Author Topic: Questions on US electrical systems  (Read 5160 times)

Offline Greekman

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Questions on US electrical systems
« on: December 04, 2013, 12:50:50 PM »
welL i am amiss of how things are working over there.

I have been watching some youtube videos on generator hookup and there are some things that i cannot understand...

1. Is the US grid a 2-phase one?
over here it is 3 phase and homes either get a single phase feed or a 3 phase one. businesses etc usually opt for 3-phase do to higher power demands

2. in one video it was said that you can get 220AC from a US socket.
I will assume it is by a different wiring were the 2 prongs get power and the neutral shares the ground prong.
( I have also seen this on a switch board in one of ricksDIY videos on setting hiw Heezy transfer switch)
But what about the appliances?

3. What is the amp rating of a regular home feed?
Overhere older setup get a 25A feed with a 35A fuse on the powermeter. newer are 35-35Amps
But i see 15A and 25A switches on the US switch boards. isn't this too little considering that you have 110V AC?

I am sure more questions will arise after your replies, so please be patient when I come back with more.


Offline cmxterra

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Re: Questions on US electrical systems
« Reply #1 on: December 04, 2013, 12:55:05 PM »
Not sure about question number three. But homes are 2 phase. The split the two phases on different banks on the panel.

Offline mxitman

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Re: Questions on US electrical systems
« Reply #2 on: December 04, 2013, 01:21:01 PM »
In general most homes here in the US get 2 phase, 240 VAC, 60 Hz.....split on a 100-200 AMP circuit breaker panel, with single phase loads of 15-20 AMP @ 120VAC and 2 phase loads of 240VAC at 20-80 AMP for heaters, stoves/oven-ranges, water heaters, dryers etc. All 3 phase is usually commercial/industrial and there is also 277VAC single phase for commercial too that is very common.

Offline wraithe

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Re: Questions on US electrical systems
« Reply #3 on: December 04, 2013, 04:49:47 PM »
US homes are single phase, they have two 120 Vac legs that come off a center tapped transformer, each leg is 120 Vac compared to neutral, because the two legs come off of one transformer secondary, the two legs are exactly 180 degrees out of phase and result in 240 Vac peak to peak. If it was two legs of a three phase supply, there would be two secondaries in the transformer and they'd only be 120 degrees out of phase. Hope that makes sense. Most new homes are set up for a 200 Amp service entrance.

Oops, almost missed one question, the US grid is 3 phase out of the generation plants, industry and some farms use 3 phase, but most homes tap off of two phases and are single phase to the home, based on what I wrote above.

Offline Greekman

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Re: Questions on US electrical systems
« Reply #4 on: December 05, 2013, 11:33:32 AM »
Ok i think i got it

mxitman,
since you replied also...
Can you explain why the ground and neutral were on the same place in one of your installation videos?

all,
how is the "2 phase loads of 240VAC" wired on the circuit board and an outlet?

how about question no3 in the OP?

Also. i see peopleusing 4-prong locking extension cords for generators. Are these 2 phase? (neutral, ground and 2 phases)
Asumming the generators outputs single phase how do they wire the prongs?



Offline wraithe

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Re: Questions on US electrical systems
« Reply #5 on: December 05, 2013, 08:11:33 PM »
Ok i think i got it

mxitman,
since you replied also...
Can you explain why the ground and neutral were on the same place in one of your installation videos?

all,
how is the "2 phase loads of 240VAC" wired on the circuit board and an outlet?

how about question no3 in the OP?

Also. i see peopleusing 4-prong locking extension cords for generators. Are these 2 phase? (neutral, ground and 2 phases)
Asumming the generators outputs single phase how do they wire the prongs?

I think it's okay to post a link to a pictorial view: Household electrical circuit. This explains how it isn't two phases, each 120 volt leg is one side of a 240 volt center tapped transformer secondary. Picture is worth a thousand words.

Question no. 3, most newly built houses have a 200 amp service entrance, and a 200 amp main breaker, from there, it's branched off to the individual loads, typically 15 or 20 amp circuits for the 120 Vac legs, if memory serves me correctly, the 240 Vac circuits are generally 30 or 50 amp.

Ground and neutral in the US go to the same point in the breaker box, but serve two significantly different functions. The neutral wire gives a return path for the AC power to return to the utility. The ground on the other hand is usually attached to the case of whatever you are turning on, that way if the line side of the power has some how failed and become attached to the case, instead of energizing the case (and you if you are touching the case), a dead short is created which will trip the load breaker and disconnect the broken appliance hopefully before you are electrocuted.

The 4 prong generator plugs are neutral, ground, and two 120 Vac hot legs that are 180 degrees out of phase, so they can run individual 120 Vac loads, or just like utility power, when run together, they make 240 volts.

