120/240VAC Question

[Nutball]

I'm wanting to put some high power outlets in the garage for some powerful tools. I don't have any more room in my breaker box, so I figure I can put the dryer on a switch so it can't be used at the same time as the garage outlets that will be using its breakers.

I have a few questions when it comes to AC wiring. Do 240v appliances only need 2 hot (120v) wires and a ground wire and no neutral? Even if they still need the neutral wire, the 240v is between the 2 hots right? My dryer has two 30A breakers does that equate to 30A 240v or 60A 240v? I assume just 30A.

So, from the wire going to the dryer I should get two 30A 120v lines when used with the neutral line, or one 30A 240v line right?

I'm mainly just trying to figure out what relays I want to use fro switching between the dryer and outlets. I hope to have two 120v outlets on each line(4 total), and two 240v outlets. Of course I'd not run both 120v and 240v tools at once because that would be unbalanced with this setup.

 

[DashApple]

I don't live in America but your system from what I know is 120V - 0V - 120V

Transformer is centre taped and grounded , so the two phases are 180 Deg out giving the 240V across them

you have two 30A 120V supply's with respect to neutral but using the same two lines will get you 240V @ 30A respect to each other

For the 240V Supply , I would run two phase conductors and earth . This will give the 240V and earth for protection .


The UK is abit easier as we only get 230V in are homes : P ,

 

[diachi]

I don't live in America but your system from what I know is 120V - 0V - 120V

Transformer is centre taped and grounded , so the two phases are 180 Deg out giving the 240V across them

you have two 30A 120V supply's with respect to neutral but using the same two lines will get you 240V @ 30A respect to each other

For the 240V Supply , I would run two phase conductors and earth . This will give the 240V and earth for protection .


The UK is abit easier as we only get 230V in are homes : P ,

You're correct, North American homes run split phase. :beer:

 

[badscr]

I’d use a few tandem circuit breaker that turns one slot into two 120v breakers. Do a few of those and you’ll free up enough space to fit a full size 240 breaker.

Or do a sub panel. All 2nd means of disconnect require all grounds and neutrals to be separated and remove the neutral/ground binding. Also check with your local electrician.

 

[Cyparagon]

Many 240V residential appliances require a neutral (aka center tap) if some of the internal circuitry is operating at 120V. Stoves and dryers for example usually have 4 pins instead of 3.

Running 120V and 240V from the same line is fine, provided either leg doesn't go above the breaker rating. for example 240V 10A heater plus 120V 5A drill plus 120V 15A bandsaw all at once would be fine.

I would recommend just running everything to the same breaker. Don't bother with additional switches and relays that just contribute to complexity, heat losses, and voltage drop. Just remember to not exceed the total load. And if you forget, well that's what the breaker is for. It won't hurt anything.

Another option is finding several other circuits in the breaker box you never seem to use at the same time, or are of a lower load and combine loads to a single breaker to free up a spot or two. A lighting circuit that draws 3A nominal for example could be in parallel with the 10A garage door opener and be fed from the same 15A breaker instead of two separate 15A breakers

 

[Benm]

If you run split phase as is common in the US (and unheard of in europe!) you do not need a neutral line if all appliances you use on that leg of the circuit are 240V. You may need/want ground for safety protection, though i doubt that would do you any good if you were to somehow touch both phases as the net current to ground would be zero even when standing in a lake.

Check with code regulations though: often it's not permitted to have wall outlets that are switched by relays or even just switches, unless those switches are right on the outlet itself as is very common in the UK.

This is for safety reasons: if you want to work on a circuit you'd just turn the switch off, decoupling both phases so you can muck with the wiring or something... but if that switch is in another room and someone else thinks it'll turn on the lights or something .. goneski!

 

[Cyparagon]

You may need/want ground for safety protection, though i doubt that would do you any good if you were to somehow touch both phases as the net current to ground would be zero even when standing in a lake.

At the bare minimum, it's for ensuring the metal chassis of the device doesn't become live.

 

[Nutball]

Our house wasn't wired to code, they made so many mistakes. We have a switch in one end of a room that operates an outlet in the other end. Anyway, thanks for the info about 240v wiring.

 

[Benm]

The sure do some unsafe wiring, but the downside is that the US split-phase is just pretty dangerous.

In europe we have 230/240 volt outlets by default, but those are not split phase, they are one neutral and one phase. Stick a nail in the neutral and nothing happens, stick one into the phase and if your connection to ground is so good you are in danger the ground fault protection will trip.

One benefit is that a 'standard' wall socket will provide 16 amps at 230 volts, well over 3 kVA.

For anything requiring more power triphase is commonly used. This is convenient when driving things like large motors such as the ones in elevator systems, or big industrial motors.

It's also used for things like electrical cooking stoves (and things like pool water heaters), though there is a a legacy system for those where 2 lines of the same phase and 2 neutrals are used to get the required amount of power. This system has been phased out though, as it used a connector very similar to the triphase ones, but plugging one into the other would give huge problems.