Why do a lot of devices run alternating current have a polarized plug? If it alternates,why a one way plug?
why polarized plugs if we run AC?
- Thread starter daves66nova
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Because one side of 110 Volt A/C is "hot" or energized with respect to ground, and the other side is actually attached to ground (the neutral) in your electrical box.
aaah,that makes sense,thanks
And the hot side is the one switched on and off in the appliance. Also the neutral will be connected to parts prone to touch. For example in a light fixture the neutral is connected to the (more exposed) threaded base, while the center contact (less prone to being touched) is connected to the hot through the lamp switch.
I always remember that the wider prong (i.e. a little bit easier to stick something in) is neutral, and the narrower prong (a little harder to stick something in) is the hot side.
It's mostly about safety.
I always remember that the wider prong (i.e. a little bit easier to stick something in) is neutral, and the narrower prong (a little harder to stick something in) is the hot side.
It's mostly about safety.
So what about older appliances with plugs that have the same sized prongs?
Originally Posted By: xxch4osxx
So what about older appliances with plugs that have the same sized prongs?
They probably don't have a metal case that is grounded (i.e. plastic?)
So what about older appliances with plugs that have the same sized prongs?
They probably don't have a metal case that is grounded (i.e. plastic?)
The older plugs were not polarized. Both prongs were the same size, the size of what is now the smaller "hot" prong. As they went to polarized plugs they did so by enlarging the one prong. That made the older (existing plugs) compatible with the newer polarized outlets.
Originally Posted By: PandaBear
Originally Posted By: xxch4osxx
So what about older appliances with plugs that have the same sized prongs?
They probably don't have a metal case that is grounded (i.e. plastic?)
Before polarized plugs, most electronics had some form of a floating ground circuit that relied on suppressor capacitors. And most also had a metal chassis, both as the manufacturing standard of the era, and as a useful RF shield. Unfortunately, as these instruments become elderly, the suppressor caps (many of which were paper types) sometimes fail closed, and the chassis then has a 50/50 chance of becoming energized at mains voltage. We see this all the time in vintage audio work. Some vintage guitar amp guys like to call them "death caps". Amazingly, many amateur restorers tend to misunderstand and/or ignore these circuits and leave them un-repaired or use incorrect parts that soon fail. Besides replacing the suppressor caps with modern Y-class rated ones, a polarized or grounded cord set as an alternative usually solves the problem.
Common vintage appliances (toasters) are a different kettle of fish from vintage electronics, and rely more on simple insulation from the chassis, which occasionally (or eventually, depending on the dielectric) breaks down and either causes a short or a hot chassis. These are more dangerous examples, as the risk of fire is much greater.
In a modern device, the greater use of more robust insulating materials throughout the product such as thermoplastics has substantially reduced the risk that once existed with unpolarized plugs.
Originally Posted By: xxch4osxx
So what about older appliances with plugs that have the same sized prongs?
They probably don't have a metal case that is grounded (i.e. plastic?)
Before polarized plugs, most electronics had some form of a floating ground circuit that relied on suppressor capacitors. And most also had a metal chassis, both as the manufacturing standard of the era, and as a useful RF shield. Unfortunately, as these instruments become elderly, the suppressor caps (many of which were paper types) sometimes fail closed, and the chassis then has a 50/50 chance of becoming energized at mains voltage. We see this all the time in vintage audio work. Some vintage guitar amp guys like to call them "death caps". Amazingly, many amateur restorers tend to misunderstand and/or ignore these circuits and leave them un-repaired or use incorrect parts that soon fail. Besides replacing the suppressor caps with modern Y-class rated ones, a polarized or grounded cord set as an alternative usually solves the problem.
Common vintage appliances (toasters) are a different kettle of fish from vintage electronics, and rely more on simple insulation from the chassis, which occasionally (or eventually, depending on the dielectric) breaks down and either causes a short or a hot chassis. These are more dangerous examples, as the risk of fire is much greater.
In a modern device, the greater use of more robust insulating materials throughout the product such as thermoplastics has substantially reduced the risk that once existed with unpolarized plugs.
