# Question about electricity **URL:** \ **Category:** Factual Questions\ **Created:** [March 14, 2001, 10:24pm UTC](https://boards.straightdope.com/t/question-about-electricity/58015 "2001-03-14T22:24:33Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [March 16, 2001, 10:38pm UTC](https://boards.straightdope.com/t/question-about-electricity/58015/21 "2001-03-16T22:38:58Z")
In addition to the reactive losses **Crafter\_Man** mentioned, AC systems suffer from the skin effect, which causes the current to concentrate more towards the edge of the conducter, rather than being uniformly distributed. DC doesn’t suffer from this loss. Although you don’t normally associate skin effect with frequencies as low as 60 Hz (the losses are neglible unless you’ve got some thick wire or buss bar), it is present. I think certain types of stranded wires are used to help minimize the effect, also. Arjuna34 ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 17, 2001, 12:21am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/22 "2001-03-17T00:21:02Z")
> [@](#): > > \*Originally posted by Arjuna34 \* > \*\*In addition to the reactive losses **Crafter\_Man** mentioned, AC systems suffer from the skin effect, which causes the current to concentrate more towards the edge of the conducter, rather than being uniformly distributed. DC doesn’t suffer from this loss. Although you don’t normally associate skin effect with frequencies as low as 60 Hz (the losses are neglible unless you’ve got some thick wire or buss bar), it is present. I think certain types of stranded wires are used to help minimize the effect, also. > > Arjuna34 \*\* Very true. Though, like you said, the effect would be almost negligible due to the low frequency. But it **is** there. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [March 17, 2001, 12:45am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/23 "2001-03-17T00:45:28Z")
For large conductors the skin loss actually is significant at 60Hz - the “skin depth” at 60Hz is about 1/3 inch. For 500 MCM wire (rated at about 380 amps in conduit), the 60Hz resistance is 1.8% higher than the DC resistance. 2000 MCM wire has a 24% higher resistance at 60Hz than DC, which might explain why you don’t see it too often 🙂 ACSR (aluminum conductor, steel reinforced) wire is common- this is aluminum wire with a steel center. Since not much current is carried in the center of the wire (due to the skin effect), steel is used there to increase strength. Hollow conductors are sometimes used in high-voltage transmission lines. This reduces skin effect losses, and the larger diameter reduces the corona voltage. The wire dissipates heat faster with a larger surface area, so you can pump more current into, too. Arjuna34 ---
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [March 17, 2001, 1:17am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/24 "2001-03-17T01:17:32Z")
Well it’s been a long time since Electronics class but I do remember a little something about increasing efficency of AC with something called three phase. In the real world three phase is the most commom way AC is recieved into your house. Thats why there are three wires. Each phase is 120 degrees out of phase with the other two. That is one reason light bulbs last as long as they do. It smoothes the “AC hum” Actually you are looking at something like 180cycles (oops) hertz.The eye cannot detect that in an incandecent light. Actually the skin effect does come into effect(can I say that?)with AC high tention lines. They are copper coated steel,hense high tention. A house wired for DC would lack many of the little luxuries that we have today. Rechargable anything comes to mind first. Although it is possible to set up a lower voltage with DC you would have to set up a voltage divider and would lose most of the 120v to ground. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [March 17, 2001, 6:30am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/25 "2001-03-17T06:30:15Z")
justwannano wrote: > [@](#): > > In the real world three phase is the most commom way AC is recieved into your house. Thats why there are three wires. Each phase is 120 degrees out of phase with the other two. > That is one reason light bulbs last as long as they do… The electric company transmits the power as three-phase, but all the appliances in your house run on the voltage across two of them, which is single-phase. This includes light bulbs. Some heavy-duty industrial machinery uses three-phase, but you don’t have any of these in your house. Common voltage for three-phase is 208 volts. then he wrote: > [@](#): > > …AC high tention lines. They are copper coated steel,hense high tention. The “tension” in “high tension lines” is just another word for “voltage.” It’s not that the wires are stretched really tight, though they probably are. I think “tension” is how the French say “voltage,” but I don’t know why you often see high-voltage lines called that over here. ---
**Author:** ![Mikahw](https://avatars.discourse-cdn.com/v4/letter/m/e9bcb4/32.png) [@Mikahw](https://boards.straightdope.com/u/Mikahw)\ **Post date:** [March 17, 2001, 11:07am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/26 "2001-03-17T11:07:24Z")
Over here at least, we don’t have 3 phase going to the houses. The 3 wires are on either side of the secondary coil of the transformer, and the centertap of the secondary coil. Simple, really. hook up something to both sides, and you have 240V. Hook something up to one side and the centertap, and you have 120V. I do remember about some place that uses 3 phase power for it’s homes though. New York, maybe? ---
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [March 17, 2001, 6:41pm UTC](https://boards.straightdope.com/t/question-about-electricity/58015/27 "2001-03-17T18:41:37Z")
😮 I told you it was a long time ago:O I forgot about Delta Wye circuits. Not so sure about the tension though. ---
**Author:** ![Catenary](https://avatars.discourse-cdn.com/v4/letter/c/e36b37/32.png) [@Catenary](https://boards.straightdope.com/u/Catenary)\ **Post date:** [March 17, 2001, 7:07pm UTC](https://boards.straightdope.com/t/question-about-electricity/58015/28 "2001-03-17T19:07:02Z")
If DC is transmitted to your house (or sub-station) at high voltage/low-current, you’re stuck with low current. High voltage can be reduced to a usable level but, unlike AC, this doesn’t increase the amount of current available. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [March 18, 2001, 2:10am UTC](https://boards.straightdope.com/t/question-about-electricity/58015/29 "2001-03-18T02:10:01Z")
> [@](#): > > \*Originally posted by Catenary \* > \*\*If DC is transmitted to your house (or sub-station) at high voltage/low-current, you’re stuck with low current. High voltage can be reduced to a usable level but, unlike AC, this doesn’t increase the amount of current available. \*\* With the right type of DC step-up/step-down circuitry, the amount of current _can_ increase. It’s possible to make a “DC transformer” with power electronics. The challenge is making it as low-loss and cheap as a transformer. For the record, here’s Cecil on single-phase/three-phase power: [How come the U.S. uses 120 volt electricity, not 240 like the rest of the world?](http://www.straightdope.com/classics/a3_292.html) Arjuna34 [Previous page](https://boards.straightdope.com/t/question-about-electricity/58015.md?page=1)