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heating element 240 volt single phase

19K views 19 replies 8 participants last post by  Speedy Petey 
#1 ·
How do heating elements in water heaters utilize 240 volts single phase?

thanks
 
#2 ·
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.
 
#3 ·
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
 
#4 ·
geeyathink said:
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.
 
#17 ·
they do not come into contact ever in a motor !

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.
The 240 volts are in fact just 2 legs of 120 however they never in any electric motor make contact at anytime ever! How an 240 volt motor works is the 2 120 volt legs are 120 degrees away from each other which in a motor creates magnetic fields at different times. the windings alternate one 120 volt leg than the other and so on. Because the 2 120 volt legs are 120 degrees away from each other they create the magnetic force at different times which turns the motor. Now to answer the question about 240 volt heating elements. As i mentioned before the 2 120 volt legs are 120 degrees out of phase with each other. What this means is as one is positive the other is negative. In the heating element there is great resistance to the electrical current which reduces the voltage greatly and while one leg is positive the other is negative and because of the extreme voltage drop the leg which is positive will disapate into the leg which is negative. Hopefully this will answere your question. These answeres are correct. I have been an industrial electritian for 10 years (journeyman).
 
#8 ·
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. :)
 
#10 ·
MAS2006 said:
Try shorting out a 480v service, thats much more entertaining.:whistling2:
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.
 
#11 · (Edited)
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.

:thumbsup: :thumbsup:

P.S. 480 v and up in not for DIYers.
 
#12 ·
MAS2006 said:
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.
 
#13 ·
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.
 
#18 ·
almost correct


acording to oasha 480 is the voltage where most fatal electricutions occur 120 volt is second. As far as lockouts go, you asked are they necessary to this I ask is it necessary you dont die on the job??? Lockout is mandatory ! Dont be in a hurry and become a statistic just do it. I do have a sugestion on this because I have had people turn breakers on while I was performing service. Instal a jumper from the hot wire to ground at the point you are working. This will prevent you from getting shocked if someone were to turn the breaker back on.(just dont forget to remove it)
 
#15 ·
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.
 
#16 ·
On remodels they are required, and if I were running the job I would shut down the entire are from the MDP and lock the electrical room door behind me. After building power is on I treat everything like it's hot, unfortunately this happened to a friend of mine, who I'm sorry to say, has blown up 3 things so far on this one job, pretty pathetic. Perhaps one day he'll realize this $hit is dangerous.
 
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