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Q: On the subject of ground fault protection: On the LSIG trip units, is “Alarm Only” possible? Or is it always “Trip+Alarm”? Are there any Z-Options corresponding to this?
A: The 3WA equivalent of the rating plug is called an Option Plug. It sets the 100% rating (like WL) but also determines whether the ETU has GF tripping.
Whether GF Alarm is available depends on two things: Whether the Option Plug enables GF or not; and the PMF-option level. For an ETU600 with current metering, ready4COM and PMF-I, GF Alarm is not available by default but can be added in the field. Adding GF Alarm is via a firmware module downloaded and installed via powerconfig.
A UL1066 breaker equipped with an ETU600 and a GF-Option Plug will have both GF Trip and GF Alarm available. Both can be disabled/enabled allowing GF Alarm-only and GF Trip-only functionality. A UL489 breaker with a GF Option Plug will have GF Trip and GF Alarm, but the GF Trip is always active and not able to be turned off.
Regardless of market, an ETU600 equipped with PMF-II/-III will always have GF Alarm available, even with an Option Plug without GF.
The kind of Option Plug is determined in the main part of the MLFB, but an alternate rating value can be given by a Z-Option: B08 = 800A.
Although the ETU300 uses an Option Plug, it does not have GF Alarm, only GF trip with fixed pickup and delay.
Q: What is meant by extended ground fault and how does it differ from Hi-Z?
A: Extended GF allows GF pickup settings up to 2000A for UL1066 breakers. UL489 breakers are restricted to 1200A pickup.
Hi-Z is completely different and should not be confused with High Resistance Grounding (HRG).
Q: What is the difference between a ETU600 Hi-Z and a standard ETU600?
A: Both variants of the ETU600 have a what's called Dual-Mode Ground Fault which allows simultaneous Restricted & Unrestricted Earth Fault Protection (abbreviated REF & UREF). Unrestricted Earth Fault protection is what we normally refer to as residual ground fault: The ETU sums the three (+neutral) phases to determine if there is an unbalance which indicates a current flowing to ground and trips the breaker if it exceeds the GF pickup setting. Restricted Earth Fault is sensing a ground current using an external sensor in the star point of a transformer. This would indicate a ground fault which would need to be interrupted by an upstream device. This function closes a output contact on the ETU or IO module which would send a signal to an upstream breaker or protective relay. If needed, the upstream protective relay can send a signal to an ETC600 which can trip and lock-out the 3WA so that it must be manually reset. Requiring a manual reset in situations like this is the reason why it is not done with a shunt trip because no manual intervention is required with a shunt trip.
The difference between the Hi-Z and standard ETU600 is the method of sensing the Restricted Earth Fault: The Hi-Z ETU uses a set if matched "X-Class" CTs which operate into a resistive burden generating a voltage signal which is measured by the ETU. The standard ETU600 uses an iron-core CT (zero sequence or multiple CTs in parallel) and senses the secondary output current of the CT.
If a breaker is ordered with a Hi-Z ETU, the ETU600 & second trip solenoid (F6 magnet) are included. If it is desired to remotely trip a 3WA that does not have a Hi-Z ETU600, the ETC600 & F6 magnet can be purchased separately (ETC600: 3WA9111-2EM62, F6: 3WA9111-2EM61).
We will have a special White Paper explaining Hi-Z in greater detail.
Q: Can ground fault be retrofit or changed in the field?
A: Unlike WL, the 3WA combines GF and rating plug into one device we call the Option Plug. All of the rating plug ratings available for WL are available for 3WA. Also unlike WL, 3WA does not have GF Alarm-only module, it always has Alarm & Trip in one. Ground fault modules come in Standard and Extended. Standard GF modules can be used in both UL 489 (3WA2) & UL 1066 (3WA3) breakers and are settable up to 1200A. Extended GF modules are settable up to 2000A and are only usable in 3WL3 UL 1066 breakers. ETU600s without a GF Option Plug still have GF Alarm capability as long as they are PMF-II or -III. GF Alarm can be added to ETUs without PMF-II/-III via a firmware upgrade.
Q: What are the equivalent 3WA trip units to ETU776 & ETU745?