JHZR2
Staff member
Polarization or not - hasnt there always been a "standard", where hot is on one side and neutral is on the other? If so, the only risk is when something goes bad, AND the plug is wired backwards.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
Originally Posted By: Rick in PA
I always remember that the wider prong (i.e. a little bit easier to stick something in) is neutral, and the narrower prong (a little harder to stick something in) is the hot side.
It's mostly about safety.
I read something similar in a house wiring book. Their explanation, which I find hard to take too seriously, was that there is a risk of the plug prongs being contacted while partially inserted, therefore the need to make the larger one safe.
I always remember that the wider prong (i.e. a little bit easier to stick something in) is neutral, and the narrower prong (a little harder to stick something in) is the hot side.
It's mostly about safety.
I read something similar in a house wiring book. Their explanation, which I find hard to take too seriously, was that there is a risk of the plug prongs being contacted while partially inserted, therefore the need to make the larger one safe.
Originally Posted By: JHZR2
Polarization or not - hasnt there always been a "standard", where hot is on one side and neutral is on the other? If so, the only risk is when something goes bad, AND the plug is wired backwards.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
How do you know which side of an unpolarized plug is neutral, and which is hot? On the old stuff, unless you open it up and mark the plug, you just don't know. Then it literally is a coin toss whether you'll have a hot chassis if it fails.
A hot chassis on a vintage appliance or electronic instrument is a very real risk, even more so today when everything else in a modern home is now grounded. For many suppressor circuits, a failure causes a hot chassis as long as it is plugged in. If you're touching ground and touch it, you're the path to ground. GFIs are helpful, but folks don't play with an old DuMont TV or Scott tuner in the kitchen and bath. People don't think that 110 mains AC can kill, but it can (it can also badly burn).
Ideally, the neutral leg should run to the suppressor/chassis side. FWIW, when I do museum-grade restorations of vintage audio equipment, I keep the original unpolarized plug, but will mark the prong face with a small black marker dot to indicate neutral. In the rare event that a modern suppressor cap fails closed, it's only failing to neutral. But this does not guarantee safety, as the unpolarized receptacle needs to be properly wired, and the user needs to know which side of the receptacle is neutral as well.
If I know kids or the elderly will be around it, a grounded cord set goes on.
Polarization or not - hasnt there always been a "standard", where hot is on one side and neutral is on the other? If so, the only risk is when something goes bad, AND the plug is wired backwards.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
How do you know which side of an unpolarized plug is neutral, and which is hot? On the old stuff, unless you open it up and mark the plug, you just don't know. Then it literally is a coin toss whether you'll have a hot chassis if it fails.
A hot chassis on a vintage appliance or electronic instrument is a very real risk, even more so today when everything else in a modern home is now grounded. For many suppressor circuits, a failure causes a hot chassis as long as it is plugged in. If you're touching ground and touch it, you're the path to ground. GFIs are helpful, but folks don't play with an old DuMont TV or Scott tuner in the kitchen and bath. People don't think that 110 mains AC can kill, but it can (it can also badly burn).
Ideally, the neutral leg should run to the suppressor/chassis side. FWIW, when I do museum-grade restorations of vintage audio equipment, I keep the original unpolarized plug, but will mark the prong face with a small black marker dot to indicate neutral. In the rare event that a modern suppressor cap fails closed, it's only failing to neutral. But this does not guarantee safety, as the unpolarized receptacle needs to be properly wired, and the user needs to know which side of the receptacle is neutral as well.
If I know kids or the elderly will be around it, a grounded cord set goes on.
JHZR2
Staff member
Originally Posted By: Volvohead
Originally Posted By: JHZR2
Polarization or not - hasnt there always been a "standard", where hot is on one side and neutral is on the other? If so, the only risk is when something goes bad, AND the plug is wired backwards.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
How do you know which side of an unpolarized plug is neutral, and which is hot? On the old stuff, unless you open it up and mark the plug, you just don't know. Then it literally is a coin toss whether you'll have a hot chassis if it fails.
