Siemens 3ug4615-1cr20

By Abdullah Zahid
14 min read
Siemens 3UG4615-1CR20 digital three-phase monitoring relay on DIN rail for motor and pump protection

Siemens 3UG4615-1CR20 Digital Monitoring Relay for Three-Phase Line Voltage: Specifications, Installation Overview and Alternatives

When a motor fails because of a lost phase or a voltage imbalance that went undetected, the downtime cost almost always dwarfs the price of the relay that could have prevented it. Controls engineers and panel designers searching for the Siemens 3UG4615-1CR20 are typically at the same decision point: confirming this specific SKU handles their voltage range, their system topology, and their response time requirement before they commit to a panel build or a retrofit. The 3UG4615-1CR20 is a compact DIN rail monitoring relay from the Siemens SIRIUS 3UG4 family, rated for 160-690V AC three-phase systems at 50/60 Hz, and capable of detecting phase failure, phase sequence reversal, overvoltage, undervoltage, and asymmetry — five protective functions in a 22.5 mm wide housing.

If you have already confirmed this is the right part, check current pricing and availability at LeadTime.ca — ships worldwide.

Who Should Buy the 3UG4615-1CR20 — and Who Shouldn't

The 3UG4615-1CR20 is the right choice for engineers and panel builders protecting three-phase AC loads where comprehensive voltage fault detection is required in a single compact module. This relay is the correct fit when all of the following are true:

  • Your three-phase line voltage falls within the 160-690V AC range (this is non-negotiable — below 160V or above 690V means the wrong model)
  • Your system is ungrounded three-phase (delta or floating neutral) and you do not need phase-to-neutral voltage monitoring
  • Your control supply voltage is AC and matches the same nominal voltage as your monitored line (160-690V AC)
  • You need 2 CO (changeover) relay contact outputs at AC-15 rating to drive downstream contactors or motor starters
  • A maximum fault response time of 450 ms meets your process protection requirement
  • You need an adjustable response delay between 0.1 and 20 seconds to tolerate motor startup transients

If your three-phase system is grounded (star/Y with neutral) and you need phase-to-neutral monitoring, the 3UG4615-1CR20 is not the correct choice — evaluate the 3UG4616-1CR20 or 3UG4618-1CR20 instead. If your voltage range is below 160V, those same models (rated 90-400V) are more appropriate. For simple phase failure detection only without overvoltage or undervoltage functions, the lower-cost 3UG4611-1CR20 may be sufficient.

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What the 3UG4615-1CR20 Actually Does in a Control Panel

The 3UG4615-1CR20 sits at the input side of a motor or load circuit and continuously reads all three phase voltages from the moment the panel is energized. When any monitored parameter — phase presence, voltage level, phase sequence, or phase-to-phase imbalance — moves outside the thresholds the engineer has set, the relay changes the state of its 2 CO output contacts within 450 ms. Those contacts then open or close the control circuit to a downstream contactor, motor starter, or alarm system, isolating the load before damage propagates.

What makes this model stand out from simpler phase-loss relays in the SIRIUS range is the combination of five distinct detection functions in one module: phase failure detection, phase sequence reversal detection, overvoltage monitoring across all three phases, undervoltage monitoring across all three phases, and asymmetry detection. Each of these can cause motor winding overheating or mechanical damage independently — having all five handled by a single 22.5 mm wide DIN rail device reduces the bill of materials and the spares inventory simultaneously. The LCD display shows live voltage readings at all times, and an error memory function stores the last fault condition to assist post-trip diagnosis without additional logging hardware.

The control supply is taken from the same 160-690V AC line being monitored, which eliminates the need for a separate lower-voltage control transformer in most installations. Startup time after power-on is 1,000 ms, after which the relay begins active monitoring. The adjustable response delay of 0.1 to 20 seconds allows commissioning engineers to accommodate motor soft-start inrush and voltage transients without nuisance trips, while still catching genuine sustained faults within the protection window. Electrical endurance is rated at 100,000 operating cycles at AC-15, and mechanical life reaches 10,000,000 cycles — specifications that comfortably exceed a 20-year facility service life in typical industrial panel applications.

