technical articles

Hydrogen production: why choose a high Service Index switchboard?

In the hydrogen production industry, the safety and availability of equipment are essential. The Service Index (SI) is a reference, defined by the UTE C 63-429 guide, which allows to characterize a LV switchboard according to the user’s needs in terms of operation, maintenance and evolution. In this article, we will explain in detail what an SI is for switchboards and why it is important to choose the right level of SI for your Hydrogen production installation.

What are Service Indexes for Electrical Switchboards?

The Service Indices (SI) are three-digit codes defined by the UTE C 63-429 guide used to determine the type of low-voltage (LV) switchboard that best meets the requirements of the installation and the customer.

They allow each user or specifier to know the requirements that the LV electrical switchboard must meet in terms of operation, maintenance and evolution. The purpose of the SIs is to qualify the level of service provided by the LV switchboard and to manage all types of interventions at the different stages of its life cycle.

There are three good reasons for specifying a Service Index (SI) for an LV switchboard:

  • Each SI corresponds to a functional unit (FU) design of the switchboard, which can be a fixed, disconnectable or withdrawable unit.
  • Each functional unit of the switchboard corresponds to a techno-economic requirement, a level of qualification of the maintenance personnel and a maximum level and time of intervention in case of failure or modification of the installations.
  • The choice of a high SI implies a precise design in terms of service continuity and operational safety of the switchboard.

The different levels of Service Index

The different levels of Service Indexes (SI) are used to determine the functionality of the switchboard in the event of subsequent operations, maintenance or evolution.

  • During the operating phase, the SI determines the consequences of a mechanical locking or electrical consignment operation of the switchboard in view of an intervention on the installation.
  • During the maintenance phase, the SI determines the suitability of the switchboard to meet a maintenance requirement.
  • During the evolution phase, the SI determines the suitability of the switchboard to respond to a future evolution.

Service index for electrical switchboards

There are several SI levels, ranging from SI111 to SI333. Each SI level corresponds to a level of design of functional units in the LV switchboard as well as a level of suitability to meet the requirements of different phases of the switchboard life cycle.

The highest SI levels (SI333 and SI 233) provide the highest levels of service continuity and safety, including the ability to add new equipment without disconnecting power to the system.

The SI333 level is often used in situations where it is crucial to maintain a constant power supply, for example in data centres or in continuous flow or critical production facilities for commodities such as electricity. This service index is also often used in safety-critical facilities, such as airport control centres.

Why is it important to choose the right Service Index level for your Hydrogen production facility?

It is important to choose the right level of service index for your hydrogen production facility to ensure the safety of your personnel and the continuity of your production. An inadequate SI level could result in operational downtime which can impact on the performance of the production facility.


A high SI level LV switchboard guarantees the continuity of hydrogen production. If the LV switchboard is of low SI level, in case of failure or maintenance it has to be shut down, which can lead to production interruptions and significant financial losses.


A high SI level LV switchboard makes it easier to retrofit the functional unit and thus extend its life and manage obsolescence.


Depending on whether or not it is necessary to keep the installation energised during maintenance or servicing, the correct mobility and/or service index must be chosen.

For example, when the installation is fixed (FFF or SI111), it is necessary to cut the power to the whole switchboard in order to carry out a service. This means that all the motors are out of service for the duration of the intervention, which can be detrimental.

A withdrawable solution (WWW or SI333) allows to carry out interventions in full safety on a single module. This means that only one motor is out of service for the duration of the intervention, allowing the others to continue operating. Intermediate service or mobility indices can also offer technical and economic solutions adapted to each case.



In summary, Service Indexes are an essential guide to designing an LV switchboard that is capable of meeting the need for continuity of service throughout its life cycle.  By opting for LV switchboards with a high SI, you can be sure that your equipment is capable of guaranteeing the continuity of service of your hydrogen production even during a failure or maintenance.

technical articles

Why digital thermal protection for electric motors?

The electrical protection regulations require thermal protection for electric motors.

In direct motor supply (motor supply without inverter or electronic starter) the thermal protection function is provided by default via a bimetal thermal relay.

This is an economical solution at the time of purchase but has some disadvantages in terms of motor availability during operation compared to digital thermal protection.

What is a bimetallic thermal protection relay?

The bimetallic thermal relay has the current flowing through it to supply the motor. It protects the motor against abnormal heating of its windings. This occurs when the current drawn by the motor is too high for a certain period causing the windings to overheat.

If the phenomenon persists, it causes melting of the windings, which makes the motor unusable and requires replacement.

The bimetallic thermal relay is set to heat up faster than the motor windings, so it will cut off power to the motor to preserve it.

Bimetal thermal protection induces uncertainty in the process management

The bimetal thermal protection relay is a simple electro-mechanical device that does not allow its overheating status to be known. Therefore, it is not possible to know how soon it will open the motor supply circuit.

The available “thermal reserve” is therefore not known before the motor is switched on and off. In this case, this uncertainty must be allowed for in the operation of the manufacturing process including the motor.

If the bimetal thermal relay protects the motor, the motor supply circuit will remain open for a given time, which corresponds to the bimetal cooling down (and also to the motor since it is no longer supplied during this period).

Once the Bimetal has cooled down, it re-establishes the circuit and the engine is again available for the next start.

From the process control, the waiting time for cooling is not known, so it is necessary to wait, with the engine stopped, without being informed about the time of this situation.

When the thermal relay re-establishes the motor supply circuit, after a trip and a certain waiting time, the motor can be restarted to re-launch the process.

The motor’s peak power consumption on start-up may cause the thermal relay to trip again, as it did not have enough thermal reserve to support a new start.

This is a return to the fault point and it is again necessary to wait for the end of the cooling cycle before attempting a restart.

These three typical examples show that using a bimetallic thermal relay can protect the electric motor, but it does not provide a smooth operation of a manufacturing process that requires availability and continuity of service.

What is a digital protection ?

The digital thermal relay also measures current to the windings of the electric motor and calculates their temperature rise using the formula I²t. Unlike the bimetallic thermal relay, it does this via electronics and a microprocessor. A motor protection curve is selected to match the protected windings.

Digital relays ensures smooth process control

The temperature rise and thermal reserve of the engine are known at all times. This provides a valuable real-time indication of the engine’s condition and thus gives early warning that the engine’s operating limits may be exceeded.

This time can then be used to start a back-up motor or to adjust the motor load to avoid tripping and consequently stopping production.

If nothing was corrected, the thermal relay is triggered after its warning countdown when the engine needs to be protected. However, the time required for the engine to cool down is calculated and thus the waiting time before a possible restart is immediately announced.

This is useful information for the process control as the waiting time before engine restart is known. The situation’s critical nature in relation to the current production process can be judged immediately.

Once this waiting time has elapsed and been counted, the digital thermal relay starts the motor again.

As seen earlier, restarting the motor with a bimetallic thermal relay after a warm-up can be uncertain. This is not the case with a digital thermal protection.

Indeed, the digital protection relay knows the motor’s temperature rise on starting. This allows it to make the motor available for restarting when its windings have cooled down but also, and above all, when the motor has enough thermal reserve to withstand a start.

Thus, the operator can be sure that he will be able to restart his motor when he is allowed to do so!

These three situations show the advantages of digital thermal protection over bimetal thermal protection. Digital protection ensures smooth operation of a manufacturing process that requires availability and continuity of service.

Going further with electronics

As the digital thermal relay has electronics and a microprocessor, it is possible to go further than just motor protection. Many other useful protections are available from current and voltage information.

For example, phase unbalance protection, over or under current protection, over or under power protection, phase reversal, detection of too long a start or limitation of the number of starts in a time period… The list is long!

> Discover GemStart 5, our digital thermal protection relay to protect your hydrogen production motors.

technical articles

Digital thermal protection for which electric motors?

Digital thermal protection relays offer significant advantages over bimetal thermal relays, although the initial investment is higher.

Improve Reliability of Small and Large Motor Production Processes

Some continuous process plants have introduced digital relays on all their electric motors to maximise the information flow and thus improve process reliability. It is also possible to opt for a selection of the motors concerned, to limit the initial investment.

An intuitive approach is to use the bimetal thermal relay for small motors and the digital thermal relay for larger motors. Indeed, the acquisition or rewinding cost of a large motor is always more significant than for a small motor. On the other hand, from a certain size of motor onwards, bimetallic thermal relays also use current transformers, which reduces the price difference between bimetallic and digital protection.

Given the early indications that digital protection can provide, and therefore the advantage in terms of availability, it is necessary to consider the motor’s critical nature in the overall manufacturing process. A small motor failure can lead to the complete shutdown of a production line or spoil a batch of production in progress, so this motor will have to be closely monitored to prevent this and it deserves digital protection even if it is a low cost motor.

Avoiding Production Stoppage with Digital Thermal protection Relay

Another consideration is what the motor drives. A motor stoppage can cause irreversible damage. For example, an overhead crane carrying a glass or molten metal bag should not fail.

Consider the downtime of the process when a motor fails: e.g. a broken conveyor belt is difficult to repair quickly, a jammed mill is not easy to release, changing a pump or motor in a hard-to-reach place are all examples that may lead to a preference for digital protection.

All of the protections provided by a digital system make it possible to double certain safeguards, which will improve the failure mode analysis, their effects and the manufacturing process criticality.

For example, under-power protection can detect cavitation or lack of fluid in the pump casing even if the process line traditionally uses a dry-running safety device.

By providing information and alarms for both the electrical and motor drive areas, digital protection is useful for collecting measurements to improve the reliability and optimisation of the manufacturing process. Once the plant is in production, any variation from the initial output is detected. The cause of this variation can be investigated and addressed to return to the original operating condition or to optimise the process. Motor ageing can lead to a decrease in efficiency or a decrease in the quality of the product produced.

Digital Thermal protection Relay to Optimise Motor Monitoring

The digital relay is an opportunity to temporarily optimise the monitoring of an electric motor.

Indeed, by taking advantage of a high service index (SI) switchboard allowing to quickly replace a drawer by another one, it is possible to equip its installation with traditional protections but foresee some reserves with digital protections.

When a motor needs to be monitored more closely, the drawer with conventional protection is replaced by a drawer with digital protection. Thus all the measurement and traceability tools are available and make it possible to study in depth a phenomenon on a motor or to seek the causes of its malfunctioning.


Discover GemStart 5, our digital thermal protection relay to protect your hydrogen production motors.