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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Fri 26, 2020 7:51 pm 
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Sundial now has nice three wire cords with molded-on plugs.

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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Fri 26, 2020 8:00 pm 
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I don't think it's a "us versus them," or being "disciples" of a belief system or not.

Some of us would install one because that would be the standard if the exact same radio would be produced today. It's not appropriate for all radios.

To be clear, a 3-prong/grounded power cord would not protect you from being shocked if you touch the wrong part. The main purpose is so that if a part of AC becomes loose inside and touches an outer chassis or metal case, the current would be sent to the household ground path and trip the breaker near-instantly. It's the tripped household circuit breaker (shutting off power) keep one from being shocked.

Definitely NOT for "hot chassis"; a 3-prong cord would make it more dangerous.

Since you mentioned being shocked, please exercise caution. My work bench has GFCI supply; makes it only slightly safer in case of a ground fault; even with an isolation transformer, not much can protect you if you touch an electrified part.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Fri 26, 2020 9:10 pm 
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Location: Near Brandon, Iowa
henry finley wrote:
Chris108 wrote:
Holy smokes, I thought the only thing dangerous about listening to the radio was some of the programs that are on. Maybe I'd be safer watching TV after all! :shock:

I don't think there's really a right answer or a wrong answer on whether to install a three-wire cord on an old radio; it's more of a question of where your comfort level lies. Which by the way includes an assessment of all the hazards involved, in addition to the performance and originality of the radio. The question of noise and interference from building grounds has been dealt with at length.

If a radio has excessive leakage current due to moisture in the transformer windings, or faulty line isolation caps, grounding it could cause those components to fail, perhaps starting a fire in the process. At a bare minimum, I would not ground a chassis unless the isolation cap(s) were replaced with modern Y2 (line to chassis) capacitors and the transformer passed a megger or hipot test.

It also has to be considered that grounding greatly increases the stress on power transformer insulation, so even if an antique transformer is good to begin with, you're not extending its life by grounding it. Since power surges and spikes can be on both sides of the line, the stress is on a grounded transformer whether the radio is on or not--unless the on/off switch opens both sides of the line, which is pretty rare. Keeping old radios unplugged when not in use is an obvious way to avoid this kind of trouble.

This is an old thread. But I was doing a search to see where these guys have been buying their 3 prong power cords they've been upgrading their gear with. And I ran up on this post. Whenever you've answered one of my posts it was good advice. It would seem you're not exactly a disciple of this grounded cord conversion campaign going around. I'm not so sure myself. I understand the Hallicrafters, Hammarlunds, and most of the others have their own transformers and there for act as their own isolation transformers, with the chassis and cabinet "floats". As long as you're not standing in a puddle of salt water while operating the radio, and the radio or autotransformer, and whatever, and the machinery is in good condition, there should be no real reason for grounding the chassis. I've read in a ham shack some operators are sticklers for hooking their receivers, transmitters, linears, and all the other gear up to a common ground. Other guys pay it no attention.
Every day you hear stories of somebody getting shot. but I don't recall one story about a ham operator who was killed by an ungrounded radio. I'm just wondering if i should put aside this new campaign I seem to be on of converting all my gear to 3 prong. Seems there's other restoration, maintenance and repair work i should be concentrating on.

It's not "ham operators" who typically fall victim to electrical shock: by dint of their training, they generally know better (how many small plane pilots walk into spinning propellers?): it's "innocents" who end up getting harmed in this way. If this is something that seriously concerns you, you must be a recent arrival to Planet Earth. I apologize for being blunt.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 3:15 am 
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Quote:
...But I was doing a search to see where these guys have been buying their 3 prong power cords they've been upgrading their gear with....
To answer the question directly: all of my sets with metal outer case have grounded power cords. I use cords from old computers. You can also find vintage looking ones on the internet (search term: "cloth covered cords"). Look carefully because some are not "UL listed."

If it's easier, may I suggest just use GFCI receptacles. That would take care of the ground fault hazard.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 4:52 am 
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Joined: Jul Sat 28, 2012 9:32 pm
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Location: Charlotte 28211
I've use old computer cords lots of times but not any more. For one thing I've always doubted the quality of them. For instance, is 18 gauge REALLY 18 gauge's worth of wire? Is the copper 100% copper? Or is is "Chinese" copper made out who knows what? Sitting over here next to me is a Hammarlund 129 I put a new cord in only a month or 2 ago. Printed on the sheath of the computer cord I made it out of said 18 AWG. If that spindly little thread is 18 gauge wire, I'm a monkey's uncle. My posting frequency on this site has gone up recently and I know that. It's because I'm on a campaign to raise the standards of my radio work. But some things are not necessary. That's time better spent on better work where it really needs being done. I'm not so sure all the pursuit of this kind of grounding or that, is all that necessary. And I'm not about to switch all the landlord's electrical sockets to GFCI's. Those things annoy me. Always popping out for no reason.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 6:04 am 
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Location: Fenton, MI 48430
I use 3 wire on transformer sets and polarized type on AC-DC sets to prevent electric shock. Never use 3 wire on a AC-DC set, of course.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 6:39 pm 
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Has anyone said this yet? If so sorry for not seeing it.
If you have a lot of noise on your house wiring, connecting the chassis directly to that noise source is not good radio.
The chassis can act as a shield, but only if the ground wire is quiet.
Also, the chassis hole won't take a big diam power cord unless you ream it out, then watch out for chips of metal in your circuitry.

