Issue:
Short Circuit Withstand Rating
Resolution:
There is a short circuit withstand rating (SCWR or SCR) on all UL-certified starter control cabinets on Pueblo built chillers. This information will also be an output from the TOPSS selection program and will be printed on the unit nameplate.
Effective April 2013, all product panels were insourced and are now built at the Trane plant.
The SCWR was added to the TOPSS output in February, 2012.
Effective July 1st of 2012, the SCWR is printed on the chiller nameplate.
There is no design special for a higher rated starter panel outside the TOPSS outputs from the factory.
A commonly asked question is whether or not an existing unit can be modified to get a higher Short Circuit Rating. The answer is yes but doing so can be very expensive. The first option would be to replace the entire starter panel with a new panel that has a higher Short Circuit Rating than what the chiller was built with. For example, if the existing starter panel was configured with terminal blocks, a replacement starter panel with a circuit breaker option can be installed that would provide a higher Short Circuit Rating. The replacement panel should have the appropriate UL label that denotes the new Short Circuit Rating.
The other option would be to field install a new power disconnect device, such as a High Interrupt Circuit Breaker, along with additional parts associated with the breaker. In addition, a UL field inspection of the unit after the modifications are completed is required to get the appropriate Short Circuit Rating. This option, in most cases, may be the most expensive route due to the cost of the UL field inspection.
AIC (Amp Interrupt Capacity) ratings are uniquely applied to circuit breakers and fuses. This term should not be used in conjunction with switches, contactors, or other power-handling devices that are not meant to open automatically under high current draw situations. Technically, a disconnect switch (even when it's a molded case switch that is very similar to a true circuit breaker) does not carry any AIC rating at all.
When the circuit breaker is ordered, the numbers in the spreadsheet that are shown for circuit breakers (either standard or high fault) are indeed the AIC rating for that breaker, which is also the short circuit rating (in this case, AIC is the more accurate term).
Notes:
For more information on Short Circuit Withstand Ratings, please see "Protecting the Electrical Distribution System...Short-Circuit Withstand Ratings Demystified", an August 1998 Engineering Bulletin. (attached)
Changes:
Other Question/Problem/Cause Statements:
- Short Circuit Withstand Rating
- What is the SCWR?
- What is the SCR?
- SCWR
- SCR
- What is the AIC rating of the breaker?
- Is the AIC rating and SCWR the same?
- What is the SCR of the circuit breaker option on this chiller?
- What is the short circuit rating for this chiller?
- Can a control cabinet in the field be modified to have a higher SCWR?
- Can a 5K SCWR rated panel be modified in the field to a 65k SCWR rating?
Facts:
- Air-Cooled Chiller (Pueblo) (CGAM 20-130 Ton)
- Air-Cooled Chiller (Pueblo) (RTAC)
- Compressor Chiller (Pueblo) (RTUD 70-200 Ton)
- Water-Cooled Chiller (Pueblo) (RTHD)
- Water-Cooled Chiller (Pueblo) (RTWD)
- Air-Cooled Chiller (Pueblo) (RTAE)
Document Identifier: DOC-100160
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.