Can't get my 220V tools to work.

[Rob Price]

We just moved to a new house, and I've spend the past couple of days off wiring everything up. I've gotten all my standard 20A 115V outlets working, I went to install my 220V lines today and the tools won't turn on.

I installed a slim line 20A double pole breaker (trying to save room, but my first trouble shooting step will be to replace this with a standard double pole) in the box. Connected the white and black wires to the breaker, ground to the ground bar and ran the wire inside. From there it goes to a 20A double pole switch so I can turn everything off and on from inside the shop. I confirmed when the switch is off there's no power to either tool. When it's on I get power to both the white and black lines. These are wired to 20A receptacles. I confirmed power is getting to both the black and white lines of my tools, but neither of them will switch on.

Thoughts?

[Mark Bolton]

My thoughts are I have no idea why in the world you'd wire through a switch.

[Jamie Buxton]

You might be feeding both hots from the same phase. Each hot will measure 110 volts to ground, but there will be 0 volts between them. If you move one hot to the other phase, you get 220 volts between them.

[Jim Neeley]

Rob,
A single unit consisting of two half-width breakers cannot provide 240V because they pull both legs from the same pole. If you take a voltmeter and measure across them, you will measure zero volts.

If you want to go with half width breakers to save space, you need to get a unit the size of a conventional 240V breaker (two 120V breakers wide) that has four half-width breakers within it and the center two tied together so they trip at the same time. In that case the center two provide 240V and the outer two provice two separate 120V circuits.

There are a few companies (Siemens is one, I have one) who make these with the two inner breakers tied together and the two outer breakers together, which gives you two 240V circuits from the space of one 240V traditional breaker. The others use the inner two as a 240V and the outer two as separate 120V circuits.

Jim

[Rob Price]

Switch: because my buddy had his shop burn down one night because one if his tools shorted in the night. With the switch, all my outlets are dead. Nothing gets left on by accident and nothing can short out while I'm not there. Not to mention it's one more step to prevent little hands from starting tools.

It was the tandem slimline. I went out and tried two regular sized 20a breakers and all is well. I'll get a true double pole tomorrow. Didn't realize the tandem was still only single phase. Not sure what I'd use on for. I'm assuming it will run two 115 20a circuits just fine?

[Ryan Mooney]

Not sure what I'd use on for. I'm assuming it will run two 115 20a circuits just fine?

I wouldn't recommend using it for that, it is actually a 220v breaker. There are some panels that support half height breakers in some of the slots. Its possible/likely your backplane supported it (otherwise I'm surprised it plugged in.. some won't let you although I can't say that's universal) and you had it plugged into the wrong position (it has to span legs just the same and the manual for your panel should diagram or explain where they need to go). You should be able to find the manual for your panel with a quick google search on the part # unless its something really obscure.

[Bill McNiel]

I have a masters degree and still have no idea how electricity works. Worse than that, I wired my house and shop!

[Kevin Goss]

Yeah, a tandem is designed simply for if you run out of spaces in your panel, you pull a current single pole breaker and replace it with a tandem. So you definitely can run 2 120v circuits off that breaker. That's the right way to do it, while others just simply put 2 wires under one 20 amp breaker since tandem breakers are not very cheap.

[Mark Wooden]

I have a masters degree and still have no idea how electricity works. Worse than that, I wired my house and shop!

Try wrapping your head around this- in my new shop space,the existing service is a "240/480v three phase, Delta service with owner supplied neutral. I'm supposed to be able to run my three phase equipment on two legs if I supply the neutral. I'm not even going to pretend to understand how it works and am trying to get the landlord to put in a new 208-230/460v three phase service

[Tom M King]

Take four of the single space breakers out of the box. Hopefully, you can find four that are side by side the same amperage. For the two farthest away from the way the wire comes into the box, put a double pole breaker there for your 220 circuit. In the other two now empty slots, put two of the space saver breakers, like you are trying to use to get 220 (which won't work), and put the four wires( from the four breakers referred to in the first sentence of this post) on those breakers.

If this doesn't make sense to you, call an electrician.

[Wade Lippman]

I have a masters degree and still have no idea how electricity works. Worse than that, I wired my house and shop!

