June 1966 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Electrocution has always been - and always should be - a hot topic (pun intended) in the realm of electrical and electronics servicing and usage. Trade and hobby magazines have dedicated many column inches to it over the years. A lot of people are deathly (there I go with the puns again) afraid of being anywhere in the proximity of an exposed electrical connection. My father, a newspaper classified advertising manager, was one of those people. He would cringe when I took the cover off the fuse panel in the house to work on it. He could barely bring himself to replace a blown fuse, which was not a completely unjustified fear given the low standards of older electrical wiring. Those screw-in fuses had a threaded metal perimeter around the bottom portion with a button connection at the bottom center (see image). Theoretically, that threaded metal perimeter is at ground potential, but it could be a big assumption based on the installer and/or what anyone might have done in the mean time (like disconnecting the service panel ground wire). The fuse contacts look like a light bulb base, the difference being the maximum current available from a lamp socket is the amperage value of the fuse protecting the circuit (usually 15 amps), whereas the fuse's supply is the amperage value available to the panel bus as protected by the main fuse (often at least 60 amps). In 1966, a large percentage of homes still had the original fuse panels installed. During my tenure as an electrician in the mid-to-late 1970s, prior to enlisting in the USAF, I worked as an electrician and did many service entrance panel change-outs replacing fuse panels with circuit breaker panels.
On a side note, I was visiting a neighbor a few days ago and noticed a ground rod sticking above the surface outside his house with a ground clamp but no wire attached to it. He showed me where someone at some point ran the breaker panel ground over to a water pipe (properly bonded to the street side) about 15 feet away and abandoned the ground rod, which is only a couple feet from the panel location. I will be reestablishing that connection for him in the near future. In case you are not aware, the primary purpose for a ground bond to the water pipe is to protect occupants from being zapped when touching a plumbing fixture during a lightning strike. Plastic pipe (for supply and waste water) is a nice natural protection, but a lot of houses still have copper installed at least for supply and are therefore vulnerable. A ground rod's purpose is to protect the electrical system from lightning strikes and to drain off any current that might for whatever reason not return properly to the street electrical service via the neutral wire. Residential service entrance panels are required by code to have the neutral bus bonded to the ground bus inside the panel, so any neutral leakage current is drained to the street service neutral and whatever is connected to the ground system. Current is divided per Mr. Kirchhoff's famous law, meaning the total current will be split according to the individual parallel resistance values to ground, with some portion of the current flowing in each branch. The old saying about current taking the path of least resistance is misleading since it will favor, but not exclusively flow through the path of least resistance. A lethal amount of current might still be flowing in the second-least path of resistance.
Look Out! It's Hot!
By Christopher Sheridan, Associate Editor
Illustration By Paul Coker
Our basement technician says to treat electricity with the respect it deserves
Ringing Ziggy Carmichael's doorbell brought no response, as usual. I'll probably catch him in the basement, I thought, making my way in through a side door with a defective CB rig in tow. Ziggy ran a TV service from his home, and he spent much of his spare time with our local CB club members, fixing their gear and sometimes giving lectures. He was president of the club and, as far as most members were concerned, the best repairman around - in spite of the fact that he charged club members little or nothing for his services.
Ziggy looked up as he heard me descend the stairs to his workshop. "How do you like this?" he asked, pointing to a shiny new CB transceiver sitting on the workbench.
"Is it yours?"
"No, it belongs to my father. He's got the CB bug, but he doesn't like to build things, so I did it for him ... Be with you in a minute, soon as I finish checking it out," he said, noticing the CB rig cradled under my arm.
I watched as Ziggy probed around the new set with a VOM, poking in and around the controls and chassis. Then, seeing him reverse the unit's plug in the wall socket and start to probe again, my curiosity got the best of me and I asked him what he was looking for.
"Shock hazards," he replied. "It's a little safety check I make on all units leaving the shop. I'm making sure there are no potentially dangerous hot spots."
I glanced at the face of the small meter. "Doesn't register, or does that mean it's good? How does this thing work, anyway?"
"I'm using a 1000 ohms-per-volt a.c. VOM shunted with a 1500-ohm, 10-watt resistor," he said, shifting his glance between the unit and meter. "One meter lead is tied to a good 'earth' ground, and with the other lead I probe the parts of the unit that are exposed to the operator. A meter reading of 7.5 volts or more indicates a potentially dangerous current leak existing between the unit and ground which needs fixing. The '7.5 volts' is based on the maximum allowable leakage current in the minimum safety requirements set up by the Underwriters Laboratory."
