240v wiring - no ground

[thrytis]

I bought a 3 hp saw recently, and i was planning on running an extension cord from my dryer outlet in the next room to power it until i got around to doing some rewiring in my shop sometime in the future. The saw came with a 6-15 plug on it (2 pole plus ground), and right now the dryer outlet uses a 10-30 receptacle (3 pole, no ground). I was thinking of switching out the dryer outlet to a 14-30 (3 pole plus ground) and then make a cord with a 10-30 plug on one end and a 6-20 receptacle on the other, but when i pulled out the outlet i found there is no ground wire. Is there a way i can use this outlet with the saw?

Thanks!

 

[DavidF]

I bought a 3 hp saw recently, and i was planning on running an extension cord from my dryer outlet in the next room to power it until i got around to doing some rewiring in my shop sometime in the future. The saw came with a 6-15 plug on it (2 pole plus ground), and right now the dryer outlet uses a 10-30 receptacle (3 pole, no ground). I was thinking of switching out the dryer outlet to a 14-30 (3 pole plus ground) and then make a cord with a 10-30 plug on one end and a 6-20 receptacle on the other, but when i pulled out the outlet i found there is no ground wire. Is there a way i can use this outlet with the saw?

Thanks!

I find that very strange that there was no ground wire at the dryer skt, that would seem to break all the rules. No Neutral I can understand. Was there really only two wires (two hots) or 3 (2 hots + Neutral may be for 120v controls). If you were feeling brave you could run the saw without a ground, but I wouldn't want to do it, especially as the state of the saw wiring is not known.

 

[thrytis]

There were three wires (red, black, and white i think), two hots and a neutral. Apparently grounded 240 outlets weren't required until 1996. From what i've read, the appliance frame is grounded through the neutral pin. I don't really understand that though, so i wasn't about to attach the neutral to the saw's ground.

I think i'll live without the DC (which is using the one 240 outlet in the shop) before trying to run without a ground. At least the dust causes a slower death. :saw:I'm just hoping there is a quick solution to having both running though.

Thanks

 

[Jim Murphy]

240v circuits use two hots and a ground. There is no neutral. If the appliance (like a dryer) uses 120v for a light and blower motor, there are two hots, a neutral (for the 120v needs) and a ground.
You need to look behind the insert in your panel. For a lond time, the neutrals (white) and grounds (green) were intermixed. Newer panels separate the neutrals from the ground. In a sub-panel, almost always the neutrals return to the main panel and the ground is through a separate ground rod system.
So, if you pull off the panel, and the neutrals (white) and grounds (green or bare) are hooked into the same "bus bar", you don't have an isolated neutral ground and you can safely run the saw with two hots (probably black and red) and a ground (probably white). If you have a tester, you will see 120 volts between the individual hot legs and the ground, and 240 volts between the two hot wires.
Actually, in my opinion, you can safely run the saw if you have two hots and neutral or two hots and ground. Just make sure you identify the two hots.
Is that right, Scott Smith <g>?

 

[junquecol]

If the dryer outlet was run using SE cable, then the ground could serve as the neutral. If was run using NM cable, then you had to have four wires, two hots, a neutral and a seperate ground. Got tagged on this once a long time ago on an elect. insp. Now all must have four wires. Originally the four wires were for mobil home applications. This was to keep the frame (and door handle) from becoming electically hot. Stand on the ground and reach door handle and get zapped! In your case, the white can become a ground. Go to panel and see if there is a seperate ground bar from the neutral bar. If there isn't, simply add a piece of green electrical tape to both ends of this conductor. Now you have a green ground wire. If there are seperate bars for the neutral and ground, then move white (in panel) to ground bar and wrap with green tape. Using colored tape you can change the color of any wire except a green ground. It is always a ground.

 

[Gotcha6]

A neutral (white or gray)wire is required on a device only if there is a load imbalance between phase legs (i.e. the light bulb example in the dryer). If you're running a 3 hp saw motor, it will show on the motor connection diagram that you will have 2 'line' wires that are 120 volts to ground each and 240 volts line to line to ensure they're on different phase legs. Each phase leg should have the same load. The third wire should be a ground wire (green) as a safety in the event of a short. The neutral would not be required in this case.

 

[thrytis]

I think Jim may be on to something! I pulled the cover off my panel, and it looks like all the neutrals (whites) and grounds (bare) share the same bus bar. The outlet has 120 volts between the hots (red/x or black/y) and the neutral (white/w) and 240 between the two hot wires.

Existing receptacle configuration:

Electrical Panel:

So it sounds like i can connect the neutral to the ground and the hot wires to the hot prongs and should be good to go for my saw. I'll leave the outlet as it is, and do the conversion of the 10-30R to 6-20P in the extension cord.

Thanks!

 

[scsmith42]

Jim, your memory reminds me of my wifes! (grin). As usual (with the rare exception of when you calculate board footage...) you're advice is sage and well presented!

Thrytis - there's a lot of good advice on this thread, and it's all pretty much spot on. Typically you would not need a four wire connection for the typical 240VAC motorized shop equipment.

A trivia point for you... REALLY OLD 240VAC equipment did not even have a neutral - simply two hots.

If it were me, I'd leave the dryer receptacle the way it is (since this is a standard dryer plug) and build an extension cord with the proper connections on each end. If you want to use a 4 wire cord (such as a SO type), then simply insert the ground and neutral wires into the same terminal on plug that will go into the dryer receptacle. Later on, if you wire your shop with 4 wire receptacles, you can still use your extension cord by swapping out the plug.

