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Frequently Asked Questions
Q: Does Siemens have breaker lugs rated for use with 90 Deg C wire? A: The short answer is no - nor does any other breaker manufacturer. However, 90 Deg C insulated wire CAN be used IF it is sized per the 75 Deg ampacity column in the NEC tables. In fact, with most of Siemens 100% rated circuit breakers, 90 Deg. Cable is required, but it must be sized per the 75 Deg ampacity.
Q: What is the difference in the operation of an Auxiliary contact and a Bell Alarm contact? A: An auxiliary contact switches in conjunction with the circuit breaker itself, the "A" contact closes when the breaker is closed and opens when the breaker is opened or tripped. The "B" auxiliary opens when the breaker is closed and closes when the breaker is opened or tripped. In contrast, the bell alarm contact only switches when the circuit breaker is TRIPPED, not when the breaker is opened and closed by the handle.
Q: When a UVR is installed in a circuit breaker does it provide complete 3-phase under-voltage protection? A: No it does not. A UVR is a single-phase device and provides only basic under-voltage protection. The UL489 requirements are: (a) the UVR must NOT drop out at 70% or higher applied voltage (b) it must drop out at 35% or lower voltage (c) the coil must pick up at 85% voltage. The UVR must be energized before the circuit breaker can be closed. The requirement for full under-voltage protection generally means, 3 Phase sensing and acting to trip the circuit breaker at about 70 to 80% voltage. An external relay must be provided for this type of protection.
Q: When should I use a UVR to trip a circuit breaker instead of a Shunt Trip? A: A UVR and a Shunt Trip will both trip a circuit breaker and the end result is the same for both. The control logic, however, is exactly opposite for each device. The Shunt Trip must have a voltage applied in order to trip; the UVR must have control power removed in order to trip. If a reliable source of control power is available, a Shunt Trip works well for most applications. If control power can fail or basic under-voltage sensing is needed, then the UVR is a better choice. The UVR will trip the circuit breaker if control power fails for any reason or if an external control contact calls for a trip operation.
Q: Why are there four wires for connecting a QJ shunt trip instead of the two wires used for all other circuit breaker shunt trips? A: The QJ breaker is an older style that has a separate coil clearing contact instead of having the contact built into the shunt trip unit itself. Therefore, there are four wires, two for the coil and two for the aux contact. These are wired in series per the diagram included with the shunt trip or in the QJ instruction manual.
Q: What can I use for a local ammeter display with our circuit breakers? A: A: All of Siemens electronic trip circuit breakers like the SENSITRIP™ and SB breakers have built in CT's that continuously send amp readings to the multi-pin port in the front of the trip unit. This port is normally used to connect the breaker to an ACCESS communications system. The SENSITRIP™ Ammeter Display Unit (SADU), designed for SENSITRIP™ MCCBs, can be mounted on this same multi-pin port and provides a local ammeter display. In addition, it has displays for current demand, average current, current unbalance, and ground fault current. Other features include breaker status, a time and date stamped trip log, and a max log for all of the above current displays. The SADU is also an excellent trouble-shooting tool for a user who wants to monitor what is happening on his system as well as with the breaker itself.
Codes or Regulations Questions
Q: Which molded case circuit breakers are HACR rated? A: All Siemens Thermal-Magnetic Molded Case Circuit Breakers from BL through RD frames carry the HACR marking for Heating, Air Conditioning, and Refrigeration applications.
Q: Are all of Siemens circuit breakers fungus proof? A: All of the Siemens Sentron™ breakers rated through 2000A, as well as the BQD/CQD, and the Siemens SB Encased Systems Breaker are inherently fungus proof in accordance with MIL-T-152.
General Molded Case Circuit Breakers Questions
Q: What is the difference between 80% and 100% breakers? A: All standard Molded Case Circuit Breakers are to be applied for continuous loads up to 80% of their marked amp rating per the NEC. If a circuit breaker is labeled “100%”, then it may be applied to continuous loads up to 100% of its marked rating. Siemens performs additional testing per UL489 to achieve this rating and labels these breakers as 100% rated.
Q: What does it mean when a specification calls for a 100% rated circuit breaker? A: The National Electrical Code (NEC) specifies that circuit breakers may only be loaded to 80% of their marked ampacity on a continuous basis. An exception to this rule allows 100% continuous loading if the circuit breaker is marked “100%”. Siemens 2004 SPEEDFAXTM shows the part numbers and prices for breakers available with 100% ratings. These breakers may be loaded to 100% of their rating and must be used with specific lugs, as shown in Siemens literature, and are for use with 90 Deg C cable. One important aspect of the use of 90 C cable is that it must be sized based on the 75 Deg C ampacity.
