Check with an electrician concerning the amount of amperage you will need. Also check with the power company as to what is allowed. Other questions must also be asked. How do you plan to heat and cool your your house, to heat water, wash and dry clothes, and cook food? How many rooms and square feet do you have? More information is needed before any suggestions are possible.
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If it is a new house that is getting built, plan for the future. Go with the 200 amp 42 circuit panel. With all of the new appliances coming out these days the old 100 amp panel is just not enough. The interim 125 amp panel was supposed to be a stop gap and have enough capacity to handle power demand for the next 10 years. Demand outstripped capacity. The bare minimum these days is a 200 amp panel. Some larger homes have 300 amp services and I have installed one 400 amp service in a single family dwelling.
You have more capacity. If you are starting from scratch you want to size the service for what you might grow into in terms of appliances and so forth. For example, a swimming pool in the future may require more capacity. If you are talking about converting from 100 to 200 amps, you would need to consider if you really need the extra capacity given the cost of a new panel or main breaker and whatever the power company might require to increase service.
It's alwas better to install the 200 amp then the 100.You may not need the 200 right now , but down the line should you deceid to change it would cost you more.
Your main service panel will have a plate or sticker telling you.
The difference is 100 amps
A #1 copper wire with an insulation rating of 90 degrees C is rated at 140 amps.
On a 200 amp or any size service the ground wire is easily identified. Look in the distribution panel for the neutral bus bar. This is where the service neutral (white wire) is connected to the distribution panel. There you will see a bare copper wire connected to the same neutral bar. This is the ground wire that is connected to the ground rods out side of the house.
A 3/0 copper conductor with an insulation factor of 90 degrees C is rated at 210 amps.
Electricians use the tables in the electrical code book. The table consists of wire sizes and insulation factors. The insulation factors include temperature ranges of 60, 75, 85-90, 110, 125, and 200 degrees C. To use the table, an amperage is selected, for example the wire size for a 200 amp service. Look down the list for 200 amps. There are two listings, one for 75 degree C wire at 200 amps and the second for 90 degree C wire at 210 amps. Local electrical code amendments, based on climate and weather, usually stipulate which of the two degree wires are to be used.
A 200 amp service panel will require a # 4 bare copper ground wire.
200
125 and 200=25
A #1 copper wire with an insulation rating of 90 degrees C is rated at 140 amps.
This is a voltage drop question. To give an answer the voltage must be stated.
As a percentage 125 out of 200 points = 62.5%
3/0 wire 3/0 wire
1.6
0.625
Not evenly. 200 divided by 125 equals 1 with a remainder of 75.
200/125 = 8/5 = 13/5 or 1.6
125/200 = 5/8 in simplest form
125% of 160= 125% * 160= 1.25 * 160= 200