Danfoss Pressure Switch: KP5 vs RT Series From a Procurement Perspective

Why I'm Comparing Two Danfoss Pressure Switches

If you work in purchasing, you already know the feeling. A maintenance tech drops a note on your desk that says “need Danfoss pressure switch” and walks off. That’s it. No part number. No pressure range. Just three words and a hope.

I’ve managed MRO purchasing for a 40-person controls company since 2020. I handle about $180,000 a year in orders across nine vendors. I’m not an engineer. I’m the person who decodes part numbers and explains to the plant manager why a $60 switch ended up costing $180 after freight.

This is a practical comparison of two Danfoss switch families I buy almost every month: the Danfoss KP5 pressure switch and the Danfoss RT pressure switch for industrial applications. These two are not interchangeable, and knowing which one to order has saved me a lot of phone calls.

What I’m Comparing and Why

From the outside, a pressure switch is just a small box with a process connection and some wires. The reality is different. The range, reset function, contact material, housing protection, and approvals all affect whether it works in your system. You have to compare those details, not just the brand.

I’m going to compare the KP5 and RT on four dimensions that hit my budget and sanity before they hit the equipment: documentation, price and availability, replacement fit, and application fit.

Dimension 1: Documentation and Technical Support

The KP5 pressure switch is a well-documented, relatively simple product. Search for “KP5 wiring diagram” and you’ll find a clear terminal diagram in the datasheet. It’s usually enough for a refrigeration or HVAC job. That’s one of the reasons I like buying it—no one has to call me to chase down a document from 2003.

The Danfoss RT pressure switch industrial line is a different story. The RT family has more variants, more wiring versions, and more approval sheets. The documentation is thorough, but you have to check variant-specific details. The term “RT series” covers a lot of ground. I’ve been burned by ordering what I thought was the right RT model only to find that the wiring diagram I had downloaded didn’t match the reset option.

Danfoss publishes separate tech leaflets for each family. As of January 2025, I still download the PDF from the Danfoss product page before I send a purchase order. It takes five minutes and prevents the whole “but the website showed a different connection” conversation.

Dimension 2: Price, Stock, and Lead Time

In my experience, the KP5 is usually the lower-cost option and easier to find in local MRO stock. It’s used in common refrigeration and air conditioning equipment, so supply houses tend to carry it. If my distributor doesn’t have it today, they can usually get it tomorrow.

The RT series is more of a special-order item unless you have an established maintenance stock. It’s built for industrial refrigeration, marine, and process environments. It typically costs more, and lead times are longer. As of January 2025, I was quoted 10 to 14 business days for a standard RT pressure switch that needed a specific contact configuration. That delay matters when the customer wants the machine running by Friday.

But don’t choose a switch based only on price. I’ve made that mistake. The “slightly cheaper alternative” choice looked smart until we needed a phone number for tech support that the vendor didn’t have. Net loss: an hour on hold and a rush order. And once, I ordered an RT variant because the earlier quote looked close to the KP5 price. The first quote didn’t include certification documentation or the special-order handling fee. Finance rejected part of it. I ate the $240 restock fee and learned to ask for total landed cost before saying yes.

Dimension 3: Replacement Fit and Maintenance

This is where most of my real-world frustration lives. I assumed that a “same brand, same general type” switch would fit the old bracket. Didn’t verify. Turned out the process connection was the same, but the cap sat differently and the wire terminals were not in the same spot. That’s not a fun mistake; that’s a “why is the electrician billing me for an extra hour” mistake.

Before you order, check three things: the pressure connection, the reset mode, and the switching function. The Danfoss data sheets list these clearly. Don’t assume a picture on a distributor website is the exact variant you need. It might be a family photo.

If the part number is not on the old switch, find it before you order. Anything else is gambling.

The most frustrating part? You can’t tell the difference by looking. The thread can be the same, the housing can look the same, but the internal switch action may be completely different. That’s why I always ask someone to read the type code off the existing switch if it’s still installed.

Dimension 4: Where Each One Actually Belongs

The KP5 pressure switch is my default for standard HVAC, air conditioning, and light commercial refrigeration. It’s the kind of switch that works for 80% of the replacement orders we see. It has the performance, the rating, and the Danfoss reliability. For a normal compressor protection job, this is where I start.

The Danfoss RT pressure switch industrial class is where I go when conditions get more demanding. Marine and offshore work, process skids, industrial refrigeration racks, or any situation where the contract says “must have class approval” or “IP66 only.” The RT line is well known for that. It’s not automatically better—it’s different, bigger, and more expensive.

And there’s a third case: sometimes you need neither. If the application is hydraulic pressure, high DC voltage, or intrinsically safe instrumentation, stop reading. Get the datasheet and talk to an engineer. A general pressure switch comparison won’t save you there.

Bottom Line: Which One Should You Order?

If you are replacing an existing switch, match what’s there. If the current device says KP5, order a KP5. If it says RT, order the RT. That sounds too simple to be useful, but it is the most common answer.

If you’re building something new and asking me which to choose, here’s my honest view: start with the KP5 pressure switch if the application is standard HVAC or refrigeration and there is no approval requirement. It’s easier to buy, easier to document, and easier on the budget. Move to the Danfoss RT pressure switch industrial line when the environment, the customer spec, or the safety case demands more. That isn’t a knock against the RT. It’s just not worth paying for capability you don’t need.

The last thing I’ll say is about trust. The reason I keep ordering Danfoss pressure switches is not that every one is perfect. It’s that the documentation is consistent enough for a non-engineer to verify a purchase. That’s actually harder to find than you’d think.