A hot chassis on a vintage appliance or electronic instrument is a very real risk, even more so today when everything else in a modern home is now grounded. For many suppressor circuits, a failure causes a hot chassis as long as it is plugged in. If you're touching ground and touch it, you're the path to ground. GFIs are helpful, but folks don't play with an old DuMont TV or Scott tuner in the kitchen and bath. People don't think that 110 mains AC can kill, but it can (it can also badly burn).
Ideally, the neutral leg should run to the suppressor/chassis side. FWIW, when I do museum-grade restorations of vintage audio equipment, I keep the original unpolarized plug, but will mark the prong face with a small black marker dot to indicate neutral. In the rare event that a modern suppressor cap fails closed, it's only failing to neutral. But this does not guarantee safety, as the unpolarized receptacle needs to be properly wired, and the user needs to know which side of the receptacle is neutral as well.
If I know kids or the elderly will be around it, a grounded cord set goes on.
My point is that on a polarized plug, one prong is supposed to ALWAYS be hot, and the other ALWAYS neutral. In Alternating Current (AC) terms it is:
HOT-LEG (brass colored screw) and NEUTRAL (silver colored screw)
On polarized plugs 120volts, the larger prong is the neutral
The larger prong is ALWAYS on the same side of the plug.
So best practices would indicate that since black and white wires have been used in household wiring (even my knob and tube in my 1930's home is black and white at the loads), then the hot is always on one side of the plug and the neutral on the other.
So thus unless someone wires a plug backwards, one can always be assured that the hot is in one place and the neutral in the other. Then the load wires itself and its switches accordingly, and no big deal.
The only safety issue arises when someone wires a plug backwards.
Originally Posted By: JHZR2
Polarization or not - hasnt there always been a "standard", where hot is on one side and neutral is on the other? If so, the only risk is when something goes bad, AND the plug is wired backwards.
Not downplaying, just thinking, there is one correct side of the plug where the hot is, and everything from there should be wired consistently.
How do you know which side of an unpolarized plug is neutral, and which is hot? On the old stuff, unless you open it up and mark the plug, you just don't know. Then it literally is a coin toss whether you'll have a hot chassis if it fails.
A hot chassis on a vintage appliance or electronic instrument is a very real risk, even more so today when everything else in a modern home is now grounded. For many suppressor circuits, a failure causes a hot chassis as long as it is plugged in. If you're touching ground and touch it, you're the path to ground. GFIs are helpful, but folks don't play with an old DuMont TV or Scott tuner in the kitchen and bath. People don't think that 110 mains AC can kill, but it can (it can also badly burn).
Ideally, the neutral leg should run to the suppressor/chassis side. FWIW, when I do museum-grade restorations of vintage audio equipment, I keep the original unpolarized plug, but will mark the prong face with a small black marker dot to indicate neutral. In the rare event that a modern suppressor cap fails closed, it's only failing to neutral. But this does not guarantee safety, as the unpolarized receptacle needs to be properly wired, and the user needs to know which side of the receptacle is neutral as well.
If I know kids or the elderly will be around it, a grounded cord set goes on.
My point is that on a polarized plug, one prong is supposed to ALWAYS be hot, and the other ALWAYS neutral. In Alternating Current (AC) terms it is:
HOT-LEG (brass colored screw) and NEUTRAL (silver colored screw)
On polarized plugs 120volts, the larger prong is the neutral
The larger prong is ALWAYS on the same side of the plug.
So best practices would indicate that since black and white wires have been used in household wiring (even my knob and tube in my 1930's home is black and white at the loads), then the hot is always on one side of the plug and the neutral on the other.
So thus unless someone wires a plug backwards, one can always be assured that the hot is in one place and the neutral in the other. Then the load wires itself and its switches accordingly, and no big deal.
The only safety issue arises when someone wires a plug backwards.
JHZR2
Staff member
Originally Posted By: Volvohead
You're correct if talking of polarized and grounded cordsets. But not unpolarized ones. I was speaking of unpolarized cordsets.
So there was absolutely no best practice for which of the two prongs was hot or neutral before the days of polarized plugs? I find that hard to believe, if true.
You're correct if talking of polarized and grounded cordsets. But not unpolarized ones. I was speaking of unpolarized cordsets.
So there was absolutely no best practice for which of the two prongs was hot or neutral before the days of polarized plugs? I find that hard to believe, if true.
