Electrical systems and protection

Electrical systems and protection

Power design, panels, cabling, grounding and bonding; From initial calculations to testing and delivery

The electrical installation of the fountain must meet three needs at the same time: the safety of people, the protection of equipment and the stable implementation of water and light effects.

The fountain environment is different from a dry facility environment. Humidity, immersion, possible contact of people with water and metal components, cleaning materials, sunlight and washing operations, all affect the choice of equipment and protection method.

The safety of this complex depends on the coordinated performance of several parts: selection of the protection method, placement of equipment, quality of cable and connection, ground connection and connection, performance of disconnection devices and accuracy of tests. The presence of a protective key or the word "waterproof" on the product alone does not prove the safety of the entire system.

This chapter presents the basics of design and control. The final determination of equipment, protection areas and settings must be done on the approved plan and by a qualified designer and contractor.

26–1. Design basis and technical references

At the beginning of the project, the type of facility, the design authority, the revision to be used and the requirements of the certifying authority should be determined.

Some relevant international references are:

The scope of these references is explained in the IEC official pages. The general part of the boards should also be used together with the appropriate special part of the same collection. Pool and fountain facilities ^[171], underwater lights ^[172], low pressure panels ^[173], facility inspection and testing ^[174]

These references do not automatically replace the applicable regulations at the project site. Also, a part of a design system should not be combined with the exceptions of another system, unless the compatibility of the set has been checked and confirmed.

26–2. Classification of the place and determination of protection areas

Before choosing the voltage and equipment, the usage status of the fountain should be clarified:

• Is the entry of people into the pool allowed or expected?

• Do children play directly with the fountains?

• Which surfaces get wet?

• Is the equipment underwater, next to the water or in an independent space?

• What is the path of high-pressure washing and the possibility of flooding?

• Where are the metal parts that can be touched?

This information is the basis for drawing protection areas in plan and section. In the map, the location of the light, pump, connection box, power supply, panel and cable route should be specified in relation to the areas.

A general zoning map cannot be applied without review for a decorative fountain, walk-in pond, and dry floor fountain. The dimensions of the areas and conditions of the permitted equipment should be extracted from the selected reference text and appropriate to the actual classification.

"Being under the floor" or "being inside the enclosure" does not necessarily remove a device from the danger zone; Access, water connection and enclosure details should be checked.

Figure note from the source manuscript

Figure 26-1 instead

Suggested image: plan and cross-section of a hypothetical fountain, showing the protection areas, the location of the panel, the power sources and the cable route. The dimensions and names of the areas should be inserted only after checking the electrical designer and based on the selected reference.

Subtitle: "Choosing electrical equipment begins with determining the type of use and protection areas."

26–3. Preparation of list of electrical loads

The load list must cover all consumers; From main pumps to small control equipment.

For each consumer, the normal, maximum and startup state must be specified.

In the musical fountain, the average power of a show is not enough to choose nutrition. In a part of the program, several pumps and all lights may reach the maximum load at the same time.

In the list of GSO equipment, control pumps, variable speed and 24V have been introduced. This variation indicates that power specifications should be recorded for the actual model of each device. Urban fountain equipment - GSO ^[175]

26–4. Calculation example of motor current and lighting

A) three-phase motor

Consider a hypothetical engine with the following specifications:

• Output mechanical power: 3 kW;

• Line voltage: 400 volts;

• Efficiency: 0.88;

• Power factor: 0.82.

For balanced and direct operation from the network:

$I=\frac{P_{out}}{\sqrt{3}U\eta \cos \phi }$

$I=\frac{3000}{1.732\times 400\times 0.88\times 0.82}\approx 6.0A$

This number is the approximate current at the assumed point. Cable selection and protection should be completed with nameplate information, starting current, installation conditions and control method.

If the motor is fed from the inverter, the input current of the drive should not be obtained only from this relationship and the power factor of the motor; Drive input information and actual working conditions are required.

b) direct current lighting load

For a hypothetical load of 120 watts at 24 volts:

$I=\frac{P}{U}=\frac{120}{24}=5A$

This current corresponds to the 24 V side. The input current of the power supply will be different according to its efficiency and input specifications.

In the calculations, it should be clear that the declared power is related to the mechanical output of the engine, the electrical input of the equipment or the output of the power supply.

26–5. Feeding structure and board design

Split circuits should help with fault diagnosis and maintenance. Pump, lighting, purification and control circuits are better defined with their appropriate identification and protection.

In the design of the board, the following are important:

• design flow and simultaneous conditions of loads;

• possible short-circuit current at the installation site;

• The capacity to cut off protective equipment;

• coordinating the protection of downstream and upstream circuits;

• increasing the temperature inside the panel;

• conditions of humidity, corrosion and flooding;

• Repair space and the possibility of safe disconnection;

• Proper isolation of power, command and very low voltage circuits.

The quality of internal parts alone does not confirm the quality of the board. Assembly method, connections, ventilation, terminals and assembly verification are also important.

In the placement, the possible level of waterlogging, the path of leaking pipes and the possibility of dripping from the upstream equipment should be checked. The appropriate degree of body protection is not a substitute for proper positioning.

