Form 4 (4a) in Switchboards (Form of Separation)

The Main and primary function of Switchgear assembly partition/separation is to protect the maintenance or installer personnel from any electrical risks (i.e. Internal Arc Flashes). It must be very well verified the IP level is in line with international standards IEC60529. Related to my own journey in switchboard manufacturing, I personally experienced that without knowing the fundamentals of Ingress Protection, it’s very difficult to achieve From of Separation in Switchgear Assembly.

ABOUT SELECTION OF FORM-4

The higher the form of separation level leads to more barrier and partition implant in switchboards but it again leads to poor ventilation, block airflow, and cover more space in the switchboard. At a higher level of separation restrict the maintenance area in switchboards and tracking of fault becomes more stringent to a quick resolution.

Form-4 level switchboards need experienced electricians or engineers to access the zones in resolve any issue by removing multiple barriers or partitions.

In many applications, I personally experienced that Form-3b will perform better for ease of maintenance or accessibility of functional units, busbars, and cable chambers. Form-4 is highly recommended due to its property of an inherently safe switchboard.

Selection of Form-4 is very critical in many areas or applications where mass transportation or use in severe applications i.e. METRO, Shopping Malls, Gas Stations, Airports, Hospitals, etc. Although maintenance at this level is very stringent but very safe to do activities Functional unit-wise which has separate cable chambers.

FORM-4 in DETAILS

There are 7 ways to achieve Form-4 in switchboards by implanting barriers and partitions according to the design in two categories 4a & 4b. These barriers can be metallic or non-metallic area-wise w.r.t. the live part protection.

For the requirement to comply with Form-4 by any of 7 methods & these are totally specified by the customer/user and the manufacturer’s mutual agreement w.r.t. IEC standards:-

(Whereas we will use?‘a’?then it denotes the terminal are inside the functional unit separated from the busbar)

FORM-4a Type-1

Here the main Busbar is separated by the insulation applied on it e.g. PVC sleeving, wrapping, or coating. Due to covering over Busbars, terminals are separated from the busbars but inside the functional units. (Refer to the figure above)

FORM-4a Type-2

Here the main Busbar is separated by metallic or non-metallic rigid barriers or partitions. Due to barriers or partitions above Busbars, terminals are separated from the busbars but inside the functional units. Cable glands outside the panel and termination in the functional unit area. (Refer to the figure above)

FORM-4a Type-3

In this criteria, the main Busbar is separated by metallic or non-metallic rigid barriers or partitions. Due to barriers or partitions above Busbars, terminals are separated from the busbars but inside the functional units. Cable glands and termination inside the functional unit area. (Refer to the figure above)

DO’s

1. Minimum IP2x level of Ingress Protection or achieve protection of ”Finger Touch Proof” in Barriers & Partitions.
2. Busbar Covering by Insulated material must be unique and with the identification of busbars.
3. Cable Chamber box design must be in accordance with Cable Sizes and arrangement w.r.t. respective current rating.
4. Inside Cable Glanding requires more space so it needs to be taken care of in design in Type 3.
5. Cable chamber Gland Plates must be of a Higher thickness (Min.2.5mm or more) in Type 3.
6. Gland Plates must be non-ferrous in the case of Single Core Cables.
7. Except for Type 3, Cable Chamber cover plates for cable entry must be cross-cut in between cable runs entry.

DON’Ts

1. Do not forget to achieve IP2x Level as well as protection of “Finger Touch Proof” in each and every partition.
2. Covering over the busbar must not punch at any level to avoid any?accidents.
3. Metallic barriers should maintain minimum clearance and creepage from busbars or live parts w.r.t. IEC Standards.
4. Avoid direct termination over Switchgear, to avoid building stress and connection feasibility.
5. Don’t under-design the Cable Chambers in Type 3.
6. Boots are sized in such a way that they should cover the whole termination area.
7. Cable Chamber Sizes should not be oversized than functional unit sizes.