Vintage Non-Polarized Two Prong Cord- Identifying Hot & Neutral?

Discussion in 'Audio Hardware' started by baconbadge, Oct 24, 2016.

  1. baconbadge

    baconbadge Active Member Thread Starter

    Location:
    Queens, NY
    A few months ago (on the recommendation of an old post by Mr. Hoffman) I bought a Fisher 500-c. Suffice it to say, I absolutely LOVE it. Steve also posted the following "instructions" that were given to him about using his new Fisher:

    "1. Power outlet:
    As you know these older devices do not come equipped with a plug that has
    the wider prong to identify it as being grounded. Nonetheless, it is
    important to pay attention to the orientation when you plug it in. The way
    to identify which way the plug goes in is by feeling the power cord. One
    side of the cord is completely curved and smooth on the outside while the
    other side of the cord has an edge. The side that is smooth should plug into
    the wider prong on your wall socket."


    I followed these instructions when I set up my Fisher, and everything works beautifully.
    So, if I understand correctly (according to these instructions), on the Fisher cord:

    The smooth side of the cord = wide prong = neutral
    &
    The ridged side = small prong = hot

    Here's my question, is this the STANDARD method of determining the hot & the neutral prongs on a vintage non-polarized two prong cord? In other words, does it apply to ALL cords? The reason I ask is that my 1964 Silvertone guitar amp has a non-polarized plug and it also has a "ridged" side and a smooth side running down the cord.

    BUT, I looked online and found a site about repairing a lamp cord that said the exact opposite! It said the RIDGED side of the wire feeds the wide prong (neutral side) & the smooth side is the hot side. I ALSO read somewhere that if one of the wires has printing on it, and the other does not, then that's usually the hot side.

    Does anyone have a definitive answer on this???

    I apologize if this has been covered before... I know that the topic of flipping the cord around (reversing polarity) and getting a different sound HAS been covered in older posts. And I have found that to be 100% true. So thank you all for that.
     
  2. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    Open it up and find out which side of the line is switched off and on and which is permanently connected. The switched side should be hot.

    In Europe a double pole switch is standard, but most American equipment opens up one side.

    Find the hot side of the outlet with a neon test light.
     
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  3. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    The ridged side is the identified conductor, the neutral conductor.
    Just check any rip cord with a 2 wire polarized plug on it. The ridged identified conductor connects to the wider blade of the plug, the neutral conductor.

    As for the correct plug orientation of the Fisher I would suggest you check it with a multi meter.

    1) Have nothing else connected to the Fisher with any interconnects.

    2) turn on the Fisher.

    3) Set meter to auto volts.

    4) Touch one test lead probe to the chassis of the fisher, the other test lead probe to the equipment ground of the wall receptacle. Note the voltage reading.

    5) Next repeat the process by reversing the test lead's probes and measure the voltage again. The lower of the two voltage measurements is the correct plug orientation.

    Determining Proper A/C Polarity »

    General Asylum: Pinging Bob Crump, Can you answer a question for me? by jea48 »

    //
    Edit:

    I agree with Burt. Especially if the Fisher has an AC line fuse. The fuse must be in series with the Hot Line.
     
    Last edited: Oct 24, 2016
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  4. baconbadge

    baconbadge Active Member Thread Starter

    Location:
    Queens, NY
    Just a layman here... I don't have a volt meter & definitely don't trust myself poking around anywhere.
    I was hoping for a general rule of thumb that could be applied when I come across an older non-polarized two prong plug (ie- my Kenwood KA-9100, or a vintage guitar amp).

    Ok, so I get that on newer polarized plugs, the ridged side is always going to be the neutral and will go to the big prong... But did that (ridged side = neutral) standard always apply, even before big prongs "debuted"?

    If so, then that would make The Fisher an anomaly?

    Thanks!
     
  5. BuddhaBob

    BuddhaBob Forum Resident

    Location:
    Erie, PA, USA
    Even with a standard on non-polarized two-wire plugs, it could be wired wrong and still operate normally. A VOM (volt/ohm/milliammeter) is easy to learn and very inexpensive. You can only be sure of the wiring by checking it. Easy, fast, reliable to accomplish using a meter.
     
  6. MrRom92

    MrRom92 Forum Supermodel

    Location:
    Long Island, NY
    Just curious, as I'm using an amp of a similar vintage... what would be the effect of plugging it in the other way around? Could it be harmful to the equipment or detrimental to its performance?
     
