A protection relay is often purchased only after something has already gone wrong.

A motor has burnt after single phasing. A pump has run dry. A conveyor has overloaded. A machine is drawing abnormal current. An insulation fault is causing earth leakage. Or a newly wired three phase motor is rotating in the wrong direction because the phase sequence has changed.

At that point, the question is usually not, "Which relay has the most features?"

The real question is, "Which electrical fault are we trying to stop before it damages the equipment?"

That is the right way to select a protection relay.

Radical TechMart's current Multispan Protection Relays category includes products for broad motor protection, current protection, phase protection and earth leakage monitoring, including MPD 13N, MPD 19N, CPR 126, CPR 22U, SPP 22 and the ELR series.

These products should not be selected only by price or enclosure size. The correct relay depends on the load, electrical fault, current sensing method, trip logic, reset philosophy, mounting arrangement and the equipment that must be disconnected when a fault occurs.

What Is an Industrial Protection Relay?

An industrial protection relay continuously monitors an electrical condition and changes its output when that condition moves outside an acceptable limit.

In simple words, it watches the electrical system and tells the control circuit when something is wrong.

The relay itself usually does not interrupt a large motor current directly. Its output is typically connected into a control circuit that can operate a contactor, breaker trip circuit, alarm, PLC input or another protection device.

Depending on the relay, it may monitor conditions such as:

• Phase failure
• Wrong phase sequence
• Current overload
• Current underload
• Short circuit condition
• Current imbalance
• Locked rotor
• Earth leakage
• Voltage abnormalities
• Three phase asymmetry

The first selection question should therefore always be:

What fault must the relay detect?

Why Protection Relays Matter in Actual Plant Conditions

Consider a three phase pump.

During normal operation, all phases are healthy and the motor draws current within its expected range.

Now imagine one phase is lost.

The motor may continue trying to operate under an abnormal condition. Current can become unbalanced, heating can increase and the motor may eventually fail if the condition continues.

Now consider a borewell or process pump.

The electrical supply may be perfectly healthy, but if the pump loses water, the mechanical load can reduce. That can appear as an undercurrent condition.

A relay selected only for phase failure may not solve that problem.

This is why protection has to match the actual failure mode.

A purchase team may compare relay prices, but the maintenance team deals with the consequences when the wrong protection philosophy is used.

Main Types of Multispan Industrial Protection Relays

1. Phase Protection Relays

Phase protection is one of the most common requirements in three phase motor and pump panels.

The Multispan SPP 22 portion of the SPP 22 / V22 RYB combination is designed around phase loss, phase asymmetry and incorrect phase sequence protection. The V22 RYB portion provides visual R, Y and B phase indication.

Best for:

Three phase pumps, motors, compressors, HVAC equipment and machines where phase condition must be checked before operation.

Why this type makes sense:

If the main risk is missing phase, reversed phase sequence or excessive phase imbalance, there may be no need to begin with a more complex current protection device.

For example, wrong phase sequence can cause a three phase motor to rotate in the opposite direction. On pumps, compressors or mechanical systems, that can become an operational problem immediately.

Selection caution:

A phase protection relay does not automatically provide full overload, underload or earth leakage protection. Confirm every required fault separately.

2. Overcurrent and Undercurrent Protection Relays

Current tells you a great deal about what is happening to a motor or electrical load.

Too much current can indicate overload, mechanical jamming or another abnormal operating condition.

Too little current can also matter.

For pumps, fans and certain machinery, undercurrent may indicate loss of load, dry running, broken coupling or another process problem.

The Multispan CPR 22U is a compact programmable overcurrent and undercurrent relay suitable for single phase and three phase systems. It also provides selectable fail safe and non fail safe operation.

Best for:

Applications where the primary protection decision should be based on current.

Why this model type makes sense:

Instead of only checking whether all phases are present, a current relay can identify whether the machine is actually operating within the expected load window.

This becomes particularly useful in pump panels, DG panels, MCCs and industrial machinery.

Selection caution:

Before selecting a current relay, identify the expected running current, starting current and fault current. An incorrectly chosen trip threshold can produce nuisance trips or inadequate protection.

3. Three Phase Current Protection Relays

For larger three phase loads, the protection logic may need to go beyond a simple overcurrent setting.

The Multispan CPR 126 is a three phase True RMS current protection relay designed around overload, underload, current asymmetry and single phase prevention. Its product information also references programmable CT ratios, which makes it relevant where load current is measured through external current transformers.

Best for:

Three phase motors, pumps, industrial loads and machinery where current condition across all phases matters.

Why this model makes sense:

Imagine a motor where one phase is drawing noticeably more current than the others.

The total load may still appear reasonable, but the imbalance itself can indicate an abnormal electrical or mechanical condition.

