Frequently Asked Questions

I am concerned that 8 - 10 ms is too slow for my critical load. What do you recommend??

The vast majority of loads can handle a one-half line cycle power interruption, and the ATS series is one of the fastest automatic transfer switches in existence.  If no interruption can be tolerated then an online energy storage based solution (e.g. dual-conversion online UPS) may be required.  TSI recommends testing critical loads and can assist with test design.  Contact us for more information.

What is the difference between the ATS-500, ATS-800, and ATS-1000??

The difference is in form factor.

All three units are electrically identical, perform identically, and even have the same internal components.

  • ATS-500:  Compact unit intended for flush-mounting (with optional MK-4000C bracket kit) which is ideal for industrial control panels.
  • ATS-800: 1-RU unit with integral rack-mounting tabs for 19" rack installation.  Ideal for datacenter and telecom applications.
  • ATS-1000: 2-RU legacy unit.  No longer available to new customers.
What is the switch-over time for TSI Power’s ATS series??

The typical switch over time is one-half (½) line cycle, or 8 - 10 ms.

Do you offer lithium-ion batteries??


How long is a battery expected to last in an outdoor environment??

Battery life is highly dependent on the operating temperature. The higher the operating temperature of the battery, the shorter the expected battery lifetime. If the average air temperature is about +40° C (operated at year-round high temperature, such as in the tropics), the expected battery lifetime is about two years. If the average air temperature is around +20° C (moderate temperature found in most areas), the expected battery life is about four years. In cold climates (near 0° C year-round), the expected battery lifetime is about six years.
Another major factor that determines expected battery lifetime is the depth of discharge and frequency of charge and discharge cycle.
For example, if a battery is fully discharged and recharged on a daily basis (such as an outdoor UPS system powered by street light circuit that is ON for eight hours and OFF for 16 hours on a daily basis), then battery lifetime is 350 full charge/discharge cycles or about one year.
However, if a battery is discharged to only 50% level then recharged to 100% level on a daily basis (so that only half of the stored energy in the battery is discharged and recharged on a daily basis), the same battery lifetime is 1,000 charge/discharge cycles, or about three years.
If only 25% of the stored energy in the battery is discharged then recharged to 100% level on a daily basis, then the expected battery lifetime is 2,000 charge/discharge cycles, or about six years, assuming that the operating temperature condition is also near 0° C at which maximum battery lifetime can be expected.

Does TSI Power develop custom products for low-volume requirements??

Yes. We offer both custom solutions and customizable products for a variety of situations. Please contact us today to discuss your requirements with an experienced sales engineer.  No inquiry is too small.

Does TSI Power require non-recurring engineering charges (NRE)??

It depends on the project and the size of the potential order. Because most of the custom products that we quote use parts from our standard toolbox of designs, we typically do not need to charge for NRE. TSI Power will quote NRE as a separate item if the project requires an extensive commitment of internal or external resources, such as CE, UL, CSA, UL or FCC safety, conducted & radiated EMI/RFI emissions testing and listing/marking services.

What is the best material for an outdoor enclosure??

It depends: If weight is a problem or for pole mounting, we use powder-coated aluminum with welded construction. If corrosion is a problem, such as near the ocean, we use powder-coated aluminum or passivated stainless steel with welded construction. For general applications indoors or outdoors, we use powder-coated galvanealed steel with riveted or bolted construction.

What security devices do you offer for your cabinets??

Besides the standard hex bolts that secure the covers or doors shut, TSi Power can provide the following fasteners and tools:
Pin-Allen head screw using an Allen wrench with a hole in the end
Cupped sems screw using a Telco 216-type can wrench
Padlock hasp-covering screw, making it non-accessible
Bail lock with pad-lock feature
1/4-turn bail lock with different actuators, such as a hex screw, cupped sems or pin-Allen head
1/4-turn slam lock with different actuators
1/4-turn 3-point handle lock with telco tool, pin-Allen or standard hex head with padlock option
All of the fasteners are stainless steel except for a few specialized locks that are die-cast zinc or plastic.

What type of specific mounting methods do you recommend to mount your products??

We offer surface, wall and rack mounting options for most products. Plus, we offer optional MK Mounting Bracket kits which can be ordered separately. See the MK Mounting Brackets page for more information and descriptions about the various mounting methods.
Our products can be mounted on pads, walls or poles. We also offer optional brackets which can be ordered separately. See the MK Mounting Brackets page for more information and descriptions about the various mounting methods.

What is a GFCI and where is it used??

