Table Saw Power 120/240?

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Splinter

New User
Dolan Brown
My Jet Table Saw can run either on 120v or 240v. It is currently set up for 120volt. Is there an advantage to switching it from 120V to 240V?
 

Joe Scharle

Joe
Corporate Member
1. The wattage will remain the same.
2. Motive force will remain the same
3. GFIC recpt will cost alot more than $10.00.

However, if the distance to the breaker is over 50', then you should goto 240V.

Joe
 

browningcw

New User
Charlie
Less Amps? Easier for the motor to get the power it needs?
Less amps means less voltage drop (voltage drop = current in circuit x resistance/foot in wire x length of wire). The motor will not receive the same voltage as the service transformer or house panel. It will receive voltage at the panel minus the voltage drop in the wire. Obviously the lower the voltage at the motor, the more current the motor needs to make the same power, which in turn raises the voltage drop.

Most tablesaw today have motors designed to run on 120VAC, 1 phase, 15 amp circuits (the size typically found in most homes; usually with 14 AWG wire). If you have a newer home, you may be lucky and have 20 amp circuits which use #12 AWG wire.

From the 2008 NEC, #14 AWG stranded copper has .00314 ohms per foot. #12 has .00198 ohms per foot (based on 75 degrees C). This is why TS (and other power tool manufacturers) stress the drop or extension cord requirements in the front of the manual. Most (typical) extension cords are #16 AWG or smaller. #16 AWG has .00499 ohms/foot.

One last thing to consider, more current means more heat and as it heats, copper's resistance increases.
 

ptt49er

Phillip
Corporate Member
Wouldn't it also use less electricity? (to switch it to 220V) Or have I completely managed to get on the wrong train of thought? I thought that it would pull less power, allowing you to use electricity more efficiently and thus dropping your power consumption and bill. Am I wrong in these thoughts?
 

Bas

Recovering tool addict
Bas
Corporate Member
The answer is: maybe. If you're running your table saw off a circuit that is close to capacity, or the circuit is a considerable distance from the panel, then going to 220V could help.

Regarding distance/ voltage drop, Charles pretty much said it all in his post.

I ran my previous saw off a 15A circuit, which was fine, until I also tried to run the shop vac at the same time (poor attempt at dust control). The whine of the shop vac actually went down in pitch when I started up the table saw. Likewise, the pitch of the table saw would rise when I then shut off the shop vac. Clear indication the circuit wasn't delivering the goods....

If you have a dedicated 20A circuit, you're not likely to see any improvement. Of course, having a big plug and industrial-looking receptacle does improve one's stature and makes your saw at least appear more powerful :)
 

Howard Acheson

New User
Howard
The only advantage to re-wiring for 240 is that it reduces the amperage in shop wiring running from the breaker to the wall outlet. This means that the voltage drop in the wiring is lessened. If your wiring is properly sized for the amperage and run length, voltage drop will be minimal and well within the operation range of any good motor. Voltage drop will be almost equal if the wire size is the required size for each different motor amperage. Only if your wiring is inadequate for the higher amperage of 120 volts will the motor run better when you convert it to 240. In this case, upgrading the 120 volt wiring one size and making it a dedicated curcuit, will accomplish the same as installing a 240 volt circuit and wiring the motor for 240.

If a motor coming up to speed very slowly or is tripping a breaker during start up or when under normal load, you either have other loads on the circuit, or the circuit is undersized for the amperage or the run length. The fixes are: remove the other loads from the circuit or upgrade the circuit. To upgrade the circuit, either rewire with heavier wire and a larger 120 volt breaker, or convert the circuit to 240 volts which has the affect of lowering the wiring amperage draw. Either of these solutions will equally fix the problem. The motor doesn't care and won't perform differently as long as it gets clean power.
 

cpowell

Chuck
Senior User
This discussion comes up all the time. Short answer - no difference.

Using browningcw's figures for resistance per foot of wire:
Regarding voltage drop, at 15 amps on a 14 AWG feed, 50 ft long you'll drop 2.4 volts across the feed wire. On a 20 amp ckt using 12 AWG with 15A load you'd have 1.5 volt drop, with 7.5 amp load a .75 volt drop. While there is technically a difference between .75 volts and 1.5 volts, in terms of percentage at 120 volts this would be .6% and 1.2% respectively. The power loss in the wires would be .011 kW and .022 kW respectively. So, if you ran the saw fully loaded at the reduced current that the 240 volt supply would give you, on 12 AWG wire, for 1000 hours you would save around 17 kW-hr. Isn't that about $1.70?

The EE in me promises you will never see a performance difference between 120 V and 240 V feed. The motor will never see a difference.

If you need to run a new ckt for the TS and plan on upgrading to a large machine in the future then go ahead and add a 240V ckt.

If you want more power go with a larger motor.

Chuck
 

woodydiver

New User
curt
hello all,
i agree with most of what has been said. I would always run the highest voltage the motor is wound for, in this case 240v. It will give you the benefits as describe eariler, with lower voltage drop, and less heat in the wiring. Less heat in the motor and lower voltage drop means the motor is not as stressed on start up and the peak starting currents will be lower,
which equates to longer life in the windings, caps and switches in the motor and a little less energy used over time. ;-)
curt
 

scsmith42

New User
Scott Smith
I know that Jim is waiting for me to stick my foot in my mouth again, so I might as well not keep him waiting!

Like Curt, I prefer to run my motors off of the highest voltage available. Any motor where I have a choice between 120 or 240 is installed at 240. Most of my new equipment will be installed on 480V circuits, versus the 240 3-phase that I've been using.

In addition to the comments already posted, operating on 240 provides the benefit of a balanced load across both legs of your power in your load center, since you're drawing amps from both legs instead of just one.

