Schneider C60H-DC Protector Practical Manual

Schneider C60H-DC Protector Practical Manual

The particularity of DC circuit protection and the positioning of C60H-DC

In the fields of industrial control, transportation (rail transit, electric vehicles), renewable energy (photovoltaics, energy storage), etc., the safe operation of DC distribution systems highly relies on reliable overload and short-circuit protection devices. Unlike AC circuits, DC current does not have a natural zero crossing point, making arc extinguishing more difficult. Therefore, higher requirements are placed on the arc extinguishing and breaking capabilities of circuit breakers. In addition, the grounding methods (equivalent to IT, TN, TT DC) and voltage levels of DC systems are widely distributed, covering from 24V control circuits to 500V photovoltaic arrays. A single specification of protective devices cannot meet all scenarios.

The Schneider Electric C60H-DC series DC supplementary protector is designed to address these challenges. It complies with UL1077, IEC60947-2, EN60947-2, and GB14048.2 multi country standards and can be used as feeder protection, motor control circuit protection, and isolation device simultaneously. This article provides a detailed analysis of the selection rules, installation points, trip characteristics, and fault protection strategies for C60H-DC from an engineering practical perspective.

Product series and selection basis

2.1 Voltage level and number of poles

C60H-DC offers two voltage level series:

12-250V DC series: rated voltage 250V DC, breaking capacity 5kA. Suitable for single pole (1P) or double pole (2P) configurations.

12~500V DC series: Rated voltage of 500V DC, with a breaking capacity of 5kA. Only available in bipolar (2P) configuration.

Each module with a width of 9mm (1P) or 18mm (2P). When selecting, the first step is to determine the nominal voltage (Un) of the system and the maximum possible short-circuit current. If the system voltage is ≤ 250V DC and the short-circuit current is ≤ 5kA, 1P or 2P can be selected; if the voltage is between 250-500V, 2P model must be used, and both poles must be connected in series in the positive and negative circuits at the same time.

2.2 Rated current level

C60H-DC provides complete current levels from 0.5A to 63A, divided into two groups:

0.5A~40A: Suitable for control circuits, electronic loads, low-power DC motors, etc. The specific specifications include 0.5, 1, 2, 3, 4, 5, 6, 10, 13, 15, 16, 20, 25, 30, 32, 40A (UL1077 list) and 50, 63A (IEC list).

50A, 63A: Suitable for higher power DC feeders or combiner boxes.

All rated currents are defined at an ambient temperature of 25 ℃. When the working environment temperature deviates from 25 ℃, adjustments must be made based on the temperature derating curve provided by the manufacturer (module 92515). The general experience is that for every 10 ℃ increase in ambient temperature, the rated current should be reduced by about 5% to 10%, and the specific value should be based on the official derating table.

2.3 Release Curve

C60H-DC only provides the C-curve, which is a thermal magnetic trip characteristic defined in IEC/EN 60947-2. The thermal trip part (overload protection) of the C-curve does not trip within 1 hour at 1.13 times the rated current, and trips within 1 hour at 1.45 times the rated current; The action range of magnetic trip (short circuit protection) is 7-10 times the rated current. The magnetic trip setting value of C60H-DC is marked as 8.5 In (± 20%), which means that the actual operating current is about 6.8-10.2 times the rated current.

The C-curve is very suitable for loads with moderate surge currents, such as small DC motors, solenoid valves, capacitive power supplies, etc. For purely resistive loads or circuits that are insensitive to transient overcurrent, the C-curve can also provide reliable overload protection.

Key rules for installation and wiring

3.1 Polarity Connection - Non Negligible Safety Points

C60H-DC is designed specifically for direct current, and its arc extinguishing system is strongly related to polarity. The polarity indicated on the front of the product must be strictly followed (usually marked with "+" and "-" next to the terminal). Reverse connection can seriously reduce the breaking capacity, which may lead to arc extinguishing failure, contact fusion welding, and even fire in the event of a short circuit fault.

