To be able to build a 300 amp service, you will need equipment that is rated for at least 300 amps. Since this is not a standard size, you will need to build it using 400 amp equipment. Use a 400 amp rated fusebox, and install 300 amp fuses in it. The service entrance conductors will be rated at least 300 amps. From the fusebox you can run 300 amp wire to a 400amp rated breaker box, using the lugs, or you could run into 2 200amp rated breaker boxes, again, using the main lugs. Most power suppliers will allow a feed thru type meter setup for 400 amps, but you should check with them.
Also you will need to check with your local/county/state electrical codes for other specifications and permits required to put in a service. Also it never hurts to contact an electrician or electrical inspector.
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A 300 amp service for your workshop is extremely large. This type of service is larger than what most people have on their homes for their main electrical services. If this is a workshop at your residence, I would suggest you putting in a 100amp service fed from your main service in your home.
If this is a workshop such as one you would fine with a commercial sized workshop, you will want to install a 400amp meter main. Its actually known as a 380amp service, but the industry just referrs to it as 400amp. This type of service will have the meter and main breakers right in it. Then you can run your wiring for your sub panels directly from the new service.
Now before telling you exactly what you need to do along with how to go about doing it, I will need to know the following information:
(1) Is this workshop at your home? If so is the workshop attached to the home or is it detatched from the home.
(2) What type of electrical equipement are you going to install in your shop? Example is 20 lights, table saw, lathe, drill presses etc. Also I would need to know the approx amperages for what your installing
(3) Is your equipment single phase or three phase. This will make a big difference in what type of service you need.
(4) Is the wiring going to be run overhead or underground.
Once I have this information - I will be able to (1) recommend what size electrical service you ned (2) tell you what permits you will need to pull (3) tell you exactly how to do it along with a materials list so you can pick this equipment up for any home improvement store and or electrical supply house. (4) I will then be able to provide you with a detailed diagram shoing you how to wire up your new service, from your main panel out to your new panel.
Hope this helps you out. If you need further assistance with this question or just need further clarification - please don’t hesitate to ask.
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