Jon Broadbent asks this question, which concerns a chiller replacement, and the sizing of cables for it, as well as the correct protection to use. It has been answered by ABB (Theme – Distribution Equipment including Cable Management):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: We are in the process of tendering for a chiller replacement and need to calculate the possible diversity and cable size of a chiller unit that has a full load current of 707.2A, a nominal draw of 555.9A, but a start up current of 940.6A.
We have presumed that these are three-phase values as they are not stated.
We would like to ascertain the cable size and breaker load. Can you please help?
Answer: When considering the cable size and protection to a chiller unit, you should calculate the cable size based upon the full load current - 707.2A in this case.
The size of cable will depend upon the insulation material, installation method and cable length required. The protection also needs to be able to cope with the start-up current. You have not stated how long the start-up is and this can have an effect upon the type of protection used.
If you select an electronic protection release type of MCCB, such as ABB’s Tmax range T6 800A with PR221DS/LS-I protection, you can select a time delay for both the overload and short circuit elements of the protection to allow for the start-up inrush to prevent unwanted tripping.
Click here to see the PDF flipbook for ABB’s Tmax technical catalogue.
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