220 breaker size question

[Charles Green]

I'm trying to figure out a way to add more 220 capability in my garage. My breaker box is full and I switched every breaker to a double that I can.

I have one 220 outlet that is on a 20 amp breaker that runs my Jointer/Planer combo. I would like to eventually upgrade my dust collector to a cyclone and need more 220. Would it be okay to up the breaker to 40 amp and run two new outlets that would be able to run two machines at the same time? What gauge wire would this need? 8 or 10?

Thanks

[Ken Fitzgerald]

Charles,

If I was in your shoes, I'd consider getting an electrician and consider adding a sub panel. Get some estimates. You can't have too much capacity IMHO.

[Dan Friedrichs]

I'm not an electrician, but that seems like a bad idea. While the purpose of a breaker is to protect the wire (not the equipment), you'd be awfully upset if you burned up the motor on your J/P because the breaker didn't trip. 40A * 240V is about 13HP - that's a lot of power to leave unchecked.

The correct solution to this is to install a subpanel.

[Rick Christopherson]

This would not be a pleasant experience for you. Not only would you need to be working with #6 or #8 wire for everything, but all of the receptacles and plugs would have to be 50 amp, and they are not cheap.

If you are breaker slot challenged, then you are much better off ganging up other circuits that are not operating simultaneously. If that's not an option, then maybe a small distribution panel would work.

[Charles Green]

Okay thanks everyone. I'll reevaluate and see what I should do.

Thanks again.

[Rob Russell]

Charles,

Take the 240v circuit that you're using for the jointer/planer and use that space in your main panelboard to feed a subpanel.

• Run #6 THHN/THWN in 3/4" conduit from your main panelboard to the subpanel. You will need (4) conductors:
  
  • (2) hots - typically a black and red or (2) blacks
  • (1) neutral - white
  • (1) equipment grounding conductor (EGC) - green. Per NEC Table 250.122, this could be #10 THHN/THWN.
• Install a 60 amp breaker.
• Make sure that the neutral buss in the subpanel is NOT bonded to the case. The neutral buss in the subpanel must "float", which means that you do not install the screw that ties the neutral, EGC buss and panelboard casing all together. That bonding is only done at your "service equipment" which is typically your main panelboard.
• Relocate the circuit for the jointer/planer to the new subpanel.

Make sure that you pull a permit for the subpanel and have the installation inspected by your local Authority Having Jurisdiction, aka the building inspector.

Rob

[Chuck Thoits]

• Make sure that the neutral buss in the subpanel is NOT bonded to the case. The neutral buss in the subpanel must "float", which means that you do not install the screw that ties the neutral, EGC buss and panelboard casing all together. That bonding is only done at your "service equipment" which is typically your main panelboard

Rob

Rob why is that?

[Dan Friedrichs]

Rob why is that?

You can run into some stange things where multiple parallel paths to ground will actually cause current to flow in your grounding "loop". This can cause electrical noise and it's obviously unsafe to have current flowing in your equipment ground.

Also, you want all your return current to flow through the neutral, only. If you tie ground and neutral together, return current will flow through both wires. Again, you should not have current normally flowing through an equipment ground.

[Rob Russell]

The short answer is that, if you were to Bond the Neutral and EGCs together in a subpanel, you would be creating a parallel path through the EGC for current to flow back to the bonding point. That’s bad because it potentially energizes the EGC when we’re not expecting it to be.

To explain …

You need to understand that the Neutral conductor carries as much current in a 120/240v single phase wiring system as a “hot” conductor does. Some people think that the white/neutral conductor is safe to touch. If you took a circuit that was drawing 15 amps, cut the white/neutral conductor, stripped the ends of the 2 wires and grabbed them – you’d have 15 amps of current trying to flow through you.

The Equipment Ground Conductor (EGC), sometimes referred to as a safety ground, is an alternate path for electricity to take in case the Neutral path is broken. Generally speaking, you should not have current flowing through the EGC.

Voltage is the difference in potential between a positive and negative terminal. The negative terminal in our wiring systems is the earth. All of our wiring systems are tied to ground. Literally. When power comes in from the utility company, they give you 2 hots and a ground. Somewhere in your wiring system, at the “service equipment”, there is a conductor that ties to the water pipe, out to ground rods, to an electrode encased in your concrete foundation or some combination of the above. That establishes a ground/negative reference for your house. It’s tied into the ground that comes from the utility company. In reality, all of our houses and the ground in the power grid are tied together in one huge ground.

Bonding is the point where the Neutral and Equipment Grounding Conductors are tied together with the grounding stuff I mentioned above. That “Bonding” is done once and only once because we don’t want to create parallel paths for current to flow.

[glenn bradley]

Okay thanks everyone. I'll reevaluate and see what I should do.

Thanks again.

Charles,

Many of us hit this wall and most of us go with a sub-panel. The rest either stop adding requirements or (shudder) do dangerous things. It sounds like you've moved well into the serious stage of woodworking, hobby or otherwise. Fall-back, regroup, add a sub-panel, move on safely and have fun.

[Chuck Thoits]

Ok got that now the next question. Why does one electrician say that the sub panel must have it's own ground and the next say that it does not? And does it really need it's own ground and why?
Ok so that was 2 questions. But I have finally found people that will give me an explanation on this stuff. most of the time when i ask these questions I get the stand by anwser. Because thats the way it done.

[Tom Veatch]

...Why does one electrician say that the sub panel must have it's own ground and the next say that it does not? And does it really need it's own ground and why?...

A couple of reasons come to mind. First is the exceptions and variances followed by the local jurisdiction. Second is a confusion of terms.

The ground bus in the subpanel must be electrically isolated from the neutral bus in the subpanel. From that standpoint, the subpanel needs its own connection to ground since it cannot share the ground connection of the neutral bus.

Technically and physically the ground bus in the subpanel can be connected to ground by running a grounding conductor (green/bare) back to the ground bus in the main panel. The neutral bus in the subpanel is grounded by running a separate neutral (white) wire back to the neutral bus in the main panel. That method is acceptable in this jurisdiction which does not require a separate "ground" (connection to water pipe, driven ground rod, etc.) for the ground bus in a nearby subpanel. There may be different rules for widely separated main and subpanels or panels located in different buildings.

By code, the neutral bus and the ground bus in the subpanel cannot be electrically bonded or share an electrical connection back to the main panel. Why? Because if they did, the wire connecting the bonded neutral/ground bus in the subpanel to the bonded neutral/ground bus in the main panel would be part of the safety ground for all circuits in the subpanel.

Why is that a bad thing? Because if it were wired that way, anytime a 120 volt circuit in the subpanel was being used, the neutral current would be flowing in the wire used for the safety ground of the subpanel. Due to electrical resistance in the wire, the current would cause the wire to have an electrical potential (voltage) at the subpanel end which would be higher than at the main panel end.

Since the main panel end is electrically connected to a "ground", it is at a voltage defined as ground potential or 0 volts. The subpanel end of the wire and the subpanel ground bus would be at a potential greater than ground so it would be charged to some voltage greater than 0 volts. Likewise, every grounded surface on every piece of equipment on any circuit fed from that subpanel would also be charged through the safety ground to a voltage greater than the 0 volt ground potential.

Why is that bad? Because if you happened to be grounded to a true ground at 0 volt potential and touched a machine that is grounded through the subpanel, the voltage on that machine would pass current through you to ground. It would probably not be enough to feel, it might only be enough to cause a slight tingle, but under some very extraordinary conditions, it might be enough to knock you on your keister. In other words, it's not a safe condition.