Legrand 409799 DX3 4-Pole 50 A C-Curve MCB 25 kA

409799: Legrand DX3 4-pole 50 A C-curve MCB, 25 kA, at a glance

The Legrand 409799 is a DX3 four-pole thermal-magnetic circuit breaker rated 50 A with a C curve and a 25 kA breaking capacity at 400 V AC. It is built on the DX3 platform that uses 1.5 modules (26.7 mm) per pole, which gives larger terminals and more thermal mass than the one-module range. All four poles are protected, the neutral is switched together with the phases and the device has a mechanical red and green position indicator. Seven Star LLC supplies 409799 in Oman and the GCC as an independent supplier in Muscat.

The data sheet for the 25 kA family describes the device as a current-limiting, trip-free breaker with positive contact indication for control, protection and isolation. It is suited to industrial and commercial boards where a high fault level is present at 400 V.

Decoding the description of 409799

Technical specifications for 409799

How the 409799 limits fault energy

The breaker has a current-limiting contact system. On a short circuit the contacts open fast enough to cut the peak of the fault current, which reduces the stress on cables and busbars downstream. At 400 V the Icu is 25 kA and the service breaking capacity Ics is 75 % of that value, so the breaker remains usable after clearing a fault up to about 18.75 kA at 400 V. At 230 V the Icu rises to 50 kA, a figure that matters for single-pole faults to earth in TN systems.

For overload, the thermal release does not operate up to 1.05 times the rated current and operates within the conventional time at 1.3 times. The same family can also be used on direct current when the derating notes are followed; the data sheet lists a 25 kA Icu for four poles in series at 230 V DC, but direct-current duty needs the data-sheet derating table and should be confirmed before use.

Where 409799 fits and related parts

Typical use is as a feeder or motor-circuit protective device inside a main distribution board or motor control centre. The 4-pole 25 kA DX3 range runs through rated currents of 32, 40, 50 and 63 A in B and C curves, with D curve versions from 16 A. The 100 A sibling 409802 keeps the same body width but is covered by its own page data, and for smaller 4-pole breakers the one-module versions such as 407929 or 409071 save space. Auxiliaries, RCD add-on blocks and a terminal accessory for aluminium cable (4 063 10) are listed by the manufacturer for the DX3 range.

Selection checklist for 409799

• Load: 50 A at the reference ambient; allow for the cabinet temperature.
• Fault level: the board must stay below 25 kA at 400 V for this breaker, or use a higher rated device.
• Curve: C for general feeders; B for long cable lengths with low fault current; D for high inrush loads.
• Terminal capacity: 1.5 to 35 mm² flexible or 1.5 to 50 mm² rigid copper.
• Coordination: check selectivity and back-up tables with the upstream breaker.
• Space: six modules wide; check that the neighbours leave room for the 1.5-module poles.

Installation, locking and maintenance of 409799

Fit the breaker on the rail and tighten the terminal screws to 3 Nm using a Pozidriv no. 2 or 5.5 mm flat screwdriver. Strip conductors to 17 mm, and remember that the terminals are 19 mm deep. The handle can be sealed in either position and locked off with a 5 mm padlock using the Legrand lock-out accessory, which is useful for permit-to-work procedures. After energising, check terminal temperature during the first load cycle and record 409799 in the circuit list.

Typical applications in Oman and the GCC

A 50 A four-pole breaker with 25 kA capacity is a good match for pump-house boards, workshop supplies, desalination skid distribution and building services boards where the transformer is close to the board and fault levels are high. In dusty and hot sites, keep the enclosure closed, use filtered ventilation and avoid mounting the breaker directly above heat-producing equipment.

Information to send with an RFQ for 409799

• Reference 409799 and the quantity, including spares for panel maintenance.
• Curve (B, C or D), rated current and number of poles.
• Prospective short-circuit current and supply system (TN, TT or IT).
• Accessories needed, such as auxiliary contacts, RCD blocks or lock-out devices.
• Delivery location (Muscat, Sohar, Salalah or elsewhere in the GCC) and the date you need the goods.
• Any documents you need with the quotation, such as a technical data sheet or a compliance statement.

Documents and quotation

The Legrand technical data sheet that covers 409799 is attached on this page. It gives the range table, dimensions, curves and accessories, so check its notes against your design before you order.

To request a quotation, send reference 409799, the quantity and your delivery location. Seven Star LLC is an independent supplier in Muscat and is not affiliated with the manufacturer; we will confirm availability and lead time for your order.