What's the difference between a hot switch and hot+neutral switch?

Thread Starter

rambomhtri

Joined Nov 9, 2015
508
Hi, quick question here. I've always thought that electrical switches are used to "break" the hot wire: OFF to open and break it, ON to short circuit the terminals.

However, I've noticed that in some power strips, the "big" red switch is actually a dual switch that breaks both the hot and neutral wires. So, the question is...

Why some switches break also the neutral at the same time?
What are the pros and cons of breaking the hot wire VS breaking both hot and neutral wires in a switch?

All of this applied to common power tools and household EQ, 120/230VAC or regular DC equipment. Nothing extremely fancy or weird/pro electrical installations like industries. installations.
 
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MisterBill2

Joined Jan 23, 2018
13,805
Hi, quick question here. I've always thought that electrical switches are used to "break" the hot wire: OFF to open and break it, ON to short circuit the terminals.

However, I've noticed that in some power strips, the "big" red switch is actually a dual switch that breaks both the hot and neutral wires. So, the question is...

Why some switches break also the neutral at the same time?
What are the pros and cons of breaking the hot wire VS breaking both hot and neutral wires in a switch?
Fair question, here is what I know: In a piece of equipment that is not permanently connected, it is entirely possible to have the connection of line and neutral reversed due to s wiring error. That would leave all of the circuits at line potential with the neutral side connected to the line.
In addition, for power tools like drill motors and power handsaws, breaking both sides provides a redundant shutoff for when one switch contact becomes welded. So there are two excellent safety benefits to opening both sides of the power connection.

With three-phase powered equipment there has been an INCREDIBLY STUPID trend of only opening 2 of the supply lines to switch the system off. That is stupid because it leaves every part of the equipment wiring at full line potential, able to delver a fatal shock, or cause damage if accidentally connected to something close to neutral.
That same stupidity has also come to 240 volt equipment, where only one side of the mains power is opened. And it is done only to save a small bit on the cost of the control device.
 

Tonyr1084

Joined Sep 24, 2015
7,199
Hot switching completely de-energizes the circuit. But as @MisterBill2 suggests, a wiring error could potentially present a problem should someone need to work on the equipment thinking the power has been shut off. I've experienced this problem a high number of times when dealing with home wiring where older homes had an "Interrupt" wiring scheme where they often switched the neutral side, leaving hot "Hot" at the fixture. I've discovered a number of times that you can get a shock when touching hot and ground, while the neutral has been taken out of circuit. Bill's right. Hot switching, when done right is fine. But hot/neutral switching is superior as the equipment becomes fully de-energized regardless of correct or incorrect wiring. I've even seen polarized plugs mis-wired. You NEVER know who did what before you put YOUR hands on the circuit.

Had a room where I plugged a computer into one outlet and a printer into a different outlet. The former owner installed three pronged outlets and wired the neutral and grounds together IN THE BOX. The trouble was that someone probably before him broke a wire and when putting it back they crossed the hot and neutral lines. The resulting double errors made my computer case HOT, not case ground. When I plugged the printer into the computer, the cable, with a grounded shield became a pathway from hot to neutral (remember, they cheated and the outlets were not properly grounded) I got a full on 120VAC shock from my pinky to my thumb and index finger. Just goes to show - you never know what idiot before me (I may be another idiot) did what that could present a potential danger to someone else.
 

Tonyr1084

Joined Sep 24, 2015
7,199
In some cases equipment for N.A. that is 120/240, If used on 240v then both should be switched.
I have a contractors table saw that switches both hot and neutral. It's operated on 120VAC. Since it can be standing on the ground, potentially wet grass, switching everything off is wise to avoid the potential shock of an operator. Plus, the motor is double insulated. And the wire is a three wire plug, hot, neutral AND ground.
 

MisterBill2

Joined Jan 23, 2018
13,805
Certainly the likelihood of exchanged line and neutral in an extension cord makes breaking both sides the only wise choice. The added benefit to the tool manufacturer is that attaching both lines to the switch eliminates the need for a splice in the unswitched side. So that is a cost saving as well as a CYA move.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
508
Yeah, but all the things you say about the neutral and line/hot wires swapped work when you have polarized plugs. In most countries, the plugs are not polarized since in AC it doesn't matter once it's running.

Anyways... as far as I know... in most houses, switches in the wall to turn off lights or outlets in rooms only break the line, right?
If breaking line and neutral is a good idea in terms of security and protection against "idiots", how is it that it's not standard to break both wires?

Just the other day I fixed a double switch in my house and it was just line, no neutral. I remember a few years ago I turned off a ceiling light, knowing it wasn't possible for it to get power or be connected to the circuit, and working on stuff I managed to touch the neutral wire of the turned off light to the ground, and BAM! No electricity in the whole house. I was kind of shocked (no the best word here as it was mental shock, not electrical), and then I realized that the switch only broke the line wire, but the neutral and ground were still connected, so a short between them triggered the breakers. This wouldn't happen if the switches killed both neutral and line.

I guess they don't do it because it would take "a lot" more neutral wire to finish the circuit and also more expensive bulkier switches?
 
