Form 4 in Switchboards (Form of Separation)

INTRODUCTION

The Main & primary function of Switchgear assembly partition/separation is to protect the maintenance or installer personal from any electrical risks (i.e. Internal Arc Flashes). It must be very well verified the IP level in line with international standards IEC60529. Related to my own journey in switchboards manufacturing, I personally experienced without knowing fundamental 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 of switchboards needs experienced electricians or engineers to access the zones in resolving any issue by removing multiple-barrier 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 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 is having separate cable chambers.

FORM-4 in DETAILS

There are 7 ways for achieving 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 terminal are inside the functional unit separated from the busbar and where we use ‘b’ then it denotes terminal outside the functional units 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 figure above)

FORM-4a Type-2

Here the main Busbar is separated by a 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 figure above)

FORM-4a Type-3

In this criteria, the main Busbar is separated by a 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 figure above)

FORM-4b Type-4

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 and functional units also separated by a metallic or non-metallic rigid barrier or partition. Cable glands outside the panel and termination in the functional unit area with a boot applied on cable termination. (refer figure above)

FORM-4b Type-5

Here the main Busbar & Functional Units are separated by a metallic or non-metallic rigid barriers or partitions. Due to barriers or partitions above Busbars, terminals are separated from the busbars as well as from the functional units. Cable glands outside the panel and termination in the functional unit area with a boot applied on cable termination. (refer figure above)

FORM-4b Type-6

Here the main Busbar and Functional Units with its individual Cable Chambers (Cable Connections Boxes) are separated by a metallic or non-metallic rigid barriers or partitions. Cable glands outside the panel and termination in its Individual Connection Box. (refer figure above)

FORM-4b Type-7

This is the highest form of separation, here the main Busbar and Functional Units with its individual Cable Chambers (Cable Connections Boxes) are separated by a metallic or non-metallic rigid barriers or partitions. Cable glands are over the Individual Cable Connection Boxes inside the panels for cable termination inside it. (refer figure above)

DO’s

1. Minimum IP2x level of Ingress Protection or achieve protection of ”Finger Touch Proof” in Barriers & Partitions.
2. Epoxy/PVC Based Boots with Higher Temperature co-efficient must be used in Type 4 & 5.
3. Busbar Covering by Insulated material must be unique and with the identification of busbars.
4. Proper Gap should be there in between two cable terminations as all terminals come in one chamber in Type-4 & 5.
5. Cable Chamber Boxes design must be in accordance with Cable Sizes & Arrangement w.r.t. respective current rating.
6. Inside Cable Glanding required more space so it needs to take care of in design in Type 3 & 7.
7. Cable chamber Gland Plates must be of a Higher thickness (Min.2.5mm or more) in Type 3 & 7.
8. Gland Plates must use non-ferrous in the case of Single Core Cables.
9. Except Type 3 & 7, 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 partitions.
2. Covering over the busbar must not puncher at any level to avoid any accidents.
3. Metallic barriers should maintain minimum clearance & creepage from busbars or live part 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 & 7.
6. Boots sizes in such a way that it should cover the whole termination area.
7. Cable Chamber Sizes should not oversizes than functional units sizes.