History Question

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synchro said:
I found this article about it, for what it's worth:

http://www.ncwhomeinspections.com/History+of+the+grounded+receptacles+in+residential+homes
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Thank you. The answer I was looking for is 1962 with NEC 210.7.

It was piecemeal fashion spanning 1947 to 1962.

1947 Laundry room required a 3-pole made for grounding.
1956 Included outdoor circuits.
1959 Kitchen sink outlet.
1962 Required all branch circuits to be 3-wire w ground.
1965 Required EGC to be the same size as the circuit conductors.

I knew it had to be when I was young (3-years old). I remember the first house we lived in had 2-wire branch circuits; I stuck a fork in an outlet once. We moved into a new home in 1976; the first thing I noticed was 3-wire branch circuits. I have been PO'ed and curious about electricity ever since I stuck a fork in a wall outlet.

I do know where the outdated 25-ohm verbiage comes from, though.

Thanks again and Happy New Year.
 
25 ohm requirement comes from telegraph systems. I have a paper on that from Mike Holt and will post that soon
 
dereckbc said:
1965 Required EGC to be the same size as the circuit conductors.
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Small correction this was accepted into the 1968 NEC.
The link has it correct.
The change was proposed by UL and possibly the Copper industry, with no electrical basis.
The only real concerns were 'mechanical' with the 16 AWG wire in 12/2 and 14/2 Romex.
Interestingly Canada's CEC and at least one northern US state that borders Canada never fully adopted this change, they allow 14 AWG EGC in 12/2 and 14/2 'NM-D' Romex, presumably without problems to this day.


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tom baker said:
25 ohm requirement comes from telegraph systems. I have a paper on that from Mike Holt and will post that soon
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Close enough. As you recall, I come from the telecom sector, and early in my career, I attended power and protection conferences held yearly. Back then, the pioneers of protective grounding were still around. I got to the bottom of the infamous 5-ohm requirement and 25-ohm NEC verbiage.

Mike is correct; it comes from the telegraph days of the civil war. It required a 5-Ohm ground using earth as the battery return conductor. It had to be low because of the high resistance of the overhead steel wire.

Along comes Ma-Bell wiring into our homes with Party Lines and rotary dial phones. One of the significant challenges was ringing individual parties with up to 12 parties sharing a common line? Telephone circuits required 3-wires, Tip & Ring, and an Earth Ground of 25-ohms or less. The Telco applied ring voltage in 3-modes of T-R, T-G, and R-G at the switch. They also used 20, 30, 40, and 50 Hz frequency-selective ringers. To make it work, the Telco would wire your ringer with a frequency selective coil. Between the 3 modes and 4 frequencies allow them to ring 12 different parties on the same line.

Ma-Bell used dirt as a circuit conductor for the ringers. To make it work required the Central Office Ground to be 5-Ohms or less, and the service drop, your home be 25-ohms or less like the telegraph. Back then was no problem in the cities with a water utility. You bonded to the same water pipe the Telco used. Rural areas without water service presented problems. The Telcos would have to drive a rod or two. Of course, we learned that is a dangerous practice, and there is no reason to have a specified impedance today. Telcos quit using party lines decades ago.

That is what I learned from the Western Electric and Bell Labs guys in 1980.
 
I remember about 40 years ago I had a party line and it would ring tip to ground or ring to ground. then Telco deregulated and I no longer had a party line, I figured out to the modify the phone so it would ring.
I have the "why 25 ohms" from Mike Holt but its too large to attach, its a PDF and I don't have a way to make it smaller.
 
Excellent info, Derrick. I remember early phone lines had a yellow wire for the ringer in addition to the red and green wires. When I started doing phone wiring as a kid, phones like the lighted Princess model came out, and I used the black/yellow pair for the plug-in transformer.

By the way, just in case there is anyone here who doesn't know this, tip and ring (and sleeve) refer to the switchboard plugs that look like stereo headphone plugs. In fact, headphone plugs were adapted from switchboard plugs, but are actually a slightly smaller diameter.

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tom baker said:
I have the "why 25 ohms" from Mike Holt but its too large to attach, its a PDF and I don't have a way to make it smaller.
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No problem, Tom, I appreciate you trying. I saw it quite some time ago. Perhaps Mike has it in an archive with a link.
LarryFine said:
Excellent info, Derrick. I remember early phone lines had a yellowThe yellow wire was ground wire for the ringer in addition to the red and green wires.
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Thanks. Today is just Tip and Ring (Red/Green). Ring voltage is applied to T/R at leaving the switching office at 105 volts @ 20 Hz.

Anyway, thank you to all. I am gathering a few bits of history for a Grounding and Bonding Class I teach to new electronic technicians, sparkies, and straighten out ham radio operators. Those guys believe in voodoo and that somehow a ground wire is magical, defying the laws of physics.

For example, some of you will get a kick out of this, and I am sure some have seen or heard it. A prevalent practice ham radio operators use is driving a ground rod where the coax enters the shack (spare bedroom or space). More times than not is located on the opposite side of the house where the AC Service enters. They might even use a 16-foot bonding jumper to sink another rod away from home. They bond the coax sheath via an ADU and run a #6 AWG to a ground bus inside. Hope that raises red flags!

After I teach them about step potential and common mode currents, they realize just how dangerous a ground loop they have put themselves in. The question always comes up how did we get it so wrong? History answers that question. Most hams are aging Babyboomers and pass down out-of-date information. Driving ground outside the shack was the best practice in the 50/60/70's before NEC required all circuits to have the 3rd EGC wire. Back then, that was the only ground they could access for any form of lightning protection. It has nothing to do with RF energy.

I leave you with this, NEC 250.94 is not only a lifesaver, but it also offers the highest performance as it is the basses of a Single Point Ground. So my fellow Sparkies, if you work for a ham, educate them and tell them to bring every circuit to the AC service and bond to a common point like a bus bar or IBT before taking anything inside. Once inside, keep isolated. Run their coax and Ground Wire from the IBT.
 
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