Revised DCS Wiring Schemes

Columbia, Maryland, May 1, 2002 --- Erroneous reports on Internet chat boards and other places have indicated that the DCS System's Track Interface Unit, or TIU, has caught on fire on several occasions. Despite these reports, MTH has been unable to substantiate any report that the TIU actually caught on fire. Futhermore, because the TIU unit itself is built according to U.L. specifications, its design and material use should prevent any fire from occurring if the unit is stressed beyond its design limitations.

Interviews with the owners of the TIU units reportedly on fire have revealed that the units failed and smoked after being overloaded from transformers with poor or no circuit breaker protection. The damaged TIUs were returned to MTH and inspected by DCS team members to determine the exact location of the failure within the TIU. Tests using the MTH Z-4000 transformer have not been able to replicate the failure because the Z-4000 employs fast-acting, microprocessor controlled circuit breakers as mandated by today's U. L. standard.

The DCS inspections have isolated the failure to a portion of the circuit board and have replicated the failure in a lab environment. They have determined that the failure can occur when older transformers incur a short. Without proper circuit breaker protection - as determined by today's U.L. standards, the transformer can send upwards of 25 amps through the TIU device causing a specific area on the TIU circuit board to eventually fail, often resulting in a small whiff of smoke. This circuit board trace failure occurs in time, rather than instantaneously because the area on the board is unable to withstand the heat generated by the 25 amp surge for long periods of time.

Older transformers, like the Lionel postwar ZW or KW models employ a bi-metallic strip to act as a circuit breaker. The strip responds to heat as high current flows through the transformer. If enough heat is generated by the high current, the strip will open the circuit and prevent further current from flowing out of the transformer. The bi-metallic strip is not a precise overload protection device and does not measure the current. As a result, it may not trip when excessive amps are being generated by the short circuit. Should the strip thus fail to trip, excessive and potentially harmful current could be sent through the TIU.

Inline fuse location for TIU surge protection

MTH therefore recommends that any user employing an older transformer that does not meet today's U.L. standards install inline fuses or circuit breakers between the transformer and the TIU input channels. An ACG/3AG series "fast-acting" or "fast-blow" fuse rated at 15 amps would be suitable protection. These can be obtained from most hardware or electronic stores including Radio Shack (Radio Shack Part No. 270-1073 (15A, 32 volts ACG/32AG series 1 1/4" x 1/4" glass pack)). Users will also need an inline fuse holder to house the fuse. Radio Shack sells a heavy duty model, part number 270-1217. Additionally, users can opt to use a 15 amp mini blade fuse (Radio Shack Part No. 270-1094) with a 30 amp mini-blade in-line fuse holder (Radio Shack Part No. 270-1237). Diagrams showing the fuse position are available for review on the Proto-Sound web site (

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