Switchboard Manufacturers Test Assembly to SANS 61439-1&2

Due to increased inquiries and requests from customers in the electrical industry, it has become advantageous to transition from the current SANS 60439-1 to the new SANS 61439-1&2.

Switchboard Manufacturers KZN have tested their upgraded assembly system at the South African Bureau Of Standards (SABS) NETFA Laboratory in Bronkhorstspruit. 

Shane O’Reilly and Andrew MCarthy lead the team that designed and developed the assembly that passed the tests with ease.
The tests were completed under the auspices of the Short-Circuit Laboratory Manager, Seth Mnisi.
The following tests were completed:
1) Strength of Materials-10.2
  • Resistance to corrosion.
  • Thermal stability and resistance to abnormal heat and fire of insulting materials.
  • resistance to ultra-violet (UV) radiation.
  • resistance to mechanical impact.
  • durability of marking.
  • lifting and transport.

2) Degree of Protection of Enclosures- 10.3 

Validate protection against direct contact with live parts, as well as protection against ingress of solid foreign objects and liquids, in accordance with IEC 60529.

3) Clearances and Creepage Distances – 10.4 

Verify that the clearance and creepage distance enable the assembly to withstand the following:

  • Exceptional, transient overvoltage (lighting, HV operations),
  • Operating voltage and temporary overvoltage.

4) Protection against electrical shock and integrity of protective circuits- 10.5

Verify that:

  • The effective continuity between the exposed conductive parts of the assembly and the protective circuit.
  • The short-circuit withstand strength of protective circuit.

5) Incorporation of switching devices and components-10.6-

Ensure the compliance of equipment implementation in accordance with the rules of manufacture and EMC regulations, if applicable.

6) Internal electrical circuits and connections- 10.7

Verify the conformity of implementation and dimensioning of internal circuits and connections. The following should be carefully checked:

  • Short-circuit withstand strength.
  • Temperature-rise withstand.
  • The section of the neutral conductor.
  • Identification of conductors.

7) Terminals for external conductors-10.8

Verify the compliance of implementation and dimensioning of terminals for external conductors.

8) Dielectric properties-10.9

Test each type of circuit in the assembly to ensure:

  • Power-frequency withstand voltage.
  • Impulse withstand voltage.

9) Verification of temperature rise -10.10

Ensure:

  • Thermal stability of the loaded assembly,
  • That the temperatures are controlled on accessible parts, connections and equipment devices.

10) Short -circuit withstand strength-10.11

In comparison to a tested reference design or by testing, verify the level of withstand assigned to the reported short circuit current (unless excluded)

11) Electromagnetic compatibility -10.12

Verify EMC requirements via tests, Except if:

  • The incorporated devices and components comply with ECM requirements for the environment that has been specified;
  • Their installation and cabling comply with the specifications of the manufacturers.

12) Mechanical operation – 10.13

Verify via tests the mechanical operation of removable parts (including any insertion locking). Enclosures, partitions and fastenings should be able to withstand the wear-and-tear of normal use under short circuit condition.

All of the above test were completed and comply with SANS/IEC 61439-2012/2011 Edition 2- part 1 & 2 

50kA Busbar Support Test at The Apollo

SWITCHBOARD MANUFACTURERS KZN TESTS 50KA BUSBAR SUPPORTS

Switchboard Manufacturers KZN put their upgraded 50kA Busbar Support System to the test at the South African Bureau Of Standards (SABS) NETFA Laboratory in Bronkhorstspruit. 

[The testing staff at NETFA and Switchboard Group. Centred Seth Mnisi, right- Shane O’Reilly, Left- Josh Berman]

Shane O’Reilly and Andrew MCarthy lead the team that designed and developed the composite supports that were able to pass the tests with ease.
[Busbar System connected up to the 127MVA transformer. Output potential: 100kA]
The tests were completed under the auspices of the Short-Circuit Laboratory Manager, Seth Mnisi, who treated the Switchboard team to a tour of the facility.
The Busbar Support System was able to withstand a short-circuit test to SANS / IEC 61439-2:2012/2011 Ed.2 up to 65kA rms per shot.
The incredible machinery coupled with the friendly and highly qualified staff keep this facility at the top of its game.

How to Select the Right Circuit Breaker for your Installation?

Selecting the correct Circuit Breaker (CB) for your distribution panel is crucial  for the longevity of the installation as well as the safety of those maintaining and occupying the premises. This article addresses the selection of key breaker attributes such as voltage, current and kA rating.

Rating Considerations:

Circuit Breaker Voltage Rating

The voltage rating of a CB is determined by the highest voltage that can be applied  across any two conductors in the circuit.  It is important to select a circuit breaker with enough voltage capacity to meet the end application. A single phase AC circuit in South Africa is generally rated at 230V  and a single pole CB rated at 230V can be used. A 3 phase AC circuit operates at 400V and requires a Triple Pole CB rated at 400V.

Circuit Breaker Current Rating

The next rating to consider is the amperage or ‘operating current’ of the breaker. CB’s are designed to operate at 100 percent of the required load . However,  in order to offset the effects of heat generated by the system, it is good practice to select a CB at approximately 125 percent of the required load.

For example: If a supply of 250A is available from the transformer, the breaker of choice for the main incomer should be rated at 250A in order to protect the transformer. However, the feeder breakers feeding a 25A load should be rated at 32A.

[Photo Taken at Switchboard Manufacturers Johannesburg]

Circuit Breaker kA Rating

Finally the ‘kA rating’ or ‘fault level’/’rupturing capacity’ of the CB should be taken into account. The kA rating of the CB indicates the maximum short circuit current that the CB can withstand without arcing or catastrophic failure. This current can be upwards of 100 times the required load and has the potential to  cause major damage to property and personnel.

For Example: A circuit breaker rated at ‘6kA’ means that the circuit breaker can withstand 6,000 amps of current during the brief time it takes to trip.

Why is it so important to choose the correct kA rating?

If the short circuit current is greater than what the CB can withstand, the contacts in the CB can weld together,  preventing it from tripping.  Another possibility is that the CB can explode, spewing dangerous plasma.

Under Rated Circuit Breaker

[Breaker fitted to a DB with an Under rated fault level]

So how do I calculate the correct kA?

The maximum current that can flow through a circuit is determined by the size of the transformer feeding the circuit as well as the length of the cable run from the transformer. This is often called the downstream short circuit current. This will determine the maximum kA rating required for the main circuit breaker.

For example: A 500kVA transformer that has a short circuit current of 35kA at its terminals. The cable run from the transformer to the main breaker is 10m and is run with 90mm2 cable. The resistance in the cable limits how much current comes from the transformer, and so after calculations it was determined that the short circuit current at the end of the cable would be 26kA. In this case, a 20kA circuit breaker cannot be used in the installation.

Switchboard Manufacturers
Distribution Panel

[Photo Taken at Switchboard Manufacturers Johannesburg]

SABS Approved Dealers:

When selecting a CB, it is vital for it to be SABS or IEC approved. This provides the assurance that the CB’s have been tested to strict quality standards and will operate in a safe manner as required. Well known brands such as ABB, Schneider and CBI are all SABS approved and are regarded as high quality devices. Switchboard Group is a registered supplier of these products and the leading manufacturer of LV panels is South Africa.

Conclusion:

In conclusion a CB should be selected based on the nominal current, kA rating, number of poles required and whether the CB is SABS approved.

Author: Brendon Swanepoel

2nd Year Electrical Engineering Student, University of the Witwatersrand

Brendon is completing Switchboard Group’s 6 week Learnership and Training program offered to students looking to further their practical skills.

Empowering South Africa’s youth.