I presume you mean you don't understand Maxwell's equations, rather than you don't understand the principles of residential wiring.

[Mark Bolton]

Switch: because my buddy had his shop burn down one night because one if his tools shorted in the night. With the switch, all my outlets are dead. Nothing gets left on by accident and nothing can short out while I'm not there. Not to mention it's one more step to prevent little hands from starting tools.

It was the tandem slimline. I went out and tried two regular sized 20a breakers and all is well. I'll get a true double pole tomorrow. Didn't realize the tandem was still only single phase. Not sure what I'd use on for. I'm assuming it will run two 115 20a circuits just fine?

I would be more apt to blame your buddies doing his own wiring or some other event as opposed to the circuits being energized when he wasn't there. Tools, or proper wiring, don't burn shops down.

If there's something in the circuit that's going to catch fire if left on you've got far greater problems than any switch will protect you from.

[Rod Sheridan]

It was the tandem slimline. I went out and tried two regular sized 20a breakers and all is well. I'll get a true double pole tomorrow. Didn't realize the tandem was still only single phase. Not sure what I'd use on for. I'm assuming it will run two 115 20a circuits just fine?

Regardless of whether you use a single pole, or two pole breaker, it's all single phase.

That's all you have at home.

The issue was that the tandem breaker is two breakers connected to the same pole, so you had 120 volts to neutral, zero volts line to line............Rod.

[Myk Rian]

I have a masters degree and still have no idea how electricity works. Worse than that, I wired my house and shop!
Lol. Good luck.

[Jason Beam]

I think the OP needs to call an electrician. There are too many signs of unfamiliarity with the way residential wiring works to trust that advice given over the internet would be safe.

[Rob Price]

I would be more apt to blame your buddies doing his own wiring or some other event as opposed to the circuits being energized when he wasn't there. Tools, or proper wiring, don't burn shops down.

If there's something in the circuit that's going to catch fire if left on you've got far greater problems than any switch will protect you from.

Fire Inspector said it was the start capacitor in his belt sander. Professional shop. Professionally wired by an electrician. Fire inspector recommended kill switch for tools when away from the shop. But he's just the fire inspector. What does he know?

Swapped out the tandem for a regular double pole and all is well. Not rocket science. I have a buddy who's an electrician. We wired my basement together a few years ago. I'll have him double check what I did.

[Michael W. Clark]

Fire Inspector said it was the start capacitor in his belt sander.

I'm not a sparky, but this sounds like a bad switch at the tool that leaked voltage/current, not a wiring problem? I understand you wanting to avoid that so you put in a switch to turn off the circuit. For peace of mind in that application, I would not use a simple toggle switch, but use a spring loaded knife switch designed to be a disconnect. I'm not sure you are gaining anything in robustness by using a toggle switch. (For toggle switch, I assume you are using one that looks like a light switch except rated for the voltage and current. I have one of those on my air compressor, but it is low amps at 220V).

Mike

[Larry Frank]

If you are concerned about fire risks, I would install heat detectors in the shop and have it wired so that you can hear the alarm in the night or have an alarm company respond to a problem.

And, of course, have a couple of the proper fire extinguishers on hand.

[Bill Orbine]

I think the OP needs to call an electrician. There are too many signs of unfamiliarity with the way residential wiring works to trust that advice given over the internet would be safe.


Oh Yes..... I pretty much have an idea what exactly went wrong for which I'll refrain from offering advice other than call a qualified electrician. It a very simple mistake that can have dire consequences.

[Mike Cutler]

Rob

I'm fairly certain, like a lot of folks, that your culprit is the tandem breaker being installed incorrectly, just put in a standard 240 breaker. If you have the room in your box, and you don't violate the panel manufacturers loading instructions, then the 120/240 tandem breaker mentioned in a previous post could simplify things for you.

The "Kill" switch is actually a very good idea, but you should have a device called a "manual disconnect", "electrical disconnect", "service disconnect", "circuit disconnect, etc, or something with those sort of word descriptors in the title between the breaker and your tools. It sounds as if you have a standard switch.

