UL 891 Low-Voltage Switchboard Manufacturer
Custom low-voltage switchboards for North American projects. 400A–6000A bus ratings, up to 600V, MCCB and ACB configurations, NEMA 1/3R enclosures, and SCCR documentation included.
Custom UL 891 Switchboards
RICHES POWERTECH is a UL 891 switchboard manufacturer serving U.S. electrical contractors, EPC firms, and industrial facilities. We design and build custom low-voltage switchboards for power distribution in commercial, industrial, solar, data center, and agricultural applications across North America.
Our switchboard range covers 400A through 6000A bus ratings, with system voltages from 208Y/120V to 600V AC, three-phase. Every unit is engineered to NEC Article 408 and manufactured in accordance with the UL 891 standard. We handle the full process — from single-line diagram review and SCCR calculation to factory acceptance testing and ocean freight delivery.
If you are specifying switchboards for a North American project, send us your SLD or BOM. Our engineering team will respond within 24 hours with a technical review and quotation.
Electrical Ratings
| Parameter | Specification |
|---|---|
| Standard | UL 891 (Low-Voltage Power Circuit Breaker Switchboards) |
| Voltage | 208Y/120V, 480Y/277V, 480V, up to 600V AC |
| Frequency | 60 Hz |
| Phase | 3-phase, 3-wire or 4-wire |
| Bus Rating | 400A – 6000A (copper or aluminum) |
| SCCR | 65kA / 100kA / 200kA interrupting capacity |
| Main Device | UL 489 MCCB or UL 1066 ACB |
| Enclosure | NEMA 1 / NEMA 3R |
| Internal Separation | Form 1, Form 2, Form 3, Form 4b |
| Bus Material | Electroplated copper or tin-plated aluminum |
Main Breaker Configurations
We supply UL 891 switchboards with the following main device configurations:
Molded Case Circuit Breakers (MCCB)
UL 489 listed molded case breakers in frame sizes from 400A to 6000A. Available in thermal-magnetic or electronic trip units. Interrupting ratings up to 200kA at 480V.
Air Circuit Breakers (ACB)
UL 1066 listed power circuit breakers for applications requiring higher continuous current ratings and adjustable long-time, short-time, and instantaneous trip settings. Typical frame sizes: 800A–6000A.
Main-Tie-Main (MTM)
Dual main breaker configuration with a normally-open tie breaker between two bus sections. Used in service entrance applications where two utility feeds supply a single facility. Tie breaker includes mechanical interlocking to prevent parallel operation of sources.
Main Lug Only (MLO)
Switchboard sections without a main disconnect, fed from an upstream device. Common in distribution boards where the upstream switchboard or transformer secondary provides overcurrent protection.
Distribution Breakers
Each switchboard section contains distribution breakers sized per the project load schedule. We supply:
- UL 489 circuit breakers, bolt-on or plug-in type
- Frame sizes from 15A to 6000A
- Thermal-magnetic or electronic trip units
- Shunt trip coils for remote tripping
- Auxiliary contacts for status indication
- Ground fault protection where required by NEC 230.95
All distribution breakers are coordinated with the main device and upstream protective devices. We provide time-current coordination curves as part of the submittal package when requested.
NEMA Enclosures
NEMA 1 — Indoor
Standard indoor enclosure for switchboards installed in electrical rooms or mechanical spaces. Constructed from 11-gauge (3.0mm) cold-rolled steel with a removable front and rear cover. Finished with ANSI 61 gray powder coat.
NEMA 3R — Outdoor
Outdoor-rated enclosure with rainproof construction, drip shields, and conduit hubs. Suitable for switchboards installed in uncovered exterior locations. Same 11-gauge steel construction with additional gasketing at cover joints.
Both enclosure types support top-entry and bottom-entry cable connections. We provide conduit entry templates based on the project's cable schedule.
