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Non-contact Voltage Testing (NCV)

As many of you may know non-contact voltage sensors (NCV’s) or “voltage sniffers” are strange and mysterious in how they work or in some cases don’t work. Due to the nature of this product and the science behind non-contact voltage testing, sensitivity is always a variable due to the components used and because your body completes the circuit which will affect your readings. We’re going to clear up some of the confusion behind NCV’s in this article, hopefully this will help bring you a better understanding of how they work. Below you’ll find useful tips and tricks for detecting voltage with a non-contact voltage detector.

One of the first things you want to do before you test for voltage at an outlet is disconnect any device that is connected to that specific outlet. This is largely due to the field that electricity creates.  If something is plugged into the outlet, the cord will generally increase the size of the field and make discrete detection difficult at best. The size of the field detected by a non-contact voltage detector can vary significantly in size for a variety of reasons, such as whether the box or cover is metal or plastic. Depending on the fixture (metal or plastic), the field may be greater.

For outlets in a metal box the field would be smaller and greater sensitivity would be required compared to a fixture in a plastic box where less sensitivity is required where the field is larger. GFCI outlets will generally have a larger field, making discrete detection even more difficult. The detection distance for a standard (non-GFCI) outlet, plastic cover, plastic box, should be less than 1 inch. As a result, to determine what is hot in an outlet using a (non-adjustable) voltage detector may require a technique that may not be obvious. We believe the natural way for most people to use a non-contact voltage detector is to approach the outlet directly from the front, as if one were plugging something into the outlet.


When the AC field is relatively large (plastic box/plastic outlet cover), this method will make it difficult to detect what openings of the outlet are hot. What we found works well is to approach each opening from the side.  To say it another way, if checking the outlet slot on the left side, approach the outlet from the left.  If checking the ground opening, approach the outlet from below. This is assuming the outlet is installed with the ground opening downward; if you approach the outlet from below you should be able to tell if the ground is hot.

If ground opening is toward the top, you can approach from above. We think if you try this, you will find that it is a much more accurate way to determine what parts of the outlet are hot. Remember that your body is part of the functionality of the device and completes the circuit.  If you move your finger toward the tip of the non-contact voltage detector (where the antenna is), you will find that this effects (reduces) the sensitivity.  Although not an official method of using the device, you may find this tip useful to know in differentiating a hot line, particularly when the field is large or there are several lines in close proximity.


Obviously, do not put your finger near the tip when checking an exposed conductor. It would also be appropriate to wear the proper protective gear for safety.Gloves

First time I used my continuity tester, the bulb went bad. What happened?

Most likely they were testing a live circuit. Continuity testers are designed to test UNENERGIZED circuits. The bulbs in these testers are only rated for around 3 volts. If you hook this up to a live circuit in your house, you just put 120 volts through the bulb and that is why it blew out.

Do we have replacement bulbs for the continuity or voltage testers?

No we do not. Due to the fact these are kind of awkward/specialty bulbs, if you can find them, most times the store carrying them is charging almost the cost of a new tester if not more. The continuity testers are pretty much designed as throw away items. For the voltage probes, most times these are soldered directly to the circuit board and are not to be replaced.

Why can’t I determine which side of my outlet is the live side with the VD6504? The unit is way too sensitive!

These testers were designed for quick basic testing to determine if there is voltage at an outlet or on a line. They are not designed to pin-point which line is the hot and which is neutral. For that you would want to use the VD6505 because they have an adjustment for the sensitivity to dial it down and give more accurate readings.

Can the new CS61200AS circuit breaker finder accessory kit be used with the older circuit breaker finder kits like the CS-500A, CS-550A, or CS-600?

No. Due to the changes in the design of the housing, we do not recommend using the new accessory kit with the older style breaker finder kits. The CS61200 transmitter that plugs into the accessory kit has a different molding shape and it clicks into the accessory adaptor. The older kits have a flat front to them that will not fully sit in the accessory kit. This will leave parts of the metal prongs for the transmitter exposed and could potentially cause a shock hazard for the user. The accessory kit for the older breaker finder kits has been discontinued with no replacement.

Can the LAN tracker trace a wire behind drywall to determine if there is a break in the wire?

This depends on how far behind the sheetrock the wire is, the type of wire it is, if it is in conduit or not, how thick the sheetrock is, and how new the batteries are in the testers. As the batteries in the tester weaken, the signal being sent is weaker and the transmitter has a harder time picking up the signal. If the sheetrock (drywall) is extremely thick or even doubled up, that is going to affect the receiver’s ability to pick up the signal. If they are trying to trace BX wire (wire in an armored sheathing) or if it is in conduit, it will not be able to detect the wire. These metal encasements will block out the signal being sent and the transmitter will not pick anything up.