Why 240V over 120V?

[RagerXS]

If I'm working in the shop solo, there is no risk of current overload on my small sub-panel because at most I'll be running a tool, DC lighting, and possibly a radio and air filtration unit. I get the impression from being a member for quite some time that most of us here work alone in their shop as well. So what are the reasons 240V is preferred to 120V for your machines?

~ Fred

[final_t]

Amps. 20 amps @ 110v == 10 amps @ 220v. If you're a home user like almost all of us are, then this is not a problem and you're fine like you mentioned above. Some items - like a "useful" shop heater, or a bigger bandsaw, requires 220v.
IMHO, 220v is like an air compressor. Once you have it, you naturally find ways to use it!

[scorrpio]

I might be totally wrong here, but if I remember my physics right, there are only so many amps you can put through motor winding before it melts. At 110 volts, to achieve 3hp of power, you need to feed just over 20 amps to a motor, which can be really taxing. At 220 volts, same 3hp is achieved with just 10 amps.

[RagerXS]

Perhaps someday I'll have a giant table saw with a motor that big. But right now the biggest motor I have is the one on my HF DC at 2 HP, and it is only capable of running at 120V. The rest of my motors are smaller...

~ Fred

[LCHIEN]

quote:Originally posted by scorrpio

I might be totally wrong here, but if I remember my physics right, there are only so many amps you can put through motor winding before it melts. ..

for a single winding this is true.
But for virtually all induction motors you'd encounter in a home workshop,
they have double pairs windings which are put in series (for 240) or parallel (for 120V) combinations to switch voltage. It turns out this clever arrangement puts the same current and voltage across each winding so as to maximize the current carrying capacity of each winding.

For practical effects, 240 vs 120 is entirely a matter of reducing current in the branch wiring of the shop; a given set of wires can double the amount of power safely delivered to an outlet for the same distance and wire gauge (heavier insulation is required but virtually all household wiring is now insulated for 240V anyway).

Loring, Electrical Engineer.

[BobSch]

quote:Originally posted by LCHIEN

For practical effects, 240 vs 120 is entirely a matter of reducing current in the branch wiring of the shop; a given set of wires can double the amount of power safely delivered to an outlet for the same distance and wire gauge (heavier insulation is required but virtually all household wiring is now insulated for 240V anyway).

Loring, Electrical Engineer.
[/quote]
Another plus for 240 is that voltage drop goes up by the square of the current. So if you double the voltage you cut the voltage drop under load to Πwhat it would be at 120V.

[RagerXS]

So, a motor capable of running at either voltage will be stronger under load if it is running on 240V than if it was running on 120V? If that is the case I may have to look into it further. But so far I've been unable to come up with any sound reasons to invest the time to have 240V outlets in my basement shop. Regardless of what I choose, I'm wiring it myself so labor cost is not a concern.

~ Fred

[Bulkley]

Some of us don't have the luxury of a dedicated shop with lots of space around a permanently placed saw. We share with cars and wheel barrows and often have to move a saw just to accomodate long stock. In the process, we may use more than one outlet. Because of this, my approach is to stay with 110v, but to use sole-use lines; thus the big motors don't share the lines with anything else. When I use an extension cord, it is rated for 20 amps.

[LCHIEN]

quote:Originally posted by RagerXS

So, a motor capable of running at either voltage will be stronger under load if it is running on 240V than if it was running on 120V? ...
~ Fred

That's not strictly correct.

Assuming that the
branch wire sizes are correctly sized for the voltage and current - then you should not be able to tell the difference between a motor wired for 120 and running on 120 vs. the same motor wired for 240 and running on 240V.

But, if the wire size is barely adequate for 120 and you use the same wire for 220, then the motor will probably run better.

And, if the motor draws more than 15-20 amps at 120 then you may be tripping breakers, since 30A circuits at 120 are rare. But it will only draw 7.5 to 10A at 240, so that's no problem for your circuit.

[RagerXS]

A dedicated circuit for each outlet in my basement shop is a consideration I'm tossing around as well. I'm still on the fence about 240V, and if it's 120V that I stick with then it will be 20amp circuits.

~ Fred

[LCHIEN]

quote:Originally posted by BobSch

quote:Originally posted by LCHIEN

For practical effects, 240 vs 120 is entirely a matter of reducing current in the branch wiring of the shop; a given set of wires can double the amount of power safely delivered to an outlet for the same distance and wire gauge (heavier insulation is required but virtually all household wiring is now insulated for 240V anyway).

Loring, Electrical Engineer.

Another plus for 240 is that voltage drop goes up by the square of the current. So if you double the voltage you cut the voltage drop under load to Πwhat it would be at 120V.

Actually that's incorrect Bob, voltage drop would be linear and 1/2, not 1/4 of what it would be at 120. Note the current is halved and the voltage drop Delta_V is Delta_I x R so delta_V is halved also.

[stewchi]

To me 240 is a pain because the supplies are expensive (outlets, cords, etc), while 120 is supplies are much cheaper. I have not seen any 240v GFI outlets (ofcourse I have not been looking) but the breakers are expensive and that is what you will need for the garage or basement shop in 240. For 120 you can use the cheaper GFI outlets instead of a GFI breaker. To me there is no justifiable reason to switch to 240 unless the equipment you are using draws more the 20A at 120 volts. Above 20Amps supplies are more expensive and special wiring is needed, plus a 30A breaker yada yada yada. So unless you have some monster big appliances (welders, dryers, big big air compressors etc) stick with 120, it will make life easier down the road.

[LCHIEN]

quote:Originally posted by stewchi

To me 240 is a pain because the supplies are expensive (outlets, cords, etc), while 120 is supplies are much cheaper. I have not seen any 240v GFI outlets (ofcourse I have not been looking) but the breakers are expensive and that is what you will need for the garage or basement shop in 240. For 120 you can use the cheaper GFI outlets instead of a GFI breaker. To me there is no justifiable reason to switch to 240 unless the equipment you are using draws more the 20A at 120 volts. Above 20Amps supplies are more expensive and special wiring is needed, plus a 30A breaker yada yada yada. So unless you have some monster big appliances (welders, dryers, big big air compressors etc) stick with 120, it will make life easier down the road.

Good points.

I agree that having a properly wired and performing 120V tool and ciruit of less than 20 amps and changing over to 240 for the sake of expecting better performance is both very expensive - a waste of money and foolhardy from the standpoint of expecting improved performance.

The only practical reason to change to 240V would be to power a tool that would draw in excess of 15Amps from 120V.

However, say the previous garage owner had some 240V outlets properly wired, I would not hesitate to convert dual-winding induction motors to use those outlets if the outlets were located where the tool was to be stationed.

[BobSch]

quote:Originally posted by LCHIEN
Actually that's incorrect Bob, voltage drop would be linear and 1/2, not 1/4 of what it would be at 120. Note the current is halved and the voltage drop Delta_V is Delta_I x R so delta_V is halved also.

Oops. Power = IČR not voltage. Too long out of electronics, I guess...

[RagerXS]

Loring, why would you convert the windings to 240V in your example? What benefit is there from doing that?

~ Fred