Control Voltage Sizing - PSU/Transformer

Just some notes on Sizing Control Transformers:

Collect all information about items connected to Transformer. (415/110V)

• Protection Devices (E/L, Protection relays , Arc detectors etc)
• Contactors (If powered by this supply to reduce inrush currents on system)
• Undervoltage/shunt trip coils in MCB's
• Motor heaters as they could be fed form this TX

Once you have accounted for all items find the nominal consumption as well as the inrush Consumption.

Calculate all the nominal consumptions (Qty x Consump) 

This will give you the min. size of the transformer

Next step is to Calculate the Inrush to ensure that the CB does not trip with the inrush current at startup. In most cases the TX will be able to handle a large inrush for a short period.

Do the Calculations your self

Just had some Cable tray designs rejected. It was not so much rejected but under designed. In most cases the engineer will select the route the cabling will be installed and then it is the trades person/ site construction team that will determine the cable tray type and installation.

Based on this these have been undersized, the fact is there is too many cables on the Tray for the support.

Tray support can handle 270kg, The span is 3m so effectively we can only place 270/3 per meter on the try. Solution change the tray supports or put more cable trays in and add more supports.

Next time do the Calculations yourself! Even if it is just to check