The Perfect Recipe for the Design of a Switchboard

The electrical LT panels market size in India is well poised at a comfortable 900 million US with a consistent annual CAGR of 12% for the years ahead as per Frost. Heartening Indeed, and the switchboards market in India has come of age in terms of designs, patents, quality and safety norms. The quintessential Indian grey market though, is still playing the spoil-sport. They gloss over all quality and safety guidelines to capture the market share and pose a serious threat to the Industry. The end-user, electrical designer and the contractor are equally held responsible both professionally and legally for the design and construction of the panel board.

The switchboard is only a fraction of the total investment on a complete panel and most often given the least care, when it comes to the design resulting in abrupt halt of operation causing huge production losses. Imagine a full-fledged production unit halted for hours to service the distribution panel!!! The safety guidelines of the operating board safeguard not only the panel but also the other related assets like transformers, wires, machines, electronics, etc. and most importantly the precious lives of operators. Hence it is extremely important that you choose the right criteria while designing the switchboard.

An eminent research expert from the field once drew an analogy of a fully built panel to the human body with switchgears & fuses analogous to the vital organs, bus-bars and other connectivity to the arteries and veins, Intelligent system to the nerves and brain and the switchboard to the skeletal and muscular systems!!! Amazing, isn’t it? No better way to highlight the significance, of a well-designed switchboard!

We have noticed a nerving conflict of interest with the end-users and Electrical design consultants on one and the contractors on the other, with quality and safety norms railed against blind cost reduction drives. Needless to say technical/safety guidelines should always be of utmost priority.

The key design and construction guide-lines:

Modularity of a panel board ensures scalability, and flexibility of design to fit well to the site conditions. An easily expandable multiple of 200mm in all three directions is ideally desired.

Switchboards have to be a fully type tested assemblies (TTA) in accordance with IEC 61439 1-2 which now supersedes the old IEC 60439-1.(Old users may as well get their panels changed to TTAs as per IEC 61439 in due course). This could be done at any independent test stations. Some of the renowned test laboratories are IPH, KEMA, etc. and they are all testing to the same rules, so a certificate from one station is not better or worse than from another!

Within EU this takes place by de-fault as all panels are to be CE marked, which also means that they have been type tested.

Arc fault safe panels – A distribution panel at work turns the inside of the panel black over a period of time. This is due to the ionized gases (atomized copper particles) from breakers and contactors during the switching cycles. This layer is highly conductive and can induce an arc. The loosening of Cable-connections and other internal parts due to constant temperature changes, which thereby melting the surrounding insulation can again induce an arc. Poor quality breakers (even new ones) could during the ‘on and offs’ emit so many gases inducing arcs. An arc is devastating and in some cases even fatal to the operators around. The damage it does to the facility, related electrical installations and the panel itself is severe. The problem can be avoided by specifying high level segregation (Form 4 a/b) and specifying arc fault containment tested panels in accordance with IEC 61641

Vibration tests and Seismic compliance as per IEC 68-3-3 are mandatory for Panels mounted near boilers, generators, machineries, engine rooms etc. which are mostly subjected to rigorous and prolonged vibrations resulting in loosening of joints causing shorts or dangerous arcs. Similar threat is also envisaged in cases of seismic effect. It is worth noting that Indian public sectors like Nuclear power corp. and the BARC has of-late made it mandatory for all suppliers to undergo seismic and vibration compliance tests for their equipment. This is a ‘post Fukushima’ precautionary step!

As part of the growing Green awareness in India especially with growing numbers of companies going for ISO 14000 compliance, RoHS (Risk of Hazardous substances) and REACH Certifications (Registration Evaluation and Certification of Chemical substances) is gaining relevance. In the EU REACH & RoHS certification is mandatory for all panels installed.

Adequate care should be taken while detailing on the test reports for strict adherence to the required configurations. Unfortunately many local manufactures in India take this ‘testing & certification’ ordeal with the only aim of getting some wider business penetration.