Grounding old test equipment is usually a good idea.

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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 7:23 pm 
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westcoastjohn wrote:
...Also, the chassis hole won't take a big diam power cord unless you ream it out, then watch out for chips of metal in your circuitry.
Also good to have a strain relief grommet so the cord doesn't rub directly against metal.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 7:56 pm 
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Location: Charlotte 28211
westcoastjohn wrote:
Has anyone said this yet? If so sorry for not seeing it.
If you have a lot of noise on your house wiring, connecting the chassis directly to that noise source is not good radio.
The chassis can act as a shield, but only if the ground wire is quiet.
Also, the chassis hole won't take a big diam power cord unless you ream it out, then watch out for chips of metal in your circuitry.

Grounding old test equipment is usually a good idea.

When I lived way out in the country in a log cabin deep in the woods I had my own power company pole transformer. Nary a peep of noise. Now that I'm stuck in an apartment back down here is this sewer of a big city called Charlotte, my electricity is filthy. Noise noise noise. Wish I could shoot out all these bright orange street lights around here. I suppose it's supposed to be a crime deterrent. The best crime deterrent in my mind would be pitch darkness so dark a ghost would get a case of the willies. Why provide the crooks with all that light to work their deeds? And all these wifi boxes. Geez and crackers, what noise.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sat 27, 2020 9:39 pm 
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Location: Fenton, MI 48430
[/quote]Also good to have a strain relief grommet so the cord doesn't rub directly against metal.[/quote]
If grommet a little small, I melt it to larger inside diameter with a solder iron. The melted plastic cleanly snaps off.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sun 28, 2020 7:30 am 
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Joined: Jul Sat 28, 2012 9:32 pm
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Location: Charlotte 28211
I've decided on this 3 wire cord conversion business on my radios with transformers. "Ground" is a place where I don't want to be laying in a box on the other side of. As for radio and any other piece of equipment with a power transformer in the cabinet, the transformer is AWAYS an isolation transformer. Except in Hammarlund radios where both sides of the incoming line are hooked to the chassis through a disc capacitor. A design that still baffles me. Today I went through extra trouble to go buy a new 3 wire cord to put on my Adjust-A-Volt autotransformer. But I did not replace the 2 prong socket on the front with a 3 prong. The chassis and metal cabinet will be forever hooked to the third prong on my electrical outlets. I can only hope that whoever built this apartment in the 1960's was not too drunk to switch the black and white wire, or the bare one. As for restoring radios I have to concentrate on the radio's side side of the self contained transformer. I already know that I am to hook the scope negative or the VTVM up to the chassis of the radio. In radio work, the chassis is "ground". Why would I want to put a 3 wire cord on it and risk de-isolating the radio chassis' side of the power transformer by connecting it up to the other side of that transformer and its incoming line, when the other side could have been switched by some electrical subcontractor? The best way I know of keeping a radio chassis from being hot is NOT putting that third leg on it. In fact, it might be the smartest thing to drive a 6 foot rod into the ground outside the building and hooking the chassis up to THAT. I've decided that the best thing for me is to pay attention to doing good work on the radio's side of its transformer. As for transformerless radios, a new 2-bladed cord is smart, as long as the electrician didn't switch wires when the building was built. Put me down as a nay on putting 3 wire cords on all my gear. When working on radios NEITHER side of the line is the best side.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sun 28, 2020 8:16 am 
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Hot Chassis, radios do not lend themselves to being grounded, however a 3 wire plug top will stop the power from being inverted. That way the Neutral, which is normally at ground potential, has a better chance of being on the chassis. They are just not considered" intrinsically safe". Regulations enforced here, as said many times, say there is one way to wire an GP outlet (GPO) and one way only. The backs of GPO's are marked, so there is absolutely no excuse for an electrician to get it wrong. Note Neutral is floated on the load side of a GFCI. This place now has them everywhere (regulations).