A: 3WA has two trip units as well but there is no direct comparison. Simply put, ETU300 has adjustable Long Time (pickup & delay), Short Time (pickup & delay), Instantaneous (pickup), and Ground Fault (fixed pickup and delay: 20% of option plug, 300ms) and no display or communications capability. ETU600 has LSIG (all adjustable) via both knobs and the unique "R.SET" setting. When set to R.SET, that function is remotely programmable via communications. When set to any other position, the setting is fixed and not remotely programmable. ETU600 has a large color display and built-in DAS (no external modules required). It can be had with metering of various flavors, supports breaker-internal voltage sensing and is upgradable and USB-C programmable using powerconfig.
Q: What should I select to be able to use DAS?
A: Order a 3WA breaker. DAS is built in to both the ETU600 & ETU300. With the ETU600 you get adjustability whereas with the ETU300 the DAS pickup levels are fixed. DAS in and out are brought out to the secondary disconnects and no additional modules are required. The ETU600 allows the selection of activating DAS with either a low- or high-level signal (0V or 24V), a button on the front of the ETU or remotely via communication. The ETU300 works only with a high-level signal to the DAS activation input. As the ETU300 cannot be powered by 24V, if it is not activated by primary current, it will not activate it’s DAS output if it receives a DAS activation signal. For the ETU600, DAS settings are programmable. For the ETU300, DAS trip to 2x for Ii > 2x and 1.5 for Ii <= 2x (where Ii = instantaneous pickup).
Q: TOCs - Position Signal Contacts – are these Form C?
A: The TOCs (for 3WA now called "PSS" - position signal switch) are all form-A. All 3WL TOCs will be available with a slight twist: Because the COM modules can now be installed in an Aux Compartment or above the secondary disconnects, they no longer directly sense the disconnect position directly. However, there are two different TOC/PSS modules that have contacts which are wired back to the COM module to provide that information. The available TOCs are:
- 1-1-1 + contact for disconnect/absent via communications (PSS111)
- 4-0-0 + contact for disconnect/absent via communications (PSS400)
- 3-2-1 – no contact for disconnect (PSS321)
- 6-0-0 – no contact for disconnect (PSS600)
Although there are digits in the breaker MLFB to specify TOC, they should not be used for 3WA2/3. TOCs are specified in the cradle MLFB, digit 15. The reason for this is that the MLFB scheme covers 3WA1, 2 & 3 and 3WA1 can be ordered with a breaker and cradle in one MLFB. For logistical reasons, 3WA2/3 cannot.
Q: What should I select to use communications?
A: An ETU600. ETU300s cannot communicate. Furthermore, select one of the "ready4COM" digits in the MLFB – some deal with metering functionality but all include the BSS (breaker status sensor) required to communicate breaker status (open/closed/tripped, etc.). You also get a Racking Shaft Sensor (RSS) that allows communication of connect and test positions. To communicate that the breaker is withdrawn into the disconnect (or farther out) position you will need a TOC (referred to as "PSS" for position sensing switch) which has an extra contact that is wired back to whichever COM module is chosen. The "COM-TOC" comes in 4-0-0 or 1-1-1. If communicating the disconnect position is not required, you can still specify 6-0-0 or 3-2-1 as a cradle option.
Q: What about an EMC filter? The WL needed one in some applications, and it could be added. What about 3WA?
A: Although the 3WA ETUs are designed to withstand much higher levels of electromagnetic interference than the WL, there is an EMC filter available as a Z-option for factory-installation only. It requires a special wiring harness and as such is not regarded as field installable.
Q: Is a Bell Alarm and Remote Reset for Bell Alarm available? How are they denoted?
A: Yes, both. A Form-C Bell Alarm is standard and is designated as S24 in the manual. A remote reset solenoid is specified in digit 14 of the breaker MLFB (along with closing coil). All 3WA2 & 3 breakers are Automatic Reset, meaning they can be closed immediately after a trip. The tripped indicator remains extended, and the Bell Alarm remains in the tripped position even after the breaker is closed and until manually (or electrically) reset.
Q: Is a second Bell Alarm available?
A: A second (Form A) Bell Alarm contact is available as an option and is designated as S25 in the manual. It is specified by Z=K06.
Q: Are signal contacts for auxiliary releases available? How are they denoted?
A: Dry signaling contacts for the ST/CC/UVR are not available for the 3WA. As a practical matter, they were really only useful for UVRs and 100% duty shunt trips. However, the BSS200 senses the status of the second auxiliary release (ST or UVR) so it can be communicated. In the event of a 5% duty 2nd shunt trip, the signal provided by that contact will be of little use.
