# A basic dumb question hot and neutral reversed on a cord



## Golden Arc (Apr 28, 2008)

Ive got a dumb question on some of the old cords with no ground, you could plug something up either way hot or neutral reversed depending on which way you turned the plug. Can anybody explain how that is? Wouldnt the hot be traced back to the nuetral bar?


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## user5941 (Mar 16, 2009)

Tim Crimson said:


> Ive got a dumb question on some of the old cords with no ground, you could plug something up either way hot or neutral reversed depending on which way you turned the plug. Can anybody explain how that is? Wouldnt the hot be traced back to the nuetral bar?


 Look at a lamp, the polarity of the plug is to keep the screw shell from being "hot" on older lamps you can "revese" polarity and the screw shell becomes hot. Some equipment is designed so that if polarity gets reversed it can damage the equipment so polarized cordand plugs are used it will not feed back to nuetral buss


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## Chris Kennedy (Nov 19, 2007)

rewire said:


> Some equipment is designed so that if polarity gets reversed it can damage the equipment


Do you have an example?


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## iaov (Apr 14, 2008)

Tim Crimson said:


> Ive got a dumb question on some of the old cords with no ground, you could plug something up either way hot or neutral reversed depending on which way you turned the plug. Can anybody explain how that is? Wouldnt the hot be traced back to the nuetral bar?


Nope. The only place hot is reversed is at your utilization equipment.


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## RePhase277 (Feb 5, 2008)

Chris Kennedy said:


> Do you have an example?


Not likely, because a piece of equipment doesn't know the difference between hot and neutral without a circuit designed to reference ground for that express purpose.

There is NO electrical difference between hot and neutral as far as the laws of physics are concerned. Lights still light, motors still turn, computers still process.


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## drsparky (Nov 13, 2008)

You will have an electrical hazard if a two wire plug is not polarized. When a power cord enters a piece of equipment the hot goes to the power on/off switch. If the plug is “backwards” the power will be through the equipment and end at the on/off switch. It will still function but everything in the equipment will be hot when the equipment is off. This is a shock hazard if you are working on it. Also internal fuses will not help because they are next after on/off switch.


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## brian john (Mar 11, 2007)

drsparky said:


> You will have an electrical hazard if a two wire plug is not polarized. When a power cord enters a piece of equipment the hot goes to the power on/off switch. If the plug is “backwards” the power will be through the equipment and end at the on/off switch. It will still function but everything in the equipment will be hot when the equipment is off. This is a shock hazard if you are working on it. Also internal fuses will not help because they are next after on/off switch.


Minimal to no hazard unless you start taking the equipment apart. Lamps as noted the shell will be energized but with out a ground even this is a minor issue.

Take a 120 VAc transformer X1 or X2 which one do you ground? Who cares it makes no difference.


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## redbeard43 (Mar 20, 2009)

drsparky said:


> You will have an electrical hazard if a two wire plug is not polarized. When a power cord enters a piece of equipment the hot goes to the power on/off switch. If the plug is “backwards” the power will be through the equipment and end at the on/off switch. It will still function but everything in the equipment will be hot when the equipment is off. This is a shock hazard if you are working on it. Also internal fuses will not help because they are next after on/off switch.


 
I believe that this is the perfect example of why we need polorized receptacles. HOs just dont understand especially the older group.:thumbup:


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## Golden Arc (Apr 28, 2008)

So it doesnt matter as long as theres no ground?


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## redbeard43 (Mar 20, 2009)

i would wire it correctly, then its up to the HO or whomever to plug something in.


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## TheRick (Apr 13, 2008)

Tim Crimson said:


> So it doesnt matter as long as theres no ground?


 
Unless something near by is grounded consider this....

An autotransformer 230/115VAC, the primary side has a non-polarized Euro-style plug, it is plugged in with reverse polarity, creating a potential difference of 230VAC between the neutral and ground on the secondary side. On the secondary side a receiver for an internet satellite is plugged in with a 2 prong polarized plug. Within the receiver there is no ground, so the neutral is tied to the equipment....now connect a piece of coax to the receiver and run it outside to the satellite dish next to the front door....now place said satellite dish on a steel frame, and place the whole thing on a steel Air Force pallet...now put the pallet about a foot away from the door of your well grounded all steel living container. Then it gets interesting....go take a shower, upon returning to your room with your "flip-flop" shower shoes on, the side of your foot touches the pallet just before you grab your door knob.


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## RePhase277 (Feb 5, 2008)

Tim Crimson said:


> So it doesnt matter as long as theres no ground?


No, it does matter, for reasons others have noted, most notably the on/off switch issue. But as a matter of operation and physics, polarity makes no difference. The biggest issue with polarity in a home appliance I would say is the polarity of the screw shell in light sockets. I haven't seen an appliance that had the neutral connected to the case in a long time. I have a radio from the 40's that does, but I checked my satellite after reading Rick's post, and it does not.


