: petroglyph
Ahhh, a sidewalk supervisor, glad to meet you. You are not the first to think the power company should change their system to better facilitate your way of thinking. lol


I like that title. I am going to have business cards made up.

I have talked to another engineer in the neighborhood who independently thought the setup seemed strange. He reasoned that they expected some expansion which never came.

Main line: 7 utility poles, 3 transformers, 5 homes
Branch A: 3 utility poles, 2 transformers, 3 homes
Branch B: 2 utility poles, 1 transformer, 1 home
Branch C: 1 utility pole, 1 transformer, 3 homes + independent garage with apartment
Branch C is 140' long, and one of the 240V lines retraces the same 140' as the high voltage line and is surrounded by trees between 80' and 100' tall.

Pole spacing is between 80' and 220'




There is at least one place where they bring two 240V lines from a transformer. One house is nearby, but the second house is to far from the pole. So they wrap the 240V line around the ground and go to the next pole with no transformer, and run to the second house. I am not sure if that is standard.
August 24th, 2015 at 6:36:39 PM permalink
kenarman
Member since: Oct 24, 2012
Threads: 14
Posts: 4470
Quote: Pacomartin

Unfortunately that would add 140' to the other two houses which are currently 110 and 120'. It would also add 140' to the existing 150' to a garage which only runs tools, lights and garage doors (maximum 150 kWh in a month over the last 5 years).

The garage could actually be the biggest problem since motor loads such as the tools can take 200% or more of full load rating to start. The voltage drop that can cause may shoot the starting current higher creating a greater voltage drop which can end with the tool not starting. Try using your skill saw on a 100' 16 gauge cord to see the effect.

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The existing pole transformer has a 50 on the side, so it is presumably good for 50,000/240=208 Amps. Now there are three houses with 200 Amp service and a garage with 100 Amp service. I don't know what kind of safety factors are used here. The smartmeter registered 12000 watts once (which I assumed meant 100 Amps).

Paco you need to divide your 12000 watts by 240 on the assumption it is balanced load. This gives you 50 Amps as the most your 200 Amp service has ever drawn. Thus illustrating some of my other points on demand above.
"but if you make yourselves sheep, the wolves will eat you." Benjamin Franklin
August 24th, 2015 at 9:09:34 PM permalink
petroglyph
Member since: Aug 3, 2014
Threads: 25
Posts: 6227
Quote: Pacomartin
The advantage to moving the pole transformer is that there would be no need for 140' high voltage run, which goes right into a stand of very tall trees. If the trees catch on fire they could fall on nearby home roofs.
Tree trimming is an absolute constant in tree country, and it is a proven fact that no tree trimming crew can go more than a full day without angering somebody. Different places have different rights of way. The company would rather cut the trees back a hundred feet from their line and not have to come back again in this lifetime. Some customers raise Caine if more than a 10ft. clearance around the wire itself is removed?

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I don't know what kind of safety factors are used here.
The NEC
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...and a garage with it's own account.
That is probably a wasted account there if the garage can be fed from the adjacent house?

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I like that title. I am going to have business cards made up.
Probably no need, the crew will recognize you, : )

What is labeled "Ground" in the photo is not a ground, it is a neutral. The difference is not insignificant. If this is close to you I have another observation, or if it is an old stock photo it reinforces my belief that it is a private elec. company.

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I am not sure if that is standard.
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 last official act of any government is to loot the treasury. GW
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