Q: Should the time current trip curve be used for a field test? A: NO! One of the notes on Siemens time current curves specifically states: "For application and coordination purposes only." The notes also state: "Based on 40 Deg. C ambient cold start. Connected with 4 feet of rated wire (75 Deg. C) per terminal. Tested in open air with current in all poles." Field tests do not duplicate these conditions and therefore will not yield the same trip characteristics. NEMA has published standard AB-4 1996 for field testing. All field-testing must follow the guidelines in this standard to be considered valid by Siemens.
Q: What is the de-rating factor for applying a thermal magnetic circuit breaker at ambient temperatures above the standard 40 Deg. C? A: UL489 dictates that circuit breakers be calibrated at 40 Deg. C ambient. Due to the thermal element in a thermal magnetic circuit breaker, the breaker will trip at lower currents in higher ambient temperatures, causing nuisance trips. The Siemens 2004 SPEEDFAXTM, page 6-100 has a table of de-rating factors for up to 60 Deg. C for thermal magnetic circuit breakers. However, since trip characteristics of electronic trip circuit breakers are not affected by ambient temperature, Siemens recommends using electronic trip circuit breakers in these applications.
Q: Is a Molded Case Switch just a switch? Can it ever trip like a circuit breaker? A: Siemens Molded Case Switches will trip instantaneously on a short circuit condition. This self-protecting element is necessary in order to allow a Molded Case Switch to be applied at a useful short circuit level. Without this element the switch would be limited to applications where the available fault current is approximately 10kA. With this element the switch may be safely applied on systems with available fault currents up to 200kA. The only exceptions are the Siemens SBN and the TD frames, which are listed as 'Non Automatic Molded Case Switches' and do NOT have a self-protecting trip element. These frames have a withstand rating that must be matched to the available fault current. The table in Siemens 2004 SPEEDFAXTM, page 6-62 lists the available frames and their self-protecting override levels.
Q: Are all circuit breakers suitable for reverse feed ('fed from the bottom') applications? A: In general, reverse feed applications are limited to circuit breakers with non-interchangeable trip units which have been specifically tested for incoming power connected at the 'bottom' or 'load' end. Most of the non-interchangeable breakers, including the Siemens SENSITRIP™ electronic breakers can be reverse fed. UL says that a breaker must be specifically marked "LINE" and "LOAD" as necessary if it fails to pass the reverse feed test. In the Siemens 2004 SPEEDFAXTM, footnotes show the appropriate listings, but the final word should be the markings on the breaker itself.
Q: Why are some circuit breakers rated 240V and some rated 120/240V? Is there a real difference? A: YES, there is a difference. The National Electric Code (NEC 240-85) has specific requirements for voltage ratings and markings for circuit breakers. A '240V' or '480V' rating is called a 'straight' rating and is applicable to a Wye or Delta system. A '120/240V' or '480Y/277V' rating is called a 'slash' rating and is generally applicable to a Wye system, but may NOT be used on a Delta system. See Application Notes & Data 2.15.1.0, page 54 for more information. Mining Duty Breakers Questions
Q: Are the bolt hole patterns for Siemens Mining Duty breakers the same as that of competitors’ breakers? A: The bolt patterns are not intentionally designed to be the same. It is possible that the patterns are the same or very close on some breakers, but the only way to determine this is by comparing drawings or breakers.
Q: For mining duty applications, is there anything, other than the catalog number, to distinguish between the shunt trips and under-voltage trips? A: Yes. The Siemens Mining Duty UVR has an orange label while the shunt trip has a blue label.
Q: Currently available competitive UVRs have a high failure rate. What would make Siemens UVRs any different? A: Siemens Beta site tested the standard UVR and found similar problems in rugged mining applications. Hence, the Siemens Mining Duty UVR was especially designed for Mining Duty applications. Subsequent Beta site testing showed significantly longer life than that of the standard UVR and that of competing products.
Q: Can shunt trips and UVRs be installed on either side of the operating handle? A: Yes, they can be installed on either side of the operating handle on Thermal-Magnetic breakers. However, the internal accessories on Electronic Trip circuit breakers must be installed on the right side of the handle. There is a channel in the back of the breaker to route control wires to either side.