Q: Current Sensors – What is configurable? Internal Current Sensors, External Current Sensors, Residual Current Transformer?
A: Like WL, the breaker has internal air-core CTs. They are replaceable but not configurable because there is no need. External air-core N-CTs are the same as for WL. Whether we will replace our WL catalog numbers with3WA MLFBs (for equivalent accessories) remains to be seen.
New CT for 3WA FS1 (no WL equivalent): 3WL9111-0AA21-0AA0
WLNCT2: 3WL9111-0AA22-0AA0
WLNCT2: 3WL9111-0AA23-0AA0
Q: Cradle – Shutter – Short and Tall? WL Shutter is Only TRUE or FALSE. When is short and tall selectable?
A: As of this writing, a short shutter is standard and there will be a Z-option to provide a cradle without a shutter. A different Z-option will change the short shutter to a tall shutter.
Q: Mechanism Operated Contacts – is this a Z-Option?
A: At the moment, MOCs must be ordered separately via MLFB. We are looking into making them a factory-installed accessory. The following MOCs will be available (no change from WL):
- MOC, cradle-mounted, 4 NO + 4 NC, Connected position only, for draw-out breaker only, 3WA FS1 & 2
- MOC, cradle-mounted, 4 NO + 4 NC, Connected position only, for draw-out breaker only, 3WA FS3
- MOC, cradle-mounted, 4 NO + 4 NC, Test and connected position, for draw-out breaker only, 3WA FS 1 & 2
- MOC, cradle-mounted, 4 NO + 4 NC, Test and connected position, for draw-out breaker only, 3WA FS3
- MOC, fixed-mount FS2/3 breaker-mount, 4 NO + 4 NC
Q: How do we select a cradle heater for 3WA? Cradle Heater – Z-Option?
A: There will be a Z-option to go with the cradle MLFB to get the heater.
Q: Are padlock hasps still included as standard?
A: Yes, the padlock hasp which is standard for the WL will likewise be standard for the 3WA2 & 3. For 3WA1 it will be optional.
Q: What is Maximum Wire length from TOC to Communication Module, when wiring “Disconnected” and “Absent Positions” to COM Module.
A: The maximum wire length of both the CubicleBUS cable and the 2-wire connection from the TOC to the secondary disconnects on the breaker is 9 meters.
Q: Are existing CubicleBUS modules compatible with 3WA? Can I keep my WL Profibus Communication Module (COM15)? Will there be a Profibus module for 3WA?
A: The new 3WA CubicleBUS is not compatible with CubicleBUS for WL and older modules cannot be used. We are uncertain about the timeline of a new Profibus module for 3WA (COM170).
Q: The “Current Rating” of “Rating Plugs” in 3WA is different from WL Breaker. Rating Plugs options for US Market will be different?
A: All of the rating plug values available for WL will be available for 3WA. They are called “Option Plugs” now.
Q: Do all the Features of Breakers and Cradle will be covered in 16-digit part numbers separately, as we have them on WL Breaker. Or should we order the components via Z-Option?
A: The MLFB system for 3WA is designed to meet the needs of multiple markets and is similar to but different from the WL catalog number scheme. For instance, specifying that a breaker does not automatically reset after a fault requires a Z-Option. A cradle heater will almost certainly require a Z-Option. The 3WA MLFB system is well documented in our published literature. Not all WL accessories are available in the base 3WA MLFB, so plan on taking Z-options into account with any system you build around 3WA2/3.
Q: Will the 3 Pack Metering CT, Single Phase Metering CT and MDGF CTs be available for 3WA?
A: Yes. For FS2 & 3, the existing 3-pack CT should work, and the other CTs are external and will continue to work. We will probably not transition those part numbers to 3WA part numbers so the current WL part numbers can continue to be used until further notice.
Q: Can a “Rating Plug” with just LSI can be fitted on ETU with LSIG Function?
A: All ETUs can be with or without GF-Trip based solely on the Option Plug installed. Removing an LSIG rating plug and replacing it with an Option Plug with no GF will turn GF-Trip off, but GF Alarm will still be available if it is an ETU600. Installing an Option Plug with LSIG in place of an Option Plug without GF will add GF to the trip unit. Option Plugs are a customer accessory and can be replaced in the field or on the shop floor.
Note that there are two kinds of Option Plugs with GF: Standard and Extended. The difference is that Extended allows setting GF pickup above 1200A (up to 2000A) whereas Standard limits setting to 1200A. Extended GF works only on 3WA3 breakers. 3WA2 limits GF to 1200A regardless of which Option Plug is installed.