I only use the isolation transformer for power ups as it has a "Kill Switch". Earth leakage mains / supply side is tested very early, when assessing it. Shielded transformers & many line capacitors can bleed "Charge to the Chassis", those are grounded. Anything transformer, with a metal cabinet no ground and line caps to it, will be modified & grounded. Radio Club people here will ground a transformer set chassis. Sometimes this is to comply with regulations. I am in a rural area so a dirty earth does not exist and most of the infeed was put underground four years ago, so at that point it was all put into compliance with regulations. The radio test bench does have a separate ground for antennas.

So its in most cases here all about safety, getting a clean RF path to ground, & regulations.

Marc


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sun 28, 2020 6:28 pm 
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AJJ wrote:
westcoastjohn wrote:
...Also, the chassis hole won't take a big diam power cord unless you ream it out, then watch out for chips of metal in your circuitry.
Also good to have a strain relief grommet so the cord doesn't rub directly against metal.
You can also use rubber grommets, with a tie-wrap on the cord inside the chassis.

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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Sun 28, 2020 7:56 pm 
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henry finley wrote:
...Except in Hammarlund radios where both sides of the incoming line are hooked to the chassis through a disc capacitor. A design that still baffles me....
It's for noise reduction. Some earlier radios have just a single capacitor while others put one on each side of AC power line. Explained here in "Elements of Radio Servicing."

https://antiqueradios.com/archive.shtml


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Mon 29, 2020 12:47 am 
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One should note that with GFCI's & such Neutral floats after the device. But it will often still be at ground potential.

Combinations where the cap goes "Active" to a metal chassis or cabinet are potentially the most dangerous, as it will put AC onto the chassis: Ideally for RF path for the antenna, it should be on Neutral. Transformer sets with a separate earth to chassis escape that issue and are intrinsically safer. Regulations here are quite specific "If a metal part can become alive it should be grounded". Some sets did have an isolated primary on the antenna coil & you could use different antennas & ground separately.

Hot chassis sets here are rare & AC / DC more prevalent in the era prior to state grids: But now rare. As are line caps on "Mains" (Domestic supply) radio's.

As I have RF & Lightning on the lines, as explained a few times, I filter it on the supply: Not the sets. Three caps two MOV's.

Theoretically, with an "Approved Line Cap" in series with it: A Hot Set with a floating chassis could be connected to a separate grounding.

Marc


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Mon 29, 2020 1:58 am 
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henry finley wrote:
... I can only hope that whoever built this apartment in the 1960's was not too drunk to switch the black and white wire, or the bare one....
..I forgot to repond to this previously...
You're not the only one worried and mistakes do happen. Some of us here use receptacle tester that costs less than $10.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Mon 29, 2020 2:35 am 
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One other note, completely modern house wiring is very sensitive to ground faults. I had one AA5 that tripped a circuit breaker because the "death cap" was leaky.


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Mon 29, 2020 4:32 am 
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I have found inverted socket wires. I made a point of testing all of the outlets at the local Men's Shed to ensure that they were right & actually alive, with one of those cheap & effective devices; While I allocated them a number related to which switchboard, or sub board they were related to and their fuse. Since then there was an upgrade and its all circuit breakers and GFCI's (RCD's here).

The death caps should be replaced on sight if they are of a non approved type. The resistance of wax paper caps (I find) is rarely higher than 100K and in the valve era 50Meg or lower, was a fail for a decoupling cap. 200Meg for coupling.

As we are required to "Tag & Test" the primary side of mains powered electrical equipment, that one would likely have never made it off the bench here with a dud cap on the line.

When you are playing with mains (utility power) powered stuff, you just have to be diligent.

Marc


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Tue 30, 2020 4:49 am 
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Location: Charlotte 28211
I thank you guys and YL's for this particular discussion. Radio can be almost a passion. And it may also top the list of dangerous things you can do. Always something more to learn, and always somebody out there who is 10,000 times smarter than yourself. There's little room for sloppiness or error, as death is one innocent touch of the finger away. I almost never think of this when working on a radio or TV or tape recorder, or whatever. I ran big press as a printer for 38 years and being smashed in a machine is something I saw a few times. But never me, thank God. That was rarely deadly though, but incredibly painful and maiming. But these radios can mean death in an instant. Thanks, guys. Work safe. HTF, KN4SMF


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 Post subject: Re: Should I go with a 3 prong cord?
PostPosted: Jun Tue 30, 2020 7:10 am 
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With the electrical regulations here in respect of fuse boxes , everything new, or where the wiring is worked on is required to be fitted, or retrofitted with earth leakage trips. However, do remember that if the power is drawn from the secondary of a transformer which is not an "auto transformer"; Then the earth leakage device (GFCI) will not trip. The circuit breaker will only trip on current with that scenario.

I have seen two "stick" welders go to ground on the secondary and fuse the grounding wire in the supply cable. In neither case did anything trip out.

Marc


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