Regards, Scott

 

[thrytis]

Thanks Scott! I'll give it a try as soon as i get the saw assembled and can put together an extension cord.

Is there any reason to put in 4 wire receptacles in the shop when i wire it? I can't think of anything that would require it unless some AC units might.

When i put in a new subpanel, will i need to add a new ground for the subpanel to meet current code since the neutral and ground are combined in the main panel?

Thanks!

 

[McRabbet]

Eric,

I would recommend you use L6-20 and L6-30 receptacles and plugs in your shop for 240 Volt circuits. These are twist lock style for assured connections. I'd also recommend #10 wire for them all. You could put more than one receptacle on a circuit as long as you are certain that only one device is ever turned on. You do not need 4-wire devices or wire.

 

[Jim Murphy]

When i put in a new subpanel, will i need to add a new ground for the subpanel to meet current code since the neutral and ground are combined in the main panel?

Yes. You will need at least one standard ground rod with appropriate connector driven into the ground. A #6 bare copper wire runs from the connector into the subpanel. One side of bus bars is wired to this ground, and all the bare wires connect here. The other side bus bar is connected to the neutral feed (typically a #2 aluminum,but depends on the run length) back to the house regardless of how the house is wired. There is usually a shunt in the panel that allows the two bus bars to be tied together or separated. You want them separated. When you connect your 240 equipment, the ground goes to the ground bus. Only your 120V receptacles and lights are tied into the neutral bar.

 

[Travis Porter]

Yes. You will need at least one standard ground rod with appropriate connector driven into the ground. A #6 bare copper wire runs from the connector into the subpanel. One side of bus bars is wired to this ground, and all the bare wires connect here. The other side bus bar is connected to the neutral feed (typically a #2 aluminum,but depends on the run length) back to the house regardless of how the house is wired. There is usually a shunt in the panel that allows the two bus bars to be tied together or separated. You want them separated. When you connect your 240 equipment, the ground goes to the ground bus. Only your 120V receptacles and lights are tied into the neutral bar.

Doesn't that just apply to detached structures? I thought for sub panels in an existing structure that already has service you had to run a ground and a neutral from the main panel and keep the neutral and ground separate in the sub panel?

 

[scsmith42]

Travis, I think that you and Jim are stating the same thing - keep the ground and the neutral's separate on all sub-panels. The only difference is that Jim is advocating a separate ground rod bonded to the remote sub-panel, and you're example ties into the ground rod already installed on the main panel. Either way, all neutral's are bonded to a single point ground.

Jim, correct me if I'm wrong (and I know that YOU will... <grin>), but the reason why the ground and neutral are kept separate at the sub-panels is to avoid a ground loop?

One question though - you mention that the neutral from the 240VAC equipment should connect to the ground buss. In the rare event that a 240V piece of equipment had a 120V accessory (such as a light bulb on a 240V drill press, mill, lathe, etc), then in this instance shouldn't the neutral be bonded to the neutral buss, and a separate ground wire run?

Scott

 

[mkepke]

Thanks Scott! I'll give it a try as soon as i get the saw assembled and can put together an extension cord.

Is there any reason to put in 4 wire receptacles in the shop when i wire it? I can't think of anything that would require it unless some AC units might.

Have never encountered a wwking machine that required it - unless you have 3 phase power to your shop (ha ha).

There are plenty of machines or workstations that have both 240V and 120V motors, but they all have separate feeds (plugs).

Note that I would co-locate my 240V plugs next to 120V plugs to avoid cords snaking across the shop in all directions. It's annoying stepping around the 240V cord for the lathe, the 120V cord for the lathe's work light, the 120V cord for the lathe's sander...

As Jim mentioned, I too would re-task the neutral wire in the dryer circuit to a ground by marking with green-tape. And I'd replace the dryer outlet with a proper 2+ground 240V outlet. It's just a couple of bucks.

-Mark

 

[thrytis]

Thanks to everyone for their help. I got the saw pretty much together now and assembled my extension cord last night. It worked great. Now i need to start thinking about adding a new subpanel and outlets.

 

[junquecol]

Have never encountered a wwking machine that required it - unless you have 3 phase power to your shop (ha ha).

There are plenty of machines or workstations that have both 240V and 120V motors, but they all have separate feeds (plugs).

Note that I would co-locate my 240V plugs next to 120V plugs to avoid cords snaking across the shop in all directions. It's annoying stepping around the 240V cord for the lathe, the 120V cord for the lathe's work light, the 120V cord for the lathe's sander...

As Jim mentioned, I too would re-task the neutral wire in the dryer circuit to a ground by marking with green-tape. And I'd replace the dryer outlet with a proper 2+ground 240V outlet. It's just a couple of bucks.

-Mark

Not quite so fast young man, there is a section in the NEC titled- Multi-Wire Branch Circuits. Using four wires: two hots, a neutral, and a ground, you can have both 110 and 220 out of the same double pole breaker. This is the wiring method of choice in my shop. One of the hots passes through DC sensor in panel box. At each location, I have two 110 recpt. and a 220 recpt. Both the 220 and one of the 110 recpt. operate the DC unit. A subpanel is basically a multiwire branch circuit.
As for three phase power, my neighbor has it in his shop, using a rotoray converter I build for him. He has a Bridgeport mill and a Sharpe lathe- what a good neighbor.