Answer first: selecting medium voltage RMU or C-GIS switchgear starts with four parameters: system voltage class, continuous current, short-circuit duty, and the switching function the project actually needs. A 38kV RMU and a 38kV C-GIS unit may share a voltage label, but they serve different duties. The RMU is a compact ring-network switching unit rated 600 A in the FP-RMU-38 series. The 38kV C-GIS is a high-current gas-insulated cubicle switchgear rated 2500 A to 4000 A in the FP-C-GIS series. The optional C-GIS monitoring package covers gas density and conductor temperature.

In the electric machinery and equipment category, medium voltage switchgear is often specified by a single-line diagram, a short-circuit study, and a site layout. Those documents turn a general product category into a real selection problem. This guide explains how to read RMU and C-GIS parameters, how 27kV and 38kV metal-clad switchgear fit the same project, and where optional C-GIS online monitoring adds useful condition data without adding unverified specifications.

Problem Definition: Same Voltage Class, Different Switching Duty

The main selection error is treating all 38kV equipment as interchangeable. A medium voltage RMU Switchgear is built around ring-network switching, load-break switching, earthing, and compact installation. The FP-RMU-38 is rated 38kV, 600A, with a 25kA short-time withstand current for 4 seconds, a 52kAp peak withstand, and an SF6 gas tank rated at 0.04MPa relative pressure at 20°C. Its gas tank protection is IP67, while the outer enclosure is IP4X with NEMA 1/2/3R options.

The 38kV C-GIS Switchgear is a different duty class. The FP-C-GIS is rated 38kV and 60Hz, with a rated current of 2500A to 4000A, a 40kA short-time withstand current for 4 seconds, a 100kA peak withstand current, 150kV lightning impulse withstand, and 80kV power-frequency withstand. It uses an SF6/N2 gas mixture and an IP6X enclosure. The C-GIS is intended for high-current buses, main incoming feeders, and large substations where current density and space both matter.

For a buyer, the question is therefore not simply which unit has a higher rating. The question is which unit matches the switching architecture, fault level, load profile, enclosure environment, and monitoring requirement. A medium voltage switchgear manufacturer should be able to show those parameters in a clear datasheet and explain where each product family applies.

Industry Background: 27kV, 38kV, and the UL Framework

North American medium voltage distribution often uses 27kV and 38kV equipment classes. The 27kV Metal-Clad Switchgear FP-MCS 2H AR is rated 27kV and 60Hz, with 1200/2000A rated current and a 2H AR rating up to 2500A. Its power-frequency withstand is 60kV, lightning impulse withstand is 125kV, short-time withstand current is 31.5/40kA for 2 seconds, and the cabinet width is 36 inches. The 38kV Metal-Clad Switchgear FP-MCS 2H and FP-MCS 1H are rated 38kV and 60Hz, with 1200/2000/3000A rated current, 80kV power-frequency withstand, 150kV lightning impulse withstand, 31.5/40kA short-time withstand current for 2 seconds, 82/104kAp peak withstand, and a 42-inch cabinet width.

These metal-clad units are different from gas-insulated cubicle switchgear. The portfolio also lists 15kV Gas Insulated Switchgear GIS and 38kV Gas Insulated Switchgear GIS, while the FP-C-GIS is the 38kV C-GIS unit. For projects that require a UL-listed medium voltage line, the UL Listed Medium Voltage Switchgear FP-MVSG-38 covers 5kV to 38kV, 1200A to 4000A, 31.5/40kA short-time withstand for 2 seconds, 82/104kAp peak withstand, 36kV to 80kV power-frequency withstand, 95kV to 150kV lightning impulse withstand, and cites UL 347 and ANSI/IEEE C37.20.2.

Low-voltage standards are a separate layer. UL 1558 covers metal-enclosed low-voltage power circuit breaker switchgear assemblies, with a nominal AC voltage scope of not more than 1,000 volts in the cited description. UL 891 covers switchboards. UL 845 covers motor control centers. UL 67 covers panelboards. UL 508A covers industrial control panels. Those standards are relevant to adjacent data center low voltage switchgear, UL switchboards, MCC, panelboards, and control panels, but they do not replace the medium voltage selection parameters for an RMU or C-GIS unit.

