GFCI Plugs for Vintage TV???

[jshorva65]

I posted inquiries with a few of my vendors regarding availability of GFCI-equipped replacement AC plugs. The one on my Andis HD-1 hair dryer has an access plate on the back near the cord strain relief which is secured by two spanner-type security screws. It's about the same size as a SMPS wall wart such as a cellphone charger. Clearly, this device (labeled "LifeLine Shock Protector" and bearing the designations "Wellong C2" and "Cat. No. P3" on the back, was designed to be used as a GFCI-equipped replacement for an ordinary two-conductor AC plug and to fit a standard SPT-1 cord.

If I can get these in wholesale lots for $4 to $6 per piece, they would be ideal for use as replacements for any non-GFCI plug on any SPT-1 cord.

Any thoughts on their use with restored vintage radio or television sets? If a panel-mount bayonet-cap or screw-cap GMA (5x20mm) fuse holder could be fitted into a hole drilled into the side of the wiring compartment, that would minimize two hazards with one small alteration which would be external to the sets themselves. A restored 630TS with a GFCI plug and in-the-plug 5A fast-acting line fuse. What a concept! The pictured device is made in China, but safety, IMO, trumps my preference for using American materials when Leviton's GFCI replacement plug is priced at $55 each and therefore is cost-prohibitive. Safety also trumps aesthetics, but I'll check to see if they are also available in brown to match 95% of vintage TV power cords.

[David Roper]

GFI protection, if desired and not already provided, can be had be replacing either a breaker or an outlet. I've seen the vintage picture of a Sentinel trapezoid perched precariously on the edge of a clawfoot tub as the foolish fellow washes and watches, but I rather doubt most of us are really planning on using our vintage TVs in wet locations.

[jshorva65]

My reasoning was that of guarding against those (admittedly rare, but possible with devices over 50 years old) cases of dielectric breakdown between primary and core of power transformers. Another possibility is that, perhaps several years after new caps are installed, the line bypass caps develop leakage to produce a shock hazard during hookup to a well-grounded antenna system if the set is plugged in and one touches the antenna terminals and antenna lead-in wires simultaneously before the two are actually connected.

A number of rules were adopted and/or amended regarding consumer products for US markets, most notably those enacted and/or amended in 1968, 1972, and 1976. Without re-checking my original sources on these, I don't recall which year corresponds to which rule or amendment. One was an amendment to FCC Rules Part 15 regarding interference with other systems and governed TV, radio, and other RF-producing appliances, presumably tightening restrictions upon RFI. The other two rules and/or amendments were in reference to product safety. As I recall, one dealt with X-ray emissions from television HV components, later amended to set stricter limits. The other specified maximum ground fault tolerance in terms of maximum AC voltage permissible between exposed metal parts of any device and earth ground as measured across a specified RC test circuit, and was later amended to set more-stringent limits. If memory serves correctly, the ground fault limits specified in 1968 allowed 7.5VAC across an RC circuit consisting of 1500 ohms shunted by 0.15uF and the 1976 amendment lowered the maximum permissible voltage drop to 1.5VAC.

I have encountered some equipment having relatively large line bypass caps, and a bypass cap of about 0.05uF has 53K capacitive reactance at 60 Hz. Such a reactance value could pass enough leakage current to exceed safety guidelines, although probably not enough to cause serious harm or even to trip a GFCI. If the caps developed significantly-low DC leakage resistances in 20 years or so from now, though, a very unpleasant shock could result from simultaneous contact with the TV chassis and, perhaps, a nearby heating duct or radiator as such structures would be made of metal and in contact with the furnace or boiler which would in turn be grounded. Perhaps not an electrocution risk for a healthy adult, but potentially an unpleasant surprise.

[ChrisW6ATV]

As David said, if I was really worried about shock hazards on old equipment, I would just replace the wall outlets with GFCIs. At about US$10 each, often less, that would be even cheaper than modifying plugs on several old devices used in that location, and would leave the devices themselves unmodified.

I remember in the mid-1970's, we had a TV with series-string tube filaments (also often the type with a hot chassis), and I touched some combination of its antenna terminal and some other object in the house, maybe a pipe or telephone, and I felt a moderate current, enough to get my attention. Nothing like my worst "zap", which was when I touched the unattached HV cap of a 23" B&W monitor chassis while it was still powered on. That event was more like getting hit by a truck.

[jshorva65]

Originally Posted by ChrisW6ATV

As David said, if I was really worried about shock hazards on old equipment, I would just replace the wall outlets with GFCIs. At about US$10 each, often less, that would be even cheaper than modifying plugs on several old devices used in that location, and would leave the devices themselves unmodified.

I remember in the mid-1970's, we had a TV with series-string tube filaments (also often the type with a hot chassis), and I touched some combination of its antenna terminal and some other object in the house, maybe a pipe or telephone, and I felt a moderate current, enough to get my attention. Nothing like my worst "zap", which was when I touched the unattached HV cap of a 23" B&W monitor chassis while it was still powered on. That event was more like getting hit by a truck.

