Sizing a 600/24 VAC transformer for a control circuit

[Anonymous user]

Hi guys, im trying to calculate how many VAs the 600/24V transfo needs to be for our control circuit. When looking the power consumption of a contactor, we have an inrush value and a sealed value. If i have say 4 contactors, do i need to consider 4x inrush values ?

[Gregoire_Brun · Accepted solution]

hello @Anonymous user 

Without knoledge of your application, I would answer "yes" if you have a risk to order on same time the 4 contactors together. to take any risk.

An Aplication FMEA need to be manage to measure risk you take if you decide to put a lower power than the maximum inrush value of the 4 contactors.

Best regards

[Yarom · Accepted solution]

Hello,

I hope I am not too late with the reply, but I agree with Gregoire.  If you would like, there here is a bit more detail about selection of the control transformer that can be found in the Schneider Control Transformer catalog, pages 7-8.

https://download.schneider-electric.com/files?p_enDocType=Catalog&p_File_Name=9070CT9901.pdf&p_Doc_R...

Add the sealed (maximum continuous load) VA's of all loads together.  Select the XFO VA above that value.

Then add the inrush VA's of all the loads.

Check the applicable column of the Inrush VA's of the secondary voltage. From the chart, if the inrush VA of the XFO is less than the total inrush VA's of the XFO, select the next higher VA XFO.

For details to understand the table, see bottom of page 7 of that catalog.

Make sure to always choose the right fuses on both primary and secondary of the XFO.

Best regards,

Yarom