---
title: "Medium-voltage service and primary metering explained | Entogo"
description: "Taking medium-voltage utility service means owning the step-down transformer and the substation behind it, in exchange for a lower primary-metering rate.…"
url: https://entogo.ca/insights/medium-voltage-service-primary-metering/
lang: en
type: article
image: https://entogo.ca/_astro/medium-voltage-service-primary-metering.iBZnMt5f.jpg
datePublished: 2026-08-11
dateModified: 2026-08-11
site: https://entogo.ca/
llms: https://entogo.ca/llms.txt
---

Home › Insights › Should your facility take medium-voltage service? Primary metering and customer-owned substations

Power & Distribution

# Should your facility take medium-voltage service? Primary metering and customer-owned substations

Entogo August 11, 2026

![Customer-owned electrical substation and medium-voltage power distribution equipment at dusk](https://entogo.ca/_astro/medium-voltage-service-primary-metering.iBZnMt5f_Z1qC1VK.webp)

In short

Taking medium-voltage utility service means owning the step-down transformer and the substation behind it, in exchange for a lower primary-metering rate. It pays off for large, steady loads but shifts transformer losses, maintenance, and protection to the buyer. Here is how to weigh the trade-off.

## Should your facility own its transformation, or let the utility do it?

Every building on the grid is fed at a voltage the utility chooses. Small commercial and residential loads take power at **low voltage** — the 600-volt class or below — and the utility owns the transformer that steps its distribution line down to the building’s service. As a facility’s demand grows, though, the utility eventually stops offering that arrangement and asks the customer to take **medium-voltage service** instead: accept power at the distribution line’s own voltage and step it down on-site, with equipment the customer owns.

That shift is one of the larger electrical decisions a big industrial plant, data center, or charging hub makes. It changes who owns the transformer, who maintains it, who pays for its losses, and how the site is billed. The savings can be real, but so are the obligations.

## What “medium-voltage service” actually means

North American codes place the line between low and medium voltage near **1,000 volts**. The National Electrical Code treats equipment “over 1,000 volts, nominal” as a distinct class governed by Article 490. Utility primary distribution runs well above that boundary — commonly 4.16, 12.47, 13.8, 25, or 34.5 kV — and a facility on medium-voltage service connects at that level rather than at 208 or 480 V.

### Primary versus secondary metering

The billing side of the decision is **metering**. With **secondary metering**, the utility’s meter sits on the low-voltage side of a utility-owned transformer. The customer buys power already stepped down and never sees the transformer. With **primary metering**, the meter sits on the medium-voltage side, ahead of a **customer-owned transformer**. The customer now buys power at medium voltage and owns everything past the meter.

Because the utility no longer owns or maintains the transformer — and because primary metering does not bill the customer for that transformer’s losses — most utilities discount the primary rate. One Colorado utility, for example, reduces both the demand charge and the energy charge by 3 percent for primary-metered service. Other utilities structure the credit differently, or offer none, so the tariff has to be read closely before the economics can be trusted.

## What a customer-owned substation contains

Taking medium-voltage service means building, in effect, a small substation on-site. A typical package includes:

- A **medium-voltage service entrance and metering** point at the utility connection.
- **Primary switchgear** — often [metal-clad switchgear](https://entogo.ca/products/metal-clad-switchgear/) or a [pad-mounted ring-main unit](https://entogo.ca/products/pad-mounted-switchgear-rmu/) — to switch and protect the incoming line.
- One or more **step-down transformers**, such as an [oil-immersed power transformer](https://entogo.ca/products/oil-immersed-power-transformer-36kv/) or a pad-mounted unit, to bring the voltage to utilization level.
- **Low-voltage switchgear or switchboards** — for example [low-voltage switchgear with motor control](https://entogo.ca/products/low-voltage-switchgear-mcc/) — to distribute power through the building.
- **Protection relays and grounding** coordinated across the whole chain.

Many buyers order this as a single engineered assembly rather than a field-assembled collection of parts. A [compact secondary unit substation](https://entogo.ca/products/compact-secondary-unit-substation/) or a [modular skid unit substation](https://entogo.ca/products/modular-skid-unit-substation/) combines the primary switch, transformer, and low-voltage section into one coordinated lineup, which shortens installation and simplifies protection coordination. For campus or utility-scale sites, [substation and power-distribution solutions](https://entogo.ca/solutions/substations-power-distribution/) scale the same idea up.

## Where medium-voltage service makes sense

The choice is mostly about load size and load profile. Below a few hundred kVA, the rate discount rarely covers the transformer, switchgear, protection, and ongoing maintenance, and utility-owned secondary service is the simpler path. Somewhere above that — the exact trigger depends on the utility and can range from a few hundred kVA to a few MVA — medium-voltage service often becomes mandatory rather than optional, because a low-voltage service simply cannot carry the current.

Facilities that cross the line early include large [industrial and EPC projects](https://entogo.ca/solutions/industrial-epc/) with heavy motor loads, [data centers](https://entogo.ca/solutions/data-centers/) whose halls draw megawatts, and high-power DC fast-charging hubs. For those sites the question is rarely “should we?” but “how do we build the on-site substation well?” A steady, high load factor strengthens the case: the more hours a year the site runs near its peak, the more a percentage rate discount is worth against the fixed cost of owning transformation.