Typical System Architecture for Three-Phase Monitoring

The 3UG4615-1CR20 sits in the signal path between the incoming three-phase supply and the motor contactor, acting as the gatekeeper that authorizes or interrupts load control based on supply quality. A typical deployment chain looks like this:

  • Incoming three-phase supply (160-690V AC) enters the panel at the main disconnect or bus bar
  • Three-phase sense leads connect from the bus to the 3UG4615-1CR20 voltage input terminals (L1, L2, L3)
  • The relay control supply taps from the same three-phase line at the nominal operating voltage (no separate transformer needed in most cases)
  • The 2 CO output contacts wire in series with the motor starter or contactor coil circuit — a normally closed or normally open contact path is chosen based on fail-safe logic requirements
  • Downstream loads (motors, compressors, pumps, conveyors) are switched by the contactor whose coil is controlled by the relay output contacts

Where Engineers Deploy the 3UG4615-1CR20

In food and beverage processing facilities, conveyors, mixers, and pump drives are typically the first assets to suffer from phase imbalance caused by aging distribution infrastructure or uneven load sharing. The 3UG4615-1CR20 is added to each motor control circuit so that a phase loss event on one production line does not burn out a motor before the maintenance team can respond.

Water and wastewater pump stations represent one of the highest-value deployments for this relay. Submersible pump motors operating unattended are vulnerable to single-phasing from corroded contacts or utility supply problems. With the relay installed and thresholds set, the pump control panel de-energizes the starter within 450 ms of a phase loss, preventing winding burnout in a motor that may be inaccessible for days.

HVAC and refrigeration compressor protection is another primary application. Compressor motors are expensive to replace, and refrigeration systems running on an unbalanced supply will overheat slowly over days or weeks before failing. Adding the 3UG4615-1CR20 to detect asymmetry early — before thermal protection triggers — can defer a compressor replacement capital expenditure by several years.

For facilities with ungrounded delta three-phase distribution — common in older industrial plants and certain marine and mining installations — the 3UG4615-1CR20 is often the only viable phase monitoring option because it measures line-to-line voltage exclusively and does not require a neutral reference. This makes it the standard choice for delta system retrofits where a newer relay with neutral-referenced monitoring cannot be wired without a system topology change.

Multi-site equipment standardization is a recurring procurement driver. Facility managers who operate plants across different voltage regions (208V, 380V, 440V, 480V, 600V) can deploy a single 3UG4615-1CR20 SKU across all sites, reducing the spare parts catalog, simplifying technician training, and enabling cross-site warranty and replacement logistics.

Application Typical Deployment
Food and beverage conveyor and pump protection Installed in MCC panel; protects motor starter circuits from phase loss during continuous production
Water and wastewater pump station Mounted in outdoor enclosure panel; monitors unattended submersible pump supply 24/7
HVAC and refrigeration compressor protection Added to compressor motor starter panel to detect asymmetry before thermal cutout activates
Ungrounded delta industrial distribution Line-to-line monitoring without neutral; only viable monitoring relay class for floating delta systems
Multi-site equipment standardization Single SKU covering 160-690V deployed identically across plants at different nominal voltages
New OEM panel build with FAT requirements Specified during design phase; tested at factory acceptance with simulated phase-loss scenario

Purchase-Decision Specifications at a Glance

Specification 3UG4615-1CR20 Value
Monitored voltage range 160-690V AC, three-phase, 50/60 Hz
Detection functions Phase failure, phase sequence reversal, overvoltage, undervoltage, asymmetry
Maximum response time 450 ms
Adjustable response delay 0.1-20 seconds
Output contacts 2 CO (changeover) at AC-15 rating
Electrical endurance 100,000 cycles at AC-15
Mechanical life 10,000,000 operating cycles
Physical dimensions (W x H x D) 22.5 mm x 92 mm x 91 mm
Operating temperature range -25°C to +60°C
Protection class IP20

Full technical specifications are available on the product page at LeadTime.ca.

3UG4615-1CR20 vs. SIRIUS 3UG4 Variants: Which One Do You Actually Need?

