The toggle switch on my HF spot welder took a shit the other day.  The Lowes website has one listed in stock at my local store.  The current rating is the same as the old switch, but the horsepower rating is lower- .75 vs 1.5.  A lot lower.  Will the Lowes switch handle the wattage of the spot welder, or should I keep looking?

Kinda need to get this thing up and running as fast as possible.

Wait...what?  Horsepower rating?

I think one horsepower is about 750 watts, if I remember right. If the current rating is drastically different, I don't know what to tell you. Can you use a small switch and a relay?

Current rating is 20A on both switches, so I'm thinking a simple light switch will work if I absolutely have to.  Wattage is calculated by amps and volts, so I'm confused as to why both switches are rated for 120v and 20A, but the HP of the old switch is twice as much as the new one...?

Am I just such an electronic imbecile that I've never heard of a switch being rated for horsepower?  Is this a common thing?

No, not very common.  I'm guessing that rating makes it easier when choosing a switch for an electric motor.

I just tagging for someone who knows the answer.  I have never heard of HP being used to describe current.

Not current, power.

Switches that are going to be subjected to high-inrush inductive loads, such as OP's spot welder which likely has an inductor, will often be rated in horsepower in addition to volts and amps. This rating reflects the amount of current the switch contacts can handle at the moment the device is turned on. An AC motor will draw up to eight times its running current when first turned on or when held stationary while energized (stalled rotor). OP, I would be wary of a switch for that application that is only half of the HP as the original.

Who made the welder?

This is what I was talking about, my day is complete, I learned something.  Thanks

Well said.  If the load is inductive then you should take that into consideration.  op should look for something at radio shack or maybe mouser/digikey/Newark.

Volts and amps are all that matter.  

 Volts is determined by the insulation, better insulation can stand up to higher volts.  

 Amps is determined by how big the cross section of the metal parts are, bigger can handle more amps without melting.  

 As far as replacing a toggle switch with a light switch, you might get some arcing with a light switch because it isn't designed to have as sharp of a an open/close function.  A good toggle switch will move the contacts together/apart much quicker so that there isn't time for an arc to develop across open contacts that are close to each other.  Arcing will burn the contacts, increasing the resistance, and giving you a poorer connection over time, until the connection is so poor that the switch doesn't provide enough of a connection to make the circuit work properly. Light switches are cheaper to make without that feature, and don't really need it with the loads they typically have.

I wouldn't try a light switch unless I really had to.  If you do use one, change it out for a toggle switch as soon as you can, and watch/smell for arcing problems in the mean time.  

Arcing can also trip an arc fault breaker.

Chicago Electric is the manufacturer.  It had probably 20 welds on the switch before it quit.

I'll keep looking. Thanks guys.

like this?

Search for a manual motor starter switch of the appropriate amperage and horsepower rating.  Grainger is your friend.

That looks like it will work, thank you.  Local store is out of stock, but I found another switch that may work. It's spring loaded and I think I can rig it up as foot activated switch.

Here's the deal:  Switching off an inductive load is much different than switching off a resistive load.

When you switch off a resistive load (like an incandescent bulb), the power gets cut, all is well.   When you switch off an inductive load, the inductor has a good bit of energy built up in the magnetic field around it, and will try to dump that by raising the voltage... and if there's enough current and inductance, the voltage can shoot up to thousands of volts.  That's why, when you unplug the vacuum cleaner while it's running, you get a nice, fat spark - but unplugging a 500W halogen light doesn't do the same thing.

Well, that arcing takes its toll on the switch contacts, as you can imagine.  Over time, the contacts will become degraded and conduct more poorly, so heat production becomes an issue.  Eventually, they can either burn up, melt the housing, or in extreme cases, even get welded together.  That's why relays can eventually "stick on" when they are controlling inductive loads.  Switches designed for inductive loads are made with contacts that are much more resistant to being damaged by the inevitable arcing, but ENOUGH arcing will still damage just about anything.

So:  When a switch tells you how many HP it can control, it's doing so because motors are entirely inductive, and if you know the HP of the motor, you have a rough approximation of both the current and inductance of the load.

Your welder, having a nice big set of coils inside, is an inductive load.  And it draws a lot of current.    You have two choices... buy a low-spec toggle, and plan on replacing it again in the future, or buy a high-spec one and not worry about it.    When I've run into relay/switch problems with inductive loads, I've always replaced them with units two to three times larger, and have never had a problem after that.  When you buy a new toggle switch, pay attention to the voltage rating, many are meant for low-voltage only.

Thanks for the explanation guys.

This is what I rigged up the other day. I had the box already, and the 1" circle was already knocked out from a previous project. I'll pick up a wire holder next time I'm at the store.  Foot activated and it works great!

If that is 120/240v you are going to electrocute the shit out of yourself one day
Metal box and a single insulation wire (solid it looks too) no knock out insert or strain relief, etc

Stranded wire. I didn't have an insert for the 1" hole when I put it together. Rest assured, it will be fixed.

So I take it that it is high voltage

Was it designed that way or did you relocate the switch
Relays man, relays
Or at least get some SJ and ground the box(still a hack)

Relocated the switch. I had some 12ga romex as well, but I figured the 10ga was a better bet. 110v.

And yeah, I agree with using relays. But I used what I had on hand (other than the switch which I found at the ACE hardware store).  I'm working on a batch of AK builds, and the original switch took a shit before I even made it to the second receiver rail installation.  I threw this together just to get me through this batch. I'll redesign it later.