For a 1P protector, the positive pole (L+) is usually connected to the terminal marked with a "+", while the negative pole (L -) can be directly connected through other means or disconnected from both poles using a 2P protector. For 2P protectors, the polarity of each pole has been clearly marked, and the positive pole must be connected to the positive pole marked, and the negative pole must be connected to the negative pole marked.

Special reminder: When two poles are connected in series for use in the US power grid (such as a 60V DC system that requires both poles to be disconnected), in order to avoid inductive interference and ensure reliable disconnection, the length of the connecting cable between the two poles should be at least 30cm (12 inches). This requirement originates from the relevant regulations of the National Electrical Code (NEC) in the United States, with the aim of ensuring that the series poles can withstand the same transient voltage distribution during a short circuit.

3.2 Power supply incoming direction

C60H-DC allows power to be supplied from either the upper or lower end, but for optimal arc extinguishing in 250-500V DC applications, it is recommended to follow the instructions in the product manual to supply power from the upper end. If it is necessary to install in the opposite direction (lower end incoming line), it should be confirmed to reduce the capacity or consult technical support. Generally speaking, it is recommended to connect the positive pole of the power supply to the upper end of the protector (marked as LINE side) and the lower end of the load (LOAD side), so that the moving contact is on the power side when disconnected, making arc extinguishing more reliable.

3.3 Isolation Function

C60H-DC meets the requirements of IEC/EN 60947-2 for isolators. When the handle is in the "OFF" position, all contacts of the poles are in the open state, and the green strip on the operating handle will be fully displayed, indicating that the circuit has been safely isolated and downstream equipment can be safely maintained. This is a visual representation of the positive break indication.

Deep interpretation of performance parameters

4.1 Breaking ability and current limiting characteristics

Icu (ultimate short-circuit breaking capacity): 5kA at 250V DC or 5kA at 500V DC. This is the maximum short-circuit current that the protector can break once, after which the equipment may fail but will not cause a fire.

Ics (service short-circuit breaking capacity): 75% of Icu (i.e. 3.75kA). After breaking at this current, the protector can still be used.

C60H-DC has a current limiting function: in the event of a short circuit fault, the contacts quickly open before the expected peak current is reached, significantly limiting the actual fault current passing through, thereby protecting downstream semiconductor devices, cable insulation, and the load itself from thermal stress and electromagnetic damage. This feature is crucial for DC powered electronic devices.

4.2 Electrical and mechanical lifespan

Mechanical lifespan: 20000 operations (under no-load or extremely low current).

Electrical lifespan:

Resistive load: 6000 times (for resistive loads such as heaters and incandescent lamps).

Inductive load (L/R=2ms): 3000 cycles. Inductive loads generate high reverse overvoltage during disconnection, accelerating contact erosion. Therefore, when used for inductive loads such as DC relays and solenoid valves, the actual switch life will be significantly reduced. If necessary, a freewheeling diode or varistor can be connected in parallel at the load end to extend the contact life.

4.3 Environmental Tolerance

Working temperature range: -25 ℃~+70 ℃

Storage temperature range: -40 ℃~+85 ℃

Relative humidity: 95% at 55 ℃ (compliant with IEC 60068-2 standard)

Pollution level: Level 3 (applicable to industrial environments, may contain non-conductive dust or occasional condensation)

Rated impulse withstand voltage (Uimp): 6kV, ensuring that the equipment does not break down when subjected to lightning strikes or overvoltage during operation.

4.4 Power loss

The power loss data of C60H-DC needs to refer to module 92517. In general, the larger the rated current, the higher the loss, and heat dissipation should be considered during dense installation. For currents above 40A, it is recommended to reserve sufficient ventilation space in the distribution box.

