Design

A 3NP1 fuse switch disconnector comprises a handle into which the fuses are inserted and the base with the contacts for fuses and terminals.

When the handle is closed, the blades of the LV HRC fuses are forced into the contacts and close the circuit.

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Suitable fuses

The 3NP1 fuse switch disconnector is suitable for all fuses with LV HRC design in sizes 000 to 3 which comply with IEC 60269-2.

This standard describes the technical constraints on fuses for the protection of cables and motor feeders, including the maximum permitted power loss of the fuses.

Conventional fuse switching devices are designed in accordance with the maximum values permitted according to this fuse standard with respect to possible heat dissipation.

Fuses for semiconductor protection (SIEMENS trade name SITOR) must disconnect much faster than standard fuses to protect the semiconductor load as reliably as possible and by virtue of their design have power loss values that in some cases significantly exceed the limit values permitted in IEC 60269-2.

To permit simple installation, not only are many application-specific special designs available but also very many fuses for semiconductor protection in the standard-compliant designs, such as the LV HRC design. If a fuse of this kind is used in a conventional fuse switching device for standard-compliant fuses for semiconductor protection, the maximum permissible fuse power loss defined by the switching device must be complied with. If the rated power loss of the fuse for semiconductor protection is above that permitted by the switching device, the fuse can only be operated in the partial load range, i.e. the load current must be reduced until the actual power loss is within the limit values defined by the switching device. The fuse manufacturer provides the data required for this (power loss as a function of the load current). If the maximum power losses of the fuse defined by the switching device are not complied with, the switching device may overheat or, in the worst case, even cause a fire in the switchgear.

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Power losses depending on the operational current for SIEMENS fuses for semiconductor protection

For use of SIEMENS fuses for semiconductor protection (SITOR) in 3NP1, the possible load values are available for each possible combination of a fuse and circuit breaker type (see chapter Derating values of 3NP1 fuse switch disconnectors when using SITOR fuses)

Fuses from third-party manufacturers can also be used, in which case the possible load values must be determined based on the technical data of the fuse.

Replacing the fuses

Fuse links can reach very high temperatures on melting. Removing them manually immediately after melting is almost impossible. The 3NP1 fuse switch disconnector offers contact-free removal of tripped fuses, thus minimizing downtimes after a trip. By operating the release shaft and tilting sideways, the fuse links drop out contactlessly.

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Removing the fuses

Number of poles

3NP1 fuse switch disconnectors are available in 1, 3 and 4-pole device versions.

Preassembled 4-pole types in commonly used versions (without fuse monitoring, N pole on the right) are available from the factory ready for installation.

The connection kits can be used to fabricate 2-pole types and application-specific 4-pole versions (e.g. N pole on the left, with fuse monitoring).

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Assembly kit for mechanical connection of two 3NP1 devices, size NH00

Switching instant of N pole in 4-pole 3NP1 devices

4-pole 3NP1 devices are used in 3-phase AC networks with a switched neutral conductor. They are supplied without an isolating blade for the N pole.

The switching instant is selected by the installed isolating blade:

  • Simultaneous switching – the N pole switches at the same time as the main contacts

  • Leading switching – the N pole switches early when the circuit breaker closes (switch-on) and late when it opens (switch-off)

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Isolating blade for leading switching of the neutral conductor
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Possible switching instants of the neutral conductor

Types of mounting

Floor mounting

All sizes of the 3NP1 fuse switch disconnectors are available in floor mounting versions.

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Floor mounting method

Mounting on a standard mounting rail

Sizes 000, 00 and 1 can also be snapped onto a standard mounting rail (TH35 according to EN 60715) using an accessory.

Whereas size 000 is mounted on a standard mounting rail, sizes 00 und 1 are mounted on two standard mounting rails with a spacing of 125 or 150 mm.

The spacing of the standard mounting rails can be freely selected when installing the standard mounting rail assembly kit.

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Mounting on a standard mounting rail

Mounting on busbar systems

3NP1 fuse switch disconnectors are available for mounting on Siemens and Rittal busbar systems with 60 mm (all sizes) or 40 mm spacing (sizes 000 to 00). The difference between the versions for the various busbar systems lies in the reach-around protection which is specially adapted to the system in order to provide optimum touch protection.