The SIRIUS 3UG4 family covers a wide range of protection levels and system topologies. Understanding where the 3UG4615-1CR20 sits in the family prevents the most common ordering mistakes.

Feature 3UG4615-1CR20 3UG4616-1CR20 3UG4613-1BR20 3UG4612-1BR20 3UG4611-1CR20
Voltage Range 160-690V 90-400V 160-690V 160-690V 160-690V
Phase Failure Detection Yes Yes Yes Yes Yes
Phase Sequence Detection Yes Yes Yes Yes No
Overvoltage Detection Yes Yes Yes No No
Undervoltage Detection Yes Yes Yes No No
Neutral Reference Required No Yes No No No
Response Time 450 ms 450 ms 450 ms 450 ms 450 ms
Display LCD LCD LCD LCD LED
Adjustable Delay 0.1-20s 0.1-20s Limited Limited No
Output Contacts 2 CO 2 CO 2 CO 2 CO 1 CO
Electrical Endurance 100K cycles AC-15 100K cycles AC-15 50K cycles 50K cycles 50K cycles
Typical Cost Position Mid-range Mid-high Budget-mid Budget Low-budget

The critical distinction is system topology: if your three-phase distribution is ungrounded delta and you need the full five-function detection package across the widest possible voltage range, the 3UG4615-1CR20 is the correct choice at a mid-range cost position with double the electrical endurance of the 3UG4613 and 3UG4611 variants. If your architecture uses a grounded star system with neutral and your voltage does not exceed 400V, the 3UG4616-1CR20 is the correct alternative — check current availability and pricing at LeadTime.ca and contact the team to confirm which variant ships fastest for your timeline.

Expert Verdict: Honest Assessment and Procurement Reality

The 3UG4615-1CR20 earns its position as a standard specification item in three-phase motor protection panels because it solves five failure modes with one device and does so reliably across a voltage range wide enough to span most industrial and light industrial applications worldwide. The 22.5 mm width keeps it panel-space-neutral, the LCD display eliminates the need for a separate voltage meter on the same circuit, and the error memory function genuinely reduces troubleshooting time after a trip event — an underrated feature for maintenance teams responding to overnight faults. The 100,000-cycle electrical endurance at AC-15 rating and 10,000,000-cycle mechanical life mean this is a relay you install once per machine lifecycle without scheduling replacement.

Where the 3UG4615-1CR20 has real limits: it cannot monitor phase-to-neutral voltage, which is a hard constraint in grounded star systems where individual phase-to-neutral sag matters. It also requires the control supply to be AC at the same nominal voltage as the monitored line — if your panel runs a 24V DC control circuit, this relay will not energize and you will need to source a transformer or select a different relay family. The minimum 160V lower boundary also disqualifies it from some lower-voltage secondary distribution circuits. These are not design flaws — they are topology-specific constraints that the 3UG4616-1CR20 and 3UG4618-1CR20 address for grounded systems, and the 3UG4511/3UG4512 series addresses for simpler single-phase requirements.

From a procurement standpoint, the SIRIUS 3UG4 family benefits from wide distributor stocking globally, which typically means shorter lead times compared to more specialized protection relay families. Volume pricing is available for panel builders specifying multiple units across a project or standardizing across a facility fleet. If you are replacing an aging electromechanical phase monitor, the DIN rail form factor and screw terminal connections of the 3UG4615-1CR20 make retrofits straightforward in most standard panel layouts. If this relay matches your system requirements, view current stock and pricing at LeadTime.ca.

For volume pricing or to confirm lead time before committing to a build, contact the LeadTime.ca team directly — we ship worldwide.

Wiring and Installation Overview

The following covers the key requirements for a safe and correct installation. Engineers requiring full wiring diagrams and terminal assignments should refer to the official Siemens 3UG4615-1CR20 operating instructions.