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  7. SandAndGlass

    SandAndGlass Forum Resident

    You don't even need a meter. A meter will give you the RMS voltage, but you may not need to know this. If you don't, and there is no real reason that you would need to.

    Extech ET25 Neon Voltage Tester from Amazon $5.47

    [​IMG]

    With this, You can see which wire is hot. When hot, the neon light, lights up.

    I always keep one of these around. They are very handy to have. Always good to know if a circuit is hot. The alternative, is to stick your finger in the socket and see if your eyes light up!

    If you use the first way, you can always avoid the second way, accidentally or otherwise.
     
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  8. Dentdog

    Dentdog Active Member

    Location:
    Atlanta
    To complicate matters further there is this; My electrician hooked up my sub panel with some dedicated lines on each leg of the fuse box. So each amp is running off a leg opposite to the other. My older Mcintosh MC 60 is a two wire captive AC line. Will being on opposite sides of the fuse box affect the polarity even when the plug is oriented correctly?
     
  9. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA

    Correction. That would be the case today with a two wire cord and polarized plug. Back then before the polarized plug the user had a 50/50 chance of plugging the non polarized plug in where the fuse would be in series with the hot conductor.
    Either way the plug is plugged into the wall receptacle the fuse is in series with the circuit and an overload or short circuit will cause the fuse to blow.

    .
     
  10. KT88

    KT88 Forum Resident

    No
    -bill
     
  11. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    This would also work.

    https://www.amazon.com/Fluke-1AC-A1...326?ie=UTF8&psc=1&refRID=QBY06RS44PE8KMFA6FBR
     
  12. KT88

    KT88 Forum Resident

    This is the only correct response here. I work on this stuff all the time. I fixed a Fisher 500 the other day and I have a Scott on the bench now. Back when the plugs were not polarized, there was no standard for wiring the ac primary. I agree that the positive should be both switched and fused, but that was not always the case back then. Many designs had one polarity switched and the other fused. i think the wire marking was largely coincidental as the transformer primaries had floating grounds. The ground was to chassis via a capacitor. As long as that cap was good, you had a ground reference to one leg of the ac. It didn't matter which leg as you only had a 50/50 chance of getting the real ground leg on the same prong whenever you plugged the thing in. You should read open circuit to chassis from either leg on these units.

    Later, when polarized plugs were common, the wide blade should have been to ground, both in the equipment chassis and to the wall outlet. Finally, we have the three prong plugs for as that have a true ground, which should go to chassis, then a negative and a positive ac leg.
    - Bill
     
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  13. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    Not necessary because the two mono amps are fed from both legs, Line 1 and Line 2 but it can have an impact on the noise floor of the amps if the AC plug polarity orientation is reversed on one or both amps.
    Read my post #3 above.



    As for one amp fed from one Line, leg, to neutral and the other fed from the other hot Line, leg, to neutral that is not recommended by most in our hobby when the equipment is connected together by wire interconnects. Especially in your case because the equipment uses a non polarized plug and the old AC power wiring of the amps is not doubled insulated.

    If you have a multi meter you might try my test in post #3 above. If you do the test make sure all interconnects are disconnected from the amp being tested.

    I just reread my post #3 above and see I screwed up #5 big time......


    1) Have nothing else connected to the Fisher with any interconnects.

    2) turn on the Fisher.

    3) Set meter to auto volts.

    4) Touch one test lead probe to the chassis of the fisher, the other test lead probe to the equipment ground of the wall receptacle. Note the voltage reading.

    5) Next reverse the AC plug at the wall and repeat #4 again noting the voltage. The lower of the two voltage measurements is the correct plug orientation. Mark the plug in some manner so you will know the correct plug orientation.
     
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  14. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    Bill, (KT88)
    Have you ever checked the voltage differences from the chassis to the safety equipment ground for the proper AC plug orientation? What you will actually be checking for is the proper polarity orientation of the primary winding of the power transformer.

