Your system?

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manfromsweden

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Hello

I work as a teacher in Sweden and we have a discussion about the electrical system in USA. Can anyone explain in a simple way how your system is built/used. I have seen the voltage 110/127/220/240/440 and others. Is it the same in all states? how long is the education to be an self employed electrician? (I hope I am in the right forum)
 
Re: Your system?

All power distribution systems within the US, Canada, and Mexico are at a frequency of 60 hertz. This differs from the 50 hertz systems used elsewhere in the world.

The system used for most households is the nominal 120/240 volt, single phase system. I emphasized the word ?nominal,? as it means the ?name of? the system. The actual voltage at any point and at any time can vary. What is now called ?120? was once called ?110? or ?115.? What is now called ?480? was once called ?440.? So the message is that you should not get too hung up on the names.

For larger facilities, the power distribution systems are three phase systems. Most of them employ a grounded WYE connection at the secondary of the distribution transformers. That system will have a line-to-line voltage that is higher than the line-to-ground voltage by a factor of about 1.732 (i.e., the square root of 3). Therefore, you will see these systems named by the two voltages (L-L and L-G), as in the following examples: 208/120 volt, 480/277 volt, and 4160/2400 volt.

I am not an electrician, so I can?t tell you how long it takes to become educated to the point that you could succeed in a self-employment role. But I can say that the licensing requirements for my state (Washington) require 8,000 hours of work experience (i.e., 4 years), before receiving a Journeyman License.
 
Re: Your system?

There are no universal requirements as to what education is required to become a self-employed electrician. Every state has its own rules about licensing. Some states don't have statewide rules; licensing is done at the local level in these states.

Generally speaking, there are two main types of electrician licenses: journeyman and master. An applicant for a journeyman license usually must have several years of experience working under the supervision of a licensed electrician. After he obtains this experience, he must take an exam in order to be licensed. Once he gets his license, he can work without supervision.

Usually, to be self-employed as an electrician, a person must obtain a master electrician's license, which requires more experience than a journeyman, and take another exam. In my state (Minnesota), to be eligible to take the exam to become a master electrician an applicant must have five years of experience working under the supervision of a licensed electrician. If an applicant has formal education in electricity, the requirements for experience are reduced a bit.

[ September 30, 2004, 02:26 PM: Message edited by: jeff43222 ]
 
Re: Your system?

Our nominal voltage systems for 600V maximum supply systems (like generators) +/- 5% are:
120V 1 phase 2 wire
240V 1 phase 2 wire
120/240V 1 phase 3 wire
240V 3 phase 3 wire
480V 3 phase 3 wire
600V 3 phase 3 wire
208Y/120 3 phase 4 wire
480Y/277 3 phase 4 wire

The corresponding nominal voltages for utilzation equipment (like motors) are:
115V 1 phase 2 wire
230V 1 phase 2 wire
200V 3 phase 3 wire
230V 3 phase 3 wire
460V 3 phase 3 wire
575V 3 phase 3 wire
(notice these are the nominal supply voltages -4.17%)

This difference between supply and utilzation voltages is one of the reasons you see references to so many different voltages. Other reasons include laziness and old habits (these nominal voltages were decided on over 50 years ago). The correct method should be to refer to nominal supply voltages not to actual measured voltages unless they fall out of the =/- tolerance range.

[ September 30, 2004, 02:47 PM: Message edited by: jim dungar ]
 
Re: Your system?

Charlie, It's nice to see someone who states 3ph voltages as 480y/277, 208y/120, and 4160y/2400 (and not 277/480, 120/208) 480v delta, 240v delta and 240/120 3ph-4w (a 240v delta w/ lighting tap so as not to be confused with 120/240), and 120/240 1ph-3w, etc. which was the rule when I worked for Westinghouse. Mess up those terms and the wrong equipment is likely to be incorrectly specifies, built, and shipped resulting in a costly error.
Also, low voltages were referred to as up to 1000v and medium voltage 1000v-50kv and high voltages above 50kv. For some that 50kv upper limit for medium voltage may be higher.
In any event it is most important that everybody talks the same language, that is that they have the same understanding of what the terminology is referring to.
For some low voltage may refer to voltages below 50v and high voltage 240 and 480v.
 
Re: Your system?

Thank you all for the answers. I can tell you a little about the electrical system in Sweden.
We have nominal 230/400 Volt 50hz 3-phase in almost every house and apartment.
In some older apartments only 230V singel phase
We have also 230V phase--neutral and 400V phase--phase
All lamps, computers, TVs and so on use 230V.
Normally with 10A fuse. Stoves and heating systems use 400v 3-phase.

Some industries have 400/690Volt

(sorry for my broken English)

//H?kan
 
Re: Your system?

manfromsweeden, I wished the US system were that simple. I further wish we could do away with a grounded system, very outdated and antiquated.

Your written English is excellent, better than a lot of US citizens. However, I would bet I would not understand a word of spoken English :D
 
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