220 power setup

[Marc Myers]

Hate to start another thread after I started the one about powering up a cabinet saws vs hybrids. I'm far more of an accomplished carpenter and a year two electrician at best, so I have a few more things I'm just not getting. It was suggested that I create a 220v extension cord from 10/3 cable and power up a 3hp cabinet saw from the line that runs the dryer. I like this idea for the time frame I need it for. Here's my dilemma: the existing dryer line is a older style (pre 1996) which if I'm understanding correctly is dual voltage. One for the dryer motor and a higher rating for the drum. This is on a 30amp fuse. I have found a matching female end that I could put on a 10/3 cable to plug into this receptacle. It matches the 30 amp rating, same poles, but the specs say it has a max of 2 horsepower. The cabinet saw draws about 13 amps but is rated for 3 hp. I understand that volts x amps = watts and that 785 watts = 1 horsepower. I'm just not understanding why a plug that is capable of 30 amps is can only carry 2 hp?? Is there any safety reason why I can't buy a 30 amp female end, tie it to a 10/3 wire, put a standard 30 amp male end and run a 3 hp 220v 13 amp cabinet saw? Is the dual voltage setup of the old dryer style going to cause issues trying to run a single phase motor? I know a lot of electrical numbers from manufactures are 'puffed up' a bit, but some of them you have to pay attention to for safety sake particularly in this case that I'm dealing with a 220 line. If someone far more knowledgable could shine a little light on this for me I'd feel a lot better and safer knowing I have the right pieces in place. I've seen enough melted wires and fire damage for me to make damn sure I get it right.

[Rod Sheridan]

Marc, if your dryer receptacle is a NEMA 10-30R (Google it) it is a 2 pole 3 wire without ground.

It has two lines and a neutral, no ground.

Modern dryers use 2 lines, a neutral and a ground.

Your saw is designed to use two lines plus a ground, such as in a 6-30R.

You're missing the ground wire in your present dryer receptacle.

The best solution would be to change your dryer wiring to 3 conductor plus ground, change to a new style dryer receptacle, and cord on your dryer.

Then you have the correct configuration for your saw.

The ground wire for the dryer receptacle can be run separately, no need to replace the existing wire................Rod.

P.S. Use single conductor 10AWG green wire for your ground.

[Chip Lindley]

Marc, your 13A 230v motor (rated as 3hp) IS an honest 2hp motor. With a 30A plug and 10-3 wiring, NO WORRIES!

[Dan Friedrichs]

Rod and Chip both said very important things - read them a second time!
Rod is right that if you don't have a ground wire present, you can't do this without adding one.

Forget what the HP rating of the motor is - it doesn't matter for what you're concerned with. The only thing you need to worry about is the current carrying capacity of your wire and plugs/sockets. Seriously - forget about HP. It's the amps that you need to worry about, nothing else.

[Marc Myers]

I had a feeling the HP rating was just something listed to be a selling feature like with most other tools. I've got the amps and wire size double checked so I'm good. Glad it's not an issue. You are correct that it is a NEMA 10-30R recpticle. You're saying I don't need to change the entire wire, just add a 10awg green ground wire and swap out to a 6-30R recpticle, correct? Since I'm not changing the entire wire, there are two ends to the ground wire to deal with. The 'grounding' will occur at a proper screw in the new 6-30R receptacle, same as any other setup, but where do I need to tie the other end to? Do I need to run this back to the breaker or is there a trick that I can get a foot of wire, tie it here, tie it there and call it good?

[Tom Cornish]

I had a feeling the HP rating was just something listed to be a selling feature like with most other tools. I've got the amps and wire size double checked so I'm good. Glad it's not an issue. You are correct that it is a NEMA 10-30R recpticle. You're saying I don't need to change the entire wire, just add a 10awg green ground wire and swap out to a 6-30R recpticle, correct? Since I'm not changing the entire wire, there are two ends to the ground wire to deal with. The 'grounding' will occur at a proper screw in the new 6-30R receptacle, same as any other setup, but where do I need to tie the other end to? Do I need to run this back to the breaker or is there a trick that I can get a foot of wire, tie it here, tie it there and call it good?

