OK, I found the information I was looking for. I wanted to thank everyone for their posts and share the information.
My concern was the use of MSPs' (Motor Starter Protectors) in motor branch circuits in the US and how they fit in with the NEC req's. The following is an outline of what I found. Hope you guys like it.
1. Short circuit/ground fault – excessive current condition that exceeds the circuit boundaries (can be 100’s of times greater than FLA.)
2. Overload – the over current condition that exceeds the normal full load current (FLA) of the motor (can be 6-10 times the FLA.)
3. Fault current- maximum amount of current available for a short circuit condition, restricted only by conductor size.
4. Breaking capacity/interrupting rating – maximum amount of current that a protection device can safely open or clear.
5. Withstand rating – the maximum amount of current that an enclosure can safely contain
6. Trip class – time in seconds measured for meltdown of heater element with 6 times the fla applied.
7. NEMA or IEC?
7.1.1. NEMA has higher withstand ratings typically
7.1.2. NEMA has a standard sizing scheme that provides for interchangeability from the different manufacturers.
7.1.3. Designed with reserve capability.
7.1.4. Molded coils
7.2.1. IEC has no standard sizing guidelines and rating selection is evaluated into utilization categories.
7.2.2. Tape wound open coils
7.3. Same trip classes 10, 20, 30
8. 5 basic parts of a motor circuit
8.1.1. NEC part j
8.2. Short circuit protection
8.2.1. NEC part d
8.3.1. NEC part g
8.4. Overload protection
8.4.1. NEC part c
8.5.1. NEC part a
9. MSP’s in NA
9.1. Does not meet UL 489
9.1.1. Cannot be used for stand alone short circuit breaking
9.2. Can be used as “group motor rating” (UL/CSA)
9.2.1. Indicates that a single short circuit protective device can protect several branch circuits under the UL/CSA definition while using the standard sizing guidelines.
9.2.2. NEC 430-53 (sizing guidelines)
9.2.3. If the short circuit current exceeds the withstand rating of the MSP then fuses must be used in series to reduce this number (short circuit current) or the system must be redesigned to accommodate (NEC 110-10.)
10. MSP’s international
10.1. IEC 947-4-1
10.1.1. Recognized as a stand-alone short circuit protecting device.
10.1.2. Back-up fuses are only required when the fault current exceeds breaking capacity of the MSP.
11. Coordination levels
11.1. Type 1
11.1.1. No danger to personnel
11.1.2. No danger to equipment other than relay itself
11.1.3. Relay must be serviced or replaced
11.2. Type 2
11.2.1. No danger to personnel
11.2.2. No danger to other equipment
11.2.3. No danger to relay other than minor welding of contacts
11.2.4. Relay can be used without service or repair
The biggest issue is how the MSP is used overseas as a stand-alone short circuit breaking device....Just not in the US.
Carl Lee Tolbert
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