Service Entrance Applications
UL 891 switchboards are commonly used as service entrance equipment per NEC Article 230. When specified for service entrance duty, we configure the switchboard with:
- 100% rated main breakers (continuous duty at 100% of frame rating)
- Equipment ground bus and neutral bus sized per NEC 250
- Service entrance rating marking on the enclosure
- Main bonding jumper factory-installed where required
- Ground fault sensor and relay for 480Y/277V systems where NEC 230.95 applies
SCCR and Short-Circuit Requirements
NEC 408.36 requires that every switchboard be marked with a Short-Circuit Current Rating (SCCR). The SCCR must equal or exceed the available fault current at the point of installation.
We provide a detailed SCCR calculation report with every UL 891 switchboard. This report:
- Identifies the available fault current at the line terminals
- Calculates the SCCR of each section based on the specific breaker types and bus configurations
- Verifies that the marked SCCR meets or exceeds the project requirement
- Documents the upstream protective device assumptions
Our standard SCCR ratings are 65kA, 100kA, and 200kA interrupting capacity. For applications requiring supplemental short-circuit protection, we use listed supplemental protectors or current-limiting devices as part of the SCCR calculation.
Switchboard Construction
Bus System
Electroplated copper or tin-plated aluminum bus bars with flame-retardant PVC or Nomex insulation. Bolted pressure connections ensure low-resistance joints. Phase identification by color-coded insulation per NEC 210.5.
Enclosure
11-gauge steel, welded frame construction. Removable front and rear covers for access to bus bars and breakers. Lifting lugs and leveling bolts included.
Instrumentation
Digital multimeters (DMM) for voltage and current monitoring, analog or digital ammeters and voltmeters, control power transformers (CPT), and potential transformers (PT) where specified.
Safety Features
Mechanical door interlocks, padlocking provisions on main breakers, arc-flash mitigation options including arc-resistant designs, and insulated barriers over live parts. Dead-front construction per NEC 408.38.
Engineering Process
Our engineering workflow for every UL 891 switchboard project:
SLD Review
We review your single-line diagram and identify any technical questions or clarifications needed.
BOM Review
We cross-check the bill of materials against the SLD to confirm breaker types, sizes, and accessories.
Submittal Drawings
We produce GA (general arrangement) drawings showing dimensions, device layout, and cable entry locations for your approval.
SCCR Calculation
We calculate the SCCR for each section and prepare the documentation package.
Production
After submittal approval, we release the switchboard for fabrication.
Factory Acceptance Test
100% testing before shipment. Test reports included in the documentation package.
We have supported North American projects since 2008. Our engineering team is experienced with NEC, IEEE, and NEMA standards, and communicates directly with your project team in English.
Testing and Quality Control
Every UL 891 switchboard undergoes a complete factory acceptance test (FAT) before shipment. Our testing includes:
Test reports are included in the shipment documentation package. All testing is performed in-house as part of our quality control process.
Applications
Service Entrance
Main utility disconnect for industrial plants, warehouses, and commercial facilities.
Power Distribution
Feeder sections supplying downstream panelboards, MCCs, and transformers.
Data Centers
High-reliability switchboards with 2N redundancy and selective coordination.
Solar Farms
AC interconnection switchboards for utility-scale PV systems.
Generator Paralleling
Generator output switchboards and transfer switch sections.
Commercial Buildings
Main distribution switchboards for office complexes, hospitals, and educational facilities.
Frequently Asked Questions
What is the difference between a UL 891 switchboard and a UL 508A control panel?▾
What SCCR ratings do you offer?▾
Can you review our single-line diagram before we place an order?▾
What voltage configurations do you support?▾
Do you provide NEMA 3R outdoor switchboards?▾
What is the typical lead time?▾
Request a Quote
Send us your project requirements. Our engineering team will review your SLD or BOM and respond within 24 hours with a technical review and quotation.
Upload Your Documents
Send your single-line diagram (SLD) or bill of materials (BOM) for a free engineering review and quotation.