A three phase current relay gives the protection system more information than a simple single current threshold.

Selection caution:

Confirm CT ratio, expected full load current and actual protection settings before commissioning.

4. Multifunction Motor Protection Devices

Sometimes one fault is not enough.

A critical motor may need protection from:

• Overcurrent
• Undercurrent
• Current unbalance
• Locked rotor
• Short circuit
• Phase loss
• Reverse phase

This is where a broader motor protection device becomes useful.

The Multispan MPD 13N combines several protection functions in a 96 × 96 mm panel mounted format. Radical TechMart's current product information lists overcurrent, undercurrent, unbalance, short circuit, locked rotor, phase loss and reverse phase protection. It also lists optional RS485 Modbus communication on request.

Best for:

Important motors, pumps, compressors, production equipment and industrial machinery where multiple electrical failure modes should be monitored from one device.

Why this model makes sense:

Instead of installing separate devices for several related motor faults, a multifunction protection device can centralize the protection logic and provide clearer monitoring.

This is useful when downtime is expensive and operators need more information about why a machine tripped.

Selection caution:

More functions only help when they are commissioned properly.

Do not install a multifunction protection relay and leave every threshold at an assumed value. Motor current, trip delays and fault thresholds should reflect the actual machine.

5. Compact Multifunction Protection

The Multispan MPD 19N is another three phase protection device in the current category. Radical TechMart describes it as providing real time voltage and current monitoring together with programmable protection parameters and tripping control.

This type is useful when the panel needs visible electrical monitoring together with protection.

Best for:

Industrial machinery, pumps and electrical panels where operators benefit from both protection and a clear local display.

Selection caution:

Confirm the exact protection functions and input requirements from the latest datasheet before treating two MPD models as interchangeable.

6. Earth Leakage Relays

Earth leakage protection solves a different problem.

Instead of looking mainly at normal load current, an earth leakage relay monitors current escaping from the intended circuit path toward earth.

Leakage can appear because of deteriorated insulation, damaged cables, moisture, equipment faults or other electrical problems.

The Multispan ELR 19N and ELR 35 are currently listed in the Protection Relays category. Both are described with adjustable leakage sensitivity from 30 mA to 30 A. The ELR 19N uses a panel mount format, while the ELR 35 is designed for DIN rail installation.

Both product pages also indicate the use of a separate core balance current transformer, or CBCT, for leakage sensing.

Best for:

LT panels, MCCs, pump panels, DG panels, distribution boards and industrial machinery where earth leakage monitoring is required.

Why this type makes sense:

An overload relay and an earth leakage relay are not performing the same job.

A circuit can have acceptable load current while still developing dangerous leakage to earth.

Selection caution:

Do not buy only the ELR and forget the CBCT requirement. Confirm CBCT size, conductor arrangement and required leakage sensitivity before ordering.

How to Choose the Right Protection Relay

A practical selection process begins with the failure you are trying to prevent.

The important part is not memorizing this table.

It is understanding why the fault happens.

Check the Current Sensing Method

Before selecting any current based protection relay, determine how the current reaches the device.

For smaller current ranges, a relay may accept current directly within its specified input.

For higher current applications, external CTs may be required.

When a CT is involved, confirm:

1. CT primary current
2. CT secondary current
3. Relay input requirement
4. Programmable CT ratio
5. Full load motor current
6. Starting current
7. Required trip threshold

A wrong CT ratio can make the displayed current and the protection setting incorrect.

Decide Between Panel Mount and DIN Rail

Mounting becomes especially important in replacement projects.

A panel mounted relay provides front access and visible indication from outside the enclosure.

A DIN rail relay is normally installed inside the panel alongside contactors, terminals, MCBs and other control components.

For example, ELR 19N is positioned as a panel mount earth leakage relay, while ELR 35 is a DIN rail version.

Choose according to panel architecture, operator visibility, available space and maintenance access.

Understand Fail Safe Operation

Fail safe logic matters in protection systems.

In fail safe operation, the relay state is arranged so that certain failures, including loss of power to the protection device, can move the control circuit toward a safe condition.

The CPR 22U specifically provides selectable fail safe and non fail safe operation.

Before commissioning, determine what the machine should do when:

• A protection fault occurs
• Supply to the relay fails
• The sensor or CT circuit is abnormal
• The fault disappears
• An operator presses reset

These questions are more important than simply asking whether the relay has NO and NC contacts.

Auto Reset or Manual Reset?

Automatic reset can be convenient where the process is expected to restart after the electrical condition returns to normal.

But automatic restart is not appropriate for every machine.

On equipment where unexpected restarting could create a mechanical or personnel hazard, the control philosophy may require manual intervention.

Always consider the complete machine safety circuit before deciding the reset method.

Common Mistakes to Avoid

Selecting one relay for every fault: Phase failure, overload and earth leakage are different problems.

Setting protection values without motor data: Full load current and actual operating conditions should guide the settings.

Ignoring starting current: Motors can draw significantly different current during starting compared with normal running.

Using undercurrent without understanding the process: Undercurrent can be useful for dry running or loss of load, but the correct threshold depends on the machine.

Ignoring CT ratio: Current protection is only as accurate as its measurement configuration.

Confusing earth leakage with overload protection: They detect different fault conditions.

Forgetting the CBCT: Earth leakage relay installations often depend on the correct CBCT arrangement.

Selecting by enclosure size alone: Two relays that fit the same panel space may perform completely different functions.

Do This, Not That

Quick Selection Checklist

Before selecting a Multispan protection relay, confirm:

1. What equipment is being protected?
2. Is the supply single phase or three phase?
3. What fault must be detected?
4. Is phase failure protection required?
5. Is phase sequence protection required?
6. Is overload protection required?
7. Is underload protection required?
8. Is current imbalance protection required?
9. Is earth leakage protection required?
10. What is the full load current?
11. What CT ratio is being used?
12. Is a CBCT required?
13. What trip delay is acceptable?
14. Should the relay reset automatically or manually?
15. Is fail safe operation required?
16. What relay output must operate?
17. Is panel mount or DIN rail preferred?
18. Is PLC or SCADA communication required?
19. Has the final setting philosophy been approved by the electrical engineer?
20. Has the latest datasheet been checked before ordering?

Specifications to Confirm Before Purchase

Specifications vary between relay models. Final details should always be confirmed from the latest manufacturer datasheet before purchase.

Check:

• Supply voltage
• Number of phases
• Monitoring range
• Current input
• CT ratio
• Leakage sensitivity
• CBCT requirement
• Overcurrent setting
• Undercurrent setting
• Phase failure protection
• Phase sequence protection
• Current asymmetry setting
• Trip delay
• Recovery delay
• Reset type
• Fail safe logic
• Relay output and contact rating
• Panel mount or DIN rail mounting
• Panel cutout where applicable
• Display and indication
• Communication requirement
• PLC or SCADA integration
• Installation environment

Why Buy Multispan Protection Relays from Radical TechMart?

The important part of protection relay selection is not finding a relay that can trip.

It is finding a relay that trips for the right reason.

Radical TechMart's current Multispan Protection Relays category includes products for phase protection, current protection, multifunction motor protection and earth leakage monitoring.

For a useful technical inquiry, provide your equipment type, motor current, supply system, CT details, fault protection requirement, mounting preference and required control output.

That information makes it much easier to compare the correct relay family instead of selecting only from a model number.

Final Thoughts

A Multispan industrial protection relay should be selected around the failure mode of the equipment.

If the problem is phase loss or wrong phase sequence, begin with phase protection.

If the machine must be protected from abnormal current, consider overcurrent and undercurrent protection.

If several motor faults must be monitored together, a multifunction protection device may be more appropriate.

If the concern is current leaking to earth, use an earth leakage protection strategy with the correct ELR and CBCT arrangement.

In an industrial panel, good protection is not about adding the maximum number of relays.

It is about understanding what can fail, detecting that condition early and making the machine respond safely before a small electrical problem becomes expensive downtime.

FAQs

1. What is a Multispan protection relay?

A Multispan protection relay monitors electrical conditions such as phase status, current or earth leakage and changes its relay output when a programmed fault condition occurs.

2. Which relay should I use for phase failure protection?

For applications primarily concerned with phase loss, phase imbalance and incorrect phase sequence, a phase protection device such as Multispan SPP 22 can be considered.

3. What is the difference between CPR 22U and CPR 126?

CPR 22U is a compact programmable overcurrent and undercurrent relay suitable for single phase and three phase applications. CPR 126 is oriented toward three phase current protection with functions including overload, underload and asymmetry monitoring.

4. What is the use of MPD 13N?

MPD 13N is intended for broader three phase equipment protection and includes functions such as overcurrent, undercurrent, current unbalance, locked rotor, phase loss and reverse phase protection.

5. What is an earth leakage relay used for?

An earth leakage relay detects leakage current flowing toward earth and operates its output when leakage crosses the selected threshold.

6. What is the difference between ELR 19N and ELR 35?

Both are used for earth leakage monitoring. The ELR 19N is a panel mount model, while the ELR 35 is designed for DIN rail mounting.

7. Does an earth leakage relay require a CBCT?

The current Radical TechMart product information for ELR 19N and ELR 35 indicates that a separate core balance CT is required for leakage sensing.

8. Can Multispan protection relays connect to PLC or SCADA?

Communication depends on the model. For example, MPD 13N is listed with optional RS485 Modbus communication on request. Always confirm the communication variant before ordering.