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## Mr. Sparkle (Jan 27, 2009)

TheRick said:


> Unless something near by is grounded consider this....
> 
> An autotransformer 230/115VAC, the primary side has a non-polarized Euro-style plug, it is plugged in with reverse polarity, creating a potential difference of 230VAC between the neutral and ground on the secondary side. On the secondary side a receiver for an internet satellite is plugged in with a 2 prong polarized plug. Within the receiver there is no ground, so the neutral is tied to the equipment....now connect a piece of coax to the receiver and run it outside to the satellite dish next to the front door....now place said satellite dish on a steel frame, and place the whole thing on a steel Air Force pallet...now put the pallet about a foot away from the door of your well grounded all steel living container. Then it gets interesting....go take a shower, upon returning to your room with your "flip-flop" shower shoes on, the side of your foot touches the pallet just before you grab your door knob.


Wow, sounds like you have seen this......


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## TheRick (Apr 13, 2008)

Mr. Sparkle said:


> Wow, sounds like you have seen this......


 
Yes, and it is a potentially (pun intended) dangerous situation!


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## waco (Dec 10, 2007)

In the "bad old days," televisions were wired such that one side of the feed went to the on/off switch and the other went to the chassis, but no metal connected to the chassis was exposed as long as the TV was intact. However, a tech could get a nasty shock working on an exposed chassis.

Remember the wider blade that was used to "polarize" plugs?

I recently worked on an entertainment center setup where an extension cord was hardwired at a receptacle and plugged into the back of a "power conditioner" component. It was reversed. The only symptom was a bad hum on a sub-woofer which used that receptacle.


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## steelersman (Mar 15, 2009)

waco said:


> Remember the wider blade that was used to "polarize" plugs?


 
Umm, that's how it is in the present day, not how it used to be.


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## user5941 (Mar 16, 2009)

Chris Kennedy said:


> Do you have an example?


 http://marinesurvey.com/yacht/ElectricalSystems_AC.htm

scroll down to polarity


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## RePhase277 (Feb 5, 2008)

rewire said:


> http://marinesurvey.com/yacht/ElectricalSystems_AC.htm
> 
> scroll down to polarity


Still no example there, just someone else saying it. Reversing the hot and neutral polarity will not cause equipment damage. How does the equipment even know which is which?


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## user5941 (Mar 16, 2009)

InPhase277 said:


> Still no example there, just someone else saying it. Reversing the hot and neutral polarity will not cause equipment damage. How does the equipment even know which is which?


 well you just keep on believing that and I hope it works out for you.


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## Golden Arc (Apr 28, 2008)

InPhase277 said:


> No, it does matter, for reasons others have noted, most notably the on/off switch issue. But as a matter of operation and physics, polarity makes no difference. The biggest issue with polarity in a home appliance I would say is the polarity of the screw shell in light sockets. I haven't seen an appliance that had the neutral connected to the case in a long time. I have a radio from the 40's that does, but I checked my satellite after reading Rick's post, and it does not.



So why are they making plugs now with a small(neutral) and a big(hot) slot?


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## brian john (Mar 11, 2007)

It adds a margin of safety.


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## RePhase277 (Feb 5, 2008)

rewire said:


> well you just keep on believing that and I hope it works out for you.


I'm just eager to learn. The link you provided had no example. Please explain it to me. How does a piece of equipment know which wire is which?


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## RePhase277 (Feb 5, 2008)

Tim Crimson said:


> So why are they making plugs now with a small(neutral) and a big(hot) slot?


You have it backwards. The neutral is the wide slot. As to why, see Brian's post, #21.


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## steelersman (Mar 15, 2009)

Tim Crimson said:


> So why are they making plugs now with a small(neutral) and a big(hot) slot?


They don't. They make them the opposite. Neutral slot is larger than the hot slot.


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## 5volts (Jan 11, 2008)

rewire said:


> well you just keep on believing that and I hope it works out for you.


I agree with InPhase277. It will work. I have hooked up 100s of 120 VAC solenoid valves where both of the coils leads are red. It does not care where you land your hot or your neutral. How would it even know especially when the current flow periodically reverses direction?

For a *matter of operation* the way I see it polarity deals with plus(+) and minus(-), not hot and neutral. However for safety purposes and code we wire it correctly when ever wires or terminal are marked L1 and N.

How do we reverse the direction of a AC motor?

In a AC circuit the current flow periodically reverses direction. In a DC circuit the current flow of a electric charge is only in one direction. 

In a DC circuit polarity can make a HUGE difference for the *operation* of equipment. Reversing polarity in a DC circuit would allow current to be able to flow through the diodes possibly letting the "_smoke out"_.

I would also like to see a example of reversed polarity in a AC circuit damaging equipment or the equipment not working.


