Figure out UPS size

[Anonymous user]

I currently have 5 Cisco 3750 48 port switches and will be looking to add a 3750 24 port POE and a Barracuda Web Filter 410. How can i determine or size the appropriate APC unit? Using APC's product selector tool it looks like he unit i would need cost over $5,000, is that possible? I currently have single power supplies in each switch.

[BillP]

Hello,

What UPS did it suggest to you?

I do technical support primarily but when I go through sales questions, here is what I keep in mind to narrow the choices of appropriate UPS.

• Is rack or tower mounting required?
• How many watts do these pieces of equipment draw, and consider any requirements for inrush?
• How much on battery runtime is required?
• Do these pieces of equipment require anything special as far as you know, i.e. 0ms transfer time to/from battery (typically seen with really sensitive equipment)
• Should we account for room for expansion, keeping in mind any required battery runtime with that expansion (like should the UPS potentially support extended run batteries)?
• Do you just want a basic UPS or do you want something with bypass, modularity, etc?
• What is the input voltage required at the site - 120V, 208V, or 240V or doesn't matter? Along with that, do you need to meet a certain input plug type at the site?
• What about the plug types on your equipment? Obviously, we'd want to make sure they'd plug into the UPS that is chosen.

The UPS selector if it had your model of equipment would at least maybe list the wattage draw? That could help us to make a manual selection too.

[BillP · Accepted solution]

Hello,

While sizing UPS "manually" we should always follow a pessimistic approach to avoid any overloads in near future. In your case I'd suggest you to follow the below method to come to any suitable conclusion.

[{(Critical Load in VA x 0.67) + (Future Load in VA x 0.67)} x 1.05] = A
(Ax 0.32) = B
Now A+B = Load in Watts

P.S : Get the VA ratings from equipment's nameplate. We are multiplying by 0.67 for a minimum power factor adjustment, 1.05 for peak values & 0.32 for UPS inefficiencies & battery charging

e.g if you have 2000VA of critical load and 500VA of future load, the UPS Watt rating you should be looking for would be

(((2500x0.67) x 1.05)
((1675 x 1.05) x 0.32)

A= 1758.75

B= 1758.75 x 0.32 = 562.8

Hence Watts = 2321

Once you have load in watts, check for the relevant technical specifications you are looking for from APC fleet of UPSs
i.e BACK UPS, SMART UPS, Symmetra UPS.....etc and choose your warrior. It is pertinent to note that a maximum of 80% load is suggested for enhancing UPS life time.

Best of luck

[Anonymous user]

Thank you both very much for your help!!!