GE Multilin 850 vs 845 for Transformer Protection: What Procurement Should Compare

Why This Comparison Starts With a Cost Mistake

Can a GE Multilin 850 used for transformer protection be the right answer? Yes, sometimes, but not because the relay price looks lower. I learned that lesson when I compared two GE relays for the same transformer project.

In late 2024, I sat on a procurement call for a 15 MVA GE transformer. One bid proposed a GE Multilin 845. The other bid was built around a GE Multilin 850 used for transformer protection. The 850 line item was lower. My first instinct was to approve it.

My project engineer stopped me with a simple question: Does the cheaper relay match the protection scheme and the wiring diagram, or does it just look like it does? He was right to ask. Since then, I compare relays differently.

Background: I manage procurement for a 140-person utility services company. I do not set protection settings, but I sign purchase orders and review invoices. I have tracked protection and transformer control equipment purchases for about six years and roughly twenty transformer projects.

The Four-Dimension Comparison I Used

I compare protection relays in four steps: protection fit, wiring diagram reality, commissioning and test equipment, and long-term support. These four dimensions decide total installed cost and risk. If you only compare relay prices, you are missing most of the actual difference.

Dimension 1: Protection Fit or Just Enough Protection?

GE positions the 845 as a transformer protection relay. The 850 is more often specified for distribution protection, although it can be used in transformer applications. If the protection study calls for overcurrent, voltage, and frequency protection on a smaller distribution transformer, the 850 can be enough.

But if the transformer is large, critical, or requires transformer-specific protection functions, the 845 is usually the safer fit. The danger is trying to make a less transformer-specific relay do the same job by adding external devices. Those external devices have to be mounted, wired, tested, and documented. By then, the initial price gap can disappear.

The relay is only one device in the circuit. The wiring diagram tells the real story.

Dimension 2: The GE Transformer Wiring Diagram Effect

The biggest surprise in my comparison was not hardware. It was drawing review. When I asked both vendors to work from the same GE transformer wiring diagram, the bids started to separate.

A protection relay connects to CTs, trip coils, breaker auxiliary contacts, marshalling box terminals, and sometimes cooling controls. The GE transformer wiring diagram defines how much panel wiring is required, how many terminal blocks are needed, and where interlocks have to be added. The relay is one box in that drawing.

One vendor treated drawing review as part of the relay quote. Another vendor listed drawing review as a separate task. That separate line is not a red flag, but it must be included in the total. If you do not require a GE transformer wiring diagram in the bid package, you are not comparing the same project.

In that 2024 project, the 845 hardware was about $2,000 more than the 850. The installed-cost difference ended up much smaller. In fact, if I remember the exact total, the 845 package was slightly cheaper once external devices and engineering labor were included. I did not expect that result. On a simpler project, the opposite is normally true.

Dimension 3: Commissioning and the Types of Electrical Tester

The GE transformer wiring diagram also tells you what commissioning tests will be needed. That is where the types of electrical tester become a procurement issue, not just a technical issue.

A point-to-point wiring check needs a multimeter. An insulation check needs an insulation resistance tester. A phase rotation check needs a phase rotation meter. A relay pickup and trip test needs a secondary injection test set. A full CT circuit test may need a primary injection test set. If a commissioning quotation lists only a voltage tester and a laptop, I treat it as incomplete.

At first, I pushed back on a commissioning quote for the 845 because it was higher than the quote for the simpler relay. Then I watched the test plan. More transformer-specific functions meant more test cases. The higher quote was fair. Not ideal, but fair.

Dimension 4: Long-Term Cost and Support

I don't have hard data on component failures for either relay model. My experience is based on about twenty orders, which is a limited sample. From a cost-control perspective, though, I have clear observations.

A simpler relay is easier to support across different technician crews. A transformer-focused relay has more settings and a larger manual. Training is a real cost. If your technicians already know one GE relay family, staying with it can lower total cost. If neither relay is familiar to your team, plan for extra commissioning time.

Part of me wanted to standardize on one relay model to simplify spare parts and training. Another part knows that one model will not fit every installation. I found a compromise: standardize the protection philosophy, not the exact part number.

Which One Should You Choose?

Choose the GE Multilin 850 if...

Your protection engineer confirms that the application is overcurrent-based, the transformer is not considered critical, and the commissioning crew has the right types of electrical tester. Also require the GE transformer wiring diagram to be part of the contract. In that scenario, the 850 can be the lower-cost decision without adding much risk.

Choose the GE Multilin 845 if...

The transformer is critical, the protection study includes transformer-specific functions, or the installed-cost comparison shows that fewer external devices will offset the higher relay price. The 845 makes sense when the GE transformer wiring diagram and test plan are more complex. It may look more expensive on the purchase order, but it can protect both the transformer and the project budget.

If you are still unsure...

Let the protection engineer make the technical call. Then do a full installed-cost comparison. Procurement should not choose a protection relay by reading a brochure.

Honest Bottom Line

I want to answer the question that probably brought you here: can a GE Multilin 850 used for transformer protection save money without creating risk? Yes, sometimes. But only when the protection study supports it, the wiring diagram is reviewed, and the commissioning scope is fully priced.

Start with the protection study. Then get the GE transformer wiring diagram. Then compare the total project cost, including the types of electrical tester and commissioning time. That order has saved me more money than any vendor discount I have negotiated.