What is the correct way to size electrical equipment for an application?

Nothing what I read from all of you is wrong. In this case the first steps are missing! what is the purpose of the electrical equipment, where will it be used, at home or for NASA? The acceptable failure mode determines the safety degree. And with that in mind you build up your equipment. That means that every item has its own weighting factor. Home based good price low quality in the consumer society where we live in most people throws broken equipment at the garbage. NASA wants no failure in space so high quality again a high price.

Correct way to size electrical equipments like transformer, cables, motors, breakers are different as their application is different in each case. However, we can consider following common areas. 1. Consider load to be supplied --> In case of transformer, cables, motors, breakers.. this is most crucial step to consider while sizing them. 2. Diversity factor --> Not all loads will be running at the same time. Designer must consider appropriate diversity factor while finalizing sizing. 3. Specific technical considerations --> For cables, short circuit capacity, voltage drop (continuous and starting) and continuous current carrying capacity. For breakers, short circuit level. For power transformer sizing, location, oil soak pit level etc.

In my experience following are the key steps to select equipment ratings for electrical system 1. Understand Application Requirements 2. Calculate Load Demand 3. Consider Power Factor 4. Voltage Compatibility 5. Select Equipment Ratings 6. Temperature and Environmental Conditions 7. Efficiency and Energy Consumption 8. Coordination with Protective Devices 9. Consideration of Harmonics 10. Future Expansion and Scalability 11. Consider scalability and flexibility in the design. 12. Compliance with Standards and Codes 13. Reliability and Redundancy 14. Coordination with System Components 15. Consultation with Experts 16. Documentation and Record-Keeping

Sizing electrical equipment for an application involves considering factors such as the load requirements, voltage levels, safety codes, and future expansion plans. Here's a general process: 1. Determine Load Requirements: - Calculate the electrical load demands, including both continuous and intermittent loads. - Consider peak demands and any potential future expansions. 2. Voltage and Current Requirements: - Determine the voltage and current requirements based on the load characteristics. - Ensure that the selected equipment operates within the specified voltage and current ratings.

In the load analysis phase, If you understand the following concepts, you can design an electrical load list Proper coordination between the electrical department and other sections such as 1️⃣ process, 2️⃣ mechanical & HVAC, and 3️⃣ instrumentation is essential. This prompts the following parameters: ✅️ rated power of motors and other loads ✅️ their duty types(Continuouse/Intermittent/Standby) ✅️ feeding types(Normal/Emergency/Vital) ✅️ diversity factors Accurate understanding of these concepts greatly aids us in sizing equipment. The first chapter of "Handbook of Electrical Engineering For Practitioners in the Oil, Gas and Petrochemical Industry" is an excellent resource for a thorough understanding of these concepts.💡 Enjoy it.

Some steps for sizing cables 1- determine load current by knowing the power I=S/V for single phase and I=S/√3V for three phase 2- determine the circuit breaker current is equal 1.25* Load current 3- the cable should withstand more current than circuit breaker so I cable=1.2*Icb 4- applying factors on the cable current factors like derating factor, grouping factor from the cable catalog. 5- choosing the proper cable C.S.A can handle the current after applying factors from catalog.

Some steps for sizing cables 1- determine load current by knowing the power I=S/V for single phase and I=S/√3V for three phase by experience I=1.5*S 2- determine the circuit breaker current is equal 1.25* Load current (circuit breaker factor is deferent according to load category by experience I=1.5*1.25*S 3- the cable should withstand more current than circuit breaker so I cable=1.2*Icb 4- applying factors on the cable current factors like derating factor, grouping factor from the cable catalog almost =0.75 5- choosing the proper cable C.S.A can handle the current after applying factors from catalog.

Always be sure to follow the correct formulas, take into consideration the installation routes, methods and the environmental influences present. Always follow up with checking for the Voltage Drop.

The load size. Current rating Voltage level The distance of the load from power supply. The mode of installation (air, duct etc) The environment of installation

The cable sizing process is basic on the following aspects: a. Cable Ampacity b. Ampacity derating due to the installation criteria. c. MV and HV cables short circuit withstand capacity. d. Voltage drops in steady state (and transient for motor loads). A good standard to do so, is the National Electrical Code (NEC), or NFPA 70.

The sizing of any transformer array may be one of the most important tasks during the desing of any industrial supply system, mostly due to it's greater unitary price. A oversized transformer will be not only more expensive but will require a greater space to be place and bigger foundation, larger protective ratings and it's more dificcult to place in site. In a existing systems, after making the load analisys, is often more economically atractive to place capacitor banks to avoid replacing supply transformers. In some special cases. Such as very low temperatures and avobe the sea level high, the sizing can be slightly diferent but is not a very often case to worry about.

- Found the operating power. - Calculate required current from the desired power. - Take at least 20 % extra size of breaker if equipment is inductive load carrier. It will take high current while starting. - For cable selection select slightly higher than rated current of the equipment. - Last select the equipment size / load as per your calculations and availability of the equipment.

Transformer sizing is the final stage to adjust all downstream design of the electrical system. Here, parameters HV/LV side, total load, % load spare capacity, SCMVA and etc.