    Determining Proper A/C Polarity »

    The other side of the coin (long) - Charles Hansen - General Asylum »

    General Asylum: Pinging Bob Crump, Can you answer a question for me? by jea48 »

    SoundStage! Synergizing I - Equipment Maximization through Electrical Minimization (06/1997) »
     
    Last edited: Oct 24, 2016
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  15. baconbadge

    baconbadge Active Member Thread Starter

    Location:
    Queens, NY
    I don't believe it's harmful to the equipment, but yes, it does affect the sound. There's a bunch of previous posts about this on the forum. I have personally found a definite difference in sound when I turned around the plug on my vintage two-prong Kenwood 9100 and my old Pioneer sx838. The difference went from a boomy/blurry sound to one that was sharper and had the instruments more focused in the soundstage.
    Regarding my original question, it *sounds like* there was no standard on the older two-prong plugs in terms of the little ridge thing on the edge of the wire. But I'm still confused about the whole Fisher thing and if Fisher had their own standard. Otherwise, how would the guy who gave Steve those instructions know definitively where one prong should go?
     
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  16. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    http://oldtech.net/fisher/500c/schem.pdf


    On this unit, the fuse and the switch are on different sides of the transformer primary and there is one AC grounding cap bypassed by an 820K (? hard to read pdf scan) resistor. That means if you set the unit on an isolated surface and plug it in, if the plug is in one way you will see about zero volts from chassis to ground and if the other way you will see almost line voltage if the meter is sensitive enough. This is of course limited to a tiny current (120/the X/c of .01 ufd @60hz in parallel with 820K ohms).


    A lot of pro equipment had two caps in parallel across the line with the center tap tied to chassis ground.

    Either worked great in the day when people knew how to ground stuff. Today conversion to a 3 wire cord is probably safest.
     
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  17. The FRiNgE

    The FRiNgE Forum Resident

    It's my understanding the current NEC std is the ribbed side as neutral. If a previous standard existed for older equipment, I have no idea at the moment.

    There is an old, old fashioned way to determine the polarity of your audio equipment. This is how we always did it back in the 60's with our guitar amps, which always had a polarity switch (and the death cap) We can employ the same polarity test for home hi fi equipment.
    1) with the volume turned down to about 9 O' Clock on your amplifier, plug an interconnect cable in the AUX jack, select AUX (do not use the phono jack)
    2) touch the center pin on the RCA cable with your finger. This will produce 60 Hz hum from your speakers, (50 Hz hum in most EU countries and others)
    3) Note the volume of the hum.
    4) Turn amp off, reverse the two prong AC plug, turn the amp on, touch the end of the RCA cable.
    5) Note the volume of the hum.
    The lesser hum level is the correct polarization, and will produce the least noise in your system. The chassis ground will be connected to neutral, which is also safer operation.
     
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  18. The FRiNgE

    The FRiNgE Forum Resident

    Yes, absolutely true, some devices were fused on the "neutral" side and switched on the "hot" side. When the unpolarized plug was plugged in "backward" the neutral side was switched, and the chassis would be "hot" in some circuit designs.
     
  19. The FRiNgE

    The FRiNgE Forum Resident

    Interesting! Normally the polarity will be unaffected since we are referencing "hot" to "neutral" (neutral bonded to ground at the panel) However when connecting devices in the same system to opposite legs, then that's asking for trouble, especially in the event a transformer melts down or any other fluky malfunction occurs. The fuses should blow, but still does not seem to be a good idea!
     
  20. SandAndGlass

    SandAndGlass Forum Resident

    I was quite young back then, but I rather doubt that Fischer had their own standard that was different from the rest of N. America.

    If the plug is non polarized, use a tester to see which side is hot, with respect to the ground. Wire with ribbing, white color, a stripe, is used to identify the neutral. There is no other electrical standard in N. America.

    That one person, made a possible (and probable) error, has no particular meaning. It certainly does not mean that he was correct. It is possible that he was misinterpreted. That has been known to happen.

    A question has been asked and there have been several answers to indicate which wire is neutral and how to positively identify it.

    That still does not preclude the possibility that someone who installed the wire on your particular unit, did not install it backwards. Quality control, back in those days was pretty high. People were properly trained and knew how to perform their jobs, so I would think this is doubtful. But it is still possible.

    Obtain an original wiring diagram and have a qualified technician check it and verify it for you. You need to find someone who is qualified to do service work and proper maintenance on your unit any way.

    Check your receptacle, make sure the larger slit is the ground with the tester. Then check to verify the other (smaller) slit is the hot connection.