Q: Can we use “Open Delta” VT configuration for External VT input for a 3 Wire System?
A: No. The parts required to use standard VTs (as we use today) can be ordered with the MLFB 3WA9111-0EK81 and installed (retrofit). Whether this can be made a factory-installed Z-option is under discussion. In any event, it will only be usable with FS2 & 3 breakers as the FS1 is missing the required secondary disconnect. It is recommended that internal voltage sensing be selected whenever possible.
Q: Is an “ETU Test Set” available for 3WA Breaker. Something like WLTS for WL Breaker?
A: No. The ETU has extensive internal self-testing and monitoring and an external test device is not required.
Q: To use DAS+, do I need to use a second parameter set?
A: No, the ETU600 has both DAS+ and a second parameter set. Those two things are not connected. The ETU300 has only one parameter set but it does have DAS+.
Q: How do I get the second protection parameter set for an ETU600?
A: A 3WA breaker ordered with and ETU600 and PMF-III will automatically include the second protection parameter set. If not ordered with PMF-III, the second parameter set can be enabled with the software option 3WA9111-0ES21. See section 3.1.4 Function packages for functional expansion in the 3WA manual.
No, the ETU600 has both DAS+ and a second parameter set. Those two things are not connected. The ETU300 has only one parameter set but it does have DAS+.
Q: The ETU600 can measure voltage directly without external VTs?
A: Yes. When so ordered, the ETU600 comes with a "Voltage Tap Module" which is internally wired to contacts which can be configured (at order time or via retrofit parts) to contact either the upper or lower stabs of the breaker. The wiring between the Voltage Taps (contacting the breaker stabs) and ETU is fused. The Voltage Tap Module is housed in a drawer and should be pulled out until it locks prior to hi-potting the breaker. The Module can be completely removed (with a tool) and replaced in the unlikely event that replacement is required.
Q: If the communication modules can now be mounted remotely in an Aux compartment, how can they know whether the breaker is in connect/test/disconnect?
A: Breakers ordered with the "Ready4COM" option are equipped with the internal components required to determine breaker status (open, closed, tripped, ready-to-close, charged) as well as connect and disconnect position. To know whether the breaker is in disconnect or pulled out beyond that, a TOC, now known as a Position Status sensor (PSS) is installed in the cradle and wired to the communications module. The PSS is configured in the cradle MLFB.
Q: If no PSS is connected to a communications module, what is communicated for disconnect?
A: As the breaker is racked out, positions between those defined as Connect & Test are communicated as "Intermediate". Starting from Connect and racking out, the COM module would communicate like this: Connect – Intermediate – Test – Intermediate – Disconnect – Intermediate – Absent
Without a connection to the PSS, the final position communicated is Intermediate.
Q: For 3WA, will CubicleBUS modules take up space in Aux compartments?
A: For applications where there is sufficient height above the breaker, such as 1-, 2-, and 3-high stacking, the CubicleBUS modules can be mounted on the breaker secondary disconnects directly using an extension to the terminals to both hold the modules in place and to raise the wiring points above the level of the modules.
Q: Does 3WA still require the use of UL Class 2 (limited energy) power supplies?
A: No. Any 24V dc +/-20% power supply meeting the requirement of less than 10% ripple can be used.
Q: If the power supply to an ETU600 is not active (e.g. gear not energized with CPT-supplied power), how do I activate the ETU for checking trip logs or programming settings?
A: The ETU600 can be powered through the USB-C connection next to the tripped indicator. That is also here a laptop would be connected for programming using powerconfig. Note that this connection does not power any other connected CubicleBUS modules.
Q: Do the ETU300 and 600 protect if there is no control power?
A: All of our ETUs are what is called “direct acting” meaning that they do not require control power to protect. In the absence of control power, the ETU will protect powered by the current flowing in the bus. We guarantee a maximum 3-cycle tipping time (50ms) on instantaneous. This is worst-case, based on starting with an unenergized ETU, as if closing onto a fault. Starting with an energized ETU (primary current or control power) the ETU is about a cycle faster. ETU timing is the same whether it is powered by control power or by primary current. Without control power, LSIG functions work the same way with the same timing.
This the case for both ETU745 and ETU776 as well.
Q: The manual says that the ETU600 has a battery. Why? What happens if the battery runs down or is not installed?
