I was hoping for a bit more specificity in answer to my first request. Such as “an example”. Then I was hoping for a response to my next two requests.
Ed
I dont have an example off the top of my head, but riddle me this, what is the purpose of providing an electrical path around the UL listed transformer against the manufacturer’s recommendations?
In theory, the transformer that steps down the 120VAC to 0-22VAC or whatever you are using should be disigned to preclude the introduction of household current to the output of the transformer.
The scenario would probably involve faulty house wiring, or where the third prong that your layout is connected to ends up being the least path of resistance.
Would running your vacuum over its own power cord and shredding the insulation, resulting in 120VAC contacting the ground wire in the vaccuum cord, running back to the outlet, through you because you happened to touch the track, while standing in a puddle of water which reaches to the household piping or some other path to ground that is shorter than the electrical box?
Fyi the GFCI you connect your drill to does not shut off the power to the wire you drilled into, please never forget that. There have been deaths that resulted from assuming that the tool was de-energized when in fact it was still energized by the 480 or 4160VAC (cant remember which it was) wire it was sticking into on the other side of a concrete wall (they were not using an electric drill stop).
But we are now kind of way off topic.
I dont know if the Op has gotten his answer yet, but:
decoder outputs are not designed to receive track power from the dcc system. The electronic circuitry on the board will literally get fried (I have some fried decoder pictures that I could dig up if you would like).
i’m not suggesting that anyone should interchangably use the neutral or ground connection. The motor of a drill, for example, should be connected to the live and neutral connection, not the ground. The ground is for protection and should be connected to the case or the motor frame.
So it would make sense to connect the ground, if there is one, to the motor frame when there is a plastic housing.
Right, the Zephyr manuals don’t mention connecting tot he house ground. But they walked it all back in the new DCS240 manual. Quote:
4.5 Ground (GR) Terminal
The terminal marked ground provides electrical safety features and an RF ground reference for minimum radiated noise. This should be the ONLY point of any DCS240 installation that is connected to the AC safety ground pin provided on most 3 pin 110V AC power sockets. Grounding the system is a sensible safety precaution that should not be ignored.
There is an extensive discussion on the ‘grounding’ and common failure modes in an article that members put together on the Digitrax yahoo group, which is pointless to link here because if you aren’t a member you can’t access the files section. This has been discussed ad naseum on the Digitrax forum, in fact it seems to come up every few months, and you get a whole lot of misinformation and finally this document gets pointed to - a document that they reviewed with AJ at one of the NMRA shows and received his blessing for on exactly how and what to wire to ‘ground’. The updated manuals for the DCS100 and DB150, and obviously the Zephyr Xtra, all walked back on the idea of connecting that terminal to the house ground. Now in the new DCS240 manual they once again are saying to connect it to house ground. That in fact is what spurred the latest 100+ message argument over how to hook things up.
You want an example? The rail boltage on a Digitrax booster is realtive to that ground terminal - it is really the common for the output H bridge. In fact one of the recommended ways to measure track voltage on a Digitrax system is to measure DC between Rail A and ‘ground’ and Rail B and ‘ground’. Each should be (assuming nothing’s failed, and no one has address 00 selected with a speed which will introduce a DC offset) equal, and added toge
Ed,
The new blue box or “RTR” this appears to be the case. The ones I have are equipped with plastic coulper boxes, but it would not hurt to check for continuity between your coupler and wheels before testing this statement, as I have only three RTR locomotives (albeit they are different models and have widely separated dates of assembly).
Here it is…
Hello all,
Here’s the long answer…
A Direct Current motor is like a water wheel.
Water is drawn or pushed over the wheel which turns the spindle in the center of the wheel to do work- -milling, running saws, turning a turbine, etc.
If the water cannot flow; either by cutting off the water supply or not allowing the water to exit, the device cannot turn.
Electrons are like water; they need a path from - to + to do work.
All modern locomotives are equipped with DC motors. There was a time that some systems used AC; Alternating Current motors, but that’s a whole other can 'O worms!
Manufacturers use the locomotives wheels as pickups to move the electrons from the negative side of the track through the motor and then back to the positive side.
To achieve this, wires are used to transmit the electrons from the energized wheels to the poles on the motor; - or +.
In this scenario the motor is considered isolated.
Note: it is possible to use wipers; small strips of conductive metal, directly contacting the rails, rather than transmitting electrons through the wheels to the motor.
The wheels on the pickup trucks are isolated from one side (rail) to the other either physically or electronically.
This electron flow turns the motor which turns the gears to power the wheels and propel it down the track.
Some DC locomotive manufacturers chose to use the metal frame as a pathway for the electrons to flow rather than wires.
Wipers were fitted from one side of the pickup trucks to the metal frame, thus energizing the entire frame either - or +. One pole of the motor was in direct contact with the energized frame.
The other side of the pickup trucks were fitted with wipers that energized a strip of copper alloy, typically attached to the top of the gear
I think you’d have to ask someone who wanted to do that. I don’t, particularly.
In theory, yes. Perhaps a short between the primary and the secondary?
If, as you state, the 120VAC contacts the ground wire, the breaker will trip. I can see a possibility of two ground paths for the fault current, as you describe: one through the standard ground system and one, at least partially, through “me”. Before the breaker trips, there will be current both through the ground system and through me. The extent of either would be deduced by comparing impedances. A properly installed ground system should have a very low impedance.
[quote]
Fyi the GFCI you connect your drill to does not shut off the power to the wire you drilled into, please never forget that. There have been deaths that resulted from assuming that the tool was de-energized when in fact it was still energized by the 480 or 4160VAC (cant remember which it was) wire it was sticking into on the other side of a concrete
I certainly think so in the case of power tools. And, since the motor frame is always metal, as are the bearings, chuck, and any installed bits, that would preclude using a “double insulated” tool that doesn’t have a three-prong plug.
Of course, I use battery powered tools a LOT. Can’t do much about them.
Ed
The simple answer is there can be no other path for motor power to flow. It has to return to the decoder. If the motor is connected to the track, either by the frame or wheels, current has another path to follow and you will destroy the decoder. In DCC, one rail is Positive and the other is held to “zero”, and this rapidly alternates, so you have a return path to if the motor isn’t isolated.
Rail A is hot while Rail B is the return, then Rail B becomes hot and Rail A is the return to the booster. So if your decoder’s output connects to a rail, the current can return to the booster anytime that rail is held to “zero”, which is many times a second. Also, you have a lot of (uncontrolled) current being supplied to the decoder’s output many times a second from the booster.