Detailed Solution: Matching RMU and C-GIS Parameters to the Project

The practical solution is to build a parameter matrix before comparing product names. Each row should be checked against the project single-line diagram, short-circuit study, site plan, and operating requirement. The matrix below uses only the published parameters for the FP-RMU-38, FP-C-GIS, 27kV metal-clad, and 38kV metal-clad units.

1. Voltage Class and Frequency

Start with the system voltage and frequency. The RMU and 38kV C-GIS are both 38kV class units. The RMU is rated 50/60Hz, while the C-GIS is rated 60Hz. The 27kV metal-clad unit is 27kV and 60Hz. The 38kV metal-clad unit is 38kV and 60Hz. A 27kV project should not be specified with a 38kV frame simply because the higher class exists; the insulation level, clearances, and cabinet width change with the class. A 38kV project should use the 38kV insulation coordinates, including 80kV power-frequency withstand and 150kV lightning impulse withstand for the RMU, C-GIS, and 38kV metal-clad line.

2. Continuous Current and Load Profile

Current rating separates the product families more sharply than voltage. The FP-RMU-38 is rated 600A. The 27kV metal-clad unit is rated 1200/2000A, with a 2H AR rating up to 2500A. The 38kV metal-clad unit is rated 1200/2000/3000A. The FP-C-GIS is rated 2500A to 4000A. A compact ring-network point may only need 600A switching, while a main incoming feeder or a high-capacity substation bus may need 2500A to 4000A. The continuous current choice should reflect the calculated load, the allowed operating margin, and the expected load profile, not only the present maximum demand.

3. Short-Circuit and Internal Arc Duty

Short-circuit ratings must be read with their duration. The RMU is rated 25kA for 4 seconds, with a 52kAp peak and a 52kA peak short-circuit making current. The C-GIS is rated 40kA for 4 seconds, with a 100kA peak. The 27kV and 38kV metal-clad units are rated 31.5/40kA for 2 seconds, with 82/104kAp peak withstand. The 27kV and 38kV metal-clad datasheets also state a 0.5-second internal arc rating of 40kA. These values should be compared with the project fault study, protection clearing time, and the specified arc-resistant requirement. A higher current rating does not automatically mean a better fit if the fault level and clearing time do not require it.

4. Insulation, Gas, and Enclosure

The RMU uses SF6 insulation. Its minimum SF6 gas pressure at 20°C is 0.02MPa relative, and its rated SF6 gas pressure at 20°C is 0.04MPa relative. The gas tank is IP67, while the outer enclosure is IP4X with NEMA 1/2/3R options. The C-GIS uses an SF6/N2 gas mixture and an IP6X enclosure. The 27kV and 38kV metal-clad units use epoxy resin insulation and vacuum interruption, with NEMA 1/2 enclosure protection. These differences affect installation environment, maintenance access, gas monitoring needs, and the interface with the building or enclosure.

5. Monitoring Parameters on 38kV C-GIS

The 38kV C-GIS Switchgear offers optional online monitoring for gas density and conductor temperature. Those two parameters are useful because they track the insulation medium condition and the thermal condition of current-carrying parts during operation. The published C-GIS data does not define additional sensor types, alarm thresholds, communication protocols, or predictive algorithms. A specification should therefore state exactly which monitoring points are required and how the signals will be used by the protection and control system. For an RMU, the published datasheet provides gas pressure values but does not list the same optional online monitoring package; buyers should not assume that C-GIS monitoring is automatically included on an RMU.

6. Dimensions, Access, and Documentation

The 27kV metal-clad unit is 36 inches wide. The 38kV metal-clad unit is 42 inches wide. The C-GIS maintains a compact footprint despite its high current rating, but the published data does not state a cabinet width. The RMU is designed for constrained spaces and ring-network layouts, but the published data does not state a width either. For room planning, the project team should request the approved general arrangement drawing, cable entry arrangement, front and rear access requirements, and the factory test plan. The manufacturer should also confirm the applicable standard for the exact product, because the UL Listed Medium Voltage Switchgear line and the RMU or C-GIS line are not the same product family.