You did not state what the horsepower was on your table saw - I am guessing maybe 2 - 3hp? As you progress into higher HP equipment utilizing 240 versus 120 becomes more important, as it also allows you to use smaller wiring (less costly) or have more safety margin in the larger wiring.

Ok Jim - over to you... :lol:

Scott
 

Cuprousworks

Mike
User
I like that 240 isn't as likely to make the lights dim, but that's just me. Someone mentioned the higher cost of a 240V GFCI, but I don't think they are required at that voltage, as they are for garages or basement 120V circuits.

Mike
 

lcottrell

New User
Lance
Mike,

I recently got a dedicated 240V circuit installed in my garage shop with the help of my neighbor. I didn't think about it until reading this thread, but we did not put in a GFCI breaker our outlet on the 240V circuit like we did on the 120V circuits that we also added. Am I understanding you correctly that even though it is in a garage that I don't need it to be GFCI protected because it is a 240V circuit?
 

Howard Acheson

New User
Howard
>> Less heat in the motor and lower voltage drop means the motor is not as stressed on start up and the peak starting currents will be lower,

This is a popular misconception.

All convertible 120/240 motors run on 120 volts internally. There are two coils each running 120 volts and using 1/2 the 120 volt amperage (The coils act as a resistance and split the amperage). All you do when you re-wire the motor to run on 240 is change the wiring connecting of the coils from parallel to series. When wired for 240 volt operation, one 120 volt leg and its associated amperage is routed to each individual coil rather than a single 120 volt line providing 120 volts to both coils. The same voltage and amperage runs through the individual coils no matter how it it wired. It is amperage that creates heat, and because the amperage in each coil is the same for both wiring configuations, there is no difference in the heat produced by either wiring configuation. The motor is perfectly happy with either voltage and doesn't even know you made the change.
 

Cuprousworks

Mike
User
Mike,

I recently got a dedicated 240V circuit installed in my garage shop with the help of my neighbor. I didn't think about it until reading this thread, but we did not put in a GFCI breaker our outlet on the 240V circuit like we did on the 120V circuits that we also added. Am I understanding you correctly that even though it is in a garage that I don't need it to be GFCI protected because it is a 240V circuit?
First, I need to disclose that I am not an electrician or inspector. But in research I was doing for my basement shop, it seems that the NEC only requires GFCI protection for 120 volt branch circuits. There's an authoritative site for NEC geeks -- mikeholt.com -- that provides good discussion of electrical codes without you going directly to the NEC.

A little off topic, but related: it's interesting that there is a new NEC code for 2008 that will change the rules somewhat for 120V circuits. Previously there was a GFCI requirement exemption for single outlet appliances (washing machine, sump pump, freezer, where the common usage was to snip the inside connectors on a duplex receptacle making a single outlet). These devices now require GFCI protection. I say interesting because there will be a whole lot of houses sold that will require retrofit if the inspector finds they don't meet code.

The other exemption was for receptacles out of reach (a garage door opener or plug-in lighting). I haven't read anything about whether the 2008 code rules changed for those, or for 240V ciruits.
 

Splinter

New User
Dolan Brown
I guess I should have explained that I don't plan to rewire my saw (which is 1 1/2HP) in its current location. It is only if I were the happen to build my "Dream Shop". :wrolleyes:

Thanks for all the input. I think I would have the TS location wired for 240volt and 120volt. I have a router mounted in my TS extension that needs 120v. But I think I would set up the TS to run on 240v if my dream happens to come true.
 

Glennbear

Moderator
Glenn
First, I need to disclose that I am not an electrician or inspector. But in research I was doing for my basement shop, it seems that the NEC only requires GFCI protection for 120 volt branch circuits. There's an authoritative site for NEC geeks -- mikeholt.com -- that provides good discussion of electrical codes without you going directly to the NEC.

A little off topic, but related: it's interesting that there is a new NEC code for 2008 that will change the rules somewhat for 120V circuits. Previously there was a GFCI requirement exemption for single outlet appliances (washing machine, sump pump, freezer, where the common usage was to snip the inside connectors on a duplex receptacle making a single outlet). These devices now require GFCI protection. I say interesting because there will be a whole lot of houses sold that will require retrofit if the inspector finds they don't meet code.

The other exemption was for receptacles out of reach (a garage door opener or plug-in lighting). I haven't read anything about whether the 2008 code rules changed for those, or for 240V ciruits.
Thanks for the info Mike, I have reached the point in my shop construction where I am installing receptacles. I put a GFCI in the box for the door opener and wired the drop cord coming from the ceiling to my center machines downstream from the GFCI I am thinking ANY protection I can give the opener electronics would be a help. I hope the plug in light exemption remains I am installing 7 eight foot flourescents all on plugs for possible future changes. I think that GFCI protection up at the ceiling is kind of overkill and I could do without the added cost of 4 more GFCIs. The lights will be wired in four banks.
 

Gofor

Mark
Corporate Member
My nephew is a level 3 inspector for the state. He said that altho the 2008 NEC is out, it won't be enforced until July, because the NC board has to have a chance to make their amendments (the state amendments take precedent over the NEC). Currently, the paragraph on the GCFI exemptions is one of the very few that NC has amended. (They added sump pumps to the exemptions). It remains to be seen what changes they make.
The only houses that will require retrofit to the new code will be the ones that have not been completed before the new rules take effect.
However, if your local inspector wants to require it meet the new code, your only option other than to comply will be to appeal it, and hope the appeal is heard before the new rules take effect.

Go
 

sawman

New User
Albert
That is good information on the codes and electrical theory, but I get the feeling that nobody sided with Bas.
I agree with him.


Later,

Albert :saw:
 
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