The idea evolved from discussions with clients regarding my recommendation of GFCI receptacle upgrades. All were novice collectors with at least one metal portable set in their small collections and all lacked the confidence in their household wiring abilities to attempt such an upgrade themselves and asked about a more-economical alternative than the quotes they had received from local electricians.

Close proximity to a metal heating vent and some computer network jacks was what prompted my GFCI upgrade to a room where such devices are not required by local codes. My reasoning was to prevent unpleasant shocks and minimize possible damage to expensive computer gear in the event that a fault in one of my low-tech items and contact with some of the high-tech infrastructure happened simultaneously.

[Phil Nelson]

Originally Posted by David Roper

I've seen the vintage picture of a Sentinel trapezoid perched precariously on the edge of a clawfoot tub as the foolish fellow washes and watches, but I rather doubt most of us are really planning on using our vintage TVs in wet locations.

I shouldn't admit this, but maybe it will give someone a laugh. When in college, I discovered that long hot baths were good for relieving stress. My miserable basement apartment had a clawfoot tub. I got into the habit of watching TV in the tub late at night, with a briefcase-type TV (Philco? Admiral?) perched on a board which I placed across the top of the tub. Some times I balanced it on the corner of the sink, too, but then the viewing angle was not so good.

Man, the stupid the things you do when young. But I lived to tell the tale.

This was the same apartment where I used the miniscule dining nook as a workspace to rebuild a vintage British motorcycle. Girlfriends didn't seem to think it was odd to eat standing at the kitchen counter, but in hindsight, I have to think, "Sheesh, dude, get a clue!" :-)

Phil Nelson

[Bill R]

Someone throw me a bone here. How does a GFCI work if there is no ground connection? The plugs like this I have taken appart only have a thermal switch that will trip like a circuit breaker. Some had two contacts to break line and neutral. Since a GFCI senses current in the ground wire you would have to have a 3 conductor plug. I thought. You would be surprised how many people come in the store and spend a lot of money on surge protectors then use a cheap adaptor to plug it into a 2 prong outlet. I agree if you need GFCI protection I would install the outlet, or a GFCI circuit breaker . Anyone comfortable working on a vintage tv should have no problem.

Bill R

[willyrover]

"A Ground Fault Circuit Interrupter (GFCI) is a device to protect against electric shock should someone come in contact with a live (Hot) wire and a path to ground which would result in a current through his/her body. The GFCI operates by sensing the difference between the currents in the Hot and Neutral conductors. Under normal conditions, these should be equal. However, if someone touches the Hot and a Ground such as a plumbing fixture or they are standing in water, these currents will not be equal as the path is to Ground - a ground fault - and not to the Neutral. This might occur if a short circuit developed inside an ungrounded appliance or if someone was working on a live circuit and accidentally touched a live wire.

GFCIs typically test for the following condition:

* A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to Ground bypassing the Neutral. This is the test that is most critical for safety.
* A Grounded Neutral fault. Due to miswiring or a short circuit, the N and G wires are connected by a low resistance path downstream of the GFCI. In this case, the GFCI will trip as soon as power is applied even if nothing is connected to its protected (load) circuit. "

The GFCI doesn't work by sensing current in the ground wire, therefore a ground prong/grounded appliance is not needed for a GFCI to work. The GFCI is supposed to prevent your body from becoming the ground.

[Bill R]

Thanks for jogging the old memory! That's what I was looking for. I stand graciously corrected. It has been a long time since I did any electrical work.

Bill R

[jshorva65]

Even with a "fully" enclosed set in a wooden or Bakelite case, wooden or Bakelite knobs, dial pointers behind a glass or plastic window, there will often be two or more chassis mounting screws with exposed heads on the underside of the case and there are, of course, the antenna terminals on a TV and most FM receivers. GFCI protection is beneficial when any vintage appliance is operated within close proximity to any grounded metal object (vents or radiators of central heating systems for example).

Any TV, radio, phono, etc. employing the "AA5 radio" power supply topology, even if the "B-" bus is isolated from chassis metal via RC networks (the GE "Locomotive" televisions: 800's; 10T1's; the wooden-case 16T1; and others used a "voltage doubler" variant of this topology) can develop a leakage path to its chassis as the new parts we install during recapping begin to age.