A GFCI (ground fault circuit interrupter) is used to detect higher-than normal-ground leakage current and turn off the circuit once it does. Under the NEC (National Electrical Code), GFCI protection of AC sockets near earth ground, bathtubs or showers is mandatory. By detecting the current through a person’s body into the ground and then turning off the AC circuit, GFCI can prevent electrocution when a person accidentally comes in contact with a live AC source.

What are the key benefits provided by ILC??

By using a low leakage isolation transformer, typical ground leakage current can be reduced to about 100 micro amps (which is typical) even if the ILC is powering a load with high-leakage current of several milliamps or even more. Therefore, using an ILC can reduce ground leakage current by 10:1 or even 100:1.
If multiple ILC units are used to power all the “leaky” IT equipment inside a high-rise building, then reducing ground leakage current by more than 90% will solve most of the problems associated with ground potential differences between floors. An ILC is designated as a “Separately Derived Power Source” under National Electrical Code 250-5D and recommended by US federal government’s FIPS Publication 94 for elimination of problems caused by presence of neutral voltage, noise and transient voltages on the neutral line (common mode noise and transients).

What is leakage current to ground and why is it possibly harmful??

Ground leakage current occurs when wire insulation is damaged or becomes frayed with age. Then, small amounts of a current can flow into the grounded metal cabinet or chassis. The maximum allowed ground leakage current is a few milliamps (thousands of an amp). A GFCI (ground fault circuit interrupter) can be used to detect higher-than-normal ground leakage current and turn off the circuit, which is the reason for mandatory GFCI-protection of AC sockets near earth ground, bathtubs or showers. By detecting the current through a person’s body into the ground and then tripping the circuit, GFCI can prevent electrocution when a person accidentally comes in contact with a live AC source.
Under UL 60950-1 (the standard for safety of information technology equipment including electrical business equipment), the maximum allowed ground leakage current per each computer or office equipment is a few milliamps.
However, when there are hundreds computers, IT equipment and electrical business equipment in each floor of a high-rise building, each floor can produce a combined leakage current of one or two amps. When there are 10, 20 or 30 floors, total leakage current for the building can exceed 10, 20 or even 30 amps.
The presence of constant leakage current violates the NEC (National Electrical Code), which allows momentary current through earth ground wire only for short-circuit protection and surge current when TVSS (transient voltage suppression system) is activated due to transients or lightning strikes.
Another consideration is differences in ground potential between floors. For example, the earth ground wire on the 20th floor may read several volts higher than the earth ground wire voltage on the ground floor. This may cause equipment malfunction and/or damage when data communication wires are connected between ground floor equipment and equipment at upper floors.
Therefore, minimizing ground leakage current in a large building is very important for ensuring personnel safety, equipment functionality and equipment protection from stray voltages and ground loop currents.

Is TSI Power’s Outdoor XUPS series protected against overload and short circuit currents??

Yes, our Outdoor XUPS units are designed to be protected against overload and accidental short circuit. The output can be shorted and will recover once the short circuit is removed.

Are all TSI Power products NRTL-safety listed??

A number of standard TSI Power products are cETLus and cULus listed. Low-volume and custom products are generally not listed unless required by the customer.

Are North American and EU standards harmonized in any way??

The most important standards are now harmonized but there are some variations to satisfy national requirements.

Can this be expedited??

Sometimes yes, depending on a number of factors. If you need an expedited NRTL safety listed, we’ll discuss the options with you.

How do I verify that a product is listed??

The various NRTLs(Nationally Recognized Testing Laboratories) maintain websites where a product safety listing can be verified online. Go to UL link for verification.

How long does the process take??

Typically 60 to 90 days.

How many safety standards exist??

There are many different standards. It is up to the manufacturer to determine the standard that applies to a particular product. These standards can be purchased from Underwriters Laboratories.

In the US, I understand that the NRTL must evaluate and test the product and after approval, must conduct quarterly safety inspections. How can an EU consumer know that products are safe when manufacturers do their own conformity assessment??

EU authorities believe that competitors police each other. If a company or consumer thinks a product is unsafe, they can ask the authorities to investigate and test a product; if found unsafe, the manufacturer/importer is required to correct the problems or take the product off the market.

Is an NRTL safety listing required by law??

Generally no, but some states and cities in the US require NRTL safety listing. In Canada, safety listing is mandatory.

Is an unlisted TSI Power product safe??

Yes, they are very safe to use. TSI Power designs and tests its products to meet applicable safety standards.

