Control power sizing calculator
- Thread starter OCPD
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xptpcrewx
Power System Engineer
- Location
- Las Vegas, Nevada, USA
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- Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
Use the SUM function in excel to add all the device VA. Also note, NEC doesn’t apply to Manufacturers equipment internals.
petersonra
Senior Member
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- Northern illinois
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- engineer
I think you're just going to have to add up the maximum amount of power required at the same time. My suspicion is that for the most part it will just be adding up the VA required by each individual device which you should be able to do fairly easily with the sum function as mention by a previous poster.
There may be some cases where some devices can never be energized at the same time so you might be able to reduce your control power requirements slightly by eliminating the non simultaneous devices but probably it won't make much difference cost-wise and you never know what somebody is going to do down the road.
Most of the time when this is an issue it has to do with the DC backup system and how much battery power you need which can get a little pricey but that's just the way it is. I would not be trying to save money on batteries. You might get away with it for a while but you could also get burned pretty bad if you have a blackout and can't restart because your battery capacity is just a hair low
Add all the sealed-in VAs of all relays and also add the inrush VAs of all connected load. You must be able to make your own load profile and start from there. Choose a CPT that can deliver the steady state(sealed-in VA+ indicating lights VA), and consider that the CPT chosen can deliver inrush VAs at a specified voltage. Ex. a certain manufacturer claims their 50VA CPT can deliver 240 inrush VA at 90% rated voltage!
As for the UPS, the total energy derived from batteries (AH) should be derived from the load profile you have created. For example: Inrush = 200A for 1 second and the steady state load amps for the whole 60 minutes = 30A. AH reqd = 200 X 1/(60sec/min X 60min/hr) + 12*60 min/60 min/hr) = 30.05 AH. Add some fudge factors to account for efficiency of UPS and backup batteries. My two cents!
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