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07-26-2006, 10:43 PM   #1
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## heating element 240 volt single phase

How do heating elements in water heaters utilize 240 volts single phase?

thanks

07-26-2006, 11:33 PM   #2

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There are two screws on the element. You run 240v to those screws through the t-stat.

I don't know, maybe I don't understand the question.

240v single ø is simply two 120v hots. It is a "line to line" circuit.

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 07-26-2006, 11:58 PM #3 Newbie   Join Date: May 2006 Posts: 19 Rewards Points: 10 Thanks. I guess I'm thinking that a heat element is just (more or less) a wire or such thats heats from resistance.Any time I touch a wire from each leg of a service together it explodes. I can see a motor using both legs because they dont actually come into contact with each other but am not understanding a 240 volt heating element
07-27-2006, 05:07 AM   #4
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Quote:
 Originally Posted by geeyathink I can see a motor using both legs because they dont actually come into contact with each other
Sure they do. They just wind round and round in the motor a bunch of times first. When the motor starts the magnetic field creates enough resistance to keep a short circuit from happening.

A common light bulb is also nearly a dead short. The bulb works like the heating element. It has a high resistance. When the electricity is applied it heats up. In the case of the bulb it also becomes bright and it is put in a glass vacume so that you can see the light.

A heating element heats up without alot of light. This is because it is made from a different type of metal. The key is that the resistance is high when they are on.

This is confusing becuase with the average meter the resistance seems like it is near zero when they are off. The resistance of these metals does change with temperature.

In the case of a motor with a copper coil. it is the magnetic field that creates an impeadance. impeadance works like resistance in an electrical circuit.

 07-27-2006, 06:09 AM #5 Newbie   Join Date: May 2006 Posts: 19 Rewards Points: 10 So as far as the actual connection of a heating element, is it one leg on each end of the element and it doesnt blow because of the resistance between them?
07-27-2006, 11:13 AM   #6
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Quote:
 Originally Posted by geeyathink So as far as the actual connection of a heating element, is it one leg on each end of the element and it doesnt blow because of the resistance between them?
Exactly

07-28-2006, 04:32 PM   #7
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Quote:
 Originally Posted by geeyathink Any time I touch a wire from each leg of a service together it explodes.
Just wondering if you do this on a regular basis or did you do it only once and learn your lesson.

 07-28-2006, 06:38 PM #8 Newbie   Join Date: May 2006 Posts: 19 Rewards Points: 10 I dont go around doing it for kicks. I know humor doesnt translate well in this medium, but I was trying to get the point across in a light mannered way that I understand the Idea that different legs of a 120/240 service shouldnt meet without special circumstances. Having said that, what happens to me most often is seeing a small flash come from behind a breaker when I go to turn on breakers and there are two hots crossed in a switch box somewhere. If I am actually holding wires, I have always found out ahead of time what if any voltage is on them so I havent actually "touched " different legs of a service together and been there to witness what I suspect would be a nice fireworks display.
 07-29-2006, 10:17 AM #9 Sciencerules     Join Date: Apr 2006 Location: Missouri Posts: 61 Rewards Points: 75 Try shorting out a 480v service, thats much more entertaining.
07-29-2006, 10:33 AM   #10
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Quote:
 Originally Posted by MAS2006 Try shorting out a 480v service, thats much more entertaining.
I have to be the party pooper who says that posts like these while well intentioned as humor are not at all funny. Someone could take it the wrong way and the results could be deadly.

In one recient event I saw the results of one leg from a 480 v system shorted to ground. That is 277volts. We believe that the wrench did not even touch ground. It doesn't need to under the right conditions. The arc can jump through the air. This gap was probably about 1/8 of an inch.

The 3/8 inch allen wrench was blown nearly in half. I was told that the fire ball was nearly a foot and a half round. The workers arch flash gloves, and the rubber liners were blown through. Luckly they did the job and protected the worker.

If this guy had not been completely suited up he would have been hospitalized or killed for sure.

 07-29-2006, 10:38 AM #11 Sciencerules     Join Date: Apr 2006 Location: Missouri Posts: 61 Rewards Points: 75 Resistance heat uses a metal element to convert electricity into heat. This element has a "resistance" to the passage of electricity, and when it is forced to conduct electricity, it heats up in the same way a light bulb filament heats when an electric current passes through it. A 4500 watt water heater element at 240 volts will pull aprox 18 amps of current. Use ohms law you get roughly 13 ohms of resistance. P.S. 480 v and up in not for DIYers. Last edited by MAS2006; 07-29-2006 at 10:54 AM.
07-29-2006, 01:30 PM   #12
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Quote:
 Originally Posted by MAS2006 P.S. 480 v and up in not for DIYers.
PS. Most people who are killed by electricity are not electrial professionals. 120v in a house is just as deadly. This is not a joke. We are posting on a web site where most people do not post they just read to find answers to a question.

Please to help them, me and yourself, by never downplaying the hazzards of electricity.

 07-29-2006, 07:41 PM #13 Member   Join Date: May 2006 Posts: 107 Rewards Points: 75 Most electrical deaths are from 120V, possibly because it is most common for unskilled people to be working on. People seem to have no idea what they're dealing with, pretty silly to me. Just pissed at the moment I guess. yesterday some a-hole door guy went flippin breakers when his radio stopped working and burned my buddy pretty who was installing an exit sign. Are lockouts really necessary on job sites? I woul've thought people would have enough common sense. Next time we'll shut down the whole building if that's what it takes.
 07-29-2006, 11:29 PM #14 Sciencerules     Join Date: Apr 2006 Location: Missouri Posts: 61 Rewards Points: 75 Are lockouts really necessary on job sites? Really are a must, the stupid are everywhere.
07-31-2006, 12:07 PM   #15

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I would think lockouts are mandatory on the commercial jobs you mainly do Joe. Didn't the union pound this into you guys?

This is one of the reasons I do NOT attach wires to breakers on new construction until circuits are ready to be hotted up. I come back to half finished jobs all the time to find every breaker on. Luckily only half of them have wires attached.

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