I couldn't help but grin, and Ziggy, noticing it, snapped out: "I know what you're thinking. I'm a worry wart and this is just a waste of time. But a little prevention goes a long way when you're playing around with electricity. Using this little gimmick can darn well save your life."
Ziggy was always in the habit of quoting facts when he wanted to get a point across. This time it was no different as he told me that this year, according to the National Safety Council, about 1000 people will lose their lives due to accidental electric shock. I was amazed, but I was even more surprised to learn that ordinary 117-volt house current was the biggest single cause of such fatalities.
"Once in a while I read of something happening to someone in the paper," I said, "but frankly, I'm probably like most people and just take electricity for granted."
"Don't take it for granted." By now his tone was pedantic. "Fact is, in electrical accidents, one out of 14 disabling injuries results in a fatality. That's a death rate two-and-one-half times the death rate of those injured in auto accidents. Food for thought, eh?"
Nodding my head in agreement, it occurred to me that Ziggy taught electrical safety and resuscitation methods to interested groups - the Boy Scouts, for one. Here was an opportunity to bolster up my electric shock I.Q.
"Ziggy, while we're on the subject, let me ask you a few questions. How many volts are dangerous? What makes shock so hazardous when you're wet? What -"
"Hold it, one question at a time," Ziggy cut in. "But first, let's take a look at your CB rig. What's the problem?"
"Probably a bad filter capacitor - it's picked up a loud hum."
After trying the rig out, Ziggy agreed.
"Getting back to your questions," he said, "if there's one rule to remember about electricity, it's that you should treat 75 volts as you would 750 volts. It doesn't take much of a shock to be lethal. In fact, as little as 25 volts at 70 ma. can be fatal. And under optimum conditions, 15 to 20 ma. will do the job if the current passes through the heart and the victim can't let go."
"Why can't the victim let go?" I asked, watching him take my set apart.
"The shock contracts the muscles and paralyzes the nerves of the victim. If a sufficiently large number of nerves are involved, sudden violent contractions of the muscles throw him away from the shock source."
Examining the 50-μf. filter capacitor, Ziggy's face was practically buried in a maze of wires. "It doesn't look too bad for an old rig. We'll bridge it with another capacitor and see what happens. I have a couple of used ones around here somewhere. Ten will get you twenty you have a bad rectifier, too."
I made my way over to a small box hidden under his workbench where he kept his good used tubes and fished out a 6X4 - just in case he would have to replace the rectifier, too.
"Can't keep any secrets from you guys," Ziggy snorted. "You know just where to look."
"Call it experience. But let me ask you something else. How does shock affect the human body?"
"Most shock fatalities," he said resignedly, "involve the heart. You see, the heart generates a small current which keeps it pumping the blood throughout the body. An outside current across the heart easily disrupts this minute current, causing the heart to flutter or stop altogether. This is called ventricular fibrillation, and once it occurs, it's very hard to start the heart beating rhythmically again. On the other hand, a shock through the brain or other parts of your breathing apparatus can stop your breathing."
"You could also say that a shock can cause you to drop what you're carrying or fall off a ladder, as well as give you painful burns," I added.
Ziggy agreed. "Okay, smart guy, which would you say is the controlling factor of shock severity - current or voltage?"
I thought I didn't have to think this one out. "Voltage!"
"Wrong," he shot back. "Amperage.
But skin resistance, voltage, current path, and shock duration all have a hand in determining its severity. All these factors work together."
"How much amperage is dangerous?" "Most authorities say 15 ma., and more."
"Fifteen milliamps! That's not much." "Well, look at it this way," Ziggy said.
"Current as small as 0.2 ma. will pass safely through the body but can be felt as a tap on the skin, and those as little as 1 ma. will cause a tingling sensation. Current stronger than 1 ma. will start to grip, and 15 to 20 ma. will cause pain and the victim might not be able to let go."
He explained that usually as little as 20 to 70 ma. can be fatal, and that most medical authorities flatly state that 70 to 90 ma. is fatal.
"Currents between 100 and 200 ma. are doubly dangerous," he continued, "as they tend to cause ventricular fibrillation and respiratory paralysis. But, strange as it may seem, those greater than 200 ma. are often less dangerous as heavier currents cause heart contractions so severe that the heart is clamped for the shock duration, thus preventing ventricular fibrillation."