A: The battery in the ETU600 is there to maintain the real-time clock in the absence of control power. It has no impact on protection aside from that. If the battery dies, all that is lost is the time. The ETU will give an indication well in advance of when the battery needs to be replaced.
Q: In the manual it shows a “termination resistor” plugged into X8-9 & -10 (Neutral CT connections). In the past we’ve always just used a wire jumper, can we still do that?
A: Either a 120? terminating resistor or a wire jumper (“zero-ohm resistor”) will work. The ETU600 will show an impossible-to-miss error on the display indicating that nothing is connected those terminals.
Q: The manual says that a rectangular terminating resistor must be connected to X8-1 & -2 if no other CubicleBUS devices are connected. Is this new?
A: A 120? terminating resistor has always been required for the WL but was rarely used because it was supplied in an easy-to-lose form factor (just a 1/4W resistor about 0.25” long in a tiny zip-closure bag). For 3WA, communication between components is via an upgraded version of CubicleBUS: CubicleBUS2. It operates at a much higher speed and installing the resistor will ensure that communication is consistently good.
Q: The direct sensing of bus voltage by the ETU involves bring that voltage back to the ETU somehow. How is this done and why do the VTap drawers need to be pulled out during hipot tests?
A: The VTap directly senses the bus voltage by selectively contacting the upper or lower stabs at the back of the breaker. That voltage is brought back to the ETU by wires with high-voltage insulation and integral fuses. In the VTap drawer is a resistive voltage divider that is conformally coated to ensure insulation resistance. We recommend the VTap drawer be withdrawn for hi-pot testing because when connected, it places an impedance across the phases and to neutral. If several of them are in apparatus together, the leakage current through it could give an incorrect result when the apparatus is hipot tested.
Q: Does the VTap measure L-L or L-N voltages?
A: The VTap / ETU measure L-N voltages and creates an artificial neutral (star point) for the calculation of L-L voltages. There is a secondary disconnect wiring point (X8.14) which is connected to the electrical neutral to prevent displacement of the star point due to asymmetrical loading.
Q: I see the metering data includes both Power Factor and “Cos Phi (?)”. What is the difference?
A: 3WA calculates both "cos phi" and "Power Factor". “cos phi” is equal to Power Factor in a perfectly sinusoidal world. 3WA calculates it from the phase angle between the fundamental of I & V. PF is the ratio of P (real power measured in watts) and S (apparent power, measured in VA): PF = P/S. Power Factor is more interesting in a distorted (harmonic-rich) environment because it takes the total power picture into account.
Q: 3WA appears to have three ways to calculate power factor: IEC Consumer, IEC Producer & IEEE Consumer. What is the difference?
A: This is explained in the breaker manual, but the quick version is that in the IEC definition, the sign of PF depends on the direction of flow of real power (hence produce or consumer) whereas in the IEEE definition, it depends on whether the load is capacitive or inductive (hence always having a consumer perspective).
Q: Can the 3WA2 UL489 breaker be used in top- and bottom-feed arrangements?
A: Yes. Top-fed or bottom-fed, no difference.
Q: Our customer wants to know what the “utilization category” is for 3WA (or 3WL) configured as a “switch disconnector” according to IEC 60947-3.
A: The short answer is “Category B” (as documented in the manuals). The longer answer is that the 3WA is not rated as a “switch disconnector” according to IEC 60947-3 because it is rated per the requirements of IEC 60947-2. What’s the difference? -3 does not require the device to be able to interrupt a fault, -2 does. If the comparison is between an ABB Emax2 & 3WA, the Emax2 is rated per -3 (no fault interruption capability) and the 3WA (& 3WL are rated per -2. You may already know this, but for the sake of completeness, Category B is “current carrying”: 3WL/3WA; Category A is “current limiting”: MCCB.
Q: What’s the difference between the two directional power functions? One is “enhanced”.
A: Reverse Power (not the enhanced one) is set in percent of the "nominal power" of the breaker which is In x Vn where In = option plug value and Vn is the set nominal voltage (menu 5.1 480v, the LL voltage). Enhanced reverse power is set directly in KW.
Q: Undervoltage/Overvoltage/Voltage Unbalance (EPF Functions) – how do they work?
