Technical FYI 120V 2 prong wall plug replacement

 

quote:

I really do not care if anyone wants to put OEM cloth insulated cord on their ZWs and restore their house wiring to the original ungrounded uninsulated knob and tube.

 

No postwar Lionel transformer left the factory with cloth insulated cord.

 

The recent threads about transformer safety leaves me wondering, which would result in a safer "environment", a ZW transformer with a ground added to the coil bracket, plugged into a non-GFI protected outlet, or a ZW transformer in proper operating condition with an original style non-polarized cord, plugged into a GFI protected outlet?

 

 

Now you're just making stuff up.

 

There's no such thing.

You guys crack me up.
Did I say that the ZW had an OEM cloth insulated cord?
Do you really think there was never an OEM cloth insulated cord made?
Were all those old appliances retrofitted by homeowners?

I may have to go to OGR Forum Anonymous.
This time I really mean it. Lol

Where is the topic that this refers to?

 

So far, all I see is Susan quoting something about electrical outlets, there is nothing in her post about ZWs, KWs, etc.

 

 

I asked Susan about the subject in this thread, which started out with a question about power strips, and wandered from there

 

I guess this thread is wanderings too.

 

quote:

Did I say that the ZW had an OEM cloth insulated cord?
Do you really think there was never an OEM cloth insulated cord made?
Were all those old appliances retrofitted by homeowners?

 

 

Many prewar transformers had cloth covered cords.
Growing up, some of my mother's kitchen appliances had cloth covered cords.
Our local electrical supply house still had replacements up into the early 1980's. Then they closed shop.

 

And continues to be manufactured for restorative purposes...

 

Guys,

 

Been away shoveling snow, not taking offense.  8-)  Returning to some questions here:

This May it will be 60 years since I began my training in engineering.  That included not only the design of electrical machinery, but hands-on lab work in the wiring, testing, measuring parameters, and operation of transformers and numerous rotary machines, mostly about 75 hp.  It was a lab with a traveling crane four stories up.

Credentials:
B.E. (Bachelor of Engineering)(Yale); M.S.E. (Master of Science in Engineering)(Princeton)
Professional Engineer-- more than one license remaining currently in force.
Member of IEEE for many years,

Electrical design experience: [In the railway field]
o  Prelim design & costing, catenary additions at Ivy City for Amtrak (~9 miles)
o  Wiring design etc Smithsonian subway station, DC (design to avoid grounding accidents here)
    (A woman died stepping on wet brass junc box cover for platform edge lights, est @70v DC.)
    (Box grounded by a wire from a distant point influenced by the rise in (-) DC traction return.)
o  Design of W Ballston traction power substation, NoVA (first substation with ~34.5 kV front end)
o  Redesign of Ballston pumping station (prototype for special condition systemwide replacement)
    (Later I was asked to join a UL panel writing a new code for pumping stations, but declined)

Particular other experience related to grounding:
o  Consultant to satellite comm firm: separation of signal from signal gear ground @base sta)
    (Before IEEE Orange book, only a small shadowy band of engineers did this; I was one)
o  Consideration of grounding motors on damp machinery deck, large bascule on I-695, Baltimore,
    as project manager. (Years later, NEC included a section for this; glad they got it right)   8-)

I know a little bit about grounding.  At least, I like to think that it is a two-edged sword.

Earlier in the thread, Tryanst 1880E wrote:

---

I have to ask after reading the surge arrestor thread why one would recommend that a individual not use a 3wire replacement cord and a grounding type plug when they are replacing both the plug and cord on a PW ZW transformer. This is clearly covered under 250-4(A)(3)

Am I missing something here?

---

Yes.  Section 250-114, which applies to cord-and-plug-connected utilization equipment.  Section 250-4 may be explicit, but it does not apply to our transformer.  Section 250-4 appears to apply more to the fixed wiring of a building, and moveable plug-in equipment of an amperage or voltage that cannot be handled by the usual 15- or 20-amp receptacle circuit.  That would include electric dryers, for example.  This part of 250-4 is not so clear, either.

Tryanst 1880E continued:

---

I've been in the trade 31yrs now and I can't think of one reason why I would recommend that someone that is replacing both the cord and plug of a PW ZW, continue to use a method which would leave metal current carrying parts not effectively bonded.

---

I can read one right on the page at 250-114.  All the Lionel postwar transformers for toy train use, up through the 150-watt KW, are listed utilization equipment, and as such may be continued in use so long as serviceable.  Since their 120-volt cordsets were rubber-insulated, they may be replaced when deteriorated with a fixture cord insulated in accordance with current practice.  The addition of a ground to any replacement cordset would change the nature of these transformers.  They are isolation transformers, and the addition of a ground wire would make a grounded surface exposed to touch on the layout.  A listed device which is rewired in such a way that its nature is changed and purpose defeated may not be continued in use.  These transformers are also double-insulated equipment.  The metal base is double-insulated, as well.