Originally Posted By: JHZR2
Originally Posted By: Volvohead
You're correct if talking of polarized and grounded cordsets. But not unpolarized ones. I was speaking of unpolarized cordsets.
So there was absolutely no best practice for which of the two prongs was hot or neutral before the days of polarized plugs? I find that hard to believe, if true.
Are you speaking of receptacles or cordsets/plugs?
If you're talking about plugs and cordsets, it is impossible to physically designate either side of an unpolarized plug hot or neutral. Both plug blades are identical, and the plug can be flipped and inserted into an outlet socket either way by the end user.
Device engineers designed around this with modest circuit safeguards such as floating grounds. But if the circuit failed, the risk was apparent.
These are fairly basic electrical concepts. You may be confusing receptacles and cordsets in your conversation.
Originally Posted By: Volvohead
You're correct if talking of polarized and grounded cordsets. But not unpolarized ones. I was speaking of unpolarized cordsets.
So there was absolutely no best practice for which of the two prongs was hot or neutral before the days of polarized plugs? I find that hard to believe, if true.
Are you speaking of receptacles or cordsets/plugs?
If you're talking about plugs and cordsets, it is impossible to physically designate either side of an unpolarized plug hot or neutral. Both plug blades are identical, and the plug can be flipped and inserted into an outlet socket either way by the end user.
Device engineers designed around this with modest circuit safeguards such as floating grounds. But if the circuit failed, the risk was apparent.
These are fairly basic electrical concepts. You may be confusing receptacles and cordsets in your conversation.
JHZR2
Staff member
No, all Im saying is that has there not been a "best practice", where on the recepticle, the left prong is one and the right prong is the other?
I fully recognize that in the end all, there is no control and any bozo can wire a plug (polarized or not) backwards. And, I fully recognize that this is because the possible ways to designate it could easily be ignored by the installer.
But I would still assume that even before polarized plugs, NEC or equivalent stated which of the female connections on the recepticle SHOULD be hot and which SHOULD be neutral, and then equipment was built assuming that these best practices were met, so the conductors on the cordset aligned to it (with appropriate safeties put in place in case not).
In fact, doing a bit of searching indicates that since the 1962 revision of the NEC, the requirement has been for receptacles that are grounded and polarized. The 120V household receptacles are designed with a 3 prong set-up consisting of a top ground plug, left hand hot plug and right sided neutral plug.
But my point is that pre-1962 NEC, for example, hasnt the left hand plug been hot and the right side neutral? If so, then it has been the "best practice" fr a long time.
I doubt that ever have manufacturers just made the hot and neutral sides of their cordset that is attached to the load just willy nilly with hot on one side or the other. It has always been done one consistent way, in alignment with the best practice of which side on the receptacle is hot and neutral.
I fully recognize that in the end all, there is no control and any bozo can wire a plug (polarized or not) backwards. And, I fully recognize that this is because the possible ways to designate it could easily be ignored by the installer.
But I would still assume that even before polarized plugs, NEC or equivalent stated which of the female connections on the recepticle SHOULD be hot and which SHOULD be neutral, and then equipment was built assuming that these best practices were met, so the conductors on the cordset aligned to it (with appropriate safeties put in place in case not).
In fact, doing a bit of searching indicates that since the 1962 revision of the NEC, the requirement has been for receptacles that are grounded and polarized. The 120V household receptacles are designed with a 3 prong set-up consisting of a top ground plug, left hand hot plug and right sided neutral plug.
But my point is that pre-1962 NEC, for example, hasnt the left hand plug been hot and the right side neutral? If so, then it has been the "best practice" fr a long time.
I doubt that ever have manufacturers just made the hot and neutral sides of their cordset that is attached to the load just willy nilly with hot on one side or the other. It has always been done one consistent way, in alignment with the best practice of which side on the receptacle is hot and neutral.
Originally Posted By: JHZR2
I doubt that ever have manufacturers just made the hot and neutral sides of their cordset that is attached to the load just willy nilly with hot on one side or the other. It has always been done one consistent way, in alignment with the best practice of which side on the receptacle is hot and neutral.