In the case of 4-pole devices, the infeed for the fourth pole is supplied via a bar and terminal (included in the scope of supply) from the neutral conductor bar located above the 3 phases.

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Mounting on Siemens 8US 4-pole busbar

All devices for mounting on the busbar are supplied from the factory with the cable feeder at the bottom. The 3-pole versions can be converted to cable feeder at the top. As all 3 phases are converted in a single sequence, the possibility of installation errors (e.g. one phase not converted) is almost totally excluded.

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Conversion of cable feeder in devices for busbar mounting

1 and 2-pole busbar mounting

1-pole 3NP1 devices for wall mounting in sizes 000 and 00 can be adapted to the 8US 60 mm busbar system using the assembly kit for busbar mounting.

The modular design of the mounting hooks for the busbar makes it possible to freely select whether the infeed for the 3NP1 comes from L1, L2 or L3.

If two 1-pole 3NP1 devices with busbar adapters are combined using the connecting kit, 2-pole disconnectors for busbar mounting can also be fabricated.

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1/2-pole busbar mounting
Red lines: Current flow

The table below shows which version of the 3NP1 fuse switch disconnector can be mounted on busbars:

Size

000

00

1

2

3

Number of poles

1/2

3

4

1/2

3

4

1/2

3

4

1/2

3

4

1/2

3

4

Mounting on 40 mm busbar system

--

--

--

--

--

--

--

--

--

--

--

--

--

Mounting on 60 mm busbar system

--

--

--

Cable feeder at the bottom

Cable feeder at the top

--

--

--

--

--

--

--

--

--

--

Electrical connection

The 3NP1 fuse switch disconnectors feature various connection options. Versions with box terminals and flat terminals are available. Further terminal types can be retrofitted as accessories so that the device can be flexibly adapted to suit any application.

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Overview of connection technology

Box terminals

All sizes of the 3NP1 device are available with box terminals, which are designed to allow the speedy connection of stripped conductors.

Flat terminals

Sizes 00 to 3 are available with flat terminals for the connection of cable lugs or busbar systems.

Saddle terminals

Saddle terminals can be mounted on 3NP1 devices with flat terminals – these allow the connection of stripped circular conductors (without cable lug) or of rectangular conductors (copper bars or Flexibars) without a drill hole.

Prism terminals

Prism terminals are available in versions for the connection of one or two stripped circular conductors. They can be retrofitted on 3NP1 devices with flat terminals.

Prism terminals were specially developed for the connection of aluminum conductors. Copper conductors can also be used however.

Three-tier terminals

Three-tier terminals are available in versions for mounting on 3NP1 devices with flat terminals or box terminals in sizes 000 and 00. They make it possible to branch to three smaller feeders directly at the 3NP1 outgoing feeder.

Feeder terminals

The feeder terminal is required for 3NP1 devices in size 000 if these are to be operated with load currents above 100 A (max. permissible 160 A). It expands the connection to the cross-sections required for this purpose.

Connection module

The connection module is used for devices in size 00 for busbar mounting. A masking plate can be mounted at the 32 mm or 70 mm level in the case of devices in size 00 for busbar mounting. The output terminals of the 3NP1 are located above the 32 mm masking plate level – the connection module moves the connection level to below the 32 mm masking plate level.

Auxiliary conductor connections

The auxiliary conductor connections are connected in the output terminals of the 3NP1 together with the main conductor.

They allow smaller loads in the control cabinet to be directly supplied using commercially available flat tab sleeves 6.4 x 0.8 mm.

Three-phase busbar

The 3-phase busbar is used for the infeed-side bridge connection of several 3NP1 devices for floor mounting in size 000.

Busbars are available for the connection of 2, 3 or 4 3NP1 devices. A connection bar can be used to connect two blocks of this kind. The infeed is supplied via the feeder terminals.

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Three-phase busbar

Terminal covers

Terminal covers are fitted on all 3NP1 devices at the factory. However, if long, non-insulated cable lugs are used which project outside these covers, these covers can also be extended using the terminal covers that are available as accessories.

The terminal covers are also available with optional rear reach-around protection so that a high degree of protection is also provided in switchboards where access from the rear is possible.