The present practice of service repair of cordsets with original but cracked rubber insulation by new fixture wire 2-wire cordsets appears to be clearly in accordance with this section of the 2014 NEC.

As to the NEC, I can't say I can quote it chapter and verse, particularly since most of my electrical work involved areas not covered by that Code.  But I can sure find grounding issues, because I know what I am looking for (I found 250-114 by using Google-- quicker that way.)  For example, [most] everyone knows the metal parts of their table lamps are not grounded (here, the wide blade now protects against the greater hazard).  One certainly doesn't want to change a bulb while holding anything grounded in one's other hand.

The PW ZW transformer is a more complicated case,  There are additional issues to be considered.  But my commentary above covers everything up thru the KW, as far as regulations go.  I'll post separately about the ZW.

--Frank         (Edited to correct format of indented lines)

Re-hash this thread.  Some of that old, old equipment needs to be recycled. Next to smoked detectors, in the last 40 years two things that have enhanced personal electrical shock protection and fire protection.  (1.) GFCI's (Ground Fault Circuit Interruption) devices. And presently (2.)Arc Fault Devices, not covered in this thread.

IMO Mike CT.

Previously posted (a.)

 

You need to understand the problem that exist when a 3 prong grounded type outlet is used as a replacement for old wiring two prong non-grounded outlets. One assumes the third prong is functional, when it in fact is not.  This section of the code addresses proper replacement of worn-out two prong outlets.  There is a lot of liability related to improper replacement of old two prong receptacles.  

2.(a) Replacement with a similar, like-kind, (2 prong receptacle.)  Yes, you can still buy two prong receptacles and it is permitted to replace them.  I uses to carry a few in the truck.  

2.(b)  You can replace (2 prong receptacles) with a GFI (Ground Fault Interrupter) receptacle, and there is a good chance that the note required is in the box of material. "No Equipment Ground"  Ground fault receptacles will work without a ground wire present and in most cases work well.   

3.(c)   Notes a circuit where a GFCI (Ground Fault Circuit Interrupter) breaker is install in the panel to protect the entire, old, two wire without ground circuit. .  You still have to install the "No Equipment Ground" note and "GFCI protected" note, on each device protected.

Properly done all lawyers should be happy.  

Mike CT 

Safety meeting of the day.  Thank you, Susan.    

 

 

Previously posted (b.)

Note again that GFCI protection will work without grounding/metal case/shell grounding installed. If there is a leak to ground, ( Assume that to be through you, since there is no safety ground path present) the threshold trip current is about 5 milliamps.  You can purchase GFI protection as a cord end add device.  Every truck/electrician, that I was responsible for, had one and was required to use it.  As time evolved large capacity battery powered tools became the norm.

 

 

In reference to old electrical equipment. IMO there come a point when it should be recycled.

Safety meeting of the day.

Very interesting reading, but I am with Fred on this.

 

Frank, I am not sure what the application was that put 60V on the neutral.  It must have been an ungrounded power system.

 

I am not sure how it can happen in a grounded power system like the home.

 

There is plenty of equipment in a home that has metal outer cases with 3 prong grounded plugs.  The ground is attached to the exposed metal.  Drill, range, washer, etc...

 

While the neutral carries current back to the source, it occurs at 0V potential.  The ground wire also is 0V but doesn't carry current unless a fault occurs.

 

The only way a home neutral can be come hot is if it becomes disconnected from the neutral buss bar at which point the circuit no longer works.  Even if it became hot and some how was still connected to the buss, the entire house neutral would become your 60V and every device would no longer work since there would be no voltage potential to operate equipment.  No lights, clocks, refrigerator, etc....

 

So grounding the only exposed metal on a ZW is not an issue.  Frankly, the method of isolation is only fiber board, with a cord that can rest on exposed metal.  Probably doesn't meet code for a non grounded device in todays requirement.

 

Anyway, here is an example that happen to me.  Computer devices connected to a grounded surge protection outlet.  Turns out the device had a bad design and faulty ground terminal on one plug.  When I plugged a new device into the terminal, the ground plug broke the internal metal tab, and pushed it directly against the HOT 120 terminal.

 

A loud boom, flash and the whole house went dead.  After I recovered from the scare, I found not only the 15amp breaker tripped, but the main 200A breaker.

 

Later when I opened the surge protector to see what happened I found the fused terminals disintegrated.

