FAQs

How far can I extend the leads of the VT Pack without materially affecting the accuracy of the meter?
The voltage burden requirements of a modern wide voltage range solid state meter are very low. For example, with a Form 9S three phase wide voltage range meter, the power supply phase is usually less than 7.5 VA when supplied with voltages from 100-240 volts as is the case when it is connected with VTs. The other two phases are essentially open circuits with burdens of <.02 VA, worst case. Unless you are trying to extend the leads many hundreds of feet, the voltage drop, and the accompanying measurement error, can usually be ignored. If you would like to see an error analysis, please contact us for that information.
I have mounted a VT Pack on the bottom of a metering enclosure with the collar facing upward. Is that OK?
No. This is similar to the question about laying the VT Pack in the bottom of an enclosure with the collar facing upward - causing the VT Pack to fill with rainwater and/or melting snow and/or heavy condensation and eventually failing. However, one cannot turn the VT Pack on its side as it is permanently mounted. The best solution is to use our Connector Cover found on our Accessories Page. When using the Connector Cover, make sure that water has not already filled the VT Pack. If it has, the VT Pack must be deenergized and dried out before installing the connector cover.
The connector on my VT Pack that has been in service for several years without a problem has a little dirt/corrosion on the pins. Can I use a spray electrical contact cleaner to burnish the contacts?
No!!!! Although at first glance it might seem like a good idea, the use of electrical contact cleaner, brake cleaner and a number of other solvents will severely damage the polycarbonate VT Pack enclosure. Contact TSTM if you are not sure if a cleaner or other substance is OK to use on or near the VT Pack. Also, electrical contact paste should not be used on the connector.
Can I ground the orange wire (tap) on your auxiliary power transformers (AKA hockey pucks)? What about those that are mounted in one of your adapters?
No and no! Sometimes it won't make much difference and in others it almost guarantees that the transformer will eventually fail. We recommend that no wires on our hockey pucks be grounded unless the phase that a lead is connected to is grounded.
Should I use a lightning arrestor to protect the VT Pack and/or the meter?
No. The VT Pack is the best "lightning arrestor" on the market! No other lightning protection is either recommended or required! In fact, it has been the experience of many of our customers that lightning arrestors cause more problems than they solve, including producing noise that may interfere with power line carrier signal propogation.
How does the cost of the VT Pack compare with the cost of three individual conventional VT?
Generally, the cost will be similar. However, when you factor in the reduced space requirements and the ease and speed of installation of the VT Pack, the total installed costs are usually substantially less with the VT Pack.
Can the VT Pack be mounted outside?
Yes, with some conditions. Many who are mounting the VT Pack externally are placing the connector collar through a knockout or a punched hole in a socket or cabinet. If that is your preferred mounting, we actually make an external mounting kit to make it quick and easy. Since the VT Pack connector and mating wiring harness connector are not designed to be directly exposed to the elements, they must be protected. If the VT Pack is to be mounted where the collar and connectors are to be exposed to the elements, we recommend that you use our connector cover. This rugged UV resistant cover covers the connector as well as the harness from the elements. In addition, if properly installed, will provide security from tampering.
Can I use the VT Pack with induction (disk type) meters?
You can use any VT Pack that has a catalog number preceded by an “A” and be assured that revenue metering accuracy is maintained with the higher burdens imposed on the voltage circuit by induction meters.
Assuming that my application is 480/277 volt 4 wire wye, the most common configuration for new 480 volt three phase applications, how many voltage connections do I have to make to install a VT Pack?
In most cases, only eight total connections must be made: four for the primary, and four for the secondary. In other words, there are no more voltage connections to make than if you did not have VTs in the circuit!
Can an individual VT in the VT Pack be replaced if it were to fail due to lightning or other causes?
No. The individual VTs in the VT Pack are solidly epoxied in the UV resistant polycarbonate enclosure and cannot be removed/changed out without destroying the unit. However, with our ten year limited warranty in place, that does specifically cover loss due to lightning, the need to change an individual VT is not important.
Can I operate two or more meters on one VT Pack?
It depends. Since the only significant burden for a wide voltage range solid state meter is on the power supply phase, one should make sure that only one power supply per VT in the VT Pack is connected. In other words, you can connect up to three meters on one VT Pack, and still maintain metering accuracy, if done properly.
Can I get a wiring harness made to my company's color code, including striping?
Certainly. SImply click here to design your own custom harness. All we ask is that any custom harnesses be purchased in quantities of 12 or more or a modest surcharge will apply. Any striping other than black or white may have additional minimum order requirements.
Can I get harnesses made in other than the standard 6 foot length?
No problem. We can make harnesses virtually any length, including lead lengths that are different for the primary and secondary. For lead lengths greater than ~20 feet, one might consider using our effectively dead front terminal block and backer strip. This kit also has self-drilling mounting screws to easily mount the strip to wood or sheet metal.
Do I have to use a TSTM, Inc. socket that has a harness incorporated in it?
No. Although our sockets make mounting the VT Pack a snap, many of our customers choose to mount the VT Pack in pad mounts, transformer enclosures or other appropriate mounting locations.
How many screws does it take to mount the VT Pack in a pad mount or other suitable enclosure?
As long as the mounting location is not going to be moved after mounting the VT Pack, a single ¼ inch mounting screw should be sufficient where the single key-hole slot is used opposite the connector. If the meter socket is mounted on the outside of a padmount transformer, one of the socket mounting screws can even be used to hang the VT Pack on the interior of the transformer!
What is the difference between the accuracy and thermal burden rating of a VT?
The accuracy burden rating of a VT is that burden that can be applied to the VT and still maintain the stated accuracy of the VT for revenue billing applications. The thermal burden rating is that burden that can be placed on a VT at a specified ambient temperature so as not to cause damage to the insulation structure as the result of excessive heat. The thermal burden rating of a VT is normally of little or no importance to a utility.
Can I use the VT Pack with some of the current AMR/AMI systems without any loss of accuracy or signal?
Yes! We have many electric utilities using VT Packs in combination with their AMR/AMI systems because many of the traditional voltage transformers don’t allow the signal to transfer without interference. Our VT Pack allows a clean transfer of signal thus producing an accurate reading for your AMR/AMI system.
Will using a 12S or a 1S/2S adapter change the meter multiplier?
No. The auxiliary power transformer in the adapter only powers the AMR/AMI device and/or possibly the meter power supply.

