Quick Facts
Nominal Rating
400 A
Ratio
400A/0.333V
Output
333 mV full scale
Accuracy
0.5% typical
Core / Window
Split core, 1.3 x 1.7 in
Warranty
10 years
Functional Devices CT-400A4-333 Split-Core Current Transformer
The Functional Devices CT-400A4-333 is an enclosed, self-powered split-core current transformer rated 400 A with a 400A/0.333V ratio and a 333 mV full-scale output. The hinged core opens to clamp around an existing conductor through a 1.3 x 1.7 in window, and the 18 AWG, 600 V rated 6-foot leads land directly on the CT inputs of the RIB BACnet power meter family or any other meter that accepts Listed 333 mV current transformers.
Accuracy is 0.5% typical with 10%-120% linearity, on circuits up to 600 Vac at 40-400 Hz, indoors. Polarity is White-Hi, Black-Low, and the RIB power meters correct automatically for CTs installed in reverse. These CTs are designed and made in the USA with global materials and carry the Functional Devices 10-year warranty.
Specifications verified against the Functional Devices CTA4 Series datasheet (rev. 2025.08.01) and Current Transformers family guide C2777D (rev. 2026.03.25).
Best For
- Power metering on 400 a circuits feeding the RIBPM413-BC meter family
- Retrofit sub-metering where the load conductor cannot be disconnected
- Tenant billing, cost allocation, and measurement-and-verification points
- Panel-level energy monitoring on BACnet building automation systems
Every Functional Devices RIB product, including the CT-400A4-333, is backed by the company's 10-year warranty — confidence and peace of mind in every box.
ZOT Supply is an authorized Functional Devices distributor. Every CT-400A4-333 ships as genuine, factory-warranted product with full manufacturer support.
Key Features
Tool-Free Split-Core Installation
The hinged split core snaps around an existing conductor — no need to disconnect and re-terminate the load wire. Window size is 1.3 x 1.7 in, sized for the conductor gauges typical at this rating.
333 mV Full-Scale Output
Outputs a 400A/0.333V signal on 6-foot, 18 AWG, 600 V rated leads — the safe, low-voltage standard accepted directly by the RIB BACnet power meter family and other 333 mV input meters.
0.5% Typical Accuracy
Rated 0.5% accuracy with 10%-120% linearity across a 40-400 Hz frequency range, on circuits up to 600 Vac.
Self-Powered Measurement
Like the meters it feeds, the CT needs no external power — the millivolt output is induced by the load current itself.
ETL Listed
ETL Listed with CE and RoHS marks, satisfying the Listed-CT requirement in RIB power meter Bulletin B2646.
Designed and Made in USA
Functional Devices designs and builds these CTs in the USA with global materials, backed by the company's 10-year warranty.
Technical Specifications
| Functional Devices CT-400A4-333 Specifications | |
|---|---|
| Selection | |
| Nominal Rating | 400 A AC, 50/60 Hz |
| Ratio | 400A/0.333V |
| Core Type | Split core |
| Window Size | 1.3 x 1.7 in |
| Electrical | |
| Secondary Output | 0.333 Vac full scale |
| Accuracy | 0.5% (typical) |
| Linearity | 10%-120% |
| Frequency Range | 40-400 Hz |
| Max Sense Voltage | 600 Vac |
| Polarity | White-Hi, Black-Low |
| Mechanical and Environment | |
| Lead Wires | 6 ft, 18 AWG, 600 V rated |
| Environment | Indoor use only; 5 to 176 °F (-15 to 80 °C); 90% RH |
| Approvals | |
| Approvals | ETL Listed, CE, RoHS |
Documentation
Specifications cutsheet, rev. 2025.08.01
C2777D — full split-core, solid-core, Rogowski, and MOD-series lineup
Related Products
Open-board BACnet MS/TP power meter
Prewired kit with disconnect and fuses
Meter in NEMA 1 housing with NPT hub
Pairs With These RIB Power Meters
Every 333 mV output on this page terminates directly on the CT inputs of the RIB BACnet power meter family.
Other Split-Core Sizes
The split-core family covers 5 A through 400 A nominal ratings, all with 333 mV full-scale output.
Frequently Asked Questions
Which power meters does this CT work with?
Any power meter that accepts Listed 333 mV current transformers. Bulletin B2646 for the RIB power meter family states the meters work with all UL or ETL Listed 333 mV CTs, so this model terminates directly on the CT inputs of the RIBPM413-BC, RIBPM413-BC-KIT, and RIBTPM413-BC. After installation, set the meter's CT-Ratings object (AV-8005) to the CT's rating.
How do I orient and wire the CT?
Polarity is White-Hi, Black-Low on the two 6-foot, 600 V rated lead wires. Twist the pair from each CT and land them on the meter's pluggable CT terminal. Reversed CTs are corrected automatically by the RIB power meter family per Bulletin B2646.
Can I use this CT on a circuit larger than its rating?
Size the CT so the metered load falls within its linear range — this model is rated 400 A nominal with 10%-120% linearity. For larger circuits, step up within the split-core family (5 A through 400 A) or move to the ROPE Rogowski coils for 4,000 A and above.
What does the 600 Vac max sense voltage mean?
It is the maximum voltage rating of the conductor the CT may be installed around. This model is rated for circuits up to 600 Vac and is for indoor use only.
Can I install it outdoors?
No. The datasheet rates it for indoor use only, 5 to 176 deg F (-15 to 80 deg C) at up to 90% relative humidity.
- Current Rating:
- 400A
- CT Style:
- Split-Core
- Revenue Grade:
- Yes
- Output Signal:
- 333 mV
- Ratio:
- 400A/0.333V
- Accuracy:
- 0.5%
- Window Size:
- 1.3 x 1.7 in
- Wire Leads:
- 6 ft
- Max Sense Voltage:
- 600 Vac
