If you're buying a GE transformer protection relay today, the single most expensive mistake you can make is assuming the Multilin 850 and 845 are interchangeable for your application. I learned this the hard way on a $3,200 order in September 2022 – and I'm still finding engineers who don't realize the critical difference.
The Truth About GE Transformer Protection Relay Functions
I've been handling industrial transformer orders for 7 years now. Personally made 14 documented mistakes totaling roughly $27,000 in wasted budget. But the one that still stings was a full Multilin 845 order configured for differential protection on a 5 MVA unit – when the customer actually needed the GE 850's integrated overcurrent and breaker control functions.
Here's what I wish someone had told me on day one: The GE Multilin 850 is primarily a feeder protection relay with transformer backup capability, while the 845 is a dedicated transformer differential relay. Swap them incorrectly and either you lose critical protection functions or you pay for features you'll never use.
How I Made the Mistake
When I first started quoting transformer protection projects, I assumed all GE Multilin relays did similar things. The product names are close, the manuals look alike – I thought I could recommend either. (Should mention: I was also under pressure to close a small order quickly, and the customer was a first-time buyer with a tight budget.)
That small order – 5 units of what I thought were the right relays – came back non-compliant after the customer's engineer reviewed the specs. The wrong relay meant they couldn't implement the slope differential tripping they needed. Cost: $3,200 in replacement units plus a 3-day production delay while we expedited the correct GE 850s. Worse, the customer almost walked away entirely.
Key Differences: GE 850 vs 845 Functions
- GE Multilin 850: Directional overcurrent, voltage protection, breaker control, and transformer through-fault monitoring – ideal for distribution substations where you need feeder protection with some transformer oversight.
- GE Multilin 845: Dedicated transformer differential (87T), harmonic restraint, and turn-to-turn fault detection – necessary for large power transformers where phase angle compensation is critical.
In my opinion, the 845 is overkill for most distribution transformers under 10 MVA. The 850 gives you 90% of what you need at about 60% of the cost. But if your transformer is over 15 MVA or requires definite-time differential, don't even think about the 850 – you need the 845 or a full transformer management relay.
Relay vs Contactor – A Confusion That Keeps Happening
I should also address a common mix-up I see in the field: the difference between a relay and a contactor. If I remember correctly, I've had three separate customers ask for a 'contactor' when they needed a protection relay (and vice versa). Here's the simple breakdown:
- Relay (like the GE Multilin 850): A low-power device that detects electrical conditions (overcurrent, voltage, frequency) and sends a signal to trip a breaker. It's the brain.
- Contactor: A high-power switching device that actually makes and breaks the main circuit. It's the muscle – often used for motor starting or heating loads.
Take this with a grain of salt: I've seen engineers order a contactor when they needed a protection relay because they saw 'relay' in the name of the Multilin. That's like ordering a diesel engine when you needed a generator – they're related but not interchangeable. (Oh, and the same confusion happens with dryer electrical outlet wiring: a simple relay in the dryer controls the heating element, but the wall outlet itself needs a contactor if it's a heavy-duty 240V circuit. Different beast entirely.)
The Surge Protection Blind Spot
Another mistake I've documented: specifying transformer protection without considering wall outlet surge protection for the control power supply. A $50 surge protector on the relay's AC supply can save you a $2,000 replacement if a lightning strike hits nearby.
I once thought: 'the transformer itself has surge arrestors, the relay is inside a panel – it'll be fine.' Then in Q1 2024, a customer's relay died because a transient on the station service voltage fried the power supply module. The fix? A $35 wall outlet surge protector that they could have installed during commissioning. That mistake cost $890 in redo plus a 1-week delay for a small client who was already unhappy.
When These Rules Don't Apply
If you're a large utility ordering 50+ relays at a time, you probably have a protection engineer who knows the 850 vs 845 difference backwards. This advice is for the smaller companies, first-time buyers, and project managers who wear 17 hats – the ones like me who got burned early.
I should add: the GE product line also includes the Multilin 750/760 for comprehensive transformer management, and the newer 850 with the 'T' firmware option. Always check the latest GE manual (available at geindustrial.com – verify current revision as of March 2025) because firmware updates sometimes add or remove functions.
As of January 2025, the GE 850 base price (list) is around $1,800 for the standard model, and the 845 starts near $2,700. But actual pricing varies dramatically by distributor and volume. For a small order of 1-2 units, expect to pay closer to list. For 10+, you can negotiate. (Don't hold me to those exact numbers – pricing accessed via GE's public price list, and I've seen 20% swings between distributors.)
Final Thought: Small Orders Deserve Big Attention
When I was starting out, the vendors who treated my $200 orders seriously are the ones I still use for $20,000 orders. If you're a small company buying a single GE 850 relay, you deserve the same accurate specs as a utility. Don't let anyone rush you into the wrong product because 'it's just a small order.' My $3,200 mistake proves the cost of getting it wrong doesn't scale with the order size.
Personally, I now maintain a pre-order checklist on our team's shared drive. We've caught 47 potential errors using it in the past 18 months – including three cases where someone almost ordered a contactor instead of a relay. If you want a copy, I'm happy to share. Oh, and always, always add a surge protector to the relay's AC supply. Trust me on this one.
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