With electrical equipment, we usually place high confidence in good, solid, earth grounding for protection. This application note illustrates some situations where unexpected "ground voltages" could cause serious instrumentation errors, not to mention safety concerns.
Our article covers the common topologies used in industry to connect single-phase and three-phase systems. We describe and show how voltage distribution panels 'distribute' working voltages as well as neutral and ground wire connections.
You may be quite surprised to learn what can happen in ground and neutral lines if something connected as a normal, innocent load should fail! We describe four (4) typical cases for your review.
Fortunately, there are ways to protect yourself and equipment from unexpected ground or neutral wire voltages. For power hungry equipment you can select circuit breakers with ground-fault detection built-in, surge protectors, lightning arrestors, uninterruptible power supplies with voltage regulation built-in and other like devices.
For your instrumentation, Dataforth recommends isolating channels from one another and from ground. Isolating your test & measurement systems and your process control systems assures long, trouble-free, worry-free performance.
We provide a block diagram of a Dataforth signal conditioner at the end of the application note. Notice that Dataforth's isolated signal conditioners provide 3-Way isolation, that is, the signal path, the electronics on the sensor side and the electronics on your system side are all isolated from ground! Moreover, the Dataforth isolated signal conditioners that provide excitation voltage for your 4-20mA loops, strain-gages, and LVDTs provide you with isolated excitation voltage as well... we refer to this as 4-Way Isolation!
Dataforth Appl. Note - "When Good Grounds Go Bad"
, AN108 (271Kb pdf)
Remember, our Application Engineers can assist you with signal conditioner selection over the phone or via fax and email. Call us at our manufacturing facility in Tucson at 520-741-1404 (fax 520-741-0762) or Email us at