Comparison Table: RMU vs C-GIS vs 27kV and 38kV Metal-Clad

The separate UL Listed Medium Voltage Switchgear line, FP-MVSG-38, covers 5kV to 38kV and 1200A to 4000A, with 31.5/40kA short-time withstand for 2 seconds. Its cited standards are UL 347 and ANSI/IEEE C37.20.2. That line should be checked separately when a project requires a UL-listed medium voltage switchgear package.

Step-by-Step Breakdown: A Selection Workflow

1. Confirm the system voltage and frequency. Use the project single-line diagram to establish whether the system is 27kV or 38kV and whether the frequency is 50Hz or 60Hz. The FP-RMU-38 accepts 50/60Hz, while the FP-C-GIS and metal-clad units in this comparison are rated 60Hz.
2. Calculate continuous current and future margin. Match the calculated load to 600A for the RMU, 1200/2000A or 2500A with 2H AR for the 27kV metal-clad unit, 1200/2000/3000A for the 38kV metal-clad unit, or 2500A to 4000A for the C-GIS. Do not use the highest current rating as a default.
3. Compare short-circuit duty with protection clearing time. Check 25kA for 4 seconds on the RMU, 31.5/40kA for 2 seconds on the metal-clad units, and 40kA for 4 seconds on the C-GIS. Confirm the peak withstand and, where specified, the internal arc rating.
4. Select the switching architecture. Use an RMU for ring-network distribution, load-break switching, earthing, and compact installation. Use a C-GIS for high-current main feeders and high-capacity substations. Use 27kV or 38kV metal-clad switchgear when the project needs a drawout circuit breaker lineup with the corresponding voltage class.
5. Define insulation, gas, and enclosure requirements. Verify SF6 or SF6/N2 insulation, gas pressure values, IP rating, NEMA rating, cable entry, and indoor or outdoor installation. The RMU gas tank is IP67, while the outer enclosure is IP4X. The C-GIS enclosure is IP6X.
6. Decide whether C-GIS online monitoring is required. If the project needs condition data for gas density and conductor temperature, specify the optional C-GIS monitoring package. Do not add sensor types or alarm thresholds that are not in the approved datasheet.
7. Check dimensions and access. Use the 36-inch width for the 27kV metal-clad unit and 42 inches for the 38kV metal-clad unit. For the RMU and C-GIS, request the approved general arrangement drawing before finalizing the electrical room layout.
8. Verify standards, tests, and delivery inputs. Confirm the exact standard for the selected product, the factory test plan, the required documentation, the MOQ, and the lead time. The published commercial terms state an MOQ of 1 unit and a typical lead time of 6 to 12 weeks, subject to product specifications and order quantity.

Use Cases: Where RMU and C-GIS Fit

The FP-RMU-38 is intended for urban ring-network distribution, residential complexes, commercial parks, street lighting systems, small industrial users, and prefabricated substation integration. Its compact fully sealed design and ring-network architecture support constrained spaces and supply reliability. In the Uzbekistan substation application recorded in the corpus, the FP-RMU-38 is used in power system projects with dust-resistance requirements. The 27kV FP-MCS 2H AR is also used in Uzbekistan substation applications under outdoor installation conditions with large ambient temperature variations, and the 38kV FP-MCS operates in 24/7 mode.

The 38kV C-GIS is intended for high-capacity substations, data center main incoming feeders, large industrial primary substations, renewable energy collection stations, and urban trunk distribution substations. Its 2500A to 4000A current rating and 40kA for 4 seconds short-time withstand make it a high-current option rather than a small ring-network substitute. For data center medium voltage switchgear projects, the C-GIS main incoming feeder duty and the 38kV metal-clad primary MV feeder duty should be evaluated against the same fault study and redundancy plan.

The 27kV Metal-Clad Switchgear fits regional district distribution substations, medium-scale industrial parks, renewable energy collection and step-up stations, large commercial complex primary distribution, municipal infrastructure, and medium-capacity mining facilities. The 38kV Metal-Clad Switchgear fits bulk power distribution substations, regional transmission nodes, large heavy industrial complexes, utility-scale wind and solar step-up substations, high-capacity urban distribution networks, large data center primary MV feeders, and heavy mining power systems. Both units use vacuum interruption and epoxy resin insulation, with NEMA 1/2 enclosure protection.