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## steelersman (Mar 15, 2009)

p_logix said:


> I agree with InPhase277. It will work. I have hooked up 100s of 120 VAC solenoid valves where both of the coils leads are red. It does not care where you land your hot or your neutral. How would it even know especially when the current flow periodically reverses direction?
> 
> For a *matter of operation* the way I see it polarity deals with plus(+) and minus(-), not hot and neutral. However for safety purposes and code we wire it correctly when ever wires or terminal are marked L1 and N.
> 
> ...


agreed. It's like how a doorbell button or a single pole light switch doesn't care how you wire it.


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## Golden Arc (Apr 28, 2008)

steelersman said:


> They don't. They make them the opposite. Neutral slot is larger than the hot slot.


But why?


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## brian john (Mar 11, 2007)

Tim Crimson said:


> But why?


It adds a margin of safety.


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## RePhase277 (Feb 5, 2008)

Tim Crimson said:


> But why?


So we put the switch and fuse in the right wire.


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## steelersman (Mar 15, 2009)

Tim Crimson said:


> But why?


so that when you plug in a lamp, the screwshell doesn't become energized.


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## user5941 (Mar 16, 2009)

InPhase277 said:


> I'm just eager to learn. The link you provided had no example. Please explain it to me. How does a piece of equipment know which wire is which?


 Simply reversing the hot and neutral will not do anything to equipment as AC does not have fixed polarity,The damage that can occur is due to the loss of the internal protection .Most electronic equipment is only fused in the hot side and not the neutral so reversal of polarity removes the fused protection.


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## steelersman (Mar 15, 2009)

rewire said:


> Simply reversing the hot and neutral will not do anything to equipment as AC does not have fixed polarity,The damage that can occur is due to the loss of the internal protection .Most electronic equipment is only fused in the hot side and not the neutral so reversal of polarity removes the fused protection.


the fuse would still function and blow if there were an overload.


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## ce2two (Oct 4, 2008)

InPhase277 said:


> Not likely, because a piece of equipment doesn't know the difference between hot and neutral without a circuit designed to reference ground for that express purpose.
> 
> There is NO electrical difference between hot and neutral as far as the laws of physics are concerned. Lights still light, motors still turn, computers still process.


  Garage door openers will not work if the polarity is reversed @ the recept. :no:


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## drsparky (Nov 13, 2008)

Quick scenario, your $2500 52” plasma TV is OFF, your crotch fruit spills his Sponge Bob flavored cool aid into the vents, shorts out power supply. The 1 Amp fast blow fuse is on the hot conductor but; alas, the TV is plugged into an extension cord that has the Neutral/Hot swapped. Now we burn out the innards of the 52” plasma while we wait for the 20Amp breaker to trip.

Can we say fire starter? 

Just because you can turn on a light bulb does not mean you did the job correctly.

What is the liability if this was a customer’s home and it burns down killing someone?

If you need an example of a circuit that will fail but reversing the neutral, a full wave rectifier common in many power supplies uses electrolytic capacitors for filtering the AC ripple out of the system. They will not blow by being backwords but will eventually delaminate internally and the capacitance will drop, causing higher ripple and noise on DC lines effecting secitivity and selectivity in communications equipment.

Chuck :thumbsup:


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## 5volts (Jan 11, 2008)

ce2two said:


> Garage door openers will not work if the polarity is reversed @ the recept. :no:


It will work just not the way you want it to work.:laughing:



drsparky said:


> ...Just because you can turn on a light bulb does not mean you did the job correctly...


I totally agree with you, but as a matter of operation it will work.



drsparky said:


> If you need an example of a circuit that will fail but reversing the neutral, a full wave rectifier common in many power supplies uses electrolytic capacitors for filtering the AC ripple out of the system. They will not blow by being backwords but will eventually delaminate internally and the capacitance will drop, causing higher ripple and noise on DC lines effecting secitivity and selectivity in communications equipment.


Huh? It's AC, and the polarity of the applied voltage will be alternating. A good example would be a VFD. VFDs are solid state electronic power conversion devices. First it converts AC input power to DC using a rectifier. The DC is then converted to AC power using an inverter switching circuit. 

So a VFD with a Cat 5e connection to ethernet communication module or a VFD with a "Blue hose", a Belden communication cable for datahighway or Remote I/O. You can reverse the AC line side all you want even single phase input, nothing will happen. It will work.

A full wave rectifier uses 4 diodes and will reverse the polarity of the incoming AC wave for half of the incoming cycles, so all of the available power that a transformer can give is used.


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## brian john (Mar 11, 2007)

Just reversed the leads on a full wave rectifier things still working.


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## drsparky (Nov 13, 2008)

My bad, I sketched out the circuit and realized I still had a full set of hair when I last worked on one. 
The electrolytic capacitors in the bridge filter circuit are on the DC side and don't care about the AC source.


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