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Complete Guide to Forms 1–4 in Electrical Switchgear (Ireland’s IS EN 61439 Explained)

  • Writer: MTS DNC ENERGY CONSULTANTS LIMITED
    MTS DNC ENERGY CONSULTANTS LIMITED
  • Nov 16
  • 4 min read

Electrical switchgear is one of the most important safety elements in any building. Whether it’s a home, an office, or a pharmaceutical plant, switchboards protect people, equipment, and the entire electrical system from faults, fire hazards, and unexpected shutdowns.

In Ireland, all switchboards must comply with IS EN 61439 — the Irish version of the European standard. This standard defines “Forms of Internal Separation,” from Form 1 to Form 4B, which determine how safely a switchboard is arranged inside.

This guide explains all Forms in detail, with simple examples, diagrams, and Irish-specific applications.


What Are “Forms of Separation”?


Inside a switchboard, there are three main internal components:

• Busbars – the main copper bars that distribute power

• Functional units – breakers, contactors, switches

• Terminals – where outgoing cables connect


Forms of Separation define how these parts are physically separated for:

• Improving safety

• Reducing risk of arc flash

• Allowing maintenance while keeping the rest energized

• Preventing touching live parts

• Minimizing the chance of faults spreading between compartments


The higher the Form number, the more internal segregation exists.

Ireland follows these exactly:

IS EN 61439 (Ireland) = EN 61439 (EU) = IEC 61439 (International)


Form 1 – No Internal Separation


This is the simplest type. Everything is inside one open chamber.

What it means:

• Busbars, breakers, terminals — all visible together

• If you open the panel, live parts are exposed

• If one part is being worked on, the entire board must be switched off


Where it’s used in Ireland:

• Small shops

• Small industrial

• Temporary boards

• Simple distribution panels

• Old legacy panels


Why it’s acceptable here:

• Low fault current

• Simple loads

• Easy replacements

• Lowest cost


Form 2 – Busbars Are Separated


Form 2 introduces the first level of safety.

What it means:

• Busbars are enclosed inside their own metal or insulated compartment

• Breakers and terminals are in another compartment

• Reduces risk of accidental contact with busbars

• Still requires the whole board to be shut down for maintenance


Form 2A: terminals are not separated

Form 2B: terminals are also separated from busbars


Where used in Ireland:

• Offices

• Retail units

• Schools

• Car showrooms

• Small industrial workshops


Why used:

• Improved safety at low cost

• Reduced risk of faults jumping to busbars



Form 3 – Each Functional Unit Is Separated


This is a major jump in safety.

What it means:

• Breakers are separated from each other by metal partitions

• A fault in one breaker cannot spread to another

• Maintenance becomes safer:

  • You can isolate one functional unit

  • Other circuits can stay energized


Form 3A: terminals are grouped together

Form 3B: terminals are separated with the breaker (more common)


Where used in Ireland:

• Modern commercial buildings

• Light industrial

• Universities

• Hotels

• Medium-sized distribution boards in factories


Why chosen:

• Much safer during maintenance

• Higher fault protection

• Better for buildings with mixed loads



Form 4 – Maximum Separation (Highest Safety Standard)


This is the most advanced and safest design.

What it means:

• Busbars are fully segregated

• Every breaker has its own metal-enclosed compartment

• Every set of outgoing terminals is also separated

• Work can be done on a circuit while:

  • The busbars stay live

  • Other circuits stay live

    • Minimizes the spread of arc flash

    • Prevents foreign objects (tools, dust, screws) from causing faults


Subtypes:

Form 4A – terminals are separated but may be in the same compartment as other terminals

Form 4B – the breaker AND its terminals are fully enclosed together

(Form 4B is used by nearly all pharma & data-centre projects)


Where used in Ireland:

• Pharmaceutical facilities

• Cleanrooms (high GMP)

• Data centres

• Hospitals

• Large manufacturing plants

• Mission-critical buildings


Why used:

• Maximum uptime — circuits can be serviced without shutting down the whole board

• Highest safety

• Meets strict client requirements (e.g. Pharma Clients)

• Reduces arc flash risk



Why Forms Matter


Think of Forms of Separation like the difference between:

• A toolbox where all tools are thrown together (Form 1)vs

• A toolbox where every tool has its own padded slot (Form 4B)


Yes, the board costs more — but downtime in pharma or data centres costs millions, so it’s worth it.


Final Summary


Form 1 → Basic

Form 2 → Busbar separated

Form 3 → Functional units separated

Form 4 → Maximum separation (pharma, data centres)


Choosing the right Form depends on:

• Safety level

• Type of building

• Maintenance requirements

• Fault levels

• Client standards


Forms 1–4 are all about safety, reliability, and uptime.


At Nexus M&E Design, we provide mechanical and electrical design services — including motor selection, starter configuration, and control panel integration — tailored to your project’s specific requirements.

👉 Contact us today to discuss your next project.


Disclaimer: The content shared in these posts is intended for informational purposes only and should not be interpreted as design advice, specifications, or a calculation template. For professional guidance or design services, please contact us through our contact form.


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