A: All voltage functions are based on the L-N voltages. Undervoltage and overvoltage are set in volts and unbalance is set in %. Every 200ms a new average value of the RMS phase voltages is calculated. For under/overvoltage, the setpoints are compared to each new calculated average to determine whether the function needs to begin timing and/or trip. There are two selectable methods for calculating unbalance, ANSI & IEC. For the ANSI method, percentage unbalance is the ratio of the greatest difference of an individual phase voltage from the arithmetic mean value of the phase voltages. For the IEC method, the percentage unbalance is the ratio of the greatest difference of a phase from the phase with the highest load.
Q: E-Class 1000v rating – is that wye- or delta-rating?
A: Wye-only at the moment.
Q: There are some standard accessories on the 3WA which were optional on the WL. What are they?
A: The ready-to-close contact (S20) is now standard, and the breaker is always equipped with one set of auxiliary (A/B) contacts (for WL = WLAS2). An additional set of aux contacts is an option on 3WA.
Q: 3WA offers both-5% and 100%-duty shunt trips and close coils. Why 100%-duty close coils?
A: The 3WA is a global breaker with a global catalog number system (“MLFB”) and is applied in markets all over the world. 100%-duty Close coils & Shunt trips are often used as interlocks in non-ANSI/NEMA/IEEE/UL markets operating under different standards. They can be selected if the application requires it and the standards permit it.
Q: How are the new 100%-duty ST/CCs different from those used in WL breakers?
A: The 5%-duty coils are the same as those used in WL. The 100%-duty coils have a current regulation circuit in front of the coil. This circuit allows the coils to run cooler as they apply the full voltage to the coil initially and then throttle back to keep the coil pulled in. The consequence of this is that 100%-duty coils cannot be used in applications requiring external wiring which permits coil continuity to be sensed by trickling a small current through it. The power-throttling circuit prevents this.
Q: What benefits does ready4COM bring with it?
A: When breakers are ordered with ready4COM, they are equipped with the BSS200, which, like the WLBSS, allows breaker status (open/closed/tripped/charged/ready-to-close, etc.) to be communicated through a COM150/190 module back to a SCADA/DCS host or PLC.
The other important feature of a ready4COM breaker is that when a 100%-duty shunt trip and/or close coil is specified, they are remotely controllable through the BSS and hence via communications. These coils connect to the BSS internally and have 3 wires that connect to the secondary disconnects and can be wired to be remotely controllable or not, as desired. If the breaker MLFB specifies 5%-duty shunt trip/close coil, they will not be remotely controllable though the BSS. Only 100% duty coils are remotely controllable.
Q: Will WLLKKT be available for 3WA breakers?
A: Yes. What we today call WLLKKT will be orderable as breaker option Z=S40 or as a separate component, 3WA9111-0BA21.
Q: The ETU776 had a feature we referred to as “underflow limit” that prevented it from communicating or displaying currents below that value. Does the ETU600 have anything similar?
A: Yes. The setting is accessible from the display. Navigate starting by pressing the button under the 3 horizontal bars, then down to Device configuration, OK, then down to Display, OK, down to Current values, OK, then the button below the pencil to change the value with the up and down arrows, confirming with OK.
Q: Does an ETU cover come standard, or is it selectable by the user as an option (F40)?
A: 3WA ETUs will come with a cover for the knobs. The cover/lock for the reset is what you get with option F40. Replacement covers can be ordered as a spare part via MLFB (3WA9111-0EM22).
Q: What about peak current & let-through energy?
A: Unfused power circuit breakers are not current-limiting. Whatever the circuit breaker is exposed to is what it lets through. We cannot predict what the impedance is on the line side of the circuit breaker nor can we predict what kind of impedance there is between the circuit breaker and the load (such as a motor control center) in any given application. These parameter must be determined by the user’s coordination study. A circuit breaker manufacturer cannot answer this question.
Q: What about clearing time?
A: There is no single answer for this. The trip unit senses and reacts based to the settings that the user has input (as a result of the coordination study). The settings result in a time-current curve which will allow the user to project the interrupting time at any particular current level. Clearing time is included in the time-current curve of the circuit breaker. Therefore the customer can look at the time-current curve and predict the clearing time at any given current level.
Q: What do the different interrupting rating abbreviations mean?
A: The literature may use abbreviations for interrupting rating which are unfamiliar to the ANSI/NEMA Market customer.
Here they are, with definitions:
Icu = rated breaking capacity (must be repaired or replaced after fault interruption)
Ics = short-circuit breaking capacity (and still serviceable)
Icw = rated short-circuit withstand
Icm = rated making capacity (and still serviceable)
