Legrand 407929 DX3 6000 A 4-Pole 20 A C-Curve MCB

407929: Legrand DX3 6000 A / 10 kA 4-pole 20 A C-curve MCB explained

The Legrand 407929 is a four-pole DX3 miniature circuit breaker rated 20 A with a C curve, a household breaking capacity of 6000 A under IEC/EN 60898-1 and 10 kA under IEC 60947-2 at 400 V. It is one of the compact one-module-per-pole breakers, so four poles occupy 70.8 mm of rail. The catalogue describes protection of wiring installations against overload and short circuit with energy limitation class 3. Seven Star LLC supplies 407929 in Oman and the GCC as an independent supplier in Muscat.

What the markings on 407929 tell you

Technical specifications for 407929

How the 407929 trips

For IEC/EN 60898-1 the breaker does not trip at 1.13 times the rated current and trips within the conventional time at 1.45 times, referred to a 30 °C reference temperature. Under IEC/EN 60947-2 the data sheet quotes 1.05 and 1.3 times at 50 °C. The magnetic release of a C curve operates between 5 and 10 times In, so a 20 A device clears a short circuit that exceeds 100 to 200 A. The data sheet gives the instantaneous trip as 7 In with a tolerance of 20 % for the IEC 60947-2 test.

The energy-limiting design cuts the peak current and the let-through energy of a fault, which helps protect downstream cable, contactors and thermal relays. Two DIN clamps, one on top and one at the bottom, allow a single breaker to be removed from a row without taking out the busbar.

Where 407929 fits among DX3 breakers

Choose 407929 for three-phase final circuits such as HVAC units, small motors, water heaters, compressors and sub-panel feeds. In the same one-module range, the catalogue lists ratings from 1 to 63 A in B and C curves and 0.5 to 63 A in D curve, in one, two, three and four poles. For higher fault levels the 25 kA family, for example 409799, is wider but stronger, and for a 10 kA household class with higher Icu, 409071 offers a 63 A B-curve alternative. Auxiliary contacts, shunt trips and RCD add-on blocks from the DX3 range can be mounted next to the breaker.

Selection checklist for 407929

• Load current: 20 A at the reference temperature; apply derating for hot cabinets.
• Fault level: stay within 10 kA at 400 V; 6 kA is the certified household rating.
• Inrush: a C curve tolerates moderate inrush; use D for transformers or heavy motor starting.
• Conductor: 1.5 to 25 mm² flexible or 1.5 to 35 mm² rigid.
• Busbar: confirm the prong or fork busbar pitch and the supply side.
• Neutral: four poles switch the neutral; confirm the board scheme requires it.

Installation and maintenance of 407929

Clip the breaker onto the rail, insert the busbar if one is used, and tighten the terminals to about 2.5 Nm with a Pozidriv no. 2 screwdriver. Strip conductors to 11 mm. Write the circuit name on the label so the identity of the load is visible, and keep the cover plate fitted so the IP20 finger-safe rating applies. Exercise the handle at each shutdown and record 407929 in the board schedule. A breaker that has tripped on a short circuit should be inspected, and replaced if it shows heat damage.

Typical applications in Oman and the GCC

Final circuits for air-conditioning units, pumps, kitchen equipment and small process skids are common uses. In the Gulf climate, board temperatures can be high and heat reduces the thermal margin, so avoid fully loaded rows and leave spare space. Dust and humidity make a closed enclosure with filtered ventilation advisable.

Information to send with an RFQ for 407929

• Reference 407929 and the quantity, including spares for panel maintenance.
• Rated current (20 A), curve (C) and number of poles.
• Fault level at the board and whether a higher Icu is needed.
• Busbar type and accessories such as auxiliary contacts.
• 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.

Storage, handling and spares for the Legrand 407929

Keep Legrand 407929 units in their original packaging until they are mounted. Store them indoors in a dry, dust-free room, away from direct sun and condensation. Panel shops in Oman and the GCC often hold stock in warehouses that get very hot in summer, so check that storage temperature stays within the limits given in the manufacturer datasheet.

• Check the label and order code on every unit against the drawing before it goes into the panel.
• Use the correct tool and tightening torque for the terminals, as given in the instructions supplied with the product.
• Keep a small number of spare units for each rating used on site, so that a failed or damaged part can be replaced without waiting for a new shipment.
• Record the order code in the panel documentation and the as-built drawings, so that maintenance teams can reorder the same part later.

When you plan spares for a project, group the Legrand 407929 with the other parts of the same panel in one RFQ. This keeps delivery dates aligned and makes it easier to confirm stock for the whole bill of materials at once.

Documents and quotation

The Legrand technical data sheet that covers 407929 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 407929, 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.