FAQs

Surge Protective Devices - FAQ (3)

CAPACITOR BANK SWITCHING

Power Utilities use capacitor banks in distribution lines for power factor correction and to maintain acceptable voltage levels. The capacitor banks improve the power factor, thus decreasing the amount of reactive power consumed. This benefits the utility company by allowing them to provide additional power capacity during peak demands and in fast growing areas.

However, utility capacitor bank switching can have negative impacts on power quality. Utility capacitor bank switching transients can be magnified at low voltage capacitor locations on customer power systems, causing premature failure of sensitive electronic equipment. The capacitor bank energizing transient is important because it is one of the most frequent utility system switching operations.

Power quality symptoms related to utility capacitor bank switching include: customer electrical and electronic equipment damage or failure (due to excessive overvoltage); nuisance tripping of adjustable-speed drives, production or process equipment shutdown and computer problems.

Protection from the harmful effects of capacitor bank switching can be achieved through the use of surge protection devices (SPD’s). Properly sized and correctly installed surge protection devices can prevent harmful voltage transients from damaging electrical equipment.

 

Please log in to rate this.
0 people found this helpful.


An electrical transient is a temporary excess of voltage and/or current in an electrical circuit which has been disturbed. Transients are short duration events, typically lasting from a few thousandths of a second (milliseconds) to billionths of a second (nanoseconds), and they are found on all types of electrical, data, and communications circuits.

 

Please log in to rate this.
0 people found this helpful.


What Arc Flash Protection Should I Wear?

Voltage Does Not Determine Hazard Category Levels !

Knowing the voltage is only one piece of determining Arc Flash PPE. The available fault current (amps), the working distance between the worker and the equipment, the clearing time of the circuit protection device, the spacing between conductors or from a conductor to ground, the number of phases, whether the conductors are in an enclosure, and the equipment configuration are also needed to determining the potential Arc Flash exposure level and the required PPE. 

NFPA 70E Table 130.7(C)(9)(a) is organized by system voltage level, but at each voltage or range of voltages, there are several different levels of PPE based on the type of task and the equipment as well as on footnote information for fault current and clearing time. For example, a 600 volts system could have a hazard level ranging from Hazard Risk Category (HRC) 0 (PPE up to 2 cal/cm cm2) to HRC 3 (PPE up to 25 cal/cm2) depending the task, the type of equipment and the footnote information on fault current available and clearing time.

The bottom line is that you cannot rely on voltage alone to figure out what arc flash protection you need. You will need to know all the factors noted above and conduct a hazard analysis to determine the potential arc exposure level. In lieu of a formal hazard analysis, you could use NFPA 70E Table 130.7(C)(9)(a) to determine the hazard risk category and Table 130.7(C)(10) to determine the PPE needed for the task. 

Reference: NFPA 70E Table 130.7(C)(9)(a).

Please log in to rate this.
0 people found this helpful.


Fire Pump Controllers -FAQ (4)

 

Method:

  1. Find out voltage and horsepower of motor
  2. Look up this value on Table 430.250 in NFPA 70
  3. Multiply number shown by 1.25 to get # amps
  4. Find # amps on Table 310.16 in NFPA 70 under the 75C (typical) column
    to get conductor size
  5. For 480V 100HP, correct conductor size is 2/0

 

References:

 

a)   A fire pump motor should be in accordance with NFPA 20 9.5.1.1 which states that it must comply with NEMA Design B standards and be listed for fire pump service.

b)   Fire Pump applications are discussed in Article 695 of NFPA 70: National Electrical Code

c)   NFPA 70 695.6(C)(2) states that conductors must have a minimum ampacity in accordance with Article 430.22.

d)   NFPA 70 430.22 says that a continuous duty application requires conductors rated for not less than 125% of the motor’s full load current as determined by Article 430.6(A)(1).

e)   NFPA 20 9.5.1.5 states that all motors shall be rated for continuous duty.

f)     NFPA 70 460.6(A)(1) states that “Tables 430.247 through 430.250 shall be used to determine the ampacity of conductors or ampere rating of switches, branch-circuit and ground fault protections instead of the actual current rating marked on the motor nameplate.”

g)   For our example of a 100HP 480V motor, Table 430.250 applies as this table is for three phase alternating current motors.  There it shows that 124 amps is the correct full-load current for a 480V, 100HP motor.  Note that the table gives nominal voltage ranges, such as 440-480 and not specific voltages such as 473V.  So, for example, if the incoming voltage happens to be 492V for instance, the 460V chart is still used.

h)   Then, for determining the correct conductors for a 124 amp motor, again NFPA 70 430.22 says that a continuous duty application requires conductors rated for not less than 125% of the motor’s full load current.  So, 124 amps times 1.25 equals 155 amps.

i)     NFPA 430.6 states that “The size of conductors supplying equipment covered by Article 430 shall be selected from the allowable ampacity tables in accordance with (section) 310.15”.

j)     NFPA 70 Table 430.5 shows that Article 430 covers fire pumps.

k)   NFPA 310.15(A)(1) and 310.15(B) state that tables 310.16 through 310.19 show the ampacities for conductors.

l)     Table 310.16 applies to our example 480V, 100HP motor.  There it shows that to provide 155 amps, 2/0 conductors are required.  The 1/0 size would not be large enough as it provides up to 150 amps and the 3/0 size would be okay as it provides up to 200 amps but is larger than necessary.

m)  Also, if the power source will supply equipment other than the fire pump only, NFPA 70 695.6(C)(1) states that 125% of the full load current of the pressure maintenance pump and 100% of the associated accessories (such as a remote alarm panel) must be added to the value found in Table 430.250 to determine conductor sizing.