 

The same would happen if you had a fault inside the ZW.  If you don't have that ground, and the hot wire was conducting to the base plate you would not have any protection kick in until something grounded the exposed metal.  That would be YOU.  Granted you have shoes on and are probably on carpet or wooden floor so your resistance to ground is very high, but you would get a tingle.  If you wound up touching a metal neutral or ground, like the U terminal and the base.  You might wind up dead.  

 

Mikes computer story kind of fits this, though most computers have chassis grounds, so I am not sure why a trip did not occur unless the outlet had a faulty or no ground.  Just think if the home owner touched the cable outlet and a grounded metal device.  Again, they would most likely be dead.  G

Mikes computer story kind of fits this, though most computers have chassis grounds, so I am not sure why a trip did not occur unless the outlet had a faulty or no ground.  Just think if the home owner touched the cable outlet and a grounded metal device.  Again, they would most likely be dead.  G

The computer was being used, with no ill effects to the owner. Apparently on carpet, in an upstairs room, the computer could be used with 120 volts applied to the other shell with no problems, until someone applied a cable modem to it.  Noted point, of my example, was that the reduced size ground, which for standard 14 ga home wiring, at that time of installation, was 16 ga, did not hold up to the fault, burned off in the panel and allowed the remaining ground wire and system to be at 120 volts.

GGG wrote:

Frank, I am not sure what the application was that put 60V on the neutral.  It must have been an ungrounded power system.

 

Just a week ago today, I was present at just such a situation, as luck would have it.  And all work including the application (totally unintended) of the short was done by an electrician.  Well, I did close the switches and helped with the fishing of the new wiring... 

 

I was at my son's recently acquired townhouse (1981 code) to let our guy in, keep the dog calm, and show him the accesses and the areas wanting work at this time.  In the master bath, new flooring and an upgraded shower had been installed.  An in-shower light had been added, apparently by the absentee former owner's renter's neighbor, or said neighbor's handyman.

 

There were loose wires in the attic, and taped splices, and rather more wiring in the double-gang switch box just inside the door of master bath than is usual, and one clipped ground that obviously could not functionally accompany the hot wire in that romex back to it's source (ie, obviously the other ground would be a higher impedance path than necessary.

 

It wasn't clear what the thinking was, and the other romex had been fed through a sharp-edged hole chiseled in a truss nailer plate.  Since the romex's to this box had to go anyway, our guy suggested just backing up and rewiring correctly to the two-gang switch.  Oddly, the new switch and box for the new in-shower light was on the opposite side of the door.  Why it was  the original box that was the way it was wasn't clear (like this sentence).

 

So I authorized this rewiring, which included taking some sections of #12 wire (20 amp) out of what was basically a #14 circuit (15 amp).  So our guy fixed the attic mess, and lastly completed the terminations at the two switches in the plastic two-gang box (plastic box and faceplate, metal faceplate screws)... now known good ground as metal faceplate screw were in reach of metal sink faucets, and standard arrangement.

 

I flipped the two switches in the still-open double-gang box up to ON, and kept my finger on the near one, my face on the other side of the wall.  I'd once seen a molten copper spray (in the electrical lab with its 7000 amp 220v DC service).  Our guy closed the breaker 2 floors below, and immediately there was the heavy tramp of excessive current.  Called down, heavy hum here.  Reply was, yeah.  I assume that a bare copper ground wire had folded onto a hot terminal screw.  Our guy prodded and closed it up.

 

Curious that the breaker didn't trip free on closing into a short.  Maybe 15-amp breakers don't have this feature... I worked too much on heavy stuff to be sure.  It was a Square D service panel.  The key thing here is that this breaker took 2 to 3 seconds to open.  Well, those were the days when a thermal breaker with no intentional delay was considered to be sufficient to "immediately" open heavy shorts (I forget the exact wording).

 

You'll realize that half the 120v drop through the fault (solid contact, no arcing) was in the #14 hot wire, and half in the parallel return of the #14 green ground wire.  Actually, it's half of 126v allowing for 5% system overvoltage, so the green ground here and at every downstream receptacle is at 63v.  This is more than twice the NEC-permitted limit of 30v.  In this case the condition persisted for as much as 3 seconds.  (This is not good time... a 5ma GFCI would have opened subcycle, most likely... or more than as much as 180 times faster.)

 

IMHO, one should not expose one's self to the green ground. 

 

By test, the typical fault current in such cases in homes is between 100 and 1000 amps, a study found.  An approximate calculation, close enough when the two wires are in the same romex, uses the AC resistance of the hot conductor out and the green ground conductor back.  In this case, I estimate the one-way wire distance was about 40 feet from point of fault back to panel.  (The path through main and branch breaker also adds impedance.)

 

--Frank