## What a buyer should specify

A customer-owned substation is only as good as its specification. The items worth pinning down early:

- **Service voltage and available fault current** from the utility, which set the interrupting rating of the primary switchgear and the transformer’s impedance.
- **Transformer rating and connection** — typically delta-wye for a step-down — plus a loss evaluation, since the owner now pays for **no-load losses** that run continuously whether or not the plant is working.
- **Standards context.** Medium-voltage switchgear is specified against **IEEE C37** standards and transformers against **ANSI/IEEE C57**; low-voltage assemblies are specified against **UL 891** or **UL 1558**; the overall installation follows the **NEC** or Canadian **CEC**. Equipment should be designed and built to these standards, with UL (cULus) or CSA certifiable on request.
- **Protection and coordination**, so a downstream fault clears at the nearest device without dropping the whole service.
- **Metering location**, confirmed against the utility’s primary-service tariff so the expected rate credit is actually captured.

## The bottom line

Medium-voltage service trades simplicity for control. A facility that takes it owns its transformation — the transformer, the switchgear, the protection, and the losses — in exchange for a lower rate and, often, quicker access to capacity than waiting on a utility-side upgrade. For loads large enough to clear the threshold, the real work is building a substation that is safe, well coordinated, and easy to maintain. Entogo’s vertically integrated factory supplies the full chain — medium-voltage switchgear, step-down transformers, unit substations, and low-voltage distribution — designed and built to the governing IEEE, ANSI, UL, and NEC/CEC standards, so the pieces of a customer-owned substation are engineered to work as one system.

- Substations
- Power Distribution
- Medium Voltage
- Switchgear
- Transformers

Glossary: [Demand charge and peak shaving](https://entogo.ca/glossary/#demand-charge-peak-shaving) [Metal-clad switchgear](https://entogo.ca/glossary/#metal-clad-switchgear) [Low-voltage switchgear](https://entogo.ca/glossary/#low-voltage-switchgear-ul-1558) [Unit substation](https://entogo.ca/glossary/#unit-substation) [kVA rating](https://entogo.ca/glossary/#kva-rating) [Interrupting rating vs. short-circuit current rating](https://entogo.ca/glossary/#interrupting-rating-sccr)

FAQ

## Common questions

- **What is the difference between primary and secondary metering**: Secondary metering measures power after a utility-owned transformer, so the utility owns and maintains the transformer. Primary metering measures at medium voltage ahead of a customer-owned transformer, so the customer owns everything downstream in exchange for a lower rate.
- **When does a facility need medium-voltage service**: Utilities generally require medium-voltage service once demand grows beyond what a low-voltage service can carry, often somewhere between a few hundred kVA and a few MVA depending on the utility. Large industrial plants, data centers, and DC fast-charging hubs commonly cross that line.
- **Does owning your own transformer save money**: It can. Many utilities discount the primary rate. One Colorado utility, for example, cuts both the demand charge and the energy charge by 3 percent for primary-metered service. The savings have to offset the cost of buying, maintaining, and protecting the transformer.
- **What equipment does a customer-owned substation need**: A typical package includes a medium-voltage service entrance and metering, primary switchgear or a ring-main unit, one or more step-down transformers, and low-voltage switchgear or switchboards for distribution, all tied together by protection relays and grounding.
- **Is medium-voltage service worth it for a smaller commercial building**: Usually not. Below a few hundred kVA the rate savings rarely cover the added transformer, switchgear, and maintenance cost, and utility-owned secondary service is simpler. The economics improve with larger loads that run near peak for many hours a year.

Keep reading

## Related insights

[![Public DC fast EV charging station with transmission lines and grid infrastructure behind it](https://entogo.ca/_astro/dc-fast-charging-site-transformer-switchgear-sizing.oT4SXZBz_15uHXg.webp) EV Charging ### What size transformer and switchgear does a DC fast charging site need? A DC fast charging site is sized from AC input kVA, not DC output kW, and EVSE loads carry no demand factor. Four 150 kW plus eight 350 kW dispensers draw 3,615 kVA, needing 5,000 kVA of transformer and two 3,000 A mains at 480 V. View](https://entogo.ca/insights/dc-fast-charging-site-transformer-switchgear-sizing/)[![Distribution transformer and secondary conductors feeding low-voltage distribution equipment, governed by NEC 240.21(C) tap rules and CEC Rule 26-256](https://entogo.ca/_astro/transformer-secondary-conductors-nec-240-21c-tap-rules.BX_tOclr_UXL9N.webp) Power & Distribution ### How long can transformer secondary conductors be? NEC 240.21(C) tap rules and CEC 26-256 Transformer secondary conductors get no next-size-up rule. NEC 240.21(C) allows 10 ft and 25 ft runs with ampacity floors of one-tenth and one-third of the primary device times the voltage ratio; CEC 26-256 instead demands 125% of rated secondary current at any length. View](https://entogo.ca/insights/transformer-secondary-conductors-nec-240-21c-tap-rules/)[![Three-phase distribution transformer and low-voltage switchgear at a North American facility substation](https://entogo.ca/_astro/choosing-a-facility-distribution-voltage.B10infhs_Z2obSGL.webp) Power & Distribution ### 208, 480, or 600 volts? Choosing a facility distribution voltage North American facilities are served at 120/208, 277/480, or 347/600 volts. A higher voltage moves the same power at lower current, cutting conductor size and losses while adding transformer and safety cost. Here is how to match the voltage to the load. View](https://entogo.ca/insights/choosing-a-facility-distribution-voltage/)

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