    Put some paint or nail polish on the rubber insulator part of the plug on the side where the ribbed or marked wire connects to the plug. That will make it easier to identify the neutral prong of the plug. Make sure that the neutral prong is inserted into the wide slit in the receptacle.
     
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  21. KT88

    KT88 Forum Resident

    Yes, but it has been a while on my own equipment. I check all components that I service for proper grounding and whenever a customer is agreeable, I convert any 2 wire system to a modern 3 wire system and insure that all switching and fusing is done on the positive lead. Out of interest here, I measured the Scott amp that I have and find that it shows 6vac in one orientation and 15vac in the other (safety ground to chassis), so the 6v leakage is proper polarity with respect to the transformer winding. That is without any other components connected to the inputs. That might effect the result also. What I did was to then follow the AC wire marking (it has a small raised line on one conductor) and found that this side was connected to the switch, then to the fuse. What was found here was that the wire as marked was the side that measured the highest AC leakage, so it was the positive lead which was marked. I can't say if that was any sort of standard for Scott or not as per the wire mark and orientation as I only have this one unit here and I'd need maybe 6 or more to feel that a large enough sample had been seen to make any sort of educated guess on that. In any event, I don't think there was any sort of industry standard back then. That goes for a lot of things too, such as output voltages, output and input impedances etc, so it made for an interesting time to listen to different combinations of gear. Now that we not only have NEC/IEC safety standards for wiring, but also AES standards for performance to help with component matching, it is much less critical now.

    Basically, my take is this: I doubt anyone will hear a difference if they have other gear connected and they reverse the AC plug in its AC outlet to this older piece of gear. Also, under no circumstances should anyone ever rewire their AC receptacle so that it has reversed polarity, that is just stupid and dangerous. Also no one should ever modify a piece of equipments AC plug, ie file down the wider spade so that it can be inserted into an outlet backwards. Further, these AC measurements are esoteric AFAIAK, as the measurements for safety should be resistance to chassis ground and current leakage/flow to chassis. These AC measurements should have extremely low ac current measurements so as to make them inconsequential, especially when other gear (likely more modern and properly grounded or isolated) is connected.
    -Bill
     
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  22. KT88

    KT88 Forum Resident

    The OP is certainly mistaken or you guys are misinterpreting the meaning of the term "leg" as used here. I feel confident that his electrician wired his outlets to NEC safety standards, so the hot conductors are always on the same and proper side of the outlets (the narrow slot). What he likely noticed while watching over the guy's shoulder or inspecting the installation afterwards was that the electrician used two circuit breakers, one for each outlet (that's a dedicated line), and installed the circuit breakers on opposite sides of the electrical panel. The panel likely has 2 positive conductors, each 120v, and then a neutral/ ground rail. So the breakers can be installed on either side and use either positive rail, but always will have the positive and the negative wires kept in the proper arrangement when the room outlets are wired.
    -Bill
     
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  23. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    I just did a test on a Marantz 2252B, that was manufactured around the middle 1970s, and here are my findings.

    First the Marantz has a 2.2m resistor that is connected to the Line opposite the switch and the fused Line. The resistor is connected to the chassis of the Marantz. The Line with the 2.2m that connects to the chassis is connected to the ridged, identified, conductor of the 2 wire cord and non polarized plug. (Note, that is meaningless to the average retail consumer out there.)
    http://akdatabase.org/AKview/albums/Marantz/Marantz 2252b Service Manual.pdf

    Voltage measurements.

    With the Marantz plugged into wall outlet receptacle power switch turned off.
    Plug in one direction the meter measured 95 volts from the chassis of the Marantz to the safety equipment ground of the wall duplex receptacle. Obviously in this direction the Hot line is feeding the side the resistor is connected to. (This voltage represents an open no load reading and does not present any electrical shock hazard. Remember the 2.2m ohm resistor is in series with the Hot line and the metal chassis of the Marantz.)

    Next with the plug reversed the meter measured 2.68V. In this instance the neutral, the identified conductor of the cord, was feeding the side with the resistor. This would be the correct plug orientation for power to be connected to the Marantz with the Hot Line feeding the switch and fuse, and the neutral Line feeding the other side of the primary winding of the power transformer. When the switch is off no voltage potential is present on the primary winding.

    //

    Now for some voltage measurements with the switch closed and the primary winding of power transformer energized.

