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Reply to "Airpax Snapac "Instant" Hydraulic-Magnetic Circuit Breaker"

Dennis, the 7A breaker you're talking about is a Potter & Brumfield W28-XQ1A-7 for use in slow-blow applications.  It uses a different Thermal Magnetic internal mechanism to operate than the Airpax.  The P&B is also heat dependent, where the Airpax isn't.

Potter and Brumfield Breaker Features

In the P&B, as the current flow through it rises above the rated trip value, it would be much slower to open the circuit than an Airpax so-called "instant" breaker with a comparable current rating.  Here is the Trip delay curve from the Potter & Brumfield W28 series datasheet:

Potter and Brumfield Trip curvejpg

I've not seen a trip delay curve for the breakers built into the PW ZWs (when they were new) but I'm guessing it's close to the same as the external circuit breakers you have.  If you're running TMCC, DCS or Lion chief equipment around the Christmas tree, some faster breakers, might be worth considering, (as well as an Adult proof railing ).  Postwar type Locos, might be fine as is.


Images (2)
  • Potter and Brumfield Breaker Features
  • Potter and Brumfield Trip curvejpg
Last edited by SteveH
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