Selection and protection strategies under different grounding systems

The grounding method of the DC system directly affects the selection of the short-circuit current path and the number of protector poles. The C60H-DC manual categorizes systems into three types: power pole grounded (e.g. negative terminal grounded in 24V systems), center point grounded (bipolar systems, e.g. ± 110V DC midpoint grounded), and ungrounded systems (IT systems, both poles insulated from ground). There are significant differences in fault analysis and protection requirements for different situations.

5.1 System wiring types

Typical Application of Grounding Type Diagram Characteristics

Power polarity grounding negative grounding (or positive grounding) 24V control power supply, telecommunications equipment

Center Point Grounding Power Supply Center Tap Grounding Railway Signal, Some Industrial DC Busbars

Non grounded (IT): Both poles are not grounded, but there is insulation monitoring for hospitals, mines, and data centers

5.2 Pole Selection Guide

Working voltage ≤ 250V DC:

If the negative electrode is grounded and only protects the positive electrode: a 1P protector (to protect the positive electrode) can be used, with the negative electrode directly connected.

If the system requires both poles to be disconnected (such as safety isolation) or the grounding method is unclear, it is recommended to use a 2P protector and disconnect the positive and negative poles at the same time.

Working voltage 250V<Un ≤ 500V DC:

2P protectors must be used. At this point, both positive and negative poles need to be protected, and the two poles must be connected in series in the circuit. The breaking capacity is still 5kA.

5.3 Fault Types and Protection Requirements

The manual defines three typical fault modes (A, B, C) corresponding to different short-circuit current sizes and protection electrode requirements.

Fault type Fault description Short circuit current size Protection requirements

Fault A grounding fault (such as positive pole to ground short circuit) is equal to the power supply voltage divided by the impedance of the grounding circuit. In the negative grounding system, the fault current is Isc_max at U. The pole of the protective grounding electrode (usually the positive pole) must have a breaking capacity of ≥ Isc_max.

Fault B: Short circuit between poles (direct short circuit between positive and negative poles) Isc_max at U (full voltage). Both poles must be able to disconnect Isc_max at U.

Fault C dual pole simultaneous grounding requires the use of insulation monitoring instrument (PIM) alarm and manual clearing for ungrounded systems. For grounding systems, it is equivalent to fault A or B. See specific wiring analysis.

Design points:

In the negative grounding system, the short-circuit current of the positive pole to ground short circuit (fault A) is equal to the total short-circuit current of the system, and the positive pole protector must be able to disconnect this current. However, a negative pole to ground short circuit will not generate a large current (because the negative pole is directly grounded), so the negative pole usually does not need protection.

In the center point grounding system, the short-circuit current of any pole to ground short circuit is U/2, and the breaking capacity of the selected protector needs to be ≥ U/2 of the short-circuit current.

In an ungrounded system, the first grounding fault will not generate a large current (alarmed by the insulation monitoring instrument), but the second grounding (of different poles) will cause a short circuit between the poles, and the fault current is a full voltage short circuit. Therefore, ungrounded systems usually require protective devices to be installed at both poles, and the breaking capacity needs to match the full voltage short-circuit current.

Buckling Curve and Coordination Design

6.1 Time current characteristics of C-curve

The trip curve of C60H-DC (Figure 3) shows the longest trip time corresponding to different multiples of rated current in cold state:

1.05 times In: 1 hour without detachment.

1.3 times In: Release within 1 hour (hot release zone).

2-5 times In: In the hot release area, the release time varies from tens of seconds to a few seconds, exhibiting inverse time characteristics.

7-10 times In: Electromagnetic trip zone (instantaneous action), with a trip time of less than 0.1 seconds, usually 20-50ms.

In engineering practice, in order to avoid the starting surge current of the load (for example, the starting current of a DC motor can reach 6-8 times the rated current), the C-curve allows for instantaneous action of 7-10 times, providing sufficient margin. But if the duration of the surge current is long (more than 0.1 seconds), it may accidentally trigger the heating trip. At this time, it should be considered to adjust the rated current of the protector or choose a higher current level.