    With the AC plug plugged into the wall receptacle in one direction the meter measured 88 volts.
    (This measurement has the Hot Line connected to the side that feeds the primary winding directly and also has the 2.2m ohm resistor connected to the chassis.)

    With the plug reversed the meter measured 29.26 volts. (This has the neutral Line connected directly to the primary winding of the power transformer and the 2.2m ohm resistor connected to the chassis.) Again this is the correct AC plug orientation.

    So why the differences in voltage measurements with the power switch of the Marantz opened or closed?

    As much as I hate to I will have to pull the bottom cover off the Marantz and lift one end of the 2.2m ohm resistor and repeat the second set of measurements again. This will verify that the primary winding of the power transformer has a proper AC polarity orientation for which side the Hot and neutral Lines should be connected to.
    .
     
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  24. P2CH

    P2CH Well-Known Member

    I had a Fisher once that apparently had been dropped on the corner where the power fuse resides. The center spring-side contact of the fuse holder was touching the chassis.

    I'ts a long story of events that this caused me but I'm just mentioning it because the AC cord first hits the fuse holder, then to the switch.

    Also, yes, it's good to know which side is the hot side but still, it ends up at the power transformer anyway so it's not like either side of the AC cord should be contacting the chassis anyway.

    Uhm, except in the case I mentioned about mine.
     
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  25. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    I agree with your post.

    Ok, so the electrician installed a sub panel and fed it 240/120V nominal.
    2 Hot ungrounded conductors
    1 neutral grounded conductor
    1 safety equipment grounding conductor

    At a sub panel the neutral conductor/ bar must be isolated/insulated from the metal enclosure. All branch circuit neutral wires must connect to this bar.
    A separate equipment ground bar is directly connected to the metal enclosure of the electrical panel. This bar is for all branch circuit equipment ground wires to connect.

    First the installation meets NEC code. This is a normal installation for a sub panel.

    It's not the fault of the electrician he fed some 120V branch circuits from Line 1 (L1) and others from Line 2 (L2) The electrician was taught to balance the branch circuit loads across the L1 and L2 of the panel. NEC also dictates the loads be balanced.

    If Dentdog wanted all the branch circuits of his audio equipment, that are connected together by wire interconnects, to be fed from the same Line, leg, he should have said that to the electrician when he first looked at the job. The electrician then would have sized the feeder, the wires feeding the new sub panel accordingly. Because, I would imagine, all the connected loads of Dentdog's audio equipment would be less than 16 amps FLA I doubt the electrician would have had a problem feeding the branch circuits for his equipment from just one Line to neutral. (All from L1 or all from L2.)

    So what does Dentdog have now?

    He may have the two power amps fed from both Lines. One from L1 and the other L2. He has both MC 60s amps connected to a preamp by wire interconnects. I assume both channels of the preamp signal grounds are tied together. That ties together the signal grounds of the two MC 60s. Does the preamp have a 3 wire cord and plug?(Uses the wall receptacle safety ground). Or does it have a modern 2 wire cord and polarized plug where the AC power wiring is double insulated.

    Now back to the AC power feeding the two amps. If the OP has a volt meter and was to measure voltage from one dedicated circuit duplex receptacle hot contact, one amp is plugged into, to the hot contact of the other dedicated branch circuit duplex receptacle, the other amp is plugged into he will measure 240V nominal if the dedicated circuits are fed from both Lines. (L1 to L2 240V nominal.) If the two dedicated branch circuits are fed from the same Line he will measure zero volt nominal. (This is the recommended way equipment should be fed if connected together wire interconnects).

    Next add to the above the MC 60 amps use a 2 wire cord and non polarized plug. He has a 50/50 chance he might have an amp plugged in the receptacle so the neutral is connected to the side with the resistor that is connected to the chassis. What are the odds both amps are connected that way?

    At the very least the OP should buy a multi meter and check for the proper AC plug orientation of each amp and then mark the plugs in some manner. I think the OP will find his system will sound better with a lower noise floor.

    Personally I would make sure how they are fed and if fed from both Lines I would refeed the amps and preamp at the electrical sub panel so they are fed from the same Line. L1 or L2 but not from both. Before doing so I would look at the size of wire feeding the sub panel. If he doesn't know the size of the wire he could look at the 2pole breaker at the main electrical panel that feeds the sub panel.
     
    Last edited: Oct 25, 2016
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