Read our response to COVID-19 (Coronavirus)
Request Service
Get a Quote

Critical Power Blog

Education, UPS

12 UPS Terms You Need To Know

Researching about UPS and running into a bunch of technical jargon that feels confusing?

UPS terms can be complex, technical, and sometimes do not have much of an impact on the quality of the UPS.


Not familiar with KW and KVA? Visit our post on “10 UPS Electrical Terms You Need To Know”.

What’s really important for the typical UPS user is to know that when comparing capacity of different UPS’s, the ONLY thing you need to look at is output KW. The rest (KVA) is smoke and mirrors.

For example, if you want to purchase a 3KVA UPS, you must compare the output capacity in KW between machines.

An APC SU300RM is 3KVA, but only 2400 Watts.

An Xtreme P90-3000 is also 3KVA, but can supply 2700 Watts for your equipment.

You get a 10% increase in capacity on the Xtreme machine for a lower purchase price. That’s a no brainer.

On- Line UPS

Also known as “Double Conversion”. This is the best protection you can provide for your sensitive equipment. Incoming power is converted to DC, and then re-converted back to AC to power your equipment. The result is clean, isolated, regulated, uninterruptible power for your load

Line Interactive UPS/ Standby UPS

Less expensive technology to power your equipment.

The inverter is normally offline and in standby mode. Essentially your load is powered by utility 99.9% of the time. When a power interruption occurs the UPS starts up its inverter to power the load.

It does so with a slight interruption , but is quick enough to prevent your equipment from shutting down. Not really an ideal scenario for any Data Center.

Run Time

Simply the amount of time the batteries will support the load, at a given load level. Typical run time is 10-15 minutes at full load.

CAUTION – If you want to increase your run time to 1 hour, or even 4 hours be prepared to pay a huge adder. Batteries are very expensive, and they also need to be replaced every three to five years.

We like to say that a two hour battery on a medium size three phase UPS is really a generator. This is because at that run time, it’s cheaper to install a generator than pay the cost of the extra batteries, along with 3-4 replacements of them during the life of the UPS.

Don’t be that person who blindly says I want a four hour battery unless you have the budget for it.


The electronic portion of the UPS that converts incoming AC Power to DC Power. Once converted to DC it is then used to charge the batteries, which are DC devices and to power the inverter.


This is an electronic portion of the UPS that converts DC to AC, which is then used to power your critical equipment. The inverter re-creates the sine wave in a near perfect form. The result is a clean, isolated and regulated output to power sensitive and critical equipment.

The inverter (in an on-line UPS), achieves its magic by being powered from (2) separate sources.

The rectifier when Utility is present, and the battery when there is no utility.

If utility power fails, the battery is continuously connected and provides power to the inverter instantly, and without interruption.

In most on-line systems, there is no delay, and no switching to battery which ensure continuous power to the load.

Static Switch

This is a protection device within the UPS.

The purpose of the Static Switch (in simplistic terms)  is to bypass the  UPS, which essentially means we connect incoming Utility Power directly to the UPS output to power the load.

In this mode, the Inverter no longer powers the load, Utility does.

The Static Switch is designed  to instantaneously  transfer the load without interruption, and in reality does so 99.5% of the time.

Any time you transfer the load there is a very slight degree of risk.

There are only two reasons the Static Switch would be used: To transfer the system offline for maintenance and in the event the Inverter has a failure and can no longer power the load.

On Line

The load is being powered by the UPS inverter, or if the UPS is a standby system, the Inverter is ready to start and carry the load in the event of a power interruption.

When you’re online, it means your Uninterruptible Power System is uninterruptible because the battery is connected and the Inverter is either on , or ready to start.

On Battery

Either the input power to the UPS  is not present, or out of acceptable tolerance (usually outside of nominal +10%  to -15%).

In this case, the rectifier ceases to provide DC power to the Inverter, so the inverter draws the DC current it needs from the battery to power the load.

Typical UPS’s will have a battery sized to provide power for 10-15 minutes. In this mode the battery is being discharged.


This means the UPS is offline, and not able to support the load in the event of a power interruption.

In this mode the load is powered by utility.

This condition is sometimes referred to as Internal bypass, or module bypass because utility power still flowing through the UPS.

Internal bypass is different than maintenance bypass, which is explained next.

The only reasons a UPS would be in bypass is for maintenance, or due to an internal failure.

Important Note: When you’re on bypass you are NOT on battery. The opposite is true. When on bypass, you’re on utility, with no battery backup.

Please keep this fundamental concept in mind and you’ll be a UPS hero.

Maintenance Bypass

This is a device which is external to the UPS and consists of 2 to 4 circuit breakers.

A maintenance bypass provides a second, parallel path around the UPS for power to flow to the load.

IT is sometimes referred to as a “wrap Around”.

The maintenance bypass has breakers that allow for  sequence of operation that makes a parallel path around the UPS, before breaking the UPS output to the load.

This action is referred to as “Make Before Break” or MBB.

A Maintenance Bypass costs a few thousand dollars to install, but is invaluable if you ever need it.

This is because that certain repairs to a UPS can only be made with all power removed from the UPS.

If you don’t have a maintenance bypass this means you will need to power down your load.

Imagine breaking that news to the CIO…

On the other hand, if you have a maintenance bypass and your UPS suffers a catastrophic failure, (or you just didn’t want to spend the money to replace your 20 year old UPS, and now there are no parts available), you can actually remove the UPS, install a new one, and cut it over to the load, all without powering down.

Now the CIO thinks you’re a hero.

Thermal Run Away

A very serious condition affecting your batteries. In thermal run away, the  battery builds up heat either due to an internal failure, or because of external conditions such as high ambient temperature.

