- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Only if he ever gets it to run long enough.
480v 60hp motor throwing breaker, now?
- Thread starter titan1021
- Start date
- Status
Depends. NEC refers to FLC and FLA but does not define them. So it’s a grey area.
Practice with some is to size the starter and maybe breaker or fuses by table but overloads by name plate. Others say all protective devices must use name plate.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
You use the table amps for sizing the circuit components (conductors and short circuit protection). You use the nameplate/actual amps for protective devices operation time and coordination.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I don't see how it's a grey area. 430.6(A)(1) is very clear.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
430.6 applies to conductor sizing and SC protection and requires use of the tables.
(A) General Motor Applications. For general motor applications,
current ratings shall be determined based on (A)(1) and
(A)(2).
(1) Table Values. Other than for motors built for low speeds
(less than 1200 RPM) or high torques, and for multispeed
motors, the values given in Table 430.247, Table 430.248,
Table 430.249, and Table 430.250 shall be used to determine
the ampacity of conductors or ampere ratings of switches,
branch-circuit short-circuit and ground-fault protection,
instead of the actual current rating marked on the motor
nameplate.
430.32 requires the overload device be selected based on the nameplate current.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
What part of the starter label "USE FUSES ONLY" allows a breaker anyway?
MTW
Senior Member
- Location
- SE Michigan
And it shows a 200A max fuse on the front of the overload relay.
Dzboyce
Senior Member
- Location
- Royal City, WA
- Occupation
- Washington 03 Electrician & plumber
Dzboyce
Senior Member
- Location
- Royal City, WA
- Occupation
- Washington 03 Electrician & plumber
Seems like a lot of the submersible pump manufacturers design their pump ends to load the motor into the service factor amperage.
Industrial air compressors are the same way.
They’re cheating anyway. The motor is water cooled. Which is why most of them have a thermal switch. Overload relays are kind of meaningless.
They are relying on duty cycle. Seen a lot of plants that have so many leaks or add so much equipment they set the pressure switch beyond what it will ever reach so it hits 100% duty. Only takes a day or two to make a motor sale.
No we don’t. Our units are designed to run flat out at 100% load at 110% of motor nameplate HP.
That’s normal throughout the industry.
ptonsparky
Tom
- Occupation
- EC - retired
I've seen irrigation well motors that have run into the SFA for decades. Not today's bare minimum material high efficiency motors.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Good catch!
A lot of people miss this issue. Some motor control equipment mfrs, especially those who do not make breakers, do not get their starters and OL relays UL listed behind breakers, they only use fuses in order to pass the UL testing because that's cheaper and easier for them. That then falls upon the installer to ONLY use fuses in the installation. So technically even if you were to feed it from a 200A breaker in a panel, you would ALSO have to have fuses in series too. That cheap starter isn't as cheap as you thought it was now...
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Ages ago, the NEMA definition of "Service Factor" used to mention it being suitable for a "intermittent" use, without ever actually defining what "intermittent" meant. Somewhere a couple of decades ago, NEMA amended it to remove all reference to SF having a time frame associated with it, so OEMs have been using that to run motors into the SF continuously. What NEMA says now though is a bit more namby-pamby...'
So from the OEM's perspective, if that "reduced life expectancy" is still beyond their stated warranty period for their equipment, they are good with it. It's only the end user that suffers.
So you operate at 1.10. On a 1.15 SF motor what happens with a 1% voltage unbalance or a 10% overvoltage as per NEMA?
Who does that? Trying to think of I’ve ever seen this.
Not a theoretical argument by the way. Ingersol Rand got burned by this in a manufacturing plant.
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