Q: Under what voltage variations will the Siemens Mining Duty UVR continue to operate? A: The Siemens 120V UVR must hold in from 102V to 120V, which is 85% to 100% of the rated voltage. This 120V UVR drops out between 30 Volts and 84 Volts. Although UL requires standard UVRs to drop out between 35% and 75% of rated voltage, mining duty UVRs are not UL-listed, therefore Siemens Mining Duty UVRs have been designed with a wider service range between 25% and 70%.
Q. How many mechanical operations can be expected with Siemens Mining Duty breakers? A. Siemens mining duty breakers meet or exceed the MSHA requirements shown on the following table:
Current Full Load No Load Total Per Operations Rating Operations Operations Breaker/Test per Minute 225A 4000 4000 8000 5400A 1000 5000 6000 4 600A 1000 5000 6000 4 800A 500 3000 3500 1
Q: Why is there not an MSHA label on Siemens Mining Duty breakers? A: MSHA has developed standards for cable protection known as Trailing Cable settings, but has not published standards for circuit breakers. Circuit breaker manufacturers self-certify their equipment to meet these MSHA requirements for Trailing Cable Settings. Siemens meets MSHA requirements for mining circuit breakers, however, since there is not a written standard for mining duty circuit breakers, no labeling has been designed for this application.
Q. Do Siemens Mining Duty Circuit Breakers have a warranty? A. Yes, these breakers are covered by Siemens standard warranty which covers defects in material and workmanship. In addition, Siemens has performed on site testing for interruption capability and calibration as well as rigorous load endurance to provide superior performance in this harsh environment.
Q: Are safety switches load break rated?
A:
Yes, all safety switches are fully load break rated. In order to
obtain this rating, Switches are repeatedly operated under full load
and also no load conditions, and must pass the following testing.
Load Break Ratings Switch
Ampere Rating Number
of ON, OFF Operations per Minute Number
of Operations With
Current Without
Current Total 30
– 100 6 6000 4000 10000 200 5 6000 2000 8000 400 4 1000 5000 6000 600 3 1000 4000 5000 800 2 500 3000 3500 1200 1 500 2000 2500 Q: Which switches are SUSE (service entrance) rated? A: All standard 2 and 3 pole GD, HD & DT Siemens switches, in both, fused and non-fused versions, are suitable for use as service entrance equipment. When used as service entrance equipment, the factory or field installed neutral must be properly bonded to ground with either bonding screw or the strap provided. Q: Are Safety Switches 80 or 100% rated devices?
A:
UL requires all fusible Safety Switches to have a statement that limits the
continuous current to not exceed 80 % of the fuses used in other than motor loads.
All switches are also HP rated and when feeding a motor, the maximum HP rating
determines the maximum load that can be connected to the switch. A fusible 30
amp switch for example, can be used at 15 HP maximum at 480 Volts. Per table 21.2
of UL 98, which is the standard for enclosed and dead-front Switches, this motor
will have a full load current rating of 21 A. However, the same standard allows
a 30 HP rating at 600 Volts AC on a non-fusible Switch and shows the full load
current rating of this motor to be 32 A. In the case of a non-fusible switch,
the actual applied current rating can be 100% and even higher as in the example
above when the switch is tested for this rating. This testing is very severe in
that the switch must be repeatedly opened and closed on locked rotor current as follows.
Max
HP Rating Number
of ON, OFF Operations per Minute Number
of Cycles of Operations 100 6 50 500 1 10
SB Encased Systems Breakers Questions
Q: Are there series ratings between SB Systems Breakers and downstream Molded Case Circuit Breakers? A: No, there are no series ratings between the SB Systems Breaker and Molded Case Circuit Breakers. Insulated Case Circuit Breakers are not designed to be current limiting and therefore are not series rated with downstream circuit breakers.
Q: What is the difference between the SB Systems Breaker stored energy operating mechanism and the toggle mechanism used on Molded Case Circuit Breakers? A: The mechanism currently used on a molded case circuit breaker (MCCB) is a quick-make-quick-break over center toggle that performs well on small frame MCCBs. The larger, heavier frame of the SB requires much more force to operate. The stored energy mechanism provides several benefits: (1) provides sufficient force to operate the heavy mechanism, (2) provides high speed operation for five-cycle closing times, and (3) provides the ability to perform an open-close-open cycle before the springs must be re-charged.
Q: What is the difference between the two interrupting ratings listed for the SB Systems Breaker? A: The two ratings for the SB are the Interrupting Rating and the Withstand Rating. The interrupting rating is the maximum fault current that the SB can interrupt while tripping instantaneously. The withstand rating is the current that the SB can hold in WITHOUT tripping for a specified time (i.e. ˝ second or 30 cycles). The purpose of the withstand rating is to allow a downstream device, like a branch breaker, to trip first and allow the SB, serving as the main breaker or major feeder, to remain closed and continue to supply power to other areas of the system.