6.2 Selective Collaboration

In complex DC distribution systems, in order to achieve selectivity (i.e. only cutting off the faulty branch without affecting the upstream power supply), it is necessary to match the tripping characteristics of upstream and downstream protectors. Due to the fact that C60H-DC only has a C-curve, if the same model is used upstream and downstream, it may trip simultaneously when the fault current is large. The suggested cooperation method is:

When using C60H-DC with a higher rated current upstream (such as 40A upstream and 10A downstream), and the fault current is expected to not exceed 10kA, it usually has a certain degree of selectivity.

Alternatively, a DC circuit breaker with short delay function can be used upstream (such as a molded case circuit breaker for C60H-DC).

Typical Applications and Case Analysis

7.1 24V PLC control cabinet DC distribution

Scenario: A 24V DC control cabinet with a total load of approximately 15A, including PLC, relays, sensors, indicator lights, etc. Use C60H-DC 2P 16A as the main switch for the incoming line, and use 1P 2A/6A/10A to protect each circuit in the downstream branch.

Attention: It is customary to ground the negative pole in a 24V system. At this point, a 1P protector can be connected in series with the positive pole and the negative pole directly grounded. But for safety isolation (while disconnecting the positive and negative poles), it is still recommended to use a 2P main switch. The branch can use 1P to protect the positive pole.

Selection: MGN61511 (16A 2P)+MGN61501 (1A 1P)+MGN61502 (2A 1P), etc.

7.2 Photovoltaic Array DC Side Protection

Scenario: A group of photovoltaic strings with an open circuit voltage of approximately 300V DC and a maximum operating current of 12A, requiring the installation of a DC protector inside the combiner box. Due to voltage exceeding 250V, 2P C60H-DC 500V series must be used. It is recommended to choose 1.25 times the working current for the rated current, which is 16A.

Selection: MGN61531 (16A 2P 500V DC). Pay attention to polarity at the same time: connect the positive pole of the photovoltaic to the positive marked terminal of the protector, connect the negative pole to the negative marked terminal, and ensure that the wire enters from above.

7.3 DC motor forward and reverse control

Scenario: A 24V DC, rated current 8A DC motor with a starting current of approximately 50A (6 times). Will the C-curve protector 10A trip at the moment of motor start-up (approximately 0.2 seconds)? According to the C-curve, a current of 6 times (60A) is between the thermal trip zone and the electromagnetic trip zone, and the electromagnetic trip requires more than 7 times. Therefore, 60A will not cause instantaneous tripping, but the thermal trip will not operate within 0.2 seconds (because the thermal element requires integration time). Therefore, it can start normally. But if the motor starts and stops frequently (more than 6 times per minute), thermal accumulation may cause false tripping. In this case, a higher rated current (such as 13A) should be selected or the starting frequency should be reduced.

Maintenance and common problems

8.1 Daily Inspection

Regularly check whether the position of the protector handle is consistent with the external indication (OFF/ON).

Observe for discoloration or deformation of the casing (which may be caused by overload heating or arcing).

Check the conductivity of the contacts with a multimeter in the power-off state (the resistance should be less than 0.1 Ω when closed).

8.2 Temperature rise and derating

When multiple C60H-DCs are installed closely side by side, mutual heating can cause the internal temperature to rise beyond the test value of a single unit. General suggestion:

The adjacent spacing should not be less than 9mm (i.e. leaving one modulus vacancy).

When the ambient temperature exceeds 45 ℃, reduce the continuous load current according to the manufacturer's derating curve.

8.3 Post fault handling

If C60H-DC is disconnected due to a short circuit fault, check whether the equipment can still be closed and tripped normally. Due to the lack of overload indication in C60H-DC, it is not possible to visually determine whether the internal contacts have been burned. It is recommended to use continuity testing and insulation resistance testing to confirm that the protector is still intact after a short circuit fault occurs. If there are uncertain factors, they should be replaced.