I am not an electrician , but was curious about this. Im working on a job where a large piece of packaging machinery is being installed. The 3 phase and ground for the equipment comes directly from the building service panel to an electrical enclosure on the machine, but there is no dedicated neutral. The electrician on site has taken one leg of the 3 phase power to ground (in the machine electrical enclosure) to derive the 120 volts for control circuitry. Is this is a normal practice and is there any related concerns, safety or otherwise?
Not trying to play skeptic, but if you're not an electrician, how are you sure he did this? (Only say that because I have had people second guess my work needlessly before...)
However to answer your question, it would be highly un-cool! It would make the ground a current carrying conductor, and pose a shock hazard from contact of the exposed conduit and metal parts of the machine. That is if he did it.! Before laying blame, or making these type of accusations it would be wise to check to see if he actually did so. If the machine in question is still being installed, wait for him to complete it, don't use it, and have it checked by a licensed EC after he's done if you question the workmanship. As it should be inspected anyway, the Inspector should catch this, if he did it.... Odds are that there is a likely answer for what you are concerned about, that he installed a transformer for the control voltage, or one wasn't nessesary as the control voltage was 208/240v. Truthfully, it is something you should take up with him, if you are concerned.
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: Is this an unsafe practice?#57942 10/24/0512:42 AM10/24/0512:42 AM
Thanks for the reply. To answer your question, I've seen the work. There is a jumper between the 120 volt neutral terminal block bus and the 3 phase ground lug on the electrical panel of the machine. There is no transformer being used and it is 120 volt control circuits. It actually also feeds a 120 volt to 24 volt transformer for additional control circuits. As I said I'm not an electrician nor do I pretend in any manner to be one. I'm a programmer, but I do have some electrical background. This is a plant electrician and I don't know what his credentials are. Industrial settings like this are very loosely regulated outside of the actual building electrical. Not that I agree with this, but very rarely will you see any industrial line equipment inspected. It's not about making accusations, I'm just looking for some some sound advice if this is a legitimate concern I should be taking up with him. Aside from the safety issue there is sensitive equipment on these machines. I don't know if I made it clear that there is an actual equipment ground wire from the building service panel to the electrical back panel. Its probably about 90 feet to from the building panel to the machine if that makes any difference.
Re: Is this an unsafe practice?#57943 10/24/0512:54 AM10/24/0512:54 AM
Yep there is a transformer. Primary voltage is 120v and the secondary is 24v which is used for the bulk of the control wiring. There is also some additional 120 volt circuits. The 120 volts is being pulled from one leg of the 3 phