# Sizing Power Supply in Electrical Cabinet

• Som_P
In summary, when selecting a power supply for control power, it is important to consider the peak inrush current, average holding current, and the current requirements of all devices being fed. Large solenoids and motors should be carefully evaluated for their potential large inrush currents. For DC supplies, the Amps can be calculated by dividing the VA by the voltage, while for 3 phase AC supplies, the calculation will depend on whether the device is being connected as a 3 phase or single phase device. When selecting a 24VDC power supply fed by 120VAC, the total current should be taken into account.
Som_P
What things do I need to consider when selecting a proper sized power supply? Basically this is control power, ouputs are pushbutton lights, alarm horn, and solenoid valves. Do I look at the peak inrush current? Average holding current?

You literally may want to make a list of all of the devices being fed and add their current requirements- in our systems this exercise is part of our design requirements. Be wary of large solenoids and motors as they may have large inrush currents - as you have alluded to.

So basically I would be adding up the total current? Then simply select a power supply with enough current capacity? If a spec sheet list inrush current in VA, what formula would I apply to find Amps(A)? This is 3-phase by the way.

Last edited:
Yep, but when you said power supply I was think of a DC supply - is it DC with a 3 Phase AC source? Or describe what it is a little more.

For DC the Amps will just be x VA / Voltage. EG 300VA and 24 V ... 12.5A...

3 ph AC is a little more complicated - but for VA it will depend if the device is being connected as a 3 phase device or a single phase device. Single phase same as above, 3 phase √3*V* A(in one phase)

I apologize for not being clear, well not proof reading my comments. Anyway, I need to get a 24VDC power supply, this is being fed by 120VAC. My main question was to select the 24VDC power supply as it relates to total current?

## 1. What is the purpose of sizing power supply in an electrical cabinet?

The purpose of sizing power supply in an electrical cabinet is to ensure that the power supply is able to provide enough electrical power to all the components and devices in the cabinet. This ensures efficient and safe operation of the electrical system.

## 2. How do you determine the required size of a power supply for an electrical cabinet?

The required size of a power supply for an electrical cabinet is determined by calculating the power consumption of all the components and devices in the cabinet. This includes taking into account their voltage and current ratings, as well as any potential future expansions or additions to the system.

## 3. Can a power supply in an electrical cabinet be too big or too small?

Yes, a power supply in an electrical cabinet can be too big or too small. If the power supply is too big, it may be more expensive and take up unnecessary space in the cabinet. If it is too small, it may not be able to provide enough power for all the components and devices, leading to potential malfunctions or failures.

## 4. What are the consequences of not properly sizing the power supply in an electrical cabinet?

If the power supply in an electrical cabinet is not properly sized, it can lead to malfunctions or failures of the components and devices in the cabinet. This can result in costly repairs, downtime, and potential safety hazards.

## 5. Is it necessary to consider the environment when sizing a power supply in an electrical cabinet?

Yes, it is important to consider the environment when sizing a power supply in an electrical cabinet. Factors such as temperature, humidity, and altitude can affect the performance and efficiency of the power supply, and should be taken into account during the sizing process.

• Electrical Engineering
Replies
8
Views
1K
• Electrical Engineering
Replies
11
Views
765
• Electrical Engineering
Replies
21
Views
5K
• Electrical Engineering
Replies
36
Views
3K
• Electrical Engineering
Replies
11
Views
1K
• Electrical Engineering
Replies
4
Views
2K
• Electrical Engineering
Replies
13
Views
3K
• Electrical Engineering
Replies
13
Views
2K
• Electrical Engineering
Replies
2
Views
1K
• Electrical Engineering
Replies
49
Views
6K