I don't know much about 240 V single phase power so please bear with me! I am confused about the wiring. Here is the situation.
In my outlet there are 3 wires, black, red and blue. I used my Fluke multimeter to check the voltages in between these lines. To my understanding, I should have L1 and L2 which are two signals 180 degrees apart, and a neutral.
I checked around with the multi meter until I found a voltage of 240 V and figured these were the L1 and L2 lines (red and black) and the third one (blue) must be the neutral, since the voltage between the third one and any of the other 2 was only 120.
So using just these two lines, I wired up my device (which is a DIY single phase to 3 phase converter for my milling machine) and it works just fine. But then I realized that the machine isn't grounded. For 120 V service, I am used to having a ground wire that I can hook up to the chassis for safety. So I go into the distribution box that the outlet is connected to and I see bare wire, which I presume is ground. So just to be sure, I shut off all of the power and did a continuity check between this bare wire and each wire in the outlet and I got continuity with the red wire! I don't understand this at all since the red and black were my L1 and L2 lines!
Can anyone explain why this is the case? I am pretty sure I CANNOT use the neutral line as a chassis ground and I want this machine to be grounded. Any help would be appreciated!
EDIT: In regards to wire color code. I am located in central PA.
Best Answer
Red, black and blue are the classic colors for 3-phase power (other than wild-leg). The color combination does not specify voltage; that's what voltmeters are for.
An important factor is the lack of neutral. In the U.S. neutrals must be white or gray. It is illegal to "tape" or "paint" another wire color to be neutral, unless the wire is 4 AWG or larger. Measure the voltage between each wire and ground/earth. You should get a significant voltage if the wires are not wrong-colored.
How well do you really know the wiring here? Are you sure you don't already have 3-phase or maybe someone beat you to it and installed a phase converter somewhere? Maybe that has since been removed? No kidding, I have a 240V 3-phase converter at a 120-240 service panel, that panel's transformer is fed from 3-phase service which is literally 20 feet away from it. The things people do!
Now, the red wire being grounded is just wrong. However this could occur if the grounding system is not proper, or if the neutral-ground bond has failed. (And I have one of those in a panel right now.) All it takes is one ground-fault to "lift the ground" to hot potential (or more accurately, lower the hot to grounding potential, lifting the neutral away from ground.)