Sorry, but you're wrong on this one where unpolarized cordsets were involved prior to the receptacle change about 50 years ago. Where there was an unpolarized cordset, there was no guide as to which blade or cordset lead would be assembled hot or neutral. They just assembled them as they came down the line.
If you look at cordsets from the 50's and 60's, most are smooth wire insulated with identical mouldings on both plug sides. Some manufacturers would even mould their logos into them on both sides. That is why on a tube era Fisher, for instance, I will often retain the original tan cordset with the trademark Fisher birds on the plug.
The ONLY change to this practice is where the wire itself eventually became molded with ribs to indicate neutral, which was a later development. But the plugs themselves almost always give zero indication of which side goes where.
But for all the devices and instruments I've worked on prior to 1970 that had unpolarized cordsets, there is simply no way to reliably designate one side from the other. That is just how it was. That is why I place a marker dot to indicate neutral on my restorations.
I've done a lot of electronics and electrical work over the years. You would be shocked (no pun intended) by some of the stuff I've seen in the field. There are plenty of 50+ year old switches and outlets still out there. And the further back you go, the more "wild west" the house wiring can become. During the era when unpolarized corsets ruled and these devices were made, 30 and 60A household service was the standard, and most homes only had a handful of branch circuits. A '50's kitchen, for instance, might only have one or two outlets (one of which was off the range controls). It was a very different and simpler era. GFI code requirements first started in the very late '60s . . . for UNDERWATER lighting fixtures. Before that, even they had no grounding protection in many cases.
I've also encountered my fair share of vintage electronics that don't even have chassis fusing. I just did an early '60s Magnavox console amp that was completely unfused. The cordset and power transmission primary was the 'fuse'. That's a fire waiting to happen. There, unless it absolutely must be purist original, I will install a chassis fuse.
The old instruments with unpolarized mains plugs were generally safe when in good working order. For most of their design lives, they generally stayed that way. The designers counted on the circuit safeguards to account for the plug being inserted either way. There was no cordset "guide" other than sufficient AWG conductors for the design load. It is only when they reach vintage or antique status, and the safety parts break down, do they become a problem.
Once polarized and grounded cordsets took greater hold by the 70's this became much less of an issue. But I still see plenty of '70s electronics gear with unpolarized cordsets. The audio practice was that an unpolarized plug could be flipped around to try and reduce ground loop induced hum issues, and some makers continued for some time with unpolarized cordsets to continue this option.
But the short answer to you is NO, there was no "best practice" for the installation of unpolarized cordsets prior to 1970. The only "best practice" was that it be well-bonded past the strain relief.
I really don't know what else to tell you on the issue, as it has never been a heavy topic of conversation among those of us that work with this stuff.
I doubt that ever have manufacturers just made the hot and neutral sides of their cordset that is attached to the load just willy nilly with hot on one side or the other. It has always been done one consistent way, in alignment with the best practice of which side on the receptacle is hot and neutral.
Sorry, but you're wrong on this one where unpolarized cordsets were involved prior to the receptacle change about 50 years ago. Where there was an unpolarized cordset, there was no guide as to which blade or cordset lead would be assembled hot or neutral. They just assembled them as they came down the line.
If you look at cordsets from the 50's and 60's, most are smooth wire insulated with identical mouldings on both plug sides. Some manufacturers would even mould their logos into them on both sides. That is why on a tube era Fisher, for instance, I will often retain the original tan cordset with the trademark Fisher birds on the plug.
The ONLY change to this practice is where the wire itself eventually became molded with ribs to indicate neutral, which was a later development. But the plugs themselves almost always give zero indication of which side goes where.
But for all the devices and instruments I've worked on prior to 1970 that had unpolarized cordsets, there is simply no way to reliably designate one side from the other. That is just how it was. That is why I place a marker dot to indicate neutral on my restorations.
I've done a lot of electronics and electrical work over the years. You would be shocked (no pun intended) by some of the stuff I've seen in the field. There are plenty of 50+ year old switches and outlets still out there. And the further back you go, the more "wild west" the house wiring can become. During the era when unpolarized corsets ruled and these devices were made, 30 and 60A household service was the standard, and most homes only had a handful of branch circuits. A '50's kitchen, for instance, might only have one or two outlets (one of which was off the range controls). It was a very different and simpler era. GFI code requirements first started in the very late '60s . . . for UNDERWATER lighting fixtures. Before that, even they had no grounding protection in many cases.