"Do different voltages act the same way?"
"Pretty much the same," Ziggy answered. "Contact with a 117- or 220- volt, 60-cycle a.c. line tends to cause ventricular fibrillation, while contact with 220 to 1000 volts usually results in both ventricular fibrillation and respiratory paralysis. Shocks of 1000 volts and more tend to cause only respiratory paralysis as high voltage clamps the heart."
After much searching, we found a replacement capacitor for my rig. Ziggy blew the dust off it and started soldering it in.
"It's not hard to understand," he continued, "why most fatal shocks involve water in some way when you consider that, ordinarily, dry human skin is highly resistive to current. But when the skin is wet, its resistance drops tremendously and more current can flow through the body."
"What is the normal skin resistance ?" "It averages between 100,000 and 600,000 ohms for the human body when dry, but drops to 1000 ohms or so when wet. Figure it out. Suppose your body was wet and you happened to handle a defective a.c. radio. More than 100 ma. would shoot through you. That's enough current to stop the heart and clamp your lung muscles. Most likely you'd be dead before you hit the floor."
"What about the body's internal resistance?" I asked.
"The internal resistance is much lower than the skin resistance. That's why electric current becomes more dangerous if it enters the body through a cut on the skin, or if it burns through the skin - as it will do if contact with the current source is continuous. From hand to foot, the internal resistance might measure 500 ohms; from ear to ear, about 100 ohms. Your skin resistance varies from point to point also. Measure it yourself sometime with an ohmmeter; wet the skin where the probes contact, and watch the resistance drop."
"But for a current to be dangerous, it has to take a path across the brain or heart area, right?"
Ziggy nodded. "The path from the head to the left leg is particularly dangerous as it involves both the heart and brain. That's why it's a good idea to keep one hand - preferably the left - in your pocket when working around electricity."
He finished soldering the capacitor in.
"The longer an electric shock lasts," he went on, "the more the heating along the path. The skin resistance drops, and more current flows through the victim. Always remove a shock victim from the source of shock as soon as possible - without, of course, giving yourself a shock."
He stated that resuscitation should be started immediately. "The longer you delay, the poorer the victim's chance of revival. You have four minutes at the most to act."
He went on to explain mouth-to-mouth artificial respiration and how it is applied to a victim whose breathing has stopped, and how closed chest cardiac massage is used with ventricular fibrillation.
"Just a few years ago," he added, "ventricular fibrillation was irreversible. Today, it's different. Hospitals use what they call a defibrillator to shock the heart back to normal. But the trick is to keep the victim alive until he can be helped."
"And that's where cardiac massage comes in," I deduced.
"Right. Cardiac massage substitutes externally applied pressure for the rhythmic contraction of normal heart muscles, thereby maintaining circulation at a level sufficient to maintain life. Everybody should know how to apply resuscitation - you never know when you or a member of your family may need it. The YMCA, Red Cross, and a lot of other organizations teach these methods."
"Well, in your experience, which would you say is worse - an a.c. or d.c. shock?"
"Make no mistake about it," Ziggy answered. "They're both deadly. Fact is, at household frequencies, authorities say that a.c. is roughly three times as dangerous as d.c. at the same voltage, but d.c. brings about ventricular fibrillation in a much shorter period of time. You'll also find that as the frequency of an a.c. source increases, the injurious effects of shock decrease. Medical reports have shown that a person tolerates only 30 ma. at 11,000 hertz, but 500 ma. at 100,000 hertz. But now we're getting up into the r.f. regions. And r.f., as you know, can give you a nasty burn."
Ziggy finally finished my CB unit, plugged it in, and tried it out. The hum was gone. We listened as a waspy-voiced CB'er tried to reach her itinerant husband with a message to pick up his mother-in-law at the railroad station. Seems she decided to pay an extended visit. I thought I heard Ziggy mutter something about "poor guy."
"This time you test the rig for shock hazards." Handing me the voltmeter probe, he added thoughtfully: "If people used more common sense and took time out to make a simple test as you're doing, there would be a heap less accidents. Take ordinary house current, for instance. Many people still believe that the electricity entering their homes is confined to two or three wires. They don't realize that the earth or ground is an important part of the distribution system, as power companies connect the neutral wire to many places along the line. The earth can be looked upon as a third or neutral wire in a two-wire system in parallel with the neutral or ground wire."