Because someone has to bring it up, I will.
Tandem breakers cannot be indiscriminately loaded into a panel. Virtually every panel manufacturer has a loading diagram that details which spaces, if any, can be utilized for a tandem breaker. Some panel manufacturers don't allow for any tandems installed in their panel. I know that a person can buy tandems at the 'Borg that fit, and work, but it's wrong, unless they are spec'd and installed per the panel manufacturer.
The problem with indiscriminately installing tandems is that a condition can unknowingly be created whereas the neutral returns become unbalanced and or overloaded. It's especially easy to do it when sub panels are involved.

[Ken Fitzgerald]

Fire Inspector said it was the start capacitor in his belt sander. Professional shop. Professionally wired by an electrician. Fire inspector recommended kill switch for tools when away from the shop. But he's just the fire inspector. What does he know?

Swapped out the tandem for a regular double pole and all is well. Not rocket science. I have a buddy who's an electrician. We wired my basement together a few years ago. I'll have him double check what I did.

Glad to hear you have it fixed Rob!

For safety's sake, I would have your electrician friend check your work.

[Bill McNiel]

Wade - you have hit the nail on the head. I tend to treat residential wiring with plumbing logic.

[Mike Henderson]

The problem with indiscriminately installing tandems is that a condition can unknowingly be created whereas the neutral returns become unbalanced and or overloaded. It's especially easy to do it when sub panels are involved.
Mike, would you mind expanding on this comment, please. I don't understand the problem you're describing.

Mike

[Jim Neeley]

Mike,

The following applies to 120V circuits only; please pardon my simple description:

On a 120V circuit, the current is supplied on the hot leg and returns on the neutral leg.

If you have two 120V circuits with the same load, each on different hot legs, the effect is to neutralize the current load on the neutral. That is, the neutral carries the *difference* between the current in the two legs.

When you install a tandem, both of those circuits are on a single leg. If you share a neutral, the neutral leg is carring the *sum* of the currents. This is typically not a problem from the neutral bus out (assuming you follow code), because code prohibits you from sharing a neutral in such an installation (assuming you know this), even though code permits sharing a neutral when the legs are on different legs (assuming there is a tie between the two breakers).

If someone were mot to take this effect into consideration, they could find that they have an unbalanced load, leading to a high level of current on the neutral return home.

The purpose of this post is to explain the phenomena, not to focus on legal vs. illegal. For that determination you need to talk to your local AHJ.

Electricity can be confusing and the code even more so. As others have said, if you are unsure, check with a qualified electrician. If the electrician is unsure, consult with a qualified electrical engineer.

Jim in Alaska

[Mike Cutler]

Mike, would you mind expanding on this comment, please. I don't understand the problem you're describing.

Mike

Mike

Each tandem, as you know, is attached to single stave of a pole of the 240 coming into the panel as they distribute down the backplane of the panel. If they're installed per a panel manufacturer's direction they can only be installed in a manner that facilitates splitting the loads equally between the two poles. If you place them just anywhere in the panel, to many the phases could now be in sync, depending on the poles they are attached too.
In a main service panels it's not as big a problem as a sub, as the wiring size of the sub makes an assumption for a balanced neutral return to the main panel so as not to over ampere the neutral return. Too many tandems on the same pole will not have the canceling effect of the different angles of two opposite poles and can cause an overloaded, or unbalanced neutral return. The more evenly distributed the hots, the more enhanced the effect of canceling on the neutral return. If the sides becomes unbalanced the neutral return may theoretically see an entire side (pole) of current.

This is the way it was taught to me many years ago.

[Mike Henderson]

Mike

Each tandem, as you know, is attached to single stave of a pole of the 240 coming into the panel as they distribute down the backplane of the panel. If they're installed per a panel manufacturer's direction they can only be installed in a manner that facilitates splitting the loads equally between the two poles. If you place them just anywhere in the panel, to many the phases could now be in sync, depending on the poles they are attached too.
In a main service panels it's not as big a problem as a sub, as the wiring size of the sub makes an assumption for a balanced neutral return to the main panel so as not to over ampere the neutral return. Too many tandems on the same pole will not have the canceling effect of the different angles of two opposite poles and can cause an overloaded, or unbalanced neutral return. The more evenly distributed the hots, the more enhanced the effect of canceling on the neutral return. If the sides becomes unbalanced the neutral return may theoretically see an entire side (pole) of current.