Q: What is the purpose of the anti-pump circuit in the SB Systems Breaker motor operator? A: The anti-pumping circuit in the Electronic Charging Motor Controller (ECMC) of the Siemens Electric Motor Operator is to prevent a maintained close signal from repeated attempts to re-close the breaker after a fault. Without the anti-pump feature, as soon as the breaker tripped the motor operator would re-close the breaker, the breaker would immediately trip again and the cycle of tripping and re-closing would continue until the breaker was destroyed.
Q: How is the SB Systems Breaker tested using the primary current injection test? A: All field-testing should be in accordance with NEMA standards Publication No. AB4. For more information on this publication and how to order, click on this link NEMA standards Publication No. AB4.
Q: How are phase or ground fault tests conducted using the breaker trip unit? A: Each SB trip unit has integral test functions for testing phase and ground fault functions. A minimum of 20% of the primary breaker rated current must be available in order to test these breaker functions.
Special Applications Questions
Q: What breakers are rated for HID lighting at 480V? A: HID stands for High Intensity Discharge and applies to several types of high output lighting such as high pressure sodium and mercury vapor. This type of lighting is particularly difficult for circuit breakers to switch and requires special testing of the breaker. Only the Siemens BQD 1 Pole 15-30 amp circuit breakers are HID rated at 480Vac.
Q: What does the SWD rating mean? A: It means "Switching Duty". This rating applies to the switching of fluorescent lights ONLY, not HID lights or any other types of loads. The rating is limited by UL to 15-20A, 1 Pole circuit breakers. See the footnotes in the Siemens 2004 SPEEDFAXTM. At 480V, only the Siemens BQD and Siemens Sentron™ ED breakers are SWD rated.
Q: Can a user install welding cable in Siemens lugs? A: Circuit breaker lugs must be tested with the type of wire to be used per UL486. UL489 dictates that manufacturers use standard Class B & C stranded wire per UL486 and therefore most standard lugs perform best with standard strand cable. The fine strand cable presents a problem for most standard lugs and can overheat under load or pull out under short circuits. Fine strand cable is not recommended unless the particular lug has been tested for such use. Siemens standard pressure lugs should not be used with fine strand wire. Compression lugs may be used or an alternate lug supplied separately. For more information see Application Notes & Data sheet 2.15.1.0 Page 55.
Q: Should a circuit breaker be de-rated for application at high altitudes? A: Yes. Due to the differences in the heat dissipation and the dielectric properties of thinner air, a circuit breaker should be de-rated for applications above 6600 feet per the table in the Siemens 2004 SPEEDFAXTM on page 6-100.
Q: Can Siemens circuit breakers be used in 400Hz applications? A: All Siemens circuit breaker with thermal-magnetic trip units may be applied on 400Hz systems, up to 480V, following the de-rating table in the Siemens 2004 SPEEDFAXTM on page 6-100. The interrupting rating will be 5kA or 10% of the 60Hz rating, whichever is greater. Siemens circuit breakers with electronic trip units have not been tested for 400Hz applications.
Q: Does a 2-pole ground fault circuit interrupter (GFCI) circuit breaker provide Personnel Protection in accordance with the NEC when no neutral is used? A: Yes. If the load does not require a neutral, for example a 240V only load, the GFCI breaker still provides the required ground fault protection. Regardless of whether or not a LOAD neutral is used, the white wire attached to the breaker MUST be connected to the panel neutral bar.
Trip Units Questions
Q: Do electronic trip circuit breakers like the Siemens SENSITRIP™ and the SB breakers come pre-set from the factory for a particular application? A: The electronic trip units on the Siemens circuit breakers are not set for particular applications, but they are shipped with the trip adjustments set at the minimum positions. Due to the wide variety of systems and loads it is impossible for Siemens to pre-set circuit breakers for a specific application. Ideally a Coordination Study should be conducted for the specific system requirements and would list the needed settings for all of the over current protective devices in the system. If a coordination study has not been performed, a knowledgeable user with Siemens Time Current Curve software can determine the basic settings for the breakers. This software is easy to use and provides the tools needed to select settings, to determine coordination between breakers at each level in the system, and to provide a printout of the time current curve and a list of settings. This software is available free of charge from Siemens web site. To access this site, click on the link Siemens Time Current Curve software.
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