Oh, recalculating transformer sizing and its perpetual challenges again. ☹️ ✅️ In industrial plants, the transformer size is calculated based on the peak load (🧐 see chapter 1 of Handbook of Electrical Engineering). ✅️ The process department is responsible for defining and notifying the electrical department of the diversity factor for Intermittent & Standby loads. ✅️ The perpetual challenge I face with the process department is either their reluctance to provide these factors or offering them as a daily or weekly operational utilization rate (e.g., x hours out of 24 hours in service). 💡However, these items represent diversity factors and should express the percentage of Intermitrent loads that may be simultaneously in service.

- Load Type: Differentiate between linear and nonlinear loads to appropriately size transformers. - Efficiency Consideration: Evaluate transformer efficiency to minimize energy losses and improve overall system performance. - Impedance Matching: Ensure proper impedance matching between the transformer and the load for optimal power transfer.

Circuit protection is vital for the components in your systems. Ensuring the longevity of your equipment and system is necessary to an electrical designer’s job. Once you estimate what the maximum current of a system will be, select the best circuit protection according to a proper tolerance of current, and start with that in your system.

Circuit Breaker is a safe and protective device, and it is important that the breaker size for the specific works should be done.

Circuit protection is vital for the components in your systems. Ensuring the longevity of your equipment and system is necessary to an electrical designer’s job. Once you estimate what the maximum current of a system will be, select the best circuit protection according to a proper tolerance of current, and start with that in your system.

Selective Coordination: Coordinate breaker sizes to achieve selective coordination, minimizing downtime during fault conditions. - Short Circuit and Overload Protection: Size breakers considering short-circuit and overload protection requirements, ensuring reliability and safety. - Temperature and Altitude Effects: Account for environmental factors such as temperature and altitude, which may influence breaker performance.

Generally, you should size a switch for 125% of the load (or 25% additional capacity) and no less. Oversized circuit breakers can allow wires to heat up above safe levels without stopping current. On the other hand, undersized switches can trip continuously during normal operation. It should also be considered when choosing a breaker that has a lower amperage than what the cable resists to avoid fire problems and can provide security, for example: cable #12 --> 25 A max then the breaker must be 20A to avoid overheating in the cable, obviously this is an example, load calculations must be made and the electrical components responsibly chosen.

1. Load analysis. 2. Starting and operating conditions. 3. Environmental factors. 4. Efficiency and power factor. 5. Compliance with standards.

Motor sizing is depend on the process or operation requirements. After have this step electrical engineer can start with load analysis, starting technique, drive types, and etc. parameters.

Motor sizing is a perpetual debate between the electrical and mechanical departments!!!! 🤼♂️ In industrial plants, motor sizing is outside the scope of the electrical department, and the process department is obligated to declare the Brake Horse power (BHP) of its motors in process consumption list. ✅️ the operating location of the motor may not adhere to standard temperature and standard height, temperature factor and height factors also play a significant role in motor sizing. ✅️ The third effective factor in motor sizing is the API factor, which is selected based on the type of mechanical load connected to the motor according to the API standard. Mechanical department is responsible to issue API , temp & height factor

- Starting Current Analysis: Analyze the starting current requirements of motors to select starters and protection devices adequately. - Inrush Current: Consider inrush current during motor starting and size components accordingly. - Load Characteristics: Understand the load characteristics to select motors that meet the specific demands of the application.

Design margin plays a crucial role in motor selection. When considering available power, having a design margin allows for a safety buffer between the motor's rated power and the actual power required by the application. This additional margin accommodates variations in operating conditions, unexpected load spikes, or inefficiencies that might arise during operation. It's prudent to account for these uncertainties to ensure reliable and efficient performance while preventing overheating or premature wear of the motor.

In the context of electric vehicle (EV) charging, the choice of RCD is paramount. Regulations often prescribe a minimum of a Type A RCD when a charger has a 6mA DC residual current monitor. Yet, a standard Type A may lead to nuisance tripping due to the complex electronics in vehicle onboard chargers. To circumvent this, high immunity RCDs like Type B or Type F should be considered. These are adept at distinguishing between fault currents and the transient disturbances common in EV chargers, thereby enhancing reliability and minimising service disruptions. It’s essential for contractors to recognise the criticality of selecting RCDs that align with the specific demands of EV charging systems, ensuring robust protection and user confidence.

Consider the environmental factors such as temperature, humidity, and potential contaminants that could impact the performance and lifespan of the electrical equipment.

In any electrical installation, the grounding system is very important. For this we must consider among others: (a) The earthing system design and installation will be in accordance with the applicable ANSI/IEEE/NEC standards. (b) The earthing system will protect the electrical network and assure personal safety in case of an electric failure and against static charges. (c) The following equipments will be connected to earth: • Non-current carrying metallic parts of electric equipment. • Neutral impedance, lightning arrestors and conductors. • Metallic structure of building and metallic reinforcement of concrete building. • Tanks, vessels, exchangers, pipes. • Lorry tanks during loading, if necessary.

- First step is to understand/assess intended technical function of desired equipment to meet process or non-process/electrical requirement. - Check available distribution voltage & freq and power system adequacy/spare capacity for required equipment. - Select & size equipment electrical specifications following applicable standards & specifications (as per company / local regulations).

Take note s of the load condition of the equipment and its specifications, then other things can follow to determine other parameters.