Is CE required by law??

Yes, it is required by all European Union countries and some other European countries.

Is the NRTL safety listing acceptable in Canada??

Yes, but the label must read cULus or cETLus.

Is the safety label a guarantee of product performance and good quality??

No, it is a guarantee that a product has been investigated and found in compliance with an applicable safety standard. It also means that quarterly compliance inspections of the manufacturer are carried out by a field inspector.

Is UL the only safety listing agency??

No. You can obtain a safety listing from one of four nationally recognized testing laboratories (NRTL) in North America:
• Underwriters Laboratories
• ETL/Intertek
• CSA (Canadian Standards Association)

What is the process for obtaining a CE listing??

CE is based on self-certification. The manufacturer is responsible for determining the applicable standards and for testing the product to ensure compliance. The manufacturer then issues a Certificate of Conformity. The manufacturer is now free to apply the CE label.

What is the safety listing for Europe called??


What is TSI Power’s procedure for obtaining a NRTL (Nationally Recognized Testing Laboratory) safety listing??

We design the product to the applicable standards and work with Intertek/ETL or Underwriters Laboratories to prepare a documentation package with all safety critical components. Intertek or UL then sends a test engineer to our factory to conduct the safety tests required by the applicable standard. If all the documentation and tests meet Intertek’s standards, they will issue an Authorization to Mark (ATM).

What are the various types of surge protection devices and where should they be used??

UL 1449, 3rd edition (effective September, 2009) provides following surge protector classifications:
Permanently Connected (PC)
Direct Plug-In (DPI)
Cord Connected (CC)
Type 1 – Permanently connected (PC) between service transformer and line side
Type 2 – Permanently connected on load side of service disconnect
Type 3 – Point of Use: minimum 10 meters from service panel
Type 4 – Component assemblies for SPD (surge protection device) or other non-SPD applications such as appliances
Type 5 – Discrete components for SPD or other non-SPD applications such as appliances

Are the outdoor surge and transient voltages on the AC power line stronger??

Much stronger. Typical 20 mm diameter MOV (metal oxide varistor)-based surge protectors will fail with first strong nearby lightning strikes near the AC power lines. A combination of 40 mm MOV, gas tubes and inductor-capacitor filters must be used to divert the incoming surge voltage and current into the earth ground. Otherwise, failure of the outdoor UPS – and equipment powered by the outdoor UPS – will occur on a regular basis. Since outdoor UPS units are typically located at remote sites and high up on poles or towers, a bucket truck must be used access to the failed unit and perform the repair work, which is time consuming and expensive. Therefore, only a professionally designed outdoor UPS with outdoor-rated surge protection circuit should be used.

Can an outdoor UPS be powered by street light circuit which is ON for only eight hours per day??

Yes. An extra-large battery bank will be required to power the load for a minimum of 24 hours, with expected battery lifetime of about 1.5 years (note: use of a 36- to 48-hour rated battery is strongly recommended if a battery lifetime of three or four years is desired). Also, this application needs a temperature-compensated, high-capacity battery charger which will ensure full charge of the battery after eight hours of overnight charging.

Can I just use a standard UPS in an outdoor NEMA 3R cabinet and call it an outdoor UPS??

No, because several problems will occur. First of all, the batteries in standard indoor UPS are rated for 0 to +40 degrees only. Also, the indoor UPS does not use a temperature-compensated battery charger. As a result, the battery lifetime will be only a few weeks (or few months), especially during the summer when temperature inside an outdoor cabinet can easily exceed +40 degrees C.
The VRLA (valve-regulated lead acid) AGM (absorbed glass mat) battery will start out-gassing and the electrolyte (battery acid) will be quickly depleted when the wrong battery charging voltage is used, which occurs when battery temperature is over +40 °C. With a loss of battery acid occurring in a just few hours or days, the glass mats become dry and current can no longer flow between the battery plates.
A fine mist of battery acid (similar to mist produced by a bug spray) will shoot out of the battery and cover everything inside the cabinet This causes severe corrosion that will destroy everything inside the cabinet, including the cabinet itself. Also, unsuspecting operators can rub their eyes with fingers after touching parts inside the cabinet and receive severe eye injury.
In conclusion, answer is an emphatic NO.

How can I choose the correct outdoor UPS unit first time, since I can’t afford the trial-and-error method and my projects require a mandatory 99.99% or higher uptime??

