Retrofit electrical upgrades tend to start with a simple goal: “we just need better visibility”. They quickly collide with the realities of existing switchboards. Space is tight. Cable routes are crowded. Main incoming conductors are difficult or risky to disturb. Outages are expensive. Compliance requirements are non-negotiable. Retrofitting and upgrading in heritage buildings create a whole new set of challenges.
In that environment, current transformer metering becomes one of the most practical ways to add accurate energy measurement without rebuilding the board from scratch. This post breaks down why retrofit sites so often hit space and access roadblocks. We’ll also cover the key design choices that make the difference between a smooth upgrade and a painful one.
Finally, we’ll look at how SATEC’s metering and software can be used as a purpose-built solution for retrofit projects.
Why Retrofits Are Different (And Harder)
New builds are designed with energy metering in mind. They include clearances, spare DIN rails, dedicated compartments and planned cable routes. Retrofits inherit whatever decisions were made years ago. These were often under older standards and with far fewer loads. Over time, boards accumulate additions: extra breakers, communications gear, control wiring and “temporary” fixes that become permanent.
The most common retrofit constraints look like this:
Space constraints: Little or no spare DIN rail. Shallow enclosures. Crowded wiring ducts. Limited room for new devices.
Access constraints: Live conductors that can’t easily be isolated. Restricted working space. Awkward panel layouts. Tenants who can’t tolerate long shutdowns.
Risk constraints: Disturbing main conductors can introduce safety risks. It may require longer outages or create re-termination issues that cascade into rework.
Documentation gaps: Uncertain cable IDs. Unclear single-line diagrams. Incomplete labelling that makes “simple” work slow and error-prone.
In short, retrofits are rarely a blank canvas. The energy metering approach has to adapt to the board, not the other way around.
What Current Transformer Metering Actually Is
In conventional “direct-connected” metering, the meter measures current by having the load current pass through the meter itself. That can be straightforward at low currents. However, it often becomes impractical in retrofit environments where conductors are large, inflexible or hard to reroute.
Split current transformer metering separates the measurement from the primary conductor. A current transformer (CT) clips around (or is installed around) the conductor. It produces a smaller, proportional secondary current (commonly 1 A or 5 A) that the meter can safely measure. The primary conductor remains in place.
The meter sits where space allows, often on DIN rail in a nearby compartment. That separation is the core retrofit advantage. You can measure high currents without physically routing those currents through the meter.
How Current Transformer Metering Solves Space and Access Issues
Less Disruption to Primary Conductors
Retrofits often fail at the moment someone realises the mains need to be cut, bent, extended and re-terminated to fit a direct-connected meter. Split core CTs reduce that disruption.
Many retrofit designs can be executed with minimal conductor movement. Sometimes this can be done with split-core CTs that open and close around existing cables.
Smaller Metering Footprint Where It Matters
When the board is full, every millimetre counts. CT-based meters can be installed in whatever “real estate” is available. This might be on a small DIN rail section, in a metering compartment or even in an adjacent enclosure. Meanwhile, CTs sit at the conductors themselves.
Shorter Outages and Easier Staging
A staged approach is often possible. Install the meter, communications and wiring routes first. Then plan the CT installation during a short outage window.
That’s a big deal in occupied buildings, healthcare facilities, retail and industrial sites where downtime is expensive.
Improved Safety and Maintainability
Measuring current indirectly reduces the need to work on high-current connections for the meter installation. Maintenance also becomes easier.
Meters can be serviced without disturbing main conductors. CT circuits can be designed with test links and shorting arrangements for safe handling.
Design Choices That Make or Break a CT Retrofit
Retrofit success depends on more than “put CTs on the cables”. A few technical decisions have an outsized impact.
CT Type: Solid-Core vs Split-Core
Solid-core CTs are robust and often preferred for accuracy. However, they require the conductor to be threaded through the CT, usually meaning disconnection.
Split-core CTs open and close around existing conductors. This is extremely helpful in space and outage constrained boards. The right choice depends on site access, outage windows and accuracy requirements.
CT Ratio Selection
CT ratio determines how the primary current maps to the meter’s input. Oversizing the ratio can reduce resolution at normal operating loads. Undersizing risks saturation at peaks.
