19th Electrical Engineering Safety Seminar Nov.09

Arc Fault containment design of LV boards1) Fault Level: (System & Equipment)Mechanical strength of the system (I peak =r.m.s. x 2.1)

3) Construction: (Operator safety)Form of construction & Segregation

2) Current Rating:Thermal Heating = I2t Watts loss Heat dissipation

Fault Rating of LV system. Typical installationFeeder CCT=??A 50kA

MSB 2000A / 50kACCT=2000A 50kA

415V LV Transformer Rating; 2000A /50kA @ Terminals

11kV

MV Cable (& cable fixing) ??kA

StandardsAS3000 Section 3 Selection and Installation of Wiring Systems3.1.2 Selection and Installation. Wiring systems shall be selected and installed to perform the following functions associated with the safe design and construction and proper operation of the electrical installation.a) b) c) d) e) f)

Protection against physical contact with live parts Satisfy minimum current carrying capacity Provide Reliability connections and joints. Provide adequate strength of supports, suspensions and fixings. Suit intended use e.g. fire resistance, safety services etc. Protection against mechanical damage

Typical Cable FixingStainless steal cable ties220mm spacingSingle Core 33kA

3 Core 28kA

Singe Core 50kA

How many stainless steel cable ties do I need??The Breaking Strength: Heavy duty 316 Grade S/Steal cable tie = 1,112N (250lb)(This does not allow for impact strength or safety factor)

EN 50368:2003 CABLE CLEATS FOR ELECTRICAL INSTALLATION

Applying the formula - Ft = (0.17 x ip2) / SFt = Maximum Force on Conductor (N/m) ip = Peak Short Circuit Current (105kA) S = Cable Diameter if cables in trefoil (0.0354mm dia)

@50kA

=

105kA Peak2 x 0.17 = 53,550Nm 0.035mmDia = 48/mtr

1mtr / 53,550Nm

How many stainless steel cable ties do I need??kA SPACING 20 mtr run = Qty Qty 1,000 Qty 714 Qty 408 Qty 180

50kA = 20mm = 40kA = 28mm = 30kA = 49mm = 20kA = 111mm =

Cable cleats @ 457mm spacing 118kA peak short circuit current for 0.1 sec.

Fault rating of SwitchboardAdditions to AS/NZS 3439.1:2002Main Circuits Within an Assembly7.5.5.1.2

The conductors between busbars and the supply side of a single functional unit, as well as the components in this unit, may be rated on the basis of reduced shortcircuit stresses occurring in the load side of the short-circuit protective device in this unit provided that such conductors: are tested as part of the short-circuit test on the functional units;

are substantial and not less than the rating of the functional units and, in no case, less than 4.0mm in cross-sectional area; are not more than 1M in length; and are provided with solid insulation (7.4.2.1) or shrouded in normal service to prevent faults between phases or between phases and earth or neutral

Additions to AS/NZS 3439.1:2002 Now in English

+ 50kA

Additions to AS3439.1:2002Main Circuits Within an Assembly

Short Circuit Strength Testsconducted at TCA Sydney (Test Report 101740-1) GE MCCBs rated 160A, 250A, 400A & 630A at a prospective fault level of 63kA

Arcing Fault Video 50kA- Elsteel

Construction: Operator safety Basics or Arcing FaultsAn arc fault has to be manually started by something creating the path of conduction, dropping a metal part or by a failure, such as a breakdown in insulation. Arc faults