Contact us by e-mail at or phone at 800-874-3160 (United States) or +715-623-0636 (international). We will send you a questionnaire with 12 questions to learn more about where and how you plan to use your outdoor UPS. When we receive your answers, one of our experienced application/sales engineers will contact you with a quote for the correct model – so you specify the correct outdoor UPS, the first time around.

What if the outdoor UPS must be placed near the ocean or at end of a pier? Or, what if the outdoor UPS is located in an area with severe dust and sand storms that can last for days??

Challenging applications like these require a special outdoor UPS with two compartments. In these products, the electronic boards are housed in a separate NEMA 4X-rated compartment while batteries, transformers and the input/output connector are housed in NEMA 3R-rated compartment. This way, possible battery outgassing does not cause accumulation of hydrogen and oxygen, since the batteries are in the ventilated compartment. Plus, wind-blown seawater, dust or sand will not be able to enter the sealed NEMA 4X compartment where the sensitive electronic boards are housed.

What is the difference between a gel and an AGM battery??

A gel battery is powered by a gelled electrolyte in a sealed container, rated non-spillable by the IATA (Air Transport Association) and the DOT (Department of Transportation), making it possible to ship it by air without restrictions. A gel battery is rated for operation at over -40 to +60° C, making it an ideal battery for outdoor use. AGM (Absorbed Glass Mat) batteries run off of electrolytes absorbed in sponge-like mats between plates. They are typically rated for use between 0 to +40° C, which is not suitable for outdoor conditions.

Which is the better choice, AC output UPS or DC output UPS??

It depends on the output capacity in watts. If the load is less than 200 watts, DC output UPS systems are about half the size, weight and cost substantially less than an AC output UPS. This is because an expensive DC to AC inverter circuit can be eliminated and there is no power conversion loss associated with DC to AC inversion circuit, resulting in substantial battery size reduction as well.
However, if the load is more than 400 watts, then the size/weight/cost penalty of AC output UPS is offset by the need for expensive, continuous-duty high powered AC to DC converter in a high capacity DC output UPS. If the UPS must power a load of 800 watts or more, AC output UPS is by far the smaller, lighter, more energy and cost effective solution.

Why don’t you provide outdoor UPS systems in NEMA 4 or NEMA 4X cabinets??

The worst-case scenario for the VRLA (valve-regulated lead acid) batteries that are most commonly used in outdoor UPS units is when a battery charger’s regulator circuit fails and it is no longer able to regulate charging voltage. When that happens, oxygen and hydrogen gas production increases dramatically, which opens the safety valve and emits a substantial amount of oxygen and hydrogen. This scenario is also known as “battery out-gassing”. When a sealed NEMA 4 or NEMA 4X cabinet is used, the trapped mixture of oxygen and hydrogen can explode when a spark ignites the gases. This creates a highly dangerous situation with flying metal shrapnel that can cause severe personnel injury. Because of this, free-breathing NEMA 3R is the correct cabinet to use whenever VRLA batteries are housed inside an outdoor UPS cabinet.

Why is your outdoor UPS rated at 45° C when some other manufacturers products are rated at 60° C??

TSi Power’s outdoor UPS products are rated typically at over -20 to +45° C outside air temperature. Most use a thermostat-controlled fan to keep the temperature inside the cabinet no more than +50° C, which is well below the maximum operating temperature limit of the gel batteries inside the cabinet.

Can the three-phase VRP receive power from a delta source??

No, the VRP must receive power from a wye source with three phase conductors plus neutral.  However, a neutral-forming transformer can be used.  The output neutral of the VRP does not need to be connected.

Does VRP have a bypass switch??

Yes, VRP has an automatic bypass switch.  Please note that this is only an internal bypass of a damaged AVR assembly and not an external maintenance bypass.  You must still disconnect power in order to service the unit.

Is VRP available with under- and over-voltage cut off??

Standard VRPs do not have OVP/UVP, but it is available as an option.  Contact us today for more information.

What does the automatic bypass switch do??

If VRP’s control PCB fails, it will automatically switch to bypass, allowing unregulated voltage to power the connected load. This feature prevents an unscheduled shutdown of the connected equipment.

What happens if the VRP control circuit board fails??

All LEDs will switch off. The load current will pass unregulated to the connected load. In some cases, the VRP main circuit breaker needs resetting. Contact TSI Power for an RMA or replacement control circuit board.

Will the VRP voltage regulator correct a distorted waveform??

No. Current to the load passes through the phase conductor. Regulation current is taken from the incoming phase. The voltage correction is ±20%. Only a dual conversion voltage regulator would be able to provide waveform correction.