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Terminal covers

Fuse monitoring

Fuse monitoring is used to detect, indicate and report faults. All the commonly used 3NP1 versions are available with factory-fitted fuse monitoring. This can also be easily retrofitted by replacing the fuse carrier if required.

Various fuse monitoring versions are available for the 3NP1 fuse switch disconnectors. These can be selected according to application-specific requirements.

All versions are equipped with floating contacts for remote signaling. With all fuse monitoring devices, the physical principle for the detection of tripped fuses is based on voltage measurement upstream and downstream of the fuse. The voltage drop across the fuse is just a few volts due to the low internal resistance of the fuse. If the fuse trips, the full line voltage is applied. Fuse monitoring picks off the voltage at the grip lugs of the fuse – fuses with insulated grip lugs cannot be used for this reason.

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Fuse monitoring versions

MFM – electromechanical fuse monitoring

MFM monitors fuses by means of an installed SIRIUS circuit breaker

External power supply

Not required (self-powered)

Output

1 NO contact + 1 NC contact

Local indication

Toggle switch position

Versions

3-pole for

  • Max. 690 V AC

  • Max. 440 V DC

EFM10/15 – electronic fuse monitoring

The EFM10 and EFM15 monitor fuses by means of an evaluation electronics circuit. Unlike the EFM10, the EFM15 is not self-powered. It requires infeed from a 24 V DC supply.

The absence of the built-in power supply unit makes it a cost-optimized alternative to the EFM10.

External power supply

EFM10: Not required

EFM15: 24 V DC

Output

EFM10: 1 CO contact

EFM15: 1 NO contact

Local indication

Indication via LEDs for each phase

EFM10 versions

3-pole for 230 ... 690 V AC

EFM15 versions

1-pole for 110 ... 690 V AC

1-pole for 24 ... 240 V AC / 24 ... 250 V DC

1-pole for 120 ... 440 V DC

3-pole for 190 ... 690 V AC

3-pole for 220 ... 440 V DC

EFM20/25 – electronic fuse monitoring with line monitoring

The EFM20 and EFM25 monitor fuses by means of an evaluation electronics circuit (EFM20 – version for AC / EFM25 – version for DC). In addition to fuse tripping, they can also detect line faults, such as a phase failure (EFM20 only) and overvoltage/undervoltage.

The limit values for overvoltage/undervoltage can be set.

External power supply

Not required (self-powered)

Output

2 CO contacts:

1 CO contact for fuse tripping, 1 CO contact for line fault

Local indication

Indication via display for each phase

EFM20 versions

3-pole for 230 ... 690 V AC

EFM25 versions

3-pole for 220 ... 440 V DC

Auxiliary switch

Auxiliary switches allow remote interrogation of the contact position of the 3NP1 fuse switch disconnector. Up to two auxiliary switches can be installed in each 3NP1.

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Auxiliary switches for remote interrogation of the contact position of the 3NP1

Switching instants of auxiliary switches

With size 00 and larger, the switching instants of the auxiliary switches can be selected during installation – simultaneously with the main circuit or lagging switch-on/leading switch-off.

One of the possible functions of leading auxiliary switches is to disconnect the circuit with the assistance of a higher-level switching device, such as a circuit breaker, before the main contacts of the 3NP1 fuse switch disconnector open.

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Switching instants of auxiliary switches

Locking and sealing

The 3NP1 fuse switch disconnectors can be sealed and locked with padlocks in order to prevent unauthorized access or operation.

The sealing function is integrated in all versions. The locking function can be retrofitted in 3-pole switch disconnectors as an accessory (the locking function is already included in 1-pole 3NP1 disconnectors).

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Locking and sealing of 3NP1

Protection against power theft

A frequently occurring requirement for fuse switch disconnectors in infrastructure applications is protection against power theft. This is provided when no unauthorized access to the live parts of a locked or sealed device is possible without causing visible damage to the switch disconnector.

This function can be retrofitted with 3NP1 fuse switch disconnectors – the holes for voltage testing in the front window are closed off and the window itself is protected against disassembly.

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Protection against power theft

Box terminals

Flat terminals

Feeder terminals

Three-tier terminals

Saddle terminals

Auxiliary conductor connections

Prism terminals

Connection module