26–6. Separation of duties of protective devices

Protective equipment has different functions:

A conventional RCCB does not provide overload and short circuit protection by itself and must be coordinated with appropriate protection. ABB explains the difference between RCCB and RCBO in its equipment introduction. Differential current protection equipment - ABB ^[176]

In circuits where the design authority stipulates additional protection with a maximum sensitivity of 30 mA, this requirement must be implemented with the correct selection of the device type and performance test. However, the 30mA number should not be considered the full version of protection for any fountain circuit.

It is not allowed to eliminate unwanted disconnection by removing protection or arbitrarily increasing the threshold; The source of the leak, the aggregation of the circuits and the compatibility of the equipment should be checked.

26–7. Why doesn't "24V" alone mean safety?

The safety of a low voltage circuit depends on the power supply, isolation from other circuits, wiring method and fault conditions.

Three concepts must be distinguished from each other:

SELV: Safe extra-low voltage system with protective isolation and specified requirements to ground and other circuits.

PELV: The protective extra low voltage system whose grounding conditions are different from SELV.

FELV: very low voltage for the functional requirement, without fulfilling all the protection requirements of the above two groups.

Schneider Electric's Electrical Installation Guide explains these differences and the necessity of maintaining SELV circuit isolation. Very low voltage systems - electrical installation guide ^[177]

Therefore, a power supply with 24V output is not necessarily suitable for powering underwater equipment. The installation location of the source, its approval, output type, connection conditions and downstream equipment should be checked.

The voltage limit also depends on the type of current, area and conditions of use. The number written on the light is not considered a license to install it in any part of the fountain.

26–8. Earth connection, protective conductor and bonding

These terms are related, but do not have a single function:

• Ground connection: the defined connection of the system with the ground;

• Protective conductor or PE: the conductor related to protection, including the connection of protected bodies;

• Protective bonding: connection of specified components to limit dangerous potential difference.

The designer must specify the type of supply network, fault current path and automatic disconnection conditions. Measuring the resistance of the earth electrode alone does not prove the safety of the facility.

Included components, connection points, material and cross section of the conductor and the possibility of inspection should be specified in the assembly plan. A joint on a painted surface, a joint prone to corrosion or a path that is removed by opening a part should be checked.

The phrase "ground all metal parts" is not a precise command. The condition of each component must be compatible with the protection method; In particular, arbitrary grounding of SELV circuit sections can conflict with its requirements.

Also, it is not possible to prescribe a fixed value of ground resistance or a fixed cross-section of the bonding conductor for all fountains.

Figure note from the source manuscript

Figure 26-2 instead

Suggested image: A conceptual map separated by showing the protective conductor of the included equipment, the interconnection network and the SELV circuit. The map should clarify the difference between these paths and be checked by the electrical designer before printing.

Caption: "Grounding, bonding and protective isolation shall be defined in a coordinated plan."

26–9. Lights, pumps and the meaning of the degree of protection IP

In choosing underwater equipment, several characteristics should be checked independently:

• Suitability for use and installation location;

• method of protection against electric shock;

• degree of protection against penetration;

• depth and allowed immersion conditions;

• compatibility with water and purification materials;

• thermal conditions and the possibility of working outside the water;

• Cable and connection specifications.

IP68 is not a generic mark for "total protection". Immersion conditions should be obtained from the manufacturer and this rating is not a substitute for checking for electrical shock, corrosion or mechanical tolerances.

For example, in the specifications of some ProfiRing lights, OASE declares a voltage of 24 V DC and a rating of IP68 with a depth of 4 meters. This information is specific to the model and should not be generalized to other lights. Specifications of ProfiRing lights - OASE ^[178]

IEC 60598-2-18 also specifically covers fixed lights used in or in contact with water. Simply having an IP label does not equate to meeting all product requirements.

26–10. Cabling and connections in wet environment

The cable should be selected for the actual installation conditions; including permanent immersion, sunlight, chemicals, movement or abrasion.

In design and implementation, it must be controlled:

• Cable route and mechanical protection;

• Bending radius and tension restraint;

• Gland's compatibility with Qatar and cable construction;

• Sealing the entrance to the equipment;

• access to repairable joints;

• preventing the transfer of moisture along the cable or inside the sheath;

• Isolation of circuits according to the protection plan and communication needs.

A typical tape-covered screw connection is not a reliable detail for permanent immersion. The underwater connection must be a suitable system with implementation instructions.

In introducing the ProNect connection, OASE states sealing, allowable depth and capillary transfer barrier as system features; This specification shows that the quality of the connection goes beyond the external sealing of the cable. ProNect - OASE underwater connection system ^[179]

26–11. Calculation example of 24 V circuit voltage drop

Consider a hypothetical circuit with the following specifications:

• Source voltage: 24 V DC;

• Constant design current in this calculation: 5 amps;

• One-way length of the route: 30 meters;

• Copper conductor;

• Hypothetical specific resistance in design conditions:

$\rho =0.0225\Omega m{m}^2/m$.

For two-wire round trip:

$\Delta U=\frac{2\rho LI}{S}$

where $S$ is the cross-sectional area of each conductor in square millimeters.