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Tonyr1084

Joined Sep 24, 2015
7,199
all the things you say about the neutral and line/hot wires swapped work when you have polarized plugs.
My dad used to hate those polarized plugs. He'd file the larger lug down to fit the outlet rather than get the correct outlet installed.
in most houses, switches in the wall to turn off lights or outlets in rooms only break the line, right?
When you say "Line" I take that to mean the "Hot" side, the side coming from the breaker. And yes, in modern homes the code requires the switch interrupts the hot. The neutral is untouched.
I remember a few years ago I turned off a ceiling light, knowing it wasn't possible for it to get power or be connected to the circuit, and working on stuff I managed to touch the neutral wire of the turned off light to the ground, and BAM! No electricity in the whole house.
Been there - done that. Too many times. That form of wiring is found in older homes when code allowed for "Interrupt" circuit wiring. In that kind of circuit, hot and neutral went directly to the light fixture. In every case I've seen the hot went directly to the light fixture while the neutral was connected to either a 12/2 or 14/2 gauge wire that ran down the wall to the light switch. The black was spliced into the fixture white (neutral) wire and the white returned to the fixture and connected to the light. The neutral was switched. I don't know the thinking, but perhaps if you've removed the lamp and were working on the switch there would be no chance of electrical shock or sparks. Too many times I've switched the light switch off then started changing the light fixture. Yeah, I touched the hot and ground (neutral was switched off) and I'd get a swift shock. OR my screwdriver leaned up against the metal (grounded) box while tightening the hot wire - and BOOF! The screwdriver would have a burn on the side and on the tip.

Modern homes require power AND neutral to go first to the switch box. From there it can go to the light fixture. In THAT circumstance you can get away with switching off the light switch and then safely work on the ceiling fixture. But because you never know who did what - it's always recommended you turn the breaker off before working on any electrical systems in the house.
 

Tonyr1084

Joined Sep 24, 2015
7,199
Pictures paint thousands of words. Here's my take on "Interrupt" circuit wiring. In many cases this reduced the amount of wiring needed. It would most often take more wiring to run hot and neutral to the switch box first, then to the ceiling box. In a few of the homes I've seen, including my current house, ground is typically a steel wire that runs independently from steel box to steel box and somewhere it makes its way to ground. That's why I didn't show a ground wire along with the line and neutral feed. In other cases where a steel flexible tubing conduit was used - the conduit itself was the ground pathway. Not always a good ground, code changed to include the ground (green or bare) wire in the cable.
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Thread Starter

rambomhtri

Joined Nov 9, 2015
508
My dad used to hate those polarized plugs. He'd file the larger lug down to fit the outlet rather than get the correct outlet installed.
When you say "Line" I take that to mean the "Hot" side, the side coming from the breaker. And yes, in modern homes the code requires the switch interrupts the hot. The neutral is untouched.
Been there - done that. Too many times. That form of wiring is found in older homes when code allowed for "Interrupt" circuit wiring. In that kind of circuit, hot and neutral went directly to the light fixture. In every case I've seen the hot went directly to the light fixture while the neutral was connected to either a 12/2 or 14/2 gauge wire that ran down the wall to the light switch. The black was spliced into the fixture white (neutral) wire and the white returned to the fixture and connected to the light. The neutral was switched. I don't know the thinking, but perhaps if you've removed the lamp and were working on the switch there would be no chance of electrical shock or sparks. Too many times I've switched the light switch off then started changing the light fixture. Yeah, I touched the hot and ground (neutral was switched off) and I'd get a swift shock. OR my screwdriver leaned up against the metal (grounded) box while tightening the hot wire - and BOOF! The screwdriver would have a burn on the side and on the tip.

Modern homes require power AND neutral to go first to the switch box. From there it can go to the light fixture. In THAT circumstance you can get away with switching off the light switch and then safely work on the ceiling fixture. But because you never know who did what - it's always recommended you turn the breaker off before working on any electrical systems in the house.
Yeah, I don't find attractive to have a one way only plug in AC. In DC it makes all sense and it's the only correct way, but in AC you can reverse polarity and nothing happens, everything works as expected.

That's why, in plugs without ground, I don't like wall outlets like the US type A. It's way more comfortable to use type C or F or L, that even with ground, they are reversible. That saves your life when plugging things to power strips because many times, when they are saturated (not electrically, but physically), you can put upside down some and make room.

About your drawing, yeah, line and hot are synonyms, and you seem to have broken the neutral instead of the line, which is not what you said, right?
 

MisterBill2

Joined Jan 23, 2018
13,805
In my part of the country the electrical code for residential buildings demands that the power feed go first to the ceiling box for the light, and then a separate run back to the switch box is used. Unfortunately that leaves a switch in a box with both black and white wires that are hot. Unless I have done the work, in which case I use an indelible marker to cover some of the white with red. Then somebody can at least guess that the white wire is not neutral. Some builders get around that by running a 3-conductor (White, black, red) cable from the switch box to the light fixture box. That makes adding a fan not controlled by the light switch simpler.
 

shortbus

Joined Sep 30, 2009
9,762
Putting black Magic marker or even a covering of electrical tape on the white wire to show that it is now a hot conductor is common. They wire the ceiling lights with the original wires to the fixture box so many ceiling light circuits are all on one breaker.

People not knowing this often get in trouble when they turn the ceiling light on in a room then send someone to turn breakers off at the panel. What a surprise when they then start working on a wall outlet, without checking first for power.
 

Reloadron

Joined Jan 15, 2015
7,084
The NEC was so fond of switches they devoted an entire article to the subject. Article 404: Switches is a good write up on the subject by Mike Holt. The actual NEC Article 404 covers just about every switching situation in detail. A Google of "nec article 404" should bring up a half dozen links to switches and what can and can't be done according to code including recent changes in 2017. The NEC is published every three years unless that has changed. My old book was 2008. So do we switch neutral? All depends on the application. :)

Ron
 
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