Note: Meter used must be capable of handling the full line voltage.
Is the transformer in the 12S or 1S/2S adapter a metering accurate VT (voltage transformer)?
No. The transformer is simply to supply voltage for the AMR/AMI device and possibly the meter power supply. The transformer is not designed or tested to be precisely accurate. TSTM does have metering accurate VTs for this type of application and you should contact TSTM for further details.
Do I have to include the ratio of the VT Pack when calculating the meter multiplier?
Yes. All instrument transformer ratios, including both CTs and VTs, must be factored into the meter multipler.
Should I fuse the primary of the VT Pack?
We do not believe that it is necessary to fuse the primary of the VT Pack. If the fuse is sized small enough to quickly blow in the case of a fault, you run the significant risk of nuisance blowing and resulting revenue loss.
Can I use self-drilling/self-tapping hex head screws to mount VT Packs?
Yes. You only need one screw at the single top key hole slot to secure the VT Pack provided that the mounting location is to remain stationary. Caution! Do not overtighten the screw by using a non-torque limiting screw gun or an impact driver as this can damage or weaken the mounting bracket! Afterall, this is not a headbolt on a HEMI! In fact, it is not even necessary for the screw head to make contact with the bracket to keep the VT Pack from sliding off of the screw.
Can I use one of your "hockey pucks" (auxiliary power transfomers) as a metering VT?
No. Our hockey pucks do a great job of powering various devices, including Hunt/L&G endpoints, but are not designed as, nor tested to be, metering VTs for revenue billing applications.
Can I lay the VT Pack in the bottom of a non-raintight or raintight enclosure with the collar facing upward?
No. Heavy rain and/or snow and/or heavy condensation can enter or accumulate in the enclosure - filling the collar with rain water, melting snow or condensation. This will cause the VT Pack to eventually fail. To prevent this from happening, simply lay the VT Pack on its side with the collar facing sideways.

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