Yup another electrical question.

[Patrick Walsh]

Thank you for the help.

Can someone explain to me the problem with running my saw off my old three prong dryer outlet.

I get that it is not grounded "although i admit i had not prior considered that" can someone explain why it is safe to run my dryer this way but not my saw?

That 13 A power draw sounds like a 3 hp motor, not a 5 hp motor. The L6-20 plug fits with that as you would run a 3 hp saw on a 20 amp circuit. A 5 hp single-phase motor will generally draw somewhere around 22-25 amps and requires a 30 amp circuit and a 30 amp plug (6-30 or L6-30).



I would NOT plug your saw into one of the old-style 10-30 3-prong dryer outlets as there is no ground in that outlet- you only have two hots and a neutral. You will either need to fish out the ground wire from the outlet box (it will be in there somewhere as the 10 ga nonmetallic cable they ran to the box always has a ground wire) and replace the receptacle (and the dryer cord) with a grounded four-prong 14-30 receptacle or run a separate circuit for a proper grounded 6-30 or L6-30 outlet.

I used to run my saw from a 14-30 four-prong dryer outlet using an extension cord with a 14-30 plug for my saw. That is perfectly safe as I connected the two hots and the ground and forgot the neutral. You can't do that with an ungrounded 10-30 outlet.

[Jim Seyfried]

Thank you for the help.

Can someone explain to me the problem with running my saw off my old three prong dryer outlet.

I get that it is not grounded "although i admit i had not prior considered that" can someone explain why it is safe to run my dryer this way but not my saw?

Pat, I was going to ask for clarification on that too. It would make more sense to me if it was a branch circuit, but dryer circuits are typically dedicated. From my experience, typically for a house the service entrance panel has a bonded neutral. In your panel are the neutral and ground wires in the same bus or have a bonding bar to the panel? If it does I'd say your saw is grounded.

Now for your dryer a three wire plug is outdated. The ground for the dryer has the potential to be current carrying as it is used as a neutral for the light and/or controls. I don't think it is allowed anymore except for existing installations.

[Patrick Walsh]

Panel has a bonding bar...

Pat, I was going to ask for clarification on that too. It would make more sense to me if it was a branch circuit, but dryer circuits are typically dedicated. From my experience, typically for a house the service entrance panel has a bonded neutral. In your panel are the neutral and ground wires in the same bus or have a bonding bar to the panel? If it does I'd say your saw is grounded.

Now for your dryer a three wire plug is outdated. The ground for the dryer has the potential to be current carrying as it is used as a neutral for the light and/or controls. I don't think it is allowed anymore except for existing installations.

[Steve Meliza]

It would make more sense to me if it was a branch circuit, but dryer circuits are typically dedicated. From my experience, typically for a house the service entrance panel has a bonded neutral. In your panel are the neutral and ground wires in the same bus or have a bonding bar to the panel? If it does I'd say your saw is grounded.

That's pretty much the size of it. This thread isn't so much about what does the law of the land require so much as what do the laws of physics require. In a dryer outlet connected to the main breaker panel the only difference between the ground and neutral wire is the insulation color and wire size.

[Phillip Gregory]

Thank you for the help.

Can someone explain to me the problem with running my saw off my old three prong dryer outlet.

I get that it is not grounded "although i admit i had not prior considered that" can someone explain why it is safe to run my dryer this way but not my saw?

The neutral in a 10-30 or 10-50 receptacle was supposed to function as a ground as well since the neutral and ground are bonded at your entrance panel. The issue with this is that your dryer or range uses 120 volts as well as 240 volts and thus there is current being carried in the neutral wire. The ground may thus not actually be at ground if there is a significant 120 volt load being drawn from the appliance. The NFPA thought better of allowing what was supposed to be a grounding wire to carry current in 1996 and mandated use of the four-wire hot-hot-neutral-ground 14-30 and 14-50 receptacles in that year's version of the NEC.

The saw would theoretically be grounded if you used the neutral wire as the ground. The neutral and ground are going to be bonded at the entrance panel and your saw does not draw any 120 volt current and thus should theoretically have no current on the neutral wire. However this is disallowed in the NEC as you are not supposed to use anything but an actual ground wire for grounding. I personally would fish out the grounding wire and use a proper 14-30 receptacle and plug to use a proper ground. There will be an actual grounding wire either inside or tucked behind your dryer's junction box as the cable being run to it is going to be a 10/3 with ground unless you have an extremely old installation. I've dug out the grounding wire and changed 10-30 to 14-30 receptacles before. The ones I've seen have had the ground wire wadded up in the back of the junction box; all I had to do is uncurl it and connect it to the new receptacle.

[Patrick Walsh]

Thank you for taking the time to explain that so well.

I intended to spend the day in the shop today but instead spent it with the dogs and family in the garden. Next weekend i will get back to this.

Again thank you very much!

The neutral in a 10-30 or 10-50 receptacle was supposed to function as a ground as well since the neutral and ground are bonded at your entrance panel. The issue with this is that your dryer or range uses 120 volts as well as 240 volts and thus there is current being carried in the neutral wire. The ground may thus not actually be at ground if there is a significant 120 volt load being drawn from the appliance. The NFPA thought better of allowing what was supposed to be a grounding wire to carry current in 1996 and mandated use of the four-wire hot-hot-neutral-ground 14-30 and 14-50 receptacles in that year's version of the NEC.

The saw would theoretically be grounded if you used the neutral wire as the ground. The neutral and ground are going to be bonded at the entrance panel and your saw does not draw any 120 volt current and thus should theoretically have no current on the neutral wire. However this is disallowed in the NEC as you are not supposed to use anything but an actual ground wire for grounding. I personally would fish out the grounding wire and use a proper 14-30 receptacle and plug to use a proper ground. There will be an actual grounding wire either inside or tucked behind your dryer's junction box as the cable being run to it is going to be a 10/3 with ground unless you have an extremely old installation. I've dug out the grounding wire and changed 10-30 to 14-30 receptacles before. The ones I've seen have had the ground wire wadded up in the back of the junction box; all I had to do is uncurl it and connect it to the new receptacle.

[Chris Friesen]

I would NOT plug your saw into one of the old-style 10-30 3-prong dryer outlets as there is no ground in that outlet- you only have two hots and a neutral.

It's a problem for a dryer since a lot of them use 120V for the electronics and light so there could actually be current on the neutral, putting it at a potential other than ground.

If you plug a pure 240V tool into a 3-prong dryer outlet it should actually be just as safe since there is no current on the "neutral", allowing it to basically act as a ground.