"That's why it's just as easy to get a shock by coming in contact with a grounded pipe while touching a 'hot' chassis as it is if you simply put both hands across a line," I commented.
"Right. Best protection you have is to use a ground wire with your electrical tools and appliances to drain off stray current. Small appliances wear out in time and are frequently a source of trouble. In fact, the Underwriters Laboratory states that no tool or appliance should be used in wet or other hazardous areas without special insulation and adequate grounding. It's also a good idea to buy only those appliances approved by the Underwriters Laboratory."
"Suppose your house hasn't a three-wire system ?" I asked.
"That's no problem. A three-wire cord plugs into a two-slot receptacle using an adapter with its own ground wire. The wire is attached to a ground screw on the faceplate of the outlet box."
"How's to tell you have a grounded faceplate ?"
"Easy. Normally a receptacle box is grounded if the house wiring is armored cable or rigid metal conduit. If it isn't, use a simple neon indicator - the type found in most hardware shops - to check. Touch one lead of the indicator to the faceplate screw and insert the other lead into each slot. If the indicator lights when contact is made on either slot, you have a ground. If you're using two-wire cord tools, make your own ground. Attach a length of No. 18 insulated single-conductor stranded copper wire to a screw on the tool's shell. The other end is tied to a grounded screw. It's not hard."
He went on to say that workshops, ham shacks and the like with damp concrete floors should be covered with wood or rubber mats as added protection. "Safety is largely a matter of habit. Learn to use common sense. Stay away from grounded pipes and other metal fixtures when near voltage. Always pull the plug out of a unit before doing anything to it, and use an isolation transformer when working on line-operated equipment. Make it a practice to consider all leads as hot leads until you have determined otherwise."
"I just thought of something," I interrupted. "How about a lecture for our CB club members on shock hazards. We could use some pointers."
Ziggy laughed. "I did give a little talk - at the last meeting. But, of course, you wouldn't know - you weren't there."
"I couldn't make it. I had a blind date that was supposed to be something special," I admitted, somewhat embarrassed.
"What happened?" Ziggy grinned.
"It turned out to be quite a shock." His laugh followed me all the way up the stairs.
Vital Seconds in Which You Can Save a Life
Apply Artificial Respiration
Tilt head far back. Pull chin upward. Pinch nostrils and blow. Check for exhalation.
(1) Lay the victim on his back. Place one hand under neck and lift. Tilt head back as far as possible so that the neck is extended.
(2) Pull chin upward until the head is extended back as far as possible. Keep victim in this position.
(3) Pinch the victim's nostrils and place your mouth firmly over his mouth. Blow hard enough to make his chest rise. With an infant, place your mouth over his mouth and nose.
(4) If the victim's chest does not rise, recheck his head and jaw position: The air pasage may be blocked. Turn the victim on his side or face down with head in a down position, tongue pulled forward. Slap victim to dislodge any foreign matter. If the victim is a child, hold him momentarily head downward over your arm or lap and slap child on the back.
(5) With adults, blow one vigorous breath every five seconds. With small children, blow shallow breaths every three seconds. Continue procedure until help arrives.
Apply Cardiac Massage
Press down firmly and quickly on breastbone.
1) The most accurate indication of ventricular fibrillation is the lack of pulse. Place he pads of your fingers alongside the victim's "Adam's Apple" and check for a pulse. If there is no pulse, check victim's pupils. If they are enlarged and do not narrow in response to light when you open the lids, immediately apply closed chest cardiac massage. Do not apply it if the victim has broken ribs.
(2) Place the victim on his back on a hard surface. Kneel at the victim's side and give him a few quick breaths of mouth-to-mouth artificial respiration.
(3) Place the heel of one hand on the lower third of the victim's breastbone and the other hand on top of the first hand.
(4) Flex your fingers so no pressure is applied to the ribs. Press down firmly and quickly, depressing the breastbone 1 1/2"-2". With children, use one hand; with babies, use two fingers. Then release pressure. Repeat this cycle every second .
(5) If you are alone, interrupt cardiac massage every 15 to 20 strokes to force two or three breaths of air into the victim's mouth. If another rescuer is present, concentrate on giving 60 strokes a minute and let him apply artificial respiration (12 times per minute). Continue procedure until help arrives.
Posted August 13, 2018