A metering CT is usually sized once and then left alone for decades. The load it measures does not stay still. New connections arrive. EV chargers go in. Rooftop solar pulls midday import down to a trickle. For a utility the real question is simple. Will the CT you install today still read accurately when that load has doubled or all but disappeared?
Extended range CTs paired with the NMI approved EM133-XM answer that question at the design stage. The alternative is answering it at the next planned outage.
Key Points
An extended range CT holds its accuracy class above its nominal primary rating. One CT therefore covers a wider band of real operating current.
The EM133-XM-5A is approved under NMI certificate 14/2/72 as a class 0.5S CT operated meter with a rated current of 5 A and a maximum current of 10 A.
That 10 A maximum lets the meter accept secondary current from a 5 A CT running at up to twice its nominal rating.
Utilities can choose a lower CT ratio so everyday load sits higher in the accurate band while peaks still stay in range.
Pattern approval covers the meter and not the CT. CT class, burden and installation must still meet the rules for the site.
SATEC supplies extended range CTs alongside the EM133-XM, with interval data flowing to Expertpower for NEM12 and NEM13 reporting.
What Makes A CT Extended Range
Every metering CT has a rated primary current. A standard CT is specified to hold its accuracy class up to a modest margin above that rating. Past that point the class is no longer guaranteed.
An extended range CT carries a higher extended current rating. Common values are 150% and 200% of rated primary current. As a worked example, a 200/5 A CT with a 200% extended rating stays within its accuracy class up to 400 A of primary current. At that point it delivers 10 A on the secondary side. The rating for any specific CT is stated on its nameplate and test certificate. Always check it there.
Why The EM133-XM Is The Right Partner
A CT can only stretch as far as the meter behind it allows. That is where many extended range schemes quietly fail.
The EM133-XM-5A is approved by the National Measurement Institute under certificate 14/2/72. Its approved field of operation lists a rated current of 5A and a maximum current of 10A. The datasheet also lists a continuous overload rating of twice rated current. In plain terms, a 5A secondary pushed to 10A is still inside the meter’s approved range.
The rest of the meter suits utility work too. It measures four quadrant import and export energy. It records interval data from one to 60 minutes, including the five minute intervals used for NEM settlement. At five minute logging it holds 227 days of data in its 8 MB memory. Its starting current is 0.2% of rated current. Very small loads therefore still register.
Why Utilities Benefit
Load Growth Without A Shutdown
Changing a CT is never just a parts job. It means isolation, a crew on site, an outage window and fresh commissioning checks. On a busy feeder or a critical site that window is hard to find.
An extended range CT absorbs growth inside its rating. Electrified heating, new tenancies and EV charging can push peak current well past the original design. The CT and the EM133-XM keep reading within class while that happens.
Better Accuracy At Light Load
CT error tends to rise as current falls toward the bottom of its range. The usual defence against peak load is to oversize the CT. That pushes everyday load into the least accurate part of the band.
Extended range CTs break that trade off. You can choose a ratio closer to typical load and rely on the extended rating to cover peaks. This matters most on sites with solar, where net import can fall close to zero in the middle of the day.
Fewer Ratios On The Shelf
Utilities and metering providers carry spares for fault replacement. Every extra ratio adds stock, storage and the risk of the wrong CT on the truck. A wider accurate band means one ratio can cover work that might otherwise need two or three. Replacements get faster and inventory gets simpler.
Cleaner Data For Billing And Reporting
Accurate measurement is only useful if the data arrives intact. The EM133-XM stores interval profiles locally and can push data to the cloud over Ethernet, WiFi or modem. NEM12 and NEM13 files are available through Expertpower. Import and export are recorded separately, which suits sites with solar or batteries.
Our View
We think headroom should be a default line in every utility CT specification. Standard CTs made sense when load profiles were flat and predictable.
That is no longer the grid most utilities are running. Specifying an extended rating costs little at design and saves an outage later.
Standard CT Versus Extended Range CT
| Attribute | Standard 5 A CT With EM133-XM-5A | Extended Range 5 A CT With EM133-XM-5A |
|---|---|---|
| Accuracy class held to | Typically 120% of rated primary current | The CT’s extended rating, commonly 150% or 200% |
| Secondary current at top of accurate band | About 6 A | Up to 10 A at a 200% rating |
| Within the meter’s 10 A approved maximum | Yes | Yes, up to a 200% rating |
| How the ratio is chosen | Sized for peak load so everyday load sits low in the band | Sized nearer everyday load with peaks still covered |
| Light load accuracy | Weaker when the CT is oversized | Stronger because the ratio sits closer to typical load |
| Response to load growth | CT replacement once peaks leave the band | Growth absorbed within the extended rating |
| CT ratios held in stock | More ratios to cover the same load range | Fewer ratios cover a wider load range |
What To Check Before You Specify
Start with the CT nameplate. Confirm the accuracy class and the extended current rating. Then confirm the total burden of the CT circuit, including the secondary leads, sits within the CT’s rated burden. The EM133-XM itself draws less than 0.2 VA per phase on its 5 A input.
Next, make sure the CT ratio is programmed into the meter so recorded energy reflects the primary circuit. For trade use the meter must also be verified under the National Instrument Test Procedures before it bills anyone.
Finally, remember that NMI approval is legal metrology. Market metering at a NEM connection point carries further obligations under the National Electricity Rules, AEMO procedures and network requirements.
How SATEC Can Help
SATEC supplies extended range CTs and the NMI approved EM133-XM as a matched pair. Our team sizes the ratio and extended rating against your real load profile rather than a guess at peak. EM133-XM meters can be ordered with NITP 14 verification.
From there, interval data can flow into Expertpower, which is hosted on Australian Microsoft Azure infrastructure. Behind it all sits more than 50 years of energy measurement engineering.
Planning a CT replacement programme or a new metering standard? Talk to the SATEC team. Send us the single line diagram, the load profile and your existing CT schedule. We will recommend the ratio and extended rating that fit. We will also tell you where a standard CT is still the better choice.
FAQs - Check Metering in Multi-Tenant Buildings
Can I use an extended range CT with the EM133-XM?
Yes. The EM133-XM-5A accepts a standard 5 A secondary. An extended range CT with a 5 A secondary is therefore electrically compatible. Choose an extended rating that keeps secondary current within the meter’s 10 A maximum.
Does NMI approval of the EM133-XM cover the CT?
No. Certificate 14/2/72 approves the meter pattern and its variants, not an external CT. CT selection and installation fall under the rules that apply to the metering installation.
Will an extended range CT improve accuracy at low load?
It can. It lets you choose a lower ratio so typical load sits higher in the CT’s accurate band. The gain depends on matching the ratio to the real load profile.
Is the EM133-XM suitable for sites with solar or batteries?
Yes. It measures four quadrant import and export energy and records interval data down to five minutes. With an extended range CT, both high export and low import periods stay within a well chosen accurate band.