Offline TexasGirl

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Re: Questions on US electrical systems
« Reply #6 on: December 05, 2013, 10:59:56 PM »
I think it's okay to post a link to a pictorial view: Household electrical circuit. This explains how it isn't two phases, each 120 volt leg is one side of a 240 volt center tapped transformer secondary. Picture is worth a thousand words.

Question no. 3, most newly built houses have a 200 amp service entrance, and a 200 amp main breaker, from there, it's branched off to the individual loads, typically 15 or 20 amp circuits for the 120 Vac legs, if memory serves me correctly, the 240 Vac circuits are generally 30 or 50 amp.

Ground and neutral in the US go to the same point in the breaker box, but serve two significantly different functions. The neutral wire gives a return path for the AC power to return to the utility. The ground on the other hand is usually attached to the case of whatever you are turning on, that way if the line side of the power has some how failed and become attached to the case, instead of energizing the case (and you if you are touching the case), a dead short is created which will trip the load breaker and disconnect the broken appliance hopefully before you are electrocuted.

The 4 prong generator plugs are neutral, ground, and two 120 Vac hot legs that are 180 degrees out of phase, so they can run individual 120 Vac loads, or just like utility power, when run together, they make 240 volts.

Bingo.  What he said is correct.

Since a picture is worth a thousand words...

Single phase residential power:


Twist Lock Generator plug and diagram:



~TG

Offline Greekman

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Re: Questions on US electrical systems
« Reply #7 on: December 06, 2013, 12:02:50 AM »
I think it's okay to post a link to a pictorial view: Household electrical circuit. This explains how it isn't two phases, each 120 volt leg is one side of a 240 volt center tapped transformer secondary. Picture is worth a thousand words.

Ok, that did it....

there some things that are so novel....
1. The GFis on the receptacles themselves
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html#c1
we have just a central one on the switch board
2. The 240V receptacle
a google search opened the fllodgates on the different types.
http://en.wikipedia.org/wiki/NEMA_connector
but i will stop at that

thanks everyone!

Offline wraithe

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Re: Questions on US electrical systems
« Reply #8 on: December 06, 2013, 02:16:39 PM »
Ok, that did it....

there some things that are so novel....
1. The GFis on the receptacles themselves
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html#c1
we have just a central one on the switch board
2. The 240V receptacle
a google search opened the fllodgates on the different types.
http://en.wikipedia.org/wiki/NEMA_connector
but i will stop at that

thanks everyone!

Per the new Fire Code (NFPA 70A), if your local authorities require the newest code, all outlets in the garage, and within 6 feet of a source of running water (I think that's the way they put it) have to be GFCI's (ground fault circuit interrupt for those that don't know the acronym), for retrofits, they usually use GFCI outlets, but new construction usually has a GFCI breaker in the box, in addition, every breaker that isn't a GFCI in new construction has to be an AFCI, arc fault circuit interrupt.

Offline IKN

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Re: Questions on US electrical systems
« Reply #9 on: February 12, 2014, 05:33:20 AM »
Hey Greekman, just a few added comments.
1. Here electrical supply is 60Hz (cycles per second) whereas most European countries use 50 Hz.
2. Old household service systems were mostly 60 amps. The advent mass use of things like air conditioning, microwave, and other large electrical loads and homeowners insurance requirements required increasing the supply to 100amp up to 400 amp service systems.
3. Basically, as Wraite answered, the 2 phased 220v supply comes into the load center through a large main breaker rated for your service, ie 100 amp, 200 amp and so forth. From there, each of the 110v phases goes to a bus bar (one on each side) that have centrally locate lugs for breaker connections that alternate up and down from one side and then the other. Hence, when you clip in a single breaker, it connects to one of the lugs for a 110v supply or connect a double breaker that clips on two lugs connecting to both supplying 220v. These breakers are of various amp ratings depending on the loads it will supply and run 10, 15, 20, 25, 30, 50, and 60 amps.

Offline Greekman

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Re: Questions on US electrical systems
« Reply #10 on: February 12, 2014, 10:29:02 AM »
that "replies" button is such a wonderful thing!

2. Your 60 amps are the same KW as us, 35Ax220V...
3. Regarding our one-phase system, breakers connect on the phase, unless theyare for high consuption devices (water heater, electrical stove) that connect a double breaker for phase AND neutral.
as i told bove, neutral and ground are different lines.
I am clueless to our phase system though, but at the mometn there are still houses on the one-phase system, and newer ones usually install 3 phase nowdays. All business are 3-phase by regulation

edit i found these:
Our electrical network

house network
« Last Edit: February 12, 2014, 10:40:38 AM by GreekMan »