FAQ

What standards should I verify on a 38kV C-GIS or medium voltage RMU datasheet?

For the UL Listed Medium Voltage Switchgear line, the cited standards are UL 347 and ANSI/IEEE C37.20.2. The FP-RMU-38 datasheet gives 38kV, 80kV power-frequency withstand, 150kV lightning impulse withstand, and 25kA for 4 seconds. The FP-C-GIS datasheet gives 38kV, 40kA for 4 seconds, 100kA peak, 150kV lightning impulse withstand, and 80kV power-frequency withstand. Confirm that the cited standard applies to the exact product configuration, not only to the general product family.

What does optional online monitoring on 38kV C-GIS cover?

The optional C-GIS online monitoring package covers gas density and conductor temperature. The published product data does not list additional sensor types, alarm thresholds, communication protocols, or predictive functions. If those functions are needed, they should be defined separately in the project specification and confirmed against the approved C-GIS configuration.

How do I choose between 27kV and 38kV metal-clad switchgear?

Use the system voltage as the first filter. The 27kV metal-clad unit is rated 27kV and 60Hz, with 60kV power-frequency withstand, 125kV lightning impulse withstand, 31.5/40kA short-time withstand for 2 seconds, a 40kA for 0.5 seconds internal arc rating, and a 36-inch width. The 38kV metal-clad unit is rated 38kV and 60Hz, with 80kV power-frequency withstand, 150kV lightning impulse withstand, 31.5/40kA short-time withstand for 2 seconds, a 40kA for 0.5 seconds internal arc rating, and a 42-inch width. Match the voltage class and insulation level to the project, then compare current and fault duty.

For a Chinese 15kV UL Listed medium-voltage switchgear inquiry for data center projects, what should be checked first?

Check the exact UL listing scope and the project single-line diagram before the country label. In the Jiangsu Dinghong Power Co., Ltd. portfolio, 15kV Metal-Clad Switchgear is listed as a product, and the UL Listed Medium Voltage Switchgear line covers 5kV to 38kV with UL 347 and ANSI/IEEE C37.20.2 cited. For data center medium voltage switchgear, the 38kV C-GIS is listed for main incoming feeders and the 38kV metal-clad unit for large data center primary MV feeders. Confirm that the exact 15kV arrangement, short-circuit rating, and UL listing match the project.

What are the MOQ and lead time for a project configuration?

The published commercial terms state an MOQ of 1 unit and a typical lead time of 6 to 12 weeks, subject to product specifications and order quantity. A final schedule should be confirmed after the voltage class, current rating, short-circuit rating, enclosure, monitoring options, and documentation requirements are fixed. For a configuration review or quotation, the brochure and contact route are available through www.firstpowerglobal.com.

Conclusion

Medium voltage RMU and C-GIS switchgear should be selected by duty, not by a single voltage label. The FP-RMU-38 is a 38kV, 600A ring-network unit with 25kA for 4 seconds, SF6 insulation, IP67 gas tank protection, and a compact sealed design. The FP-C-GIS is a 38kV, 2500A to 4000A high-current C-GIS unit with 40kA for 4 seconds, 100kA peak, SF6/N2 insulation, IP6X protection, and optional online monitoring for gas density and conductor temperature. The 27kV and 38kV metal-clad lines provide drawout circuit breaker solutions with 36-inch and 42-inch widths, 31.5/40kA for 2 seconds, and 40kA for 0.5 seconds internal arc ratings.

Jiangsu Dinghong Power Co., Ltd. lists these medium voltage switchgear families alongside a UL Listed Medium Voltage Switchgear line, LV switchgear and switchboard ranges, and a broader electric machinery and equipment portfolio for projects that combine medium voltage switchgear and transformer scope. The selection sequence remains the same: establish voltage and frequency, calculate current and fault duty, choose the switching architecture, confirm insulation and enclosure, decide on C-GIS monitoring, and verify standards and delivery inputs.

Next step: review the product brochure for configuration details, or send the project single-line diagram, voltage class, current rating, short-time withstand current, enclosure requirement, and monitoring requirement for a quotation review. Brochure: download the English switchgear catalog. Website: www.firstpowerglobal.com.