I wanted to post this comment because of discussions on RYPN and other sites regarding loss of control functions, lack of loading, or having groups of lights not working on EMD locomotives. Electro-Motive uses wiring strings to reduce the complexity and wire run distances in their electrical cabinets. This reduces wire usage and makes individual runs shorter, but a loose connection in a wiring string can result in loss of function of more than one device simultaneously.

Negative side wiring sometimes tends to get overlooked in troubleshooting. The possibility of a loose connection on the negative wiring string to locomotive power control devices can show up as unexplained presence of higher than normal positive voltages at test points in circuit modules. Lacking a solid negative return connection, the voltage in modules tends to drift up to that of the highest positive source in the circuit. This is particularly encountered in Dash-2 modules with a bad negative string connection.

You can save some time in troubleshooting negative string wiring problems by checking for continuity from the point in the string most distant from the negative circuit breaker back to the wiring string side of the breaker and also to battery knife switch negative blade (checking with the knife switch open, breaker closed). If there is no continuity to the end of the string, then testing negative connections to devices sequentially back toward the breaker may find the point where the string has become disconnected.

PC

Thank you, real words of wisdom...

Practically speaking, how much amperage should be used in this test? perhaps equal to some major proportion of the 'peak' that each section of the string will encounter in service?

I'd think that if you can make the time, the 'best' procedure would be to test the continuity with a standard meter, and then repeat the checking of segments with appropriately higher current. Is that a justifiable procedure?

In my experience a Bright Star 2618CT Circuit Testing flashlight provides adequate load to determine whether string wiring has continuity or not.

Wiring continuity checks, including checks of circuit breaker continuity, must be done with the battery knife switch open, all circuits de-energized. Circuits not being checked should be isolated with the circuit breakers turned OFF. Keep in mind that the movable blades of the battery knife switch are the connection to the locomotive circuits, the fixed contacts of the battery knife switch are the connection to the battery.

PC

A test light is essential. Mine was made with a marker light socket and 15 foot leads so I could go from the 30 series terminal boards to the front of the electrical cabinet. A load on a circuit reviles bad connections and interlock/switch contacts. These will show good using just a meter, and under a couple amp load they will open. Digital meters can be problematic in themselves as they are too accurate. A good Simson has stood me well even checking -2 modules. I had a SD40E SP upgrade and it was pissing me off! Any electrician will tell you if it's working the problem is hard to find. So you cycle it a bunch of times trying to make it fail. So I had checked all through this 13T, I believe, circuit went home had a brew or two went to bed and woke up 2:30 in the morning and knew exactly the problem. Went in next morning, went to the connection I thought of and it was loose but tighter than I thought it would be. Tightened it no problems! A test light is best for checking low voltage grounds. Quite often that was something I would check first if a loco was acting up. Negative or positive grounds can make things a little more complicated. We had two locos that until I fixed them couldn't be mu'd. One had a positive ground the other a negative one. They acted real strange hooked together!! Happy Holidays

It is true that many electrical systems combine "current return paths" (aka Negative Wiring String) to save on the cost of wire and installation, etc. Older automobiles (pre 1980's) use the chassis of the auto as a return path for the exterior lights. Often a non functioning license plate lamp is caused by corrosion in the lamp mounting fixture. A voltage meter connected between the lamp supply conductor and a good "ground/return" point will make you think the circuit is fine, yet the light bulb still has a "failure to illuminate"....

I might suggest you invest in a good modern "clamp on" current meter. A unit like the Fluke 325 is about $300. And it can tell you how much (if any) DC current is flowing though any wire in a locomotive. It can tell you the direction of the DC current (separates the goesinta's from the comesouta's). These can do AC and DC up to 400 amps.

They do require that the system be "live" so you can follow the electrons, but they can give you quite a bit of insight about where those dang electrons are actually going (or not going in the case of broken/loose return conductors).

I do not work for or have any financial interest in Fluke, but I trust their products. And be sure to watch the "safety" rating of any electrical test equipment. The Fluke 325 is rated at: CAT IV 300 V/CAT III 600 V. That means it is safe to use it to test a 600 volt circuit and the insulation of the meter will not fail and electrocute you.

A few unfortunate folks have mistakenly used 600 volt meters on > 2000 volts systems with very bad outcomes.

Other vendors have similar offerings.

When connecting probes to bare conductors at high voltages it is always safest to isolate that circuit before connecting if possible. And always wear safety glasses to protect your eyes from the sparks from a short circuit/arc flash. And be sure any test leads you use are also rated for the voltages you are working with.

"Electricity, they've been studying it for years, nobody knows how the heck it works"

Cheers, Kevin, BSEE, MSEE, decades of electrical work without electrocuting myself (or anyone else).

I still turn my face away when flipping a circuit breaker live "just in case".

(edit) I did a little more "shopping" and the Fluke 362 (about $125) looks very attractive. And the Klein Tools CL800 (about $125) also looks like a very useful tool. Just watch those safety ratings, would really stink if some one gets hurt testing a 600 volt circuit because they "saved" $100 on their test gear.

Although I've never had the opportunity to peer into the nervous system of a locomotive, I do happen to know that electrical connections between dissimilar metals in a hostile work environment has been, and always will be, a major PITA.

I use this stuff on my vintage Dodge trucks which are rather famous for their electrical bugaboos. Does great on other items like antique radios also. From what I understand, you might need several 55-gallon drums full for a couple old Geeps, however...

https://caig.com/

Like Eli the Ice Man says, "Ground is ground the world around". Always check those connections first since many times they were put in places they shouldn't have been put in the first place.

And as far as multimeters go, you can't beat grandpa's good ol' well-calibrated Simpson 260. You've got to try pretty hard to smoke those suckers...

https://www.simpsonelectric.com/product ... 0-8-260-8p

Have fun chasing those unruly electrons around!!! LOL

The Simpson 260 is exactly what EMD issued to their field service staff for working with the 40-series and Dash-2 locomotive product lines. The first widely used digital meters did not appear in railroad shops until several years after the Dash-2 locomotives were introduced.

PC

I was curious so I looked up the Simpson 260 and they had a "you might be interested in this" blurb, and it listed this:

TRIPLETT Analog Railroad Tester, 600 Max. AC Volts

https://www.grainger.com/product/TRIPLE ... IDPPLARECS

-Hudson

When EMD released those locomotives clamp on DC current meters did not exist. They are relatively new (~ 20 years). They use "Hall Effect" semiconductor sensors.

The nice feature is you clamp them around an insulated wire with no need to disconnect anything.

The Simpson Multimeters require you to disconnect the circuit and pass the current through the meter. More work, and you risk disturbing the corrosion at the joint you disconnect. You might fix the problem by disconnecting the wire leading to more confusion.

Cheers, Kevin

Hope this helps keep everybody safe;

https://content.fluke.com/promotions/pr ... elines.pdf

These guidelines were developed for connections to the commercial "Electricity Grid" and do not translate directly into Diesel Electric or Electric Railroad Locomotives. But most electrical work on the "high current" (Generator to Traction Motor) side of a locomotive is best characterized as a CAT III (maybe a CAT IV).

Often times it's the transient voltage/current spike (when a relay opens) that overpowers the electrical test gear and exposes the worker to fatal voltages.

Be safe.

Happy Holidays, Kevin

East Troy Railroad Museum purchased a brand new Fluke
clamp meter recently. I've used it for examining
the 32 volt battery leads, and for load testing.

It's indeed a very useful tool.