This is the way it was taught to me many years ago.
Okay, I understand. But I'm not sure it would be a problem. Let's say that you have a subpanel and you wire it up with 4 gauge wire. So that's a 4 gauge for each hot, a 4 gauge for the neutral, and maybe a 4 gauge for ground.

Then, let's say that someone had a bunch of 120V circuits and they put them all on one side of the line (one hot essentially unused and the other one carrying all the current). Let's say that the total load on the single side is 25 amps and everything is turned on so it's drawing 25 amps.

You'd have 25 amps through one hot, zero through the other hot, and 25 amps through the neutral. The wire sizes are okay for that. The neutral is not going to be overloaded, it's just carrying the same current as the hot.

And if there were any circuits on the other hot, the current through that hot will subtract from the current in the neutral. So in my above example, let's say the other hot is now carrying 5 amps. The current in the neutral will now be 20 amps.

I understand the problem of someone using something like 12/3 to wire up multidrop circuits and "sharing" the neutral on that wire - if the two circuits are now on the same side of the line. In this case, the currents in the hots will add in the neutral so it would be easy to overload the neutral.

But for something like wiring a subpanel, I don't see a problem with the current in the neutral.

Mike

[I never heard of being able to downrate the size of the neutral to a subpanel. Is that really code? How much can you down rate it? When I installed my subpanel, with an electrician, he put in all of the wires the same size and never suggested that the neutral could be smaller. Seems to me that downrating the neutral would be dangerous.]

[Rob Price]

Wow. Talk about off topic- but good info. No sharing of neutrals here. The panel is full on one side and has open open slot on the other. Trying to keep it balanced just because.

[Chris Padilla]

[I never heard of being able to downrate the size of the neutral to a subpanel. Is that really code? How much can you down rate it? When I installed my subpanel, with an electrician, he put in all of the wires the same size and never suggested that the neutral could be smaller. Seems to me that downrating the neutral would be dangerous.]

Me neither but I have heard of being able to downrate the green/bare ground.

[Greg Portland]

Connected the white and black wires to the breaker, ground to the ground bar and ran the wire inside. From there it goes to a 20A double pole switch so I can turn everything off and on from inside the shop.
My gut reaction is that your circuit is undersized if everything is running off of a single 20A breaker.

[Rob Price]

Oh no. I have one breaker for DC, two breakers for shop tools (one for each side of shop), one double pole for 220, one for lights and one for AC. The 220 has the switch. Planning to add switches to the other tool circuits. Prob overkill, but that way no circuit ever has more than one thing running on it at a time and my lights stay on if I trip something. My only 220 tools so far are lathe and table saw. Haven't figured out how to run both yet simultaneously. Hoping to add a jointer/planer to that list.

[Chris Padilla]

Can you take a pic of your panel with the guts displayed for us?

[Rob Price]

But I just met you...

I'll get a pic next time I'm working on it. It'll be a few days before I have some time to get out there.

[Rollie Meyers]

It depends on the make of circuit breaker whether a twin breaker can be used for a 240V circuit, GE THQP will work (GE twins can only be used in GE panels because of the way they are designed), the now obsolete Zinsco/Sylvania, Murray/Crouse-Hinds & pre Westinghouse Challenger also could be used for 240V, current Murray breakers are of a ITE design which is the same as Siemens but they are not interchangeable because of UL issues*, Bryant/Westinghouse/Cutler-Hammer/Eaton BR line, Murray MP, Siemens QP, Square D QO & HOM, Cutler-Hammer CH, all will not supply 240V when their twin breakers are used, a quad breaker would be required or a full size circuit breaker, a full size is the only choice w/ SQ D QO, or the Cutler-Hammer CH, as they do not offer a quad breaker.

FPE, Federal Pacific Electric, also known as Fisher Price Electric, Stab-Lok twin breakers could also be used for a 240V circuit but had to be careful where they were plugged in so they were on opposite legs , ( they are garbage panels like Zinsco/Sylvania though). They have a very bad reputation & replacing them is the best choice plus very expensive breaker replacements can make a decision to replace easier.

* A breaker has to be UL classified to be used in a competitive make of panel, very few are.