A shock from simultaneous contact with a grounded heating vent and chassis (mounting or antenna terminal) screw with some moderately-leaky components inside the set (perhaps 20 years after being recapped) represents little more than an unpleasant surprise to a healthy adult, but what of the 80-year-old with an undiagnosed heart condition? As a professional provider of restoration services, I encounter many clients having little or no familiarity with the technical details of the sets' inner workings. The motivation of these individuals in having a set restored may be nostalgia, perhaps the set is a family heirloom and stirs up fond memories of watching TV at Grandma's house as a child. When a client is willing to spend $900 to restore a Dumont RA-104 TV/AM/FM/Phono combo once owned by great-grandparents, complete with mechanical rebuild of the phono, correcting poorly-done repairs from 40 or more years ago, replacement of a bad yoke or flyback, fusing of the B+ line, NOS exact-replacement delay relay, along with the standard recapping, I find myself inclined to expect the set to remain a family heirloom for another generation or more. I also hope to maximize safety toward considering that there may be grandchildren visiting their homes 20 years from now.

Speaking of children, even a harmless, mild shock can result in emotional trauma to, perhaps, a three-year-old. My fascination with technology began, ironically, with a household accident at age 3 in which a defective appliance plug exploded in my hand. A teenage cousin was studying for a career as a Science/Technology teacher at that time, and transformed a small child’s fear into intellectual curiosity tempered by a healthy respect for an awesome force.

When recapping a set for a client, I also make it a matter of policy that the clients' sole responsibilities should another repair be needed within a year after recapping will be those of transporting the set here for service and cost of materials. Labor for any in-warranty repairs is always free unless the chassis has been removed from the cabinet by unauthorized persons or other tampering, misuse, or accidental damage has occurred. An instructional presentation of the set or text instructions for care and handling are also provided, and these include recommendations for upgrading the receptacle to be used for powering the set to a GFCI unit, use of a quality home-theater surge protection device, making of antenna and other signal source connections before plugging in the set's power cord, never using the cabinet as a stand for any item containing any liquid or placing hanging pots containing house plants near the set's cabinet, etc. A hanging planter above one of my grandparents' 1966 Zenith color sets proved disastrous to the 21FJP22 during watering of the plants while the set was operating and the CRT neck was at full operating temperature (splash, crack, whoosh, POW!). In those days, rebuilt 21FJP22 were advertised for only $100 installed ($20 or $25 extra without a rebuildable "bottle" to exchange), and all house plants were immediately moved far from all of the three sets for which they had paid $500 each. Only a few drops of cold water striking the hot glass was sufficient to crack the tube, spoil its vacuum, and cause a spectacular display of arcing inside the set.

[markthefixer]

Originally Posted by Bill R

Someone throw me a bone here. How does a GFCI work if there is no ground connection? The plugs like this I have taken appart only have a thermal switch that will trip like a circuit breaker. Some had two contacts to break line and neutral. Since a GFCI senses current in the ground wire you would have to have a 3 conductor plug. I thought. You would be surprised how many people come in the store and spend a lot of money on surge protectors then use a cheap adaptor to plug it into a 2 prong outlet. I agree if you need GFCI protection I would install the outlet, or a GFCI circuit breaker . Anyone comfortable working on a vintage tv should have no problem.

Bill R

The hot and neutral wires wrap through a toroid transformer core and constitute the primary of the transformer. Then they go to a PAIR of relay contacts hooked up to a spring loaded disconnect mechanism. The other side of the relay is the outlet plug. Meanwhile back at the transformer, the secondary has a gazillion windings, making it very sensitive. When the current going OUT the hot wire is EXACTLY balanced by the current going BACK through the neutral, there is NO magnetism induced in the transformer. When an inbalance occurs, then that sensitive secondary with the gazillion turns gets energized. Then an integrated circuit (usually) powered by the line (before the relay) senses the voltage and energizes a coil that trips the spring loaded disconnect mechanism on the relay , sort of like a mousetrap.
The hot and neutral open up immediately. No ground is needed.

IF you were insulated from ground and got across the hot and neutral, you could get zapped without a disconnect.

The GFCI BOX breaker has an extra white wire which is the dedicated neutral that HAS to be run to every outlet serviced by that breaker. That might account for any "ground" confusion.

The internals of the GFCI outlet haven't changed much in the last 20 years or more, I recently replaced one and opened up the old OLD GFCI that was in the house when I got it 15 years ago, and the design was the same. The internal inspection sticker was early 80's.

[Bill R]

Originally Posted by markthefixer

The hot and neutral wires wrap through a toroid transformer core and constitute the primary of the transformer. Then they go to a PAIR of relay contacts hooked up to a spring loaded disconnect mechanism. The other side of the relay is the outlet plug. Meanwhile back at the transformer, the secondary has a gazillion windings, making it very sensitive. When the current going OUT the hot wire is EXACTLY balanced by the current going BACK through the neutral, there is NO magnetism induced in the transformer. When an inbalance occurs, then that sensitive secondary with the gazillion turns gets energized. Then an integrated circuit (usually) powered by the line (before the relay) senses the voltage and energizes a coil that trips the spring loaded disconnect mechanism on the relay , sort of like a mousetrap.
The hot and neutral open up immediately. No ground is needed.

.

Thanks for the explanation.