- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
What does 'rated 489A' mean? Where is the UL or other NRTL label?
I don't understand WHY you can apply the 125% rule.
- Thread starter Elecestim123
- Start date
- Status
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The temperature correction values in the NEC apply only to conductors.
Breaker manufacturers provide temperature correction curves for their products, and maybe used per their instructions.
The NEC has you select your conduct first and then your protective device so most people do not bother with the temperature correction curves particularly because the ambient temperature is rarely static.
- Location
- Illinois
- Occupation
- retired electrician
All of the breaker manufacturer's have temperature correction information for where the breakers are in an ambient other than 40°C.
One manufacturer shows a 25% increase in the trip point where the breaker is in a 10°C (50°F) ambient.
- Location
- Illinois
- Occupation
- retired electrician
Typically when a manufacturer says something like that, they have done a CE type self evaluation of the product and it has not actually been listed by a 3rd party listing agency.
Don’t forget your motor example is WAY off.
Motor inrush is a big problem because most motors exceed limits UL sets for UL 489 breakers, particularly curve B. There is a variety of devices that are technically not breakers for this such as manual motor starters and MCPs and time delay fuses. Breakers as motor protection don’t do a good job.
Motor stall or locked rotor current is what I think you are referring to. Few people can easily measure inrush which lasts about 1-2 cycles and is similar to transformer inrush. Locked rotor current lasts a few seconds until it gets to around 85% speed.
For protecting wire it basically follows the inverse time curve, or I-squared-R. Motors are a little different thermally (different exponent). So there are specialized devices (overload relays) specifically for motor protection. The breaker curve is too steep. It is only used for short circuits. This is why 430 and 440 are very different from chapter 2. And above 200 HP
Motor inrush is a big problem because most motors exceed limits UL sets for UL 489 breakers, particularly curve B. There is a variety of devices that are technically not breakers for this such as manual motor starters and MCPs and time delay fuses. Breakers as motor protection don’t do a good job.
Motor stall or locked rotor current is what I think you are referring to. Few people can easily measure inrush which lasts about 1-2 cycles and is similar to transformer inrush. Locked rotor current lasts a few seconds until it gets to around 85% speed.
For protecting wire it basically follows the inverse time curve, or I-squared-R. Motors are a little different thermally (different exponent). So there are specialized devices (overload relays) specifically for motor protection. The breaker curve is too steep. It is only used for short circuits. This is why 430 and 440 are very different from chapter 2. And above 200 HP
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
I have frequently heard that there is no difference between a regular and a 100% breaker, however I have noticed in breaker catalogs they have a different part number. IIRC the Siemens catalog says something like " for a 100% rated breaker, add XYZ to the part number."
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
It does sound a bit suspicious.
Looking at UL 489, 9.1.4.4 and 9.1.4.5 limit marking for 100% rated breakers to "circuit breaker(s), having a frame size of 250A or greater, or a multi-pole type of any ampere rating rated over 250V; and intended for continuous operation at 100 percent of rating."
So that alone excludes almost all of the breakers I linked to earlier.
Cheers, Wayne
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