How do you get 3-Phase power to a residential workshop

[Chris Padilla]

with the exception of SJ cord which is only rated for 300 volts, virtually all of the wire (THHN/THWN, XHHW, etc.), cord (SO, SOW, SOOE, etc.) and cable (NM-B, AC, MC) used today is rated for 600 volts.

Well, finally something I think I can add to the conversation. So, as has been stated, the size (diameter or more correctly, cross-sectional area since its a volume of metal that the current flows through) of a wire (copper or otherwise) will determine the amount of amperage it can handle before melting or getting too hot to cause other problems. Or as a power company sees it, they want as small a current as possible so they can use as small a wire as possible to save as much money as possible. This is why power lines run in hundreds of thousands of volts and why they use step-down transformers to bring the couple hundred volts into our businesses and homes. As to the insulation on the wire, that is a voltage or more correctly, an electric-field issue. It is known as dielectric breakdown or dielectric strength and is measured in Volts/meter (V/m). There is a particular field strength that a material can handle--usually done on an insulator or a dielectric--before it is no longer an insulator. At the atomic level, the field strength rips normally tightly-bound electrons free from the insulator and it begins to conduct. Once this happens, the insulator is basically destroyed. We all see it burning/melting of the insulator. I'll also note that high voltage power lines are not insulated: costs money and their voltage levels are very high. However, air is also a dielectric/insulator and air also will break down if the field strength is high enough. I think air is around 3 million V/m. I've never heard of a power company running much higher than 800,000 V. But lightning can hit many millions (even billions) of volts so that is why we see it: air is being broken down, electrons ripped from their source, and current flowing--a bolt!

[Chris Padilla]

But, my original question was is amperage amperage regardless of voltage? Insulation rating is a separate factor.

Amperage is the flow of charge. Charge is free electrons that are moving about. In a metal like copper, it has very loosely bound electrons that are easy to break free and move. In fact, most metals exhibit this characteristic.

Resistance is what holds back the flow of charge and takes away energy from the charge moving where it wants to. Resistance can come about from many things but mostly it is energy lost from heat since the electrons bounce around hit things, vibrate, don't travel in straight paths, etc.

From those two, we get voltage: V=iR. Voltage is a convenient form in which to measure and understand and use current and resistance. Current comes from the pure geometry of whatever it is flowing through and resistance as well. One can't talk about voltage without implying current or resistance although we often do. Voltage is easier to use and understand. If one really wants to get to the nitty-gritty of electricity, we should talk in electric (V/m) and magnetic fields (A/m). Current and voltage come about from simplifications of Maxwell's equations but they are still very powerful and easier to use than field theory.

So I hope this helps to answer your question as I'm not sure how to EXACTLY answer your question.

[Alan Lightstone]

Well, finally something I think I can add to the conversation. So, as has been stated, the size (diameter or more correctly, cross-sectional area since its a volume of metal that the current flows through) of a wire (copper or otherwise) will determine the amount of amperage it can handle before melting or getting too hot to cause other problems. Or as a power company sees it, they want as small a current as possible so they can use as small a wire as possible to save as much money as possible. This is why power lines run in hundreds of thousands of volts and why they use step-down transformers to bring the couple hundred volts into our businesses and homes. As to the insulation on the wire, that is a voltage or more correctly, an electric-field issue. It is known as dielectric breakdown or dielectric strength and is measured in Volts/meter (V/m). There is a particular field strength that a material can handle--usually done on an insulator or a dielectric--before it is no longer an insulator. At the atomic level, the field strength rips normally tightly-bound electrons free from the insulator and it begins to conduct. Once this happens, the insulator is basically destroyed. We all see it burning/melting of the insulator. I'll also note that high voltage power lines are not insulated: costs money and their voltage levels are very high. However, air is also a dielectric/insulator and air also will break down if the field strength is high enough. I think air is around 3 million V/m. I've never heard of a power company running much higher than 800,000 V. But lightning can hit many millions (even billions) of volts so that is why we see it: air is being broken down, electrons ripped from their source, and current flowing--a bolt!

6.007???????

[CPeter James]

An interesting thought to add to this thread is that here in New Hampshire, the power company tariffs (rules) on file with the Utilities Commission actually limit the size of electric motors in residential locations to 3 HP. More that that and you are charged at much higher commercial electric rates and a whole new set of rules apply. I would expect that many other locations have similar rules. That being said, I suspect that many of us are in violation of these rules. Fortunately for me, I do not share a transformer with anyone and that probably makes my neighbors happy when my air compressor kicks on or I am out in the shop welding.
C
Peter

[Alan Lightstone]

An interesting thought to add to this thread is that here in New Hampshire, the power company tariffs (rules) on file with the Utilities Commission actually limit the size of electric motors in residential locations to 3 HP. More that that and you are charged at much higher commercial electric rates and a whole new set of rules apply. I would expect that many other locations have similar rules. That being said, I suspect that many of us are in violation of these rules. Fortunately for me, I do not share a transformer with anyone and that probably makes my neighbors happy when my air compressor kicks on or I am out in the shop welding.
C
Peter

I never knew that. Might make for a good reason to not get officially quoted for the cost to bring 3-phase power to the house, just update my 1-phase to add an additional 200 amp service.

[Chris Padilla]

6.007???????

come again?

[Alan Lightstone]

come again?

An MIT Electrical Engineering course that would cover this topic.

I was taking a wild guess as to your Alma Mater, Chris.

Swing and a miss, I guess.