NICEIC

Q & A of the Day - How do I calculate the rated current of the cable to this plant room?

Published: 17 January 2011 Category: Q&A

Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning a three-phase steam generator and the provision of a 7kW supply, is answered by the NICEIC:

Q & A of the Day - How do I calculate the rated current of the cable to this plant room?
Question: I have asked to provide a 7kW supply to satisfy the demand to serve a 6kW three-phase steam generator, which is simply elements and 1kW of single-phase auxiliary equipment, lighting etc.

What is the correct calculation that will determine the rated current of the supply cable to the plant room?

Answer: The design current of the load may be calculated in two parts:

Three-phase load: I = 6000/1.732 x 400 = 8.6A/phase

(or I = 2000/230 = 8.6A/phase)

Single-phase load: I = 1000/230 = 4.34A

Therefore, cable sizing should proceed on the basis of a design current, Ib, of 8.6 + 4.34 = 12.94A.

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