  • Mount the relay on a standard 35 mm DIN top-hat rail inside an enclosed control panel rated for IP20 or higher; the relay itself carries an IP20 rating and is not suitable for direct exposure to dust, water, or washdown environments
  • Connect the three monitored phase voltages (L1, L2, L3) using solid conductors of 0.5-4.0 mm² or stranded conductors of 0.5-2.5 mm² (two conductors per terminal maximum) to the corresponding screw terminals
  • Connect the AC control supply — rated 160-690V AC, matching the nominal line voltage being monitored — to the designated control supply terminals; verify with a multimeter in AC voltage mode before energizing
  • Wire the 2 CO output contacts in series with the motor starter or contactor coil control circuit; choose normally closed or normally open contact based on your required fail-safe logic (NC breaks the circuit on fault; NO closes an alarm circuit on fault)
  • Confirm 0 mm spacing is maintained as required — adjacent modules can be mounted directly alongside the relay without air gap — and verify all screw terminals are tightened to prevent intermittent connections that generate nuisance trips

Commissioning Overview: First Power-On and Threshold Setup

Full commissioning procedures, including potentiometer calibration sequences and threshold verification methods, are documented in the manufacturer's operating instructions. The following is an overview of the key commissioning steps:

  • After wiring, apply AC line voltage and observe the LCD display — the relay requires a 1,000 ms startup time before active monitoring begins, after which a live voltage reading should appear; verify the displayed value is within the 5% measurement accuracy tolerance of your multimeter phase-to-phase reading
  • Set the overvoltage threshold using the front-accessible potentiometer — a typical starting point is 110% of your nominal line voltage; set the undervoltage threshold at 85% of nominal, and confirm the gap between the two thresholds is at least 10% of nominal to prevent logic oscillation
  • Adjust the response delay potentiometer to a setting between 0.1 and 20 seconds appropriate for your load type — motor soft-start applications typically use 0.5-2 seconds to filter inrush transients without masking real fault conditions
  • Test the auto-reset function by temporarily removing one phase under controlled commissioning conditions and confirming the output contacts change state, then restoring the phase and confirming the relay recovers automatically without manual intervention
  • Document the final potentiometer positions for all thresholds and delay settings on the panel drawing for future reference and consistency across identical panels in the facility

Wrong-Part Prevention Checklist Before You Order

Before placing an order for the 3UG4615-1CR20, verify every item on this checklist against your actual system requirements. A single mismatch on any of these points means a different model is needed.

  1. Confirm your line voltage is 160V minimum, 690V maximum (below 160V or above 690V = wrong model).
  2. Verify you are monitoring ungrounded three-phase voltage (neutral reference not required); if you need neutral, select 3UG4616 or 3UG4618.
  3. Check that your contactor control voltage matches your line voltage (3UG4615 control supply is rated for 160-690V AC same as line); if control voltage differs, wrong choice.
  4. Confirm you need 2 CO relay contacts (output); if you need single contact or different contact type, verify against your load requirement.
  5. Verify physical space allows 22.5 mm width x 92 mm height x 91 mm depth DIN rail module; check panel layout before ordering.
  6. Ensure response time of 450 ms maximum meets your process (fast enough for motor soft-start transient tolerance); if slower response acceptable, cheaper alternatives exist.
  7. Confirm your facility can provide AC control supply at the same nominal voltage as your three-phase line.

If all seven checks pass, the 3UG4615-1CR20 is the correct part for your application — confirm stock and request a quote at LeadTime.ca. If any item raises a flag, contact the LeadTime.ca team to identify the correct variant before ordering.

Frequently Asked Questions

Can the 3UG4615-1CR20 be used on a grounded star (Y) three-phase system?

The 3UG4615-1CR20 monitors line-to-line voltage only and does not use a neutral reference connection. It will physically operate on a grounded star system, but it cannot detect individual phase-to-neutral voltage anomalies that may be relevant for grounded system protection requirements. If your application requires neutral-referenced monitoring, the 3UG4616-1CR20 or 3UG4618-1CR20 are the appropriate alternatives.

What happens if the response delay is set too short for a motor with a long soft-start?