I've also encountered my fair share of vintage electronics that don't even have chassis fusing. I just did an early '60s Magnavox console amp that was completely unfused. The cordset and power transmission primary was the 'fuse'. That's a fire waiting to happen. There, unless it absolutely must be purist original, I will install a chassis fuse.
The old instruments with unpolarized mains plugs were generally safe when in good working order. For most of their design lives, they generally stayed that way. The designers counted on the circuit safeguards to account for the plug being inserted either way. There was no cordset "guide" other than sufficient AWG conductors for the design load. It is only when they reach vintage or antique status, and the safety parts break down, do they become a problem.
Once polarized and grounded cordsets took greater hold by the 70's this became much less of an issue. But I still see plenty of '70s electronics gear with unpolarized cordsets. The audio practice was that an unpolarized plug could be flipped around to try and reduce ground loop induced hum issues, and some makers continued for some time with unpolarized cordsets to continue this option.
But the short answer to you is NO, there was no "best practice" for the installation of unpolarized cordsets prior to 1970. The only "best practice" was that it be well-bonded past the strain relief.
I really don't know what else to tell you on the issue, as it has never been a heavy topic of conversation among those of us that work with this stuff.
Originally Posted By: JHZR2
But my point is that pre-1962 NEC, for example, hasnt the left hand plug been hot and the right side neutral? If so, then it has been the "best practice" fr a long time.
Not in the old work (literally) that I've seen. A lot of the old '40s and '50s stuff was brass fasteners all around, and the installer/electrician sometimes fastened whichever lead was most convenient to either pole as he was going through the boxes. Other times, they followed a standard pattern. It wasn't as regulated as you might think. The field standards got more uniform starting in the '60s. TV and all the '50s appliances that invaded homes may have had something to do with it.
This was the era of unpolarized outlets, so the device designers really didn't try to pick "one side or the other" for installing a cordset.
But my point is that pre-1962 NEC, for example, hasnt the left hand plug been hot and the right side neutral? If so, then it has been the "best practice" fr a long time.
Not in the old work (literally) that I've seen. A lot of the old '40s and '50s stuff was brass fasteners all around, and the installer/electrician sometimes fastened whichever lead was most convenient to either pole as he was going through the boxes. Other times, they followed a standard pattern. It wasn't as regulated as you might think. The field standards got more uniform starting in the '60s. TV and all the '50s appliances that invaded homes may have had something to do with it.
This was the era of unpolarized outlets, so the device designers really didn't try to pick "one side or the other" for installing a cordset.
JHZR2
Staff member
Good stuff, thanks!
Its so odd because in my 1930's home, the wires at the loads (lights and plugs) have a light and dark colored (cloth covered) wire. Ive pulled a lot of it out, but it was showing neutral/hot even then.
Pretty neat to read about this stuff. Amazing to think that it was just connected up back in the day...
Despite old homes, all our homes still have circuit breakers, not fuses. On old work was both the hot and neutral fused?
I assume that there was a bona-fide hot and neutral coming into the house and it got connected up to the fuse box in a standard manner, or did it?
In my home, the K&T was done in a very organized manner, and the splices to make all the branch circuits (looks like my home originally had four) are pretty much works of art.
Interesting stuff, thanks!
Its so odd because in my 1930's home, the wires at the loads (lights and plugs) have a light and dark colored (cloth covered) wire. Ive pulled a lot of it out, but it was showing neutral/hot even then.
Pretty neat to read about this stuff. Amazing to think that it was just connected up back in the day...
Despite old homes, all our homes still have circuit breakers, not fuses. On old work was both the hot and neutral fused?
I assume that there was a bona-fide hot and neutral coming into the house and it got connected up to the fuse box in a standard manner, or did it?
In my home, the K&T was done in a very organized manner, and the splices to make all the branch circuits (looks like my home originally had four) are pretty much works of art.
Interesting stuff, thanks!
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