Please log in to rate this.
0 people found this helpful.


Method:

  1. If the motor/controller starting method is:

a)   Across-the-Line (FTA1000)

b)   Primary Resistance (FTA1500)

c)   Autotransformer (FTA1800)

d)   Soft-Starter (FTA1930)

  • Use the same method to determine wire size as shown above for between power source(s) and controller.  (In our example a 480V, 100HP motor uses 2/0 conductors).
  • For these controllers, three conductors (plus ground) are used between the controller and the motor.
  1. If the motor/controller starting method is Part Winding (FTA1250):

a)   Find the motor full load amps from Table 430.250.

b)   Multiply the # amps by 1.25

c)   Divide this number of amps result by 2

d)   Divide this number by .80 and find this result in Table 310.16 in the 75C column *

e)   Connect six conductors (plus ground) between the controller and the motor.

f)     480V,100HP uses 3 AWG

  1. If the motor/controller starting method is Wye-Delta Open (FTA1300) or Wye-Delta Closed (FTA1350):

a)   Find the # amps from Table 430.250.

b)   Multiply this # amps by 1.25

c)   Multiply this number of amps result by 0.58

d)   Divide this number by .80 and find this result in Table 310.16 in the 75C column *

e)   Connect six conductors (plus ground) between the controller and the motor.

f)     480V,100HP uses 2 AWG

      Example:  Part Winding Start & Six conductors ran in common conduit:

                  100hp. 460V = 124 FLA  (Table 430.25)

(124 X 1.25) divided by 2 = 77.50, then 77.50 divided by .80 = 96.88

Answer:  96.88A = 3 AWG per Table 310.16

 

Reference:

Reduced Voltage Motor Wiring: Reference NFPA 70 Article 430.22(A), (C) & (D)

Do not derate 20% if two conduits are usedSix conductors in common conduit: The conductors must be derated by 20% to account for the additional heating of six conductors together in one conduit. Reference NFPA70, Article 310.15(2) and Table 310.15(B) (2) (a).

 

 

 

 

Important Disclaimer

 

Information contained herein was assembled from national electrical and fire protection codes and references to assist engineers, pump distributors and installing contractors.

Flotronix Corporation disclaims liability for any personal injury, property or other damages of any nature whatsoever, resulting from the use of this document. No guaranty or warranty is made as to the accuracy or completeness of any information published herein. Anyone using this document should rely on their own research or seek the advice of a competent professional.  

 

Copyright © 2005

Please log in to rate this.
0 people found this helpful.



Question:
 How do I size a disconnect (circuit breaker or fused) when installed upstream of a fire pump controller?

Method:

  1.     The disconnecting means should be sized with a rating higher than the locked-rotor current of the fire pump motor.
  2.     In our example, the fire pump only is being fed from the 480V power source.  The locked-rotor current for our 100HP motor is 725 amps.  A disconnect must be selected that is rated for a current higher than this.  The nearest common size disconnect of 800A would be suitable.

References:

a)     NFPA 20 9.3.2.2.3.1 states that a disconnecting means and associated overcurrent protective device(s) is allowed if desired.  It is not required, however.

b)     NFPA 20 9.3.2.2.3.2(A) states that this disconnecting means and its overcurrent protective device must be able to carry indefinitely the sum of the locked-rotor current of the fire pump motor and the

pressure maintenance pump along with the full-load current of all other equipment fed from that disconnect.

c)     Locked-rotor current is determined from NFPA 70 Tables 430.251(A) & (B).

Please log in to rate this.
0 people found this helpful.


What Arc Flash Protection Should I Wear?

Voltage Does Not Determine Hazard Category Levels !

Knowing the voltage is only one piece of determining Arc Flash PPE. The available fault current (amps), the working distance between the worker and the equipment, the clearing time of the circuit protection device, the spacing between conductors or from a conductor to ground, the number of phases, whether the conductors are in an enclosure, and the equipment configuration are also needed to determining the potential Arc Flash exposure level and the required PPE. 

NFPA 70E Table 130.7(C)(9)(a) is organized by system voltage level, but at each voltage or range of voltages, there are several different levels of PPE based on the type of task and the equipment as well as on footnote information for fault current and clearing time. For example, a 600 volts system could have a hazard level ranging from Hazard Risk Category (HRC) 0 (PPE up to 2 cal/cm cm2) to HRC 3 (PPE up to 25 cal/cm2) depending the task, the type of equipment and the footnote information on fault current available and clearing time.

The bottom line is that you cannot rely on voltage alone to figure out what arc flash protection you need. You will need to know all the factors noted above and conduct a hazard analysis to determine the potential arc exposure level. In lieu of a formal hazard analysis, you could use NFPA 70E Table 130.7(C)(9)(a) to determine the hazard risk category and Table 130.7(C)(10) to determine the PPE needed for the task. 

Reference: NFPA 70E Table 130.7(C)(9)(a).

Please log in to rate this.
0 people found this helpful.