Withdraw-able type feeders (sometimes called fully withdraw-able type) are used where you need to do very fast changes/repairs to the system without interrupting other feeders. This is typically used where the lives of people are at stake (tunnels – metro rails) or where it involves high capital and production cost where the operation is critical and calls for maximum uptime. (Oil platforms, refineries, airports, etc.) Every additional penny you spend on this type of feeders covers the losses you might incur otherwise in the long term. A calculation, of cost per minute of your plant downtime will easily gauge you on the ROI!!

Plug in or removable units are plugged directly onto the bus bars in the panel board and can easily be changed while the panel is live. This system is used in relatively less critical operation, viz. shopping malls, hospitals, and some factories.

A Fixed type feeder means that all equipment like breakers, contactors, terminals etc. are connected by bolted cables/wires/solid copper. This system is widely used for schools, factories, gas filling stations etc. where it is OK to switch off the power to do maintenance repairs or changes.

Another important criteria is the finish. Especially in a coastal country like India, durability of switchboard is also dependent on the corrosion free finish given to the metal board. Ideally all load bearing components of the modular structure has to be pre-galvanized and powder coated.The powder coating has to be uniform at around 60-80 microns to ensure no peel-offs or cracks. This aspect is more significant for marine installations like offshore rigs, engine rooms of ships etc. to ensure prolonged durability.

IP rating: It is a common misunderstanding that the higher the IP rating the better the panel! It is much more important that your panel be able to ‘breathe’ and get rid of the heat generated inside! So the IP rating has to be decided based on the ambience, indoor /outdoor installation etc. upto IP55

Ensure that the enclosure has at least 30% expansion capacity both in terms of electrical rating and space!

Ensure that the panel has a short-circuit withstand strength equal or higher than the transformer that feeds the power! Do not buy from a manufacturer that does not have a QA system in place!

Bus-bars can be chosen between copper or aluminum! When correctly dimensioned they are equally good. Aluminum is cheaper but requires slightly more care when installing. Tinned copper should not be specified! Bare copper will become darker over the time and this is actually an advantage as a matt dark surface emits heat better than a blank surface. (about 8-11 %).Ideally a drillfree design of busbars are used to ensure minimum losses and thus reduced heat dissipation.

The right separation Form type is another aspect deciding on the safety of your panel. The four different forms of internal separation are Form 1/2/3/4 Type a / b as detailed below:

Form 1: No internal separation! Should never be considered.

Form 2a: Separation of bus bars from the functional units Terminals for external conductors not separated from bus bars. Again not to be considered.

Form 2b: Separation of bus bars from the functional units Terminals for external conductors separated from bus bars. Here again safety aspect is not addressed.

Form 3a: Separation of bus bars from the functional units and separation of all functional units from one another. Separation of the terminals for external conductors from the functional units, but not from each other Terminals for external conductors not separated from bus bars

Form 3b: Separation of bus bars from the functional units and separation of all functional units from one another. Separation of the terminals for external conductors from the functional units, but not from each other Terminals for external conductors separated from bus bars

Form 4 a: Separation of bus bars from the functional units and separation of all functional units from one another, including the terminals for external conductors which are integral parts of the functional unit. Terminals for external conductors in the same compartment as the associated functional unit

Form 4 b: Separation of bus bars from the functional units and separation of all functional units from one another, including the terminals for external conductors which are an integral part of the functional unit. Terminals for external conductors not in the same compartment as the associated functional unit, but in separate, enclosed protected spaces

N.B This type of separation Manufacturing and Electrical Platform Design 4 a/b is the right choice where safety is given the highest priority and recommended in the design of the right panel. Ionized gases emitted from equipment during switching will not spread to adjacent equipment & not even to adjacent terminals. It is possible and legally correct to work on the panel while it is live,- however do ensure that particular compartment you work on, is switched off!

In the nutshell following are the key design and construction features for right and safe Switchboard:

1. TTA in accordance with IEC 61439-1&2

2. Arc fault containment compliance in accordance with IEC 61641

3. Vibration & Seismic tests in accordance with IEC 68-3-3 standards

4. Choose the right separation type, Form 4 a/b

5. RoHS, REACH certifications, Marine certifications(DNV) etc. – Desirable

6. Corrosion free finish as per IEC standards

7. Modularity, Scalability and expandability in easy multiples of 200mm

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