Do you think the rules in 430.52 for sizing SCGF protection multiple motors to the same branch circuit is incorrectly used and overused? This lets your size the branch circuit breaker to largest motor's SCGF device + the sum of the remaining FLCs not exceeding the largest motor's breaker size. But, reading the rule it seems like you can only use this formula for listed group installations, right? This general rule does not apply if you're putting two exhaust fans on one circuit let's say or putting two evaporators on one circuit, etc. Right??
When is Motor Group Installations really used?
- Thread starter cppoly
- Start date
- Status
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Where does it say anything about group motor installations needing to be listed?
For instance, the code requires a motor using a cb as ocpd to have a cb rating that does not exceed the motor flc by more than 250%(not including any next size up allowance).
If you wire two motors that are ten amps flc each to a 25 amp cb, you have met the requirements.
For instance, the code requires a motor using a cb as ocpd to have a cb rating that does not exceed the motor flc by more than 250%(not including any next size up allowance).
If you wire two motors that are ten amps flc each to a 25 amp cb, you have met the requirements.
430.53(C) Other Group Installation (2014NEC):
Two or more motors of any rating or one or more motors and other loads(s), with each motor having individual overload protection, shall be permitted to be connected to one branch circuit where the motor controller(s) and overload device(s) are (1) installed as a listed factory assembly and the motor branch circuit short circuit and ground fault protective device either is provided as part of the assembly or is specified by a marking on the assembly or (2) the motor branch circuit short circuit and ground fault protective device, the motor controllers (2), and overload device(s) are field-installed as separate assemblies listed for such use and provided with manufacturer's instructions for use with each other, and (3) all of the following conditions are complied with...
Two or more motors of any rating or one or more motors and other loads(s), with each motor having individual overload protection, shall be permitted to be connected to one branch circuit where the motor controller(s) and overload device(s) are (1) installed as a listed factory assembly and the motor branch circuit short circuit and ground fault protective device either is provided as part of the assembly or is specified by a marking on the assembly or (2) the motor branch circuit short circuit and ground fault protective device, the motor controllers (2), and overload device(s) are field-installed as separate assemblies listed for such use and provided with manufacturer's instructions for use with each other, and (3) all of the following conditions are complied with...
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
when would you ever use a motor controller and overload assembly that were not listed to be used together?
are you planning to try to use an AB contactor with a Siemens overload?
are you planning to try to use an AB contactor with a Siemens overload?
- Location
- Illinois
- Occupation
- retired electrician
In my experience that is typically used where there are multiple motor controllers in a common cabinet. For example a control panel for a set of conveyors.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
or for a multi-motor piece of equipment like a machine or piece of process equipment.
Well the way it's worded is that I interpret that since it also says the SCGF protection is to be listed with the controller and overload, it makes this a very specific installation.
My point being is, I've always taken 2.5 amps let's say and multiplied it by 250% to get a 15A C.B. then added 1.1A, 1.3A, 1.4A then rounded down to stick with a 15A C.B. as the SCGF protection if I'm connecting several exhaust fans to the same circuit. But doing the math this way is not how it's supposed to be done since this is not a "group installation" with listed equipment as described.
kwired
Electron manager
- Location
- NE Nebraska
I think where it will get used the most is where say a 15 amp breaker is the SCGF device but you have multiple smaller motors.
480 volts 5 hp and smaller this 15 amp breaker can hold with multiple motors much easier than if any the motors are larger. 120 single phase however will be probably be 1/2 HP and less.
- Status