basics of USA mains supply

[justin_t]

Hello

I have a product that at present runs on mains electricity in the UK and europe only.

The components that are exposed to ac are as follows:

Heater
motor
relay (switching side)
opto coupler
triac
varistor (across mains)
transformer (providing 9 vac for rectifying to control circuit

What are the main issues i need to be concerned with i.e. the motor and heater, if it is also rated for the us voltage and frequency will it draw more current during operation?


Is the US supply between 0 volts and 110v single phase or is it 2 phase?

Ive only started looking at this today and was wondering if anyone had any input or thoughts on the main things i should look out for.

Thanks

Justin

 

[Hero999]

The US system is split phase, 120VAC-0-120VAC.

As far as I know there are three different types of US sockets:

• Two pin - 120V only, no earth connection so class 2 appliances only.
• Three pin - 120V with earth.
• 240V - two lives each 120V and one earth.

Most of them will probably be 120V three pin, 240V is only used for high drain appliances like cookers, airconditioning and clothes dryers.

If you use a 240V socket, you'll need a double pole switch and two fuses if you need to protect against live to earth shorts.

How much power does this appliance use?

If it's fairly low power say <500W then a set up transformer is probably your best option, if it's high power then use 240V sockets.

 

[Speakerguy]

120VAC single phase 60Hz. Older homes will only have live and neutral; construction since the 1980's will generally have 3-terminal (line, neutral, safety earth) connections. Neutral is connected to earth ground at the breaker box.

The only place you see other voltages is for large home appliances and machinery (like 5HP table saw motors).

 

[jpanhalt]

If you have just moved to the USA, welcome. Not everyone carries a gun, but assume they do.

As for wiring, there is a little book called "Wiring Simplified", which is based on the National Electrical Code. The 2002-code edition was the 40th edition and cost $10.95. It's available at most home improvement centers and is well worth the cost.

John

 

[Willbe]

single phase or is it 2 phase?

The debate on this is endless but I think residences are supplied by a single phase center tapped transformer secondary.
You can get 120v and 240v.
In MD the voltage at the house is allowed to go between 114v and 126v.
The source impedance at a residence outlet is about 1/4Ω so a 10 A load drops the voltage 2.5v.

 

[Hero999]

Was I wrong about 240V sockets; do they not exist?

 

[saturn1bguy]

Was I wrong about 240V sockets; do they not exist?

Your post is correct.

Split-phase (AKA single phase, center-tapped xfmr) is correct, 120V and 240V voltages and their respective sockets both exist and are ubiquitous in most residential dwellings.

 

[BaCaRdi]

Sure do! We use that for appliances with large motors, like driers, air-conditioners, think about it, 2 phase better than 1..hehe In the industries they do use 3 phase as you would think....

I am not sure but would the 60hz / 50hz make a big difference in your designs? I am a beginner mind you, especially with AC direcly.

-BaC
EDIT: Well said saturn1bguy!

Was I wrong about 240V sockets; do they not exist?

 

[BaCaRdi]

Exactly! Man before I get the post in..there is 20more replies I haven't seen.lolol

One note, which was stated, there ARE believe it or not, two plug house, which usually also have had a fuse conversion and are running aluminum cores! The Main Ground (Earth) are at the ingress power point, however they need to carry those line in the wiring, which old people or slum lords(where I live) don't want to make it safe, cause it cost money!

I even have seen here even!, electric earth connections to the copper pluming pipes! Think about that, taking a shower and ZAP!

Hopefully those will fall out of the picture in time, so can disregard it...
These 240vac types are custom, require a existing one, old a/c line or dryer, otherwise an electrician (added expense) needs to combine the two 120v legs for a 240v. This is not standard, allot of homes don't have any 240vac receptacles.

Guess useless information to a point, but information nonetheless.lol
-BaC

The US system is split phase, 120VAC-0-120VAC.

As far as I know there are three different types of US sockets:

• Two pin - 120V only, no earth connection so class 2 appliances only.
• Three pin - 120V with earth.
• 240V - two lives each 120V and one earth.

Most of them will probably be 120V three pin, 240V is only used for high drain appliances like cookers, airconditioning and clothes dryers.

If you use a 240V socket, you'll need a double pole switch and two fuses if you need to protect against live to earth shorts.

How much power does this appliance use?

If it's fairly low power say <500W then a set up transformer is probably your best option, if it's high power then use 240V sockets.

 

[Hero999]

Sure do! We use that for appliances with large motors, like driers, air-conditioners, think about it, 2 phase better than 1.

The US system isn't two phase, it's split phase.

 

[BaCaRdi]

Ohh right duh..... 120---0---120 I getcha..


Cheers,
-BaC

The US system isn't two phase, it's split phase.

 

[Hero999]

240V is used for air conditioners and dryers because doubling the voltage halves the current.

Here in the UK all domestic appliances run off 230V and lots of industrial appliances run off three phase 400V (three 240V lives 120° apart).

110V isn't used much but some industrial portable tools run from it which is 55-0-55V or two 63.5V phases 120° apart as it's far safer than 230V.

 

[BaCaRdi]

Cheers for that, making more sense now
EDIT: Also explains the cost saving on 240v devices over there 120v counterparts

I forget to remember unlike DC the current and voltage are not always in-phase as with DC, cheers all for the information. I do remember that here in the USA if you return back to the grid out-of-phase, there is heavy fines, in industrial areas.

-BaC

240V is used for air conditioners and dryers because doubling the voltage halves the current.

Here in the UK all domestic appliances run off 230V and lots of industrial appliances run off three phase 400V (three 240V lives 120° apart).

110V isn't used much but some industrial portable tools run from it which is 55-0-55V or two 63.5V phases 120° apart as it's far safer than 230V.