Results:

If, just for this example, the design goal is to drop less than 5%, a cross section of 6 mm2 can be considered for conductor drop.

But the final choice still needs to control the following:

• The minimum allowed voltage of the equipment;

• connection and driver drop;

• resource output tolerance;

• Actual current at lower voltage;

• Cable current capacity and its protection.

Some electronic loads draw more current by reducing the voltage to maintain power. Therefore, the constant flow assumption of this example should be adapted to the actual behavior of the equipment.

This calculation shows why in the low-voltage circuit, cable selection based on amperage alone is not enough. Shortening the path or dividing the load between branches can also be effective; Moving the power supply is done only in the authorized place.

Figure note from the source manuscript

Figure 26-3 instead

Suggested image: voltage drop diagram of four example cross-sections, along with showing the length of 30 meters one-way and round trip. Enter 5 amps as a fixed assumption.

Caption: "In low-voltage power supply, path loss can become decisive before limiting cable current."

26–12. Inverter, leakage protection and electromagnetic compatibility

The inverter can change the shape of the leakage current compared to a simple load. Therefore, choosing an RCD based only on the rated current and sensitivity is not enough.

ABB explains that some converters and drives can produce a differential current with a smooth DC component; Recognizing this current form is one of the issues of RCD type B selection. Differential current protection in converter circuits - ABB ^[180]

This does not mean to choose the same type B for all equipment. The type of protection must be coordinated with the drive building, manufacturer's instructions and project requirements.

In the design of the drive circuit, other things are also considered:

• length and type of motor cable;

• The requirements of the shield and its connection;

• The effect of EMC filters on leakage current;

• possible need for an output filter;

• compatibility of motor insulation with drive power supply;

• Separation of the power cable route from communications and sensors.

The connection of shield and PE should not be done with empirical rules and the same for all cables. System instructions and electromagnetic compatibility plan should be based.

26–13. Overvoltage, backup power and control circuits

Outdoor fountains may have long power and data cables. Overvoltage protection should be checked with network conditions, routes and lightning protection scheme.

The presence of SPD in the main switchboard does not necessarily mean adequate protection of all remote equipment. Its location, type, coordination and connection must be designed; Communication lines also contribute to this review.

If the UPS is used for controller or data logging, the boundary of the backup circuit must be clear. A main power failure may not mean that all parts are de-energized.

Data circuits such as DMX or network must also be implemented with appropriate equipment, environmental protection and the correct connection method. Details of planning and communication will be discussed in the relevant chapter.

26–14. Interlocks, emergency stop and repairs

An interlock is a defined dependency that prevents an operation from continuing in an improper state.

"Manual" mode should not leave the necessary protections unattended in the circuit. A power return or the removal of a fault should also not cause an unwanted start-up during repair.

A command stop is different from a safe electrical disconnect. Zeroing the pump revolution, stopping the program or turning off the display is not a proof of no electricity.

For repair, energy sources must be disconnected, locked and identified according to the approved method, and de-energization must be verified. Energy stored in drives and backup sources should also be considered. Tests and work on installations must be performed by qualified personnel.

26–15. Inspection and test before operation

The final test should show that the installation is as designed and that the protections are functioning as expected.

The test program can include the following:

IEC 60364-6 is dedicated to the initial and periodic inspection and testing of installations. Acceptance values ​​and methods should be derived from selected reference and equipment specifications. Inspection and test authority - IEC

Before the insulation test, the condition of the electronic equipment should be checked. Applying an inappropriate test voltage to the drive, power supply, or control equipment can damage them; The manufacturer's instructions for isolation and testing are the criteria.

Pressing the RCD test button is also not a substitute for a complete test of the installation, protective continuity and recording the results.

Figure note from the source manuscript

Figure 26-4

Suggested Image: Four photos of board inspection in safe condition, alignment control, measurement with appropriate tool and test result sheet. Images should be selected from actual supervised operations and do not depict unsafe waterside work.

Caption: “Safe delivery requires recordable results; Turning on the standard equipment is not enough."

26–16. Periodic delivery and maintenance documents

The operator must be able to identify, disconnect and track each circuit. Delivery documents must include at least the following:

• Single-line map and construction maps;

• List of loads and circuits;

• map of protection areas;

• Specifications of cable, gland and connections;

• Map of ground connection and coordination;

• Type and configuration of protective devices;

• specifications of power supplies and drives;

• The results of the tests and the identifier of the measuring instrument;

• Interlock logic and emergency stop;

• repair, lockout and restart instructions;

• Periodic inspection program and training records.

During maintenance, cable damage, connection loosening, corrosion, water penetration, the condition of seals, and the functioning of protections should be checked. After changing the lamp, pump, cable, power supply or changing the program affecting the safety, the test of the affected parts should be repeated.

Inspection frequency should be determined by environmental conditions, usage rate, failure history and project requirements. A high-traffic public fountain with constantly submerged fittings has different maintenance requirements than an underpowered system in a controlled environment.

In Chapter 27: Control, Automation and Fountain Communication Networks, the structure of controllers, pump and valve and light communication, sensors, operation logic, fault management and remote access will be reviewed.