Like anything else, your inspector has final say, but you do need a completely separate from the neutral path for the ground all the way back to the panel. If this particular run is done in metallic conduit you can use the conduit as a ground (subject to the inspector's opinion of the condition of your particular conduit). If you have only a romex-type non-metallic wire with only 3 conductors - two hots and a neutral, you are out of luck and will need to re-pull.

[Ryan Hellmer]

disclaimer, I am not an electrician. In the not-so-distant past virtually all 220v household circuits would have had 2 poles (hots) and a neutral. The neutral is a bit of a misnomer though as the 220v circuit needs no neutral (since the hots have alternating polarity). To further complicate matters, the "neutrals" and "grounds" would have run to a single bus in the panel. While I won't argue that having 4 conductors in a 220v circuit may have advantages (provided the panel has appropriately separated neutral and ground busses), there is no reason that this cannot be run. In any 220v single phase situation you have 2 110v legs that are combined to create the requisite voltage, in the dryer scenario it has been my impression that the 110v features simply relied on one hot leg and the neutral to complete the circuit resulting in slightly unbalanced legs (not a big issue in single phase).

[Tom Cornish]

disclaimer, I am not an electrician. In the not-so-distant past virtually all 220v household circuits would have had 2 poles (hots) and a neutral. The neutral is a bit of a misnomer though as the 220v circuit needs no neutral (since the hots have alternating polarity). To further complicate matters, the "neutrals" and "grounds" would have run to a single bus in the panel. While I won't argue that having 4 conductors in a 220v circuit may have advantages (provided the panel has appropriately separated neutral and ground busses), there is no reason that this cannot be run. In any 220v single phase situation you have 2 110v legs that are combined to create the requisite voltage, in the dryer scenario it has been my impression that the 110v features simply relied on one hot leg and the neutral to complete the circuit resulting in slightly unbalanced legs (not a big issue in single phase).

One may be able to make an argument that unplugging the dryer and plugging in the table saw may be safe in some specific cases, but there are some REALLY good reasons this isn't done in the general practice.

IF the place where this circuit is fed from is the service entrance, then the neutral bus and ground bus will be bonded, and you can call that wire either a neutral or a ground, but not simultaneously both. If the OP was replacing the dryer with a table saw, it would then be acceptable to replace the receptacle with a NEMA 6-series with no other wiring changes. The third wire is a now a ground, and you're all set.

IF the circuit is fed from a sub panel, the neutral and ground busses will not be bonded, so replacing the 10-series socket with a 6 series will also require moving that wire from the neutral bus in the subpanel to the ground bus. Again, this is fine if the saw assumes the use of this outlet and there won't ever be a dryer again.

If the outlet will be shared use - sometimes that wire will be a neutral wire returning current for 120 volt components in that wire (dryer mode), it cannot also be used as a safety ground (table saw mode).

One reason for this rule is that if there were to be a wiring fault on the neutral/ground wire at the electrical panel, the dryer in this case, would be returning electrical current to the chassis of the saw, creating a very dangerous shock hazard.

Another reason this is a no-no is that passing current through the neutral wire raises its electrical potential - i.e. it's not at ground potential (0 volts) anymore, so again, this wire if also connected in a safety ground situation (table saw), there is a shock hazard, even if there isn't an electrical fault in the neutral wire.

[Andrew Pitonyak]

I thought that the purpose for the Neutral was for devices that used both 220 and 120 so that the dryer could use 220 for the dryer portion and 120 for the controls.

Even worse than I thought, I assume (and we know what that means) that the 220 plug with a ground at least provides a ground, and that it is not difficult to convert the 220 to 120 internally for things that want/desire it.

Please correct my ignorance...

[Marc Myers]

Oh boy...this is getting confusing! Might be time for an electrician!! It seemed a simple enough idea done by a few others, but the plug will be used for both the dryer and the table saw so I need something safe for both. Would it be smarter to just start back at the 30 amp breaker (this one is NOT in the subpanel) pull the existing wire and receptacle, and just start over with a 10/4 wire and the new dryer receptacle design? I could then buy a male/female ends on a 10/3 cord to run the table saw? Last thing I need is to get zapped with a 220 line! Won't see too many more post from me after that...