A good ratio matches the typical operating range whilst allowing for realistic maximum currents.
Accuracy Class and Burden
Accuracy class (and the total burden of the CT circuit) matters when billing, compliance or performance reporting is involved. Long secondary cable runs, poor terminations or adding devices into the CT loop can push burden up and accuracy down.
Keeping CT wiring neat, short and correctly sized is a practical accuracy win.
Installation Discipline for Polarity and Phasing
CT polarity and phase mapping errors are common in retrofits, especially when labelling is incomplete. When CTs are reversed or phases are mixed, data becomes misleading fast. Power factor looks wrong. kW can go negative. Alarms trigger unnecessarily.
A proper commissioning process verifies phase rotation and CT orientation before anyone relies on the data.
Planning for Comms and Data Outcomes
Meters don’t create value until the data is used. Retrofits should consider where communications will run, how data will be collected and what decisions it will drive. This might include tenant billing, load profiling, demand management, power quality investigation or compliance reporting.
Where Current Transformer Metering Fits Best in Retrofit Projects
CT-based approaches are particularly effective in:
- Commercial office upgrades where boards are full and outage windows are short
- Strata and mixed-use buildings needing tenant or tenancy-level visibility
- Industrial sites with high currents and limited appetite for conductor disturbance
- Healthcare and critical facilities where shutdowns must be tightly controlled
- Retail and hospitality where trading hours constrain access
The pattern is consistent. The more the site resists being “rebuilt”, the more current transformer metering earns its place.
How SATEC's Products Are the Energy Metering Solution
Retrofit teams need energy metering hardware and current transformers that respect the realities of existing switchboards. This includes compact form factors, flexible CT compatibility, dependable communications and data that can be turned into action.
SATEC’s energy metering solutions are designed to support CT-based deployments where space and access are limited. With NMI approved metering options, advanced measurement capability and strong power monitoring features, SATEC meters can be deployed in retrofit environments. They deliver accurate energy data without demanding major board rework.
For sites where power quality matters (nuisance trips, harmonics, voltage issues or unexplained equipment faults), SATEC’s strength in power quality monitoring helps move the conversation. It shifts from “what happened?” to “what do we do next?”
On the software side, Expertpower can be used to bring retrofit data together for reporting, analysis and operational visibility. That matters when you want the upgrade to do more than produce numbers.
The combination of CT-friendly metering and a practical software layer supports outcomes like:
- Validating savings
- Spotting abnormal consumption early
- Improving load management
- Building evidence for targeted electrical remediation
For retrofit projects, that “meter plus insight” pairing is often the difference between a metering install that gets ignored and one that actively supports better decisions.
A Practical Approach to Getting CT Retrofits Right
The best retrofit outcomes usually come from a straightforward sequence.
- Confirm goals (billing, visibility, power quality, compliance).
- Survey board constraints.
- Select CT type and ratio based on real operating currents.
- Plan wiring and comms routes.
- Then commission with phase/polarity verification and sanity checks against expected loads.
Current transformer metering fits that workflow well because it gives you multiple options to work around the physical limits of existing infrastructure.
Retrofits will always involve compromises. The win is choosing compromises that protect safety, minimise downtime and still deliver trustworthy data. In that context, current transformer metering is less of a “specialist technique” and more of a sensible default for modern upgrades where space and access are the main constraints.
Talk to our team about your energy metering needs.
FAQs - Current Transformer Metering for Retrofit Projects
What is current transformer metering?
Current transformer metering uses CTs to measure current indirectly, sending a small proportional signal to the meter so you can monitor large loads without routing the full current through the meter.
Do I need to shut down power to install CTs in a retrofit switchboard?
Often only a short planned outage is needed, especially if the metering, wiring routes and communications are prepared first and the CT installation is staged. Using split core CTs can help reduce the outage time.
Are split-core CTs accurate enough for retrofit monitoring?
Yes. When correctly selected, installed and commissioned, split-core CTs can deliver reliable results, though the right CT class and ratio matter for your accuracy requirements. The devil is in the details.
What causes inaccurate readings with current transformer metering?
The most common causes are incorrect CT orientation or phase mapping, an unsuitable CT ratio or poor secondary wiring practices that affect the CT circuit burden or the accuracy of the CT.