A response delay shorter than the motor's startup voltage transient duration will cause the relay to trip on every power-up because inrush current temporarily depresses line voltage below the undervoltage threshold. The adjustable delay range of 0.1 to 20 seconds is specifically designed to accommodate startup transients — increasing the delay to 2-5 seconds is the standard solution for motors with extended soft-start profiles. The relay does not suppress detection of genuine sustained faults during the delay period; it filters only transients shorter than the delay setting.

Does the 3UG4615-1CR20 support manual reset, or is it auto-reset only?

The relay supports both automatic reset and manual reset operation. In auto-reset mode, the output contacts restore to their normal state once the fault condition clears — useful for remote installations where manual intervention is impractical. Manual reset mode requires operator action to restore the output contacts after a fault, which is preferred in safety-critical circuits where an operator should acknowledge the fault before the load restarts. The operating mode is selectable during commissioning.

What is the difference between the 3UG4615-1CR20 and the 3UG4614-1BR20?

The 3UG4614-1BR20 offers a full feature set including phase failure, phase sequence, overvoltage, undervoltage, and asymmetry detection — comparable to the 3UG4615-1CR20 — but with ON/OFF delay functionality and operates on the 160-690V range. The 3UG4615-1CR20 includes digitally adjustable thresholds via potentiometer and an LCD display, which supports finer threshold tuning and live voltage readout compared to models with fixed hysteresis. Confirm which variant your panel documentation specifies, as the two models are not identical in their adjustment capability.

What conductor sizes are compatible with the 3UG4615-1CR20 screw terminals?

The screw terminals accept solid conductors from 0.5 mm² to 4.0 mm² when using one conductor per terminal, and stranded conductors from 0.5 mm² to 2.5 mm² when using two conductors per terminal. These are the verified terminal specifications — using conductors outside this range risks either a poor mechanical connection or terminal damage. Crimped ferrules are recommended for stranded conductors to ensure consistent termination.

Is the 3UG4615-1CR20 rated for outdoor or washdown panel environments?

The relay carries an IP20 protection rating, which covers protection against solid objects greater than 12.5 mm but provides no protection against water ingress. It is suitable for mounting inside enclosed control panels in indoor industrial environments and outdoor weatherproof enclosures, but is not rated for direct washdown exposure. The operating temperature range of -25°C to +60°C covers most outdoor panel applications in temperate to cold climates.

Why Order from LeadTime.ca

  • LeadTime.ca ships the Siemens 3UG4615-1CR20 and SIRIUS 3UG4 family variants worldwide — no geographic restrictions on orders
  • Hard-to-find or short-run variants of the SIRIUS monitoring relay family can be sourced and confirmed for availability before you commit to a build schedule
  • Volume pricing is available for panel builders and OEMs specifying multiple units across a project — contact the team before placing large quantity orders
  • The LeadTime.ca team can confirm current lead times and stock levels directly, reducing the risk of a supply gap on a time-sensitive panel build

At-a-Glance Summary

  • Model: Siemens 3UG4615-1CR20 — digital monitoring relay for three-phase line voltage, part of the SIRIUS 3UG4 family
  • Monitored voltage range: 160-690V AC, three-phase, 50/60 Hz — widest range in the SIRIUS 3UG4 lineup for delta/ungrounded systems
  • Five detection functions in one module: phase failure, phase sequence reversal, overvoltage, undervoltage, and asymmetry
  • Maximum response time: 450 ms; adjustable response delay: 0.1-20 seconds
  • Output: 2 CO (changeover) relay contacts at AC-15 rating; 100,000 electrical endurance cycles
  • Mechanical life: 10,000,000 operating cycles
  • Dimensions: 22.5 mm W x 92 mm H x 91 mm D; standard 35 mm DIN rail mount; 0 mm spacing required between adjacent modules
  • Operating temperature: -25°C to +60°C; IP20 protection class
  • Control supply: AC, 160-690V — same as monitored line voltage; no separate transformer required in standard installations
  • LCD display with error memory and live voltage readout; display accuracy +/- 1 digit; relative measurement precision 5%
  • Not suitable for: grounded star systems requiring neutral reference (use 3UG4616-1CR20), voltages below 160V (use 3UG4616/3UG4618), or DC control supply panels