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Metering Current Transformers
Low-voltage watt-hour metering current transformers with high-accuracy options, on precision toroidal ring cores.
Low Voltage Watt-Hour Metering Current Transformers
Metering current transformers scale primary current to a standard 5 A secondary so watt-hour meters can bill, interchange, and monitor without sitting on the line. Bridgeport builds 600 V window-type toroidal CTs for utilities, co-ops, and industrial service entrances — standard 500:5 and 2000:5 models, plus custom ratios, windows, and 0.15% extended-range class.
Cores are GOSS toroids, wound, annealed, and insulated in Shelton, then precision-wound with double-enameled copper and molded in thermoplastic polyester. Every unit is serial-marked, bar-coded, and individually tested to IEEE C57.13 / C57.13.6. The test report ships with the CT.
Use them at commercial and industrial service entrances, substation and interchange points, net-metering, and any transformer-rated installation where the meter is only as good as the CT in front of it.
Standard Metering CT Models
Representative models – other ratios and window sizes available to order.
600V Metering CT - 500:5
Dimensions: 3.1″ dia. window · Height 7.3″ × Width 5.5″ × Depth 3.8″.
600V Metering CT - 2000:5
Dimensions: 5.5″ dia. window · Height 10.6″ × Width 8″ × Depth 3.15″. Four mounting holes 0.28″ dia on a 6″ × 6″ pattern.
Metering CT Specifications
600 V window-type metering current transformers for revenue metering. Standard ratios below; 0.15% and 0.15S extended-range class available on every ratio. Other windows and 1 A secondaries to order.
| Ratio | Primary | Secondary | Window | Voltage | Accuracy | Rating factor | Typical use |
|---|---|---|---|---|---|---|---|
| 200:5 | 200 A | 5 A | 3.1″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–4.0 | Small C&I service |
| 400:5 | 400 A | 5 A | 3.1″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–4.0 | C&I service entrance |
| 500:5 | 500 A | 5 A | 3.1″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–4.0 | C&I / co-op metering |
| 600:5 | 600 A | 5 A | 3.1″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–4.0 | Service entrance |
| 800:5 | 800 A | 5 A | 3.1″ or 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–4.0 | Large C&I / bus |
| 1000:5 | 1000 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–3.0 | Pad-mount / large service |
| 1200:5 | 1200 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0–3.0 | Industrial / interchange |
| 1500:5 | 1500 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0 | Large industrial |
| 2000:5 | 2000 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 2.0 | Interchange / heavy service |
| 3000:5 | 3000 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 1.5–2.0 | Bus / wholesale point |
| 4000:5 | 4000 A | 5 A | 5.5″ | 600 V | 0.3 / 0.15 / 0.15S | RF 1.5–2.0 | High-current bus |
3.1″ window body: 7.3″ H × 5.5″ W × 3.8″ D. 5.5″ window body: 10.6″ H × 8″ W × 3.15″ D, 6″ × 6″ mount. Brass compression terminals, integral shorting device, clear cover. IEEE C57.13 / C57.13.6. Other ratios, 1 A secondaries, and non-standard windows to order.
Accuracy classes
| Class | Standard | Where it belongs |
|---|---|---|
| 0.3 | IEEE C57.13 | Standard utility and C&I revenue metering |
| 0.15 | IEEE C57.13.6 | High-accuracy billing, large accounts |
| 0.15S extended range | IEEE C57.13.6 | Interchange, light-load to rating factor — the spec that competes with Ritz ERCT |
Custom ratings
Need a ratio not in the table, a 1 A secondary, a different window, or 0.15S to a stated burden and rating factor? We build the CT to the meter and the bus in Shelton, Connecticut.
The Metering Current Transformer was engineered for US utilities - GOSS toroidal window, 0.15S extended-range accuracy, sealed shorting cover and serialized IEEE C57.13 test reports - built for revenue-grade metering.
0.15S extended-range accuracy
Holds IEEE C57.13.6 high-accuracy class from light load through rating factor — the spec utilities use at interchange and large-account metering.
Closed toroidal window, not a split core
A GOSS ring with no air gap gives low phase error and stable ratio. Revenue metering current transformers belong on a closed core.
Standard ratios from 200:5 to 4000:5
600 V window-type CTs in 3.1″ and 5.5″ bodies, 5 A secondary, 0.3 / 0.15 / 0.15S class. Quote the chart, not a custom drawing.
Shorting cover and sealable terminals
Finger-nut shorting device under a clear cover, optional pilfer tag — the hardware a metering cabinet actually uses.
Serialized test report from Shelton
Every metering CT is manufactured and bar-coded, serial-marked, individually tested to IEEE C57.13 / C57.13.6 in Shelton CT. The report ships with the unit.
When the Meter Is Only as Good as the CT, Don't Guess the Class
A watt-hour meter cannot sit on a 200 A to 4,000 A service. Without a metering current transformer, there is no safe way to bill that load – and a split-core monitor is not a revenue-grade CT.
A 600 V window-type metering CT solves this by putting the primary conductor through a closed GOSS toroidal window. The secondary produces a standard 5 A signal at rated primary. The ratio – 200:5 through 4000:5 – is the constant the meter uses to reconstruct true current for billing, interchange, and transformer-rated installations.
Accuracy class is the allowed ratio and phase error at defined current and burden under IEEE C57.13 and C57.13.6. A 0.15S extended-range unit holds that class from light load through rating factor. Specify ratio, window, class, and rating factor; we wind, mold, test, and ship the report with the CT.
Let's build your Current (Metering) Transformer
600 V metering current transformers – engineered and manufactured in Shelton, Connecticut. Send the ratio, window, class, and rating factor and we will quote the CT.
Frequently Asked Questions
What is a metering current transformer?
A metering current transformer is a 600 V instrument transformer that scales primary current to a standard 5 A secondary so a watt-hour meter can bill the service. Bridgeport units are window-type toroidal CTs for utility, co-op, and industrial revenue metering.
What accuracy class do I need for revenue metering?
Most North American revenue work uses IEEE C57.13 class 0.3. High-accuracy billing, wholesale interchange, and large industrial accounts use 0.15 or 0.15S under IEEE C57.13.6. Do not use a 0.5 or 1.0 monitoring CT on a revenue meter.
What is 0.15S extended-range accuracy?
0.15S holds IEEE C57.13.6 high-accuracy class from a small fraction of rated current up through the rating factor, not only at 100% load. That is the spec used at interchange points and the spec that competes with extended-range utility CTs.
What is the difference between a metering CT and a protection CT?
A metering CT is accurate at normal load and saturates early to protect the meter during a fault. A protection CT stays linear at high fault current so relays see the fault. This page is for revenue metering current transformers
What ratios and window sizes are available?
Standard 600 V ratios are 200:5, 400:5, 500:5, 600:5, 800:5, 1000:5, 1200:5, 1500:5, 2000:5, 3000:5, and 4000:5. Windows are 3.1″ on the smaller body and 5.5″ on the larger body. Other ratios, windows, and 1 A secondaries are built to order.
Are these split-core current transformers?
No. These are closed-core toroidal window CTs. Split-core units are for retrofit monitoring. Revenue metering needs a closed GOSS core for phase-angle accuracy and long-term stability.
Do you provide a test report with each metering CT?
Yes. Every unit is bar-coded, serial-marked, and individually tested to IEEE C57.13 / C57.13.6. Ratio and accuracy data are stored electronically and emailed with the shipment.
Can you match another manufacturer’s ratio and window?
Often yes. Send the ratio, window diameter, burden, accuracy class, and rating factor. We quote a Shelton-built 600 V window-type metering CT that meets the same IEEE class.
