The Nuisance Current Blocker offers many benefits, which we describe elsewhere. Beyond the essential benefits, there are multiple other uses for the NCB, which we describe in this article.
Table of Contents
Representing the Body
Normally when you measure contact current, your body needs to be in the equation, as in this diagram.
Using the NCB, you can remove the body from the equation as diagrammed here.
Instead of holding onto the red lead on the Fluke 287 or 289 and use your body as the contact point, plug the black lead into the NCB, set the NCB dial from anywhere between 1000-2000 ohms to represent your body and put the red lead on the object. That will test between the object and the grounding reference simulating your body in between the points.
Wet conditions could be between 300-500 ohms and dry ideal conditions with no frequencies up to 10,000 ohms of resistance.
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Using a differential probe to measure noise on a grounding conductor is difficult, unless you have an NCB.
The red lead attaches to the grounding mat that is plugged into an outlet and the black lead typically plugs into the outlet as well.
Measuring the same point won’t give you very good results.
But putting the black lead into the NCB, finally you can then see the red lead pop up the frequencies on the grounding conductor in the wall.
Removing Grounding Loops
A grounding loop is two or more appliances, connected together in some way (common grounding system) but fed (powered and grounded) from different outlets. It creates a loop.
Using the NCB on one of the appliances will help remove the loop. Caution: remember to always measure the possible rise in electric field if the appliance can’t find a ground reference. You want appliances grounded in one place, from one source, not two.
Very applicable to Oscilloscope testing equipment, being sure to not blow up your equipment. You don’t want to have the grounding systems from two sources coming together on delicate grounded test leads.
If you have found a certain appliance is leaking current or dirty electricity “noise” to its grounding conductor, use the NCB plug.
This will reduce the “noise” contaminating your grounding system from that appliance but likely increase the electric field around the appliance and possibly increase contact current exposure should you touch the appliance.
It is best to have appliances, especially ones with metal frames and handles, solidly grounded with no resistance on the grounding conductor.
So, start by turning the dial all the way to the left, allow as much current through as the NCB will allow, while still filtering the grounding conductor. The setting provides about 14 Ohms of resistance.
Adjust the dial to the desired balance between the variables, current/noise on grounding system and electric field/contact current in immediate environment.
The basic principle is ground appliances, not humans. But if you have to be tethered to a grounded wrist strap at work, because of the possible static build up and discharge, the NCB may work very well to reduce the current through your body, slowly discharge the static build up and most of all, maintain an effective ground-fault path to keep you safe.
In all applications with the NCB, it is best to have a GFCI outlet in the wall outlet to add some much needed protection. Our home circuit breakers are pretty dumb and hard to trip. GFCI outlets improves your chances of ground-fault protection significantly.