[Tom Cornish]

I thought that the purpose for the Neutral was for devices that used both 220 and 120 so that the dryer could use 220 for the dryer portion and 120 for the controls.

Correct.

Even worse than I thought, I assume (and we know what that means) that the 220 plug with a ground at least provides a ground, and that it is not difficult to convert the 220 to 120 internally for things that want/desire it.

Please correct my ignorance...

Also correct provided that you have 4 wires - two hots, a neutral, and a ground. This is a NEMA 14-series plug/receptacle. The NEMA 14-30 and 14-50 are commonly used for this purpose.

NEMA 10-series sockets (no ground) are practically obsolete. The NEC has evolved over the years - there are a number of things that used to be "OK", at least from a code compliance standpoint, that are no longer acceptable. The OP may have some kind of grounding lug that the dryer is attached to - water pipe, electrical conduit, etc. This may or may not be acceptable for new use depending on the circumstances.

[Tom Cornish]

Oh boy...this is getting confusing! Might be time for an electrician!! It seemed a simple enough idea done by a few others, but the plug will be used for both the dryer and the table saw so I need something safe for both. Would it be smarter to just start back at the 30 amp breaker (this one is NOT in the subpanel) pull the existing wire and receptacle, and just start over with a 10/4 wire and the new dryer receptacle design? I could then buy a male/female ends on a 10/3 cord to run the table saw? Last thing I need is to get zapped with a 220 line! Won't see too many more post from me after that...

It's up to you as far as what's a managable project. Modernizing old wiring is often a good idea, but you will likely need to have your work inspected, and this can sometimes open a can of worms related to grandfather laws - at some point you may be required to fix/upgrade more than just this outlet.

I can't remember the circumstances of your original post, but if it were me I would try to do it as right as possible the first time - putting my time and energy into a new outlet (or better yet a subpanel) in your shop area that you won't have to be climbing over the dryer all the time to use.

[Marc Myers]

That is exactly what I'm trying to do....get it as right as I can and do it once. Just unfortunate that the wiring I already have is outdated. When the dryer was replaced several years ago it came with the new style plug, and a 3' old style plug that could be swapped out. The older plug is what I have been running ever since. I'm starting to wonder if this is worth the effort and additional expense. I was pushing it by going for the cabinet saw over a hybrid, and now all this rewiring to get a bigger saw up and going. I guess the big question is: If I were going to install a dryer from scratch today, what would be the proper breaker, wire, and receptacle? With this setup, would I be safe to create a 220 extention cord with the properly rated ends to power up a cabinet saw? I'd need the plug to be able to safely run BOTH the dryer and table saw.

[Tom Cornish]

That is exactly what I'm trying to do....get it as right as I can and do it once. Just unfortunate that the wiring I already have is outdated. When the dryer was replaced several years ago it came with the new style plug, and a 3' old style plug that could be swapped out. The older plug is what I have been running ever since. I'm starting to wonder if this is worth the effort and additional expense. I was pushing it by going for the cabinet saw over a hybrid, and now all this rewiring to get a bigger saw up and going. I guess the big question is: If I were going to install a dryer from scratch today, what would be the proper breaker, wire, and receptacle? With this setup, would I be safe to create a 220 extention cord with the properly rated ends to power up a cabinet saw? I'd need the plug to be able to safely run BOTH the dryer and table saw.

The "rightest" plug for what you are talking about is probably the NEMA 14-30. This will require four wires - hot, hot, neutral, ground. I think it would be worth trying to find an electrician in your area to see if this could be adapted to your existing wiring without purchasing and re-pulling new wire. The cost of repulling could pretty easily exceed the cost of an electrician coming to do a quick inspection, if there's a chance of re-using what's there.

Edit: If you do get an electrician - have him examine your dryer to see if you still are using the neutral. It may be that your dryer is perfectly happy with a NEMA 6-30 (hot, hot, ground - no 120 vol components), in which case you can simply update the receptacle to a NEMA 6-30 which will be fine for your saw. This is easily the least work if your dryer can do it.