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  • What is the potential/voltage of the power line on a city street?
  • Where does the potential/voltage of the line drop to the indoor value, e.g., 120 V in the US?
  • If I need to upgrade the whole electric circuitry of a house, do I need to worry about the high voltage and if so, where does the high voltage starts to drop down to the indoor value coming into the house?
  • To address the concern expressed in the comment below, I am looking to hire an electrician to upgrade the electric circuitry including the panel, meter, distributor, weather head and riser. I am wondering what are actually involved and what kind of price I would expect to be charged. The house is a single family house in Sacramento county, CA, USA.
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    I’m voting to close this question because it's not about home improvement – Ack Aug 13 at 2:43
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    @Ack: It is about home improvement as I have now stated the reason. – Hans Aug 13 at 2:50
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    The answer is to call an electrician. If you need to upgrade the whole electric circuitry of the house and you don't know about the transformers from utility power to residential power, please don't burn your house down. – Jason Aug 13 at 2:56
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    Frankly, the slant of the question and follow on comments smells a lot like "I'm planning to do something with the utility conductors and have no grasp of how dead that will make me" but ...whatever... Not to mention how dead (or homeless due to the fire) you can get messing with 240, particularly before it hits your main breaker, when you think it's 110 and that makes it "safe." If you do survive that, the utility will have a fun time suing you into homelessness anyway. – Ecnerwal Aug 13 at 12:39
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    I agree with @Ecnerwal - your knowledge of residential wiring seems extremely thin, and that lack of knowledge can kill you! If you're planning on doing this work yourself, please spend a LOT of time learning (a licensed electrician in the US will spend about 5 years of book learning & OTJ apprenticeship) before you start, or plan on hiring this out. We'd love to answer your questions, but you have to be alive to ask them – FreeMan Aug 13 at 14:29
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The power delivery utility company distributes the AC power to locations away from the power generating stations using high voltages. This is done to help minimize the amount of power loss in the distribution wires and cables. The power loss is always related to the amount of current being distributed to the loads. For each doubling of the voltage used in the distribution network the amount of current for the same load is cut in half.

The voltage levels used will depend in part upon the type, location and distance that section of the power grid needs to deliver electrical power to the consumer loads. Voltages can be in the 1000s of volts.

When high voltage power distribution reaches a residential neighborhood or a business center transformers are used to step the high voltage down to the voltages used in the homes and businesses. Pictures of some typical power transformers are shown below. Typically these transformers are owned and maintained by the power delivery utility company. When you would need service at a particular current level the power company will deploy the proper transformers and then provide a power line connection from the transformer to the electrical usage meter which would be on or adjacent to the home or business.

Typical Transformers:

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  • +1. Nice answer. Thank you. – Hans Aug 14 at 0:52
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In most places in the US, residential power comes into the meter at 240V/120V - three conductors, 2 hot and 1 neutral. The hots are 240V apart (there are some situations where they may 208V or some other value, but 240V is most common) and the hots are each 120V from neutral.

Typically there will be a transformer either on a pole or in an underground vault or on a street corner which transforms power from some higher voltage to 240V. But you don't need to worry about that. Your utility provides 240V, and how it gets there is up to them. In some large buildings, that transformer may even be inside the building, but you, as the ordinary consumer, only get 240V/120V.

If you have to upgrade the entire electrical system of a house, the safest thing to do is often to have the utility pull the meter (or lock it out in some fashion). That will make your main electrical panel "dead" so that it can be replaced safely. Once you have a new main panel with a shutoff of some sort (either a main breaker or a separate shutoff switch) then any additional work can be done with the meter connected and power "live" to the house.

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  • Just curious, so is the voltage of the power line on the street much higher than 240V? How high is it? – Hans Aug 13 at 3:14
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    It could 240V for anywhere from your closest pole to several houses down the street. Then it will jump up to something higher - potentially multiple steps, possibly as high as 13,000V. A lot depends on the particular utility and how far you are from a power substation. – manassehkatz-Moving 2 Codidact Aug 13 at 3:25
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    @Hans The next step depends on the population density and other factors (as how much high the poles can be in the area). Here in Europe, it is called "intermediate voltage grid" and can be anywhere from 1kV (legacy setups in a small vilages) up to 35kV for a brand new, power-hungry building complex. It is probably the same in US. Usually, you don't have to deal with the intermediate voltage, unless you are a big industrial power consumer that has its own power transformers and get the power directly at the higher voltage (it is cheaper). – fraxinus Aug 13 at 12:20
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    In addition, you will notice (in the photos) that things come in threes. Most power companies run 3-phase supplies (plus an earth safety) down your street with 415 (or 208) volt AC. Your house supply is tapped off any two of the three phases, which reduces the phase voltage by a factor of sqrt(3). – Paul_Pedant Aug 13 at 12:44
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    @Paul_Pedant To be a pedant, the house supply is tapped off of one of the three phases (using two of the three wires). The grid is all delta, so the phases are the three line-line combinations (ie: A-B, B-C, C-A) – J... Aug 13 at 17:35
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What is the potential/voltage of the power line on a city street?

Usually distribution 2300, 4160, 12.47k, or 13.8k, but can be higher. Transmission would be higher and can be run around city streets, but would generally go to a substation.

Where does the potential/voltage of the line drop to the indoor value, e.g., 110 V in the US?

As shown by Michael, there are transformers that convert the higher voltage to lower voltage to your house. The voltage to a residence is 240V, but between two lines. The 120 (110) that you refer to is between one line and neutral.

If I need to upgrade the whole electric circuitry of a house, do I need to worry about the high voltage and if so, where does the high voltage starts to drop down to the indoor value coming into the house?

The lower 240V lines will start at the transformer. This is either on the pole, or on a padmount transformer. In a residence, the voltage would only be 240V.

If you are modifying or updating in your residence, you'll either use 120V (single pole), or 240V (double pole). You would choose based on the need of the line. Generally, you'll always use a single unless it's a high load device such as an electric oven or air conditioner. Devices are built for a voltage and you'll just need to supply what they need. When in doubt, you can ask at a hardware store, or get help from an electrician.

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  • +1. Informative answer. Thank you. – Hans Aug 14 at 0:53

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