How To Buy A UPS

Here are two examples of businesses looking to install UPS Emergency Power Systems.  We will use these examples to discuss the process of shopping and planning for the right UPS. The objective is to give a proper recommendation and avoid having the customer “over-buy” or “under buy” a system that is not required, is too expensive, or too cheap.  You will also see an example of the logic that goes into planning and securing a proper UPS.   Both examples offer some tips and pitfalls to watch out for in the purchase process.

Example 1:  Company needing to install a UPS

In the first example, the current requirements are that there is a 400A load, which is due to all the servers and required cooling systems.   The room is about 20’x25′, and there is a natural gas generator in place.

First off, we need to give some consideration to the requirements:  In order to cover 400A (amps) at 480 VAC (volts alternating current) we will need a 400kva UPS.   The 400kva UPS will provide 480 AAC (amps alternating current) at 480 VAC and still leave us 20% of capacity at 400 amp requirement. If this is an existing load and customer promises this 400 AAC load is not going to increase in anyway then I would feel comfortable selling him this UPS.

We like to have the customer, on paper, provide the types of loads that will be on the UPS to figure power factor.  One more consideration is the length of the wiring run which will factor in when determining line loss that will add to UPS load.  Another question:  Are all loads at 480 VAC or is there step down transformers?  All of these losses in efficiency need to factor into the sizing of the UPS.

TIP:  If these factors are not taken into account the unscrupulous sales person will slide in with a 325 kva UPS which will provide 97.5 of the customers 400 AAC requirement.   They do this to “get the sale” to “have a lower cost” while taking advantage of uneducated customers.   This happens more often than not, and it is very disturbing to the people that actually do the work to fit the application, only to have someone with absolutely no practical experience propose a system that is  $30,000 below the proposal the experienced engineers delivered.  There is a saying in the industry:  “it is easier to sell ice to an Eskimo than a true electrical engineer to sell a UPS to a bean counter”.

Example #2:  Getting Replacement UPS

We had a customer with a load that was VERY critical. It was being power by an APC unit that had been out of manufacturing for 15 years and parts were not available.  Due to our contacts in the industry, and the ability that allowed us to get hard to find parts, we kept the UPS running up until the absolute end of life.  At that point, the customer requested that we design and draw a system that you would replace the current end-of-life unit.  Well, after knowing the site and the customer for ten years or better, we did just that.  We drew him a set of parallel 225kva UPS units with required switchgear and remote monitoring.  They gave me a new air conditioned room to put this in but they did not consider backing the air conditioners up  (by the way this is in the middle of a glass manufacturing plant. Normal ambient temperature is near 100 hundred degrees or more depending on outdoor temperature) so we added that into the plan as well.

We quoted them two Toshiba G8000’s with parallel cabinets and remote monitoring from their office 400′ away.  We used Toshiba G8000 even though the G9000 was available, and this did not make Toshiba happy. The equipment vendor wanted to sell more of the new units, but the G8000 is a component discrete dual conversion UPS.  By putting these in parallel, we gained redundancy and could repair the units at 30% of the cost of the modular units.  Modular units have a single point of failure.  That would be the back plane Bd. which is a single layer Bd. that can be 6′ long depending on the unit.  Every module slides into a rack and large male contacts slide into female contacts mounted on the back plane Bd. (You can destroy this unit by t sliding modules into it)  That worked into my theory of the perfect system and if the customer bought spare parts kits, I would have parts on site should some unplanned mishap occur.  The units were sized for 75% load even if we only had one module on line just in case the HVAC failed in this room, which oftentimes is when you would expect a UPS to fail.  But no problem here, based on our plan, the system would still be at 75% on one unit. That was our recommendation based on, “What would you build to supply our load?”

Then this happened:  Siemens did use my drawings but Siemens came in with two 150KVA units in parallel, so the units are at 100% when load is on one unit.  They have a hot tie cabinet that does not require a parallel cabinet. They did not have remote monitoring available, the result was that our quote came in over 30% higher than Siemens.   In the end, our customer chose the Siemans over the Toshiba, the engineers understood the logic, but there was an impass in convincing the accounting department of the realities of the situation.

TIP:   It does not behoove the customer to go with lowest bid

What happened?  This was a brand new unit from Siemens, and the other vendor did not have a technician trained to connect all the cabinets, so the customer comes back to Power Source Service to install their unit!  Which cost them $10,000!


There is nothing wrong with used units at all, but please have an experienced UPS technician look at it and document everything before its shut down (at it’s current site), or do what I am doing:  buy used units and test them. TEST!!!! That is one of the big industry problems, no one does sufficient testing with used units right now.


The differences between UPS systems are is major.  Liebert/Emerson/Vertiv systems are virtually a commodity to corporate accounting departments and are quality systems, both old and new.

Our experience with some systems, notably Exide, Powerware, Inveses, EPE, SquareD, Merlingerin, , Siemans, APC:  these companies were the big three in the 1990’s, but they are all now just brand-names that are bought and sold by Wall Street, and they are scratching the bottom of the barrel trying to make things cheaper than the competitor, the quality that once existed is gone in my opinion.   We will not sell any of their new equipment, in our opinion it is junk.  If you hear the mantra “… it’s cheaper to replace a $60K unit than repair it!”  The customer needs to BEWARE!  Also, they are almost all modular units.

What NEW systems do we have the most confidence in?  You will see the brand names on this site.