The excess heat causes more current to flow. The additional current creates more heat.

The additional heat causes more current to flow…. You get the idea.

We’re talking Fire Department time if you don’t disconnect the battery from the charger quickly.

If a battery is in thermal run away you will smell sulfur or rotten eggs.

If you smell this, don’t wait, contact your service provider immediately.

Sadly – most cases of thermal run away are caused by poor or no maintenance, or the desire to save money.

UPS’s and batteries are reliable, but do need to be maintained.

Don’t let thermal run away be your reminder. If you do, you’ll get a long meeting with your bosses boss (and maybe their boss too).

Education, UPS

10 UPS Electrical Terms You Need To Know

Researching backup units or UPS often means learning lingo that you don’t use in everyday life. Volts? Phase? Single Phase? Three Phase?

Don’t worry we put this guide together to make things easier.

Alternating Current

Commonly referred to as AC. It is the way the raw power is delivered to you, as generated, by your utility company.

AC takes the form of a sinusoidal waveform which changes in amplitude and direction a fixed number of times per second.

AC is the opposite of DC, and was chosen because it can be sent over many miles by the utility company with relatively low line losses.

Direct Current

Commonly referred to as DC. It is the same type of current that is in a battery. The current is direct, constant and flows from negative to positive.

It is only suitable for transmission over short distances.

DC is the opposite of AC


Frequency only applies to AC, and is the number cycles per second that the sine wave repeats itself. Also referred to as Hertz (abbreviated Hz).

In North America the frequency is 60Hz. In the rest of the world it’s 50hz.


The measure of electrical potential that is available for use. Look at it like pressure in your water pipe. It’s always there, just waiting for someone to open the faucet.

In the US, the standard residential voltage is 120V. Commercial voltage is generally 208V or 480V

Helpful Tip: Volts can be converted to Watts. Here is a Volts to Watts calculator to help.


This is the measure of true power, and in and AC System it is similar to KVA, with one very important, critical difference. Power Factor.

An explanation of Power Factor is beyond the scope of this blog, but suffice to say it is a rating determined by your load, and then applied in the calculation to determine KW, which for a three phase system is V * A * 1.73 * Pf

Power factor in a perfect system will be 1, and if so KVA = KW (also known as unity).

In real life the Power factor is rarely one, and is typically somewhere between .9 to .97.

In practice , it acts as a de-rating factor, because the typical UPS can deliver less KW than KVA.


The actual flow, or movement of electrons which is also known as current.

The flow of electrons performs a useful task such as lighting a light, turning a motor, or powering a computer.

Using the example above under voltage, current would be the flow of water that comes out of the faucet, and is dependent upon how much you open the faucet and the pressure behind it.


Thousands (Kilo) or Volt Amps.

If your UPS operates on 120 Volts and can deliver 10 Amps then the UPS is rated at 1200 Volt Amps OR 1.2KVA (1.2 Thousand Volt Amps).

In single phase systems KVA = V * A

In three phase systems the formula is V * A * 1.73 (the square root of 3).

Important Note: KVA is apparent power, and doesn’t tell the full story of your UPS’s capacity.


This refers to voltage and defines the number of input wires supplying voltage that are connected to the device.

Each wire carrying voltage is sometimes referred to as a “Hot”.

Single Phase

The 120V outlets in your house are all single phase.

This means there is one “Hot” wire supplying power to the load. Single phase is used in residential, and low power commercial applications.

Single phase UPS’s are small desktop or rack mount systems, and range from 300VA to about 10KVA.

Typical manufacturers are APC and Xtreme Power Conversion

Three Phase

Commercial voltage is generally 3 phase, which means there are three separate wires connected to a device each supplying 120V, or a different voltage.

Essentially 3 “hots” Three Phase Power is used in Commercial and Industrial applications, and delivers high power.

Three Phase UPS’s are larger systems that power many racks of equipment, to large data centers.

Three Phase UPS’s will start at around 10KVA and can be as large as 1100KVA. The Eaton 9355 is a great example of a three phase UPS.

Hopefully you found this guide helpful.  

Still have questions? Get a response immediately.

Click above to get started or call 240.772.1710 for instant help.

Batteries, UPS

Battery Temperature

Battery Temperature – With summer upon us, it’s important to ensure your air conditioning system is maintaining your UPS and Batteries at or below 77 degrees.

Slight temperature increases above 77 degrees will result in a reduction in battery life, and significant temperature increases (90 degrees and above) can result in thermal runaway.

Your A/C system should be monitored, and if it fails you need to be alerted and take immediate action to reduce the temperature for the batteries and UPS. Also be alert for any planned building maintenance activities that could effect the A/C for your batteries. If there is an 8 hour A/C shutdown over a weekend, it could spell disaster for your UPS batteries.

1 2 6 7 8
show blocks helper

Filter by Brand

Filter by Configuration


Filter by Amps

Filter by Phase

Filter by Power Rating (kVA)

Filter by Voltage

Privacy Settings
We use cookies to enhance your experience while using our website. If you are using our Services via a browser you can restrict, block or remove cookies through your web browser settings. We also use content and scripts from third parties that may use tracking technologies. You can selectively provide your consent below to allow such third party embeds. For complete information about the cookies we use, data we collect and how we process them, please check our Privacy Policy
Consent to display content from Youtube
Consent to display content from Vimeo
Google Maps
Consent to display content from Google
Consent to display content from Spotify
Sound Cloud
Consent to display content from Sound
Quick Quote
Or call (240) 772-1710 for immediate help.
Quick Quote
Cart Overview