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Use of the 3VA1 breaker as a switch disconnector

Switch disconnectors are deployed as:

Switch disconnectors are capable of switching equipment and parts of electrical installations when they are conducting their operational current under normal operating conditions.

Switch disconnectors do not have an overload or short-circuit release. For this reason, a molded case circuit breaker or a fuse must be installed upstream of every switch disconnector. Refer to chapter Upstream protection of switch disconnectors.

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Compatibility of 3VA switch disconnectors and accessories

3VA1 switch disconnectors have been developed from the 3VA1 molded case circuit breaker design. Both share the same attributes listed below:

  • Sizes

  • Dimensions

  • Mounting options

  • Procedure for installing accessories

This means that a shunt trip can trip the switch disconnectors by remote control, or that the disconnector can be opened or closed by a side wall mounted rotary operator.

Isolating features

A switch disconnector isolates individual circuits or items of equipment so that maintenance or repair work can be carried out. This is a health and safety requirement.

In compliance with IEC 60947-3, the symbol below is clearly displayed on the front panel of switch disconnectors:

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In accordance with the requirements of the standard regarding isolating function, the 3VA1 switch disconnector features:

  • the switch disconnector symbol

  • a correctly dimensioned isolating distance in the OFF position

When the switch disconnector handle is in the OFF position, the isolating distance between the main contacts is guaranteed to meet the requirements stipulated by standards pertaining to isolating features. This also applies when manual or motor operators installed on the disconnector are in the OFF position.
Only when the disconnector is in this safe position can it be locked by various methods (e.g. door mounted rotary operator, motor operator).

Making capacity

Switch disconnectors have a predefined rated making and rated breaking capacity. As a result, loads are reliably switched on and off up to the specified breaking capacity.

Features

Switch disconnectors are primarily designed to conduct uninterrupted current up to the magnitude of the permissible rated uninterrupted current Iu.

Another important feature of these devices is their rated short-circuit making capacity Icm, as this defines the capability of the switch disconnector to withstand dynamic and thermal current loads. Current loads can reach very high values when the switch disconnector makes on a short circuit. Switch disconnectors are designed to withstand these short-circuit currents without sustaining damage up to the value of their rated short-circuit making capacity.

Utilization categories for switch disconnectors

Utilization categories are differentiated according to the following criteria:

  • The relationship between operational current and rated operational current

  • The relationship between operational voltage and rated operational voltage

  • Power factor (p.f.)

  • Time constant

The utilization category is also identified by a letter:
A - for frequent operation
B - for infrequent operation, e.g. disconnectors which are used only to isolate parts of electrical installations for maintenance purposes.

It is important to note, however, that the term "frequent operation" does not mean that the switch disconnector may be used to start up, accelerate or shut down individual motors in normal operation.

For example, a switch disconnector with a rated operational current Ie of 160 A and a rated operational voltage Ue of 400 V AC may be used for frequent switching of a mixture of resistive and inductive loads including moderate overload only if it can conduct a making current I of 480 A (3 x Ie) and withstand a making voltage U of 420 V AC (1.05 x Ue) with a power factor of 0.65. This capability corresponds to utilization category AC-22A.

I

Making current

Ic

Breaking current

Ie

Rated operational current

U

Applied voltage

Ue

Rated operational voltage

Ur

Recovery voltage

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I

Making current

Ic

Breaking current

Ie

Rated operational current

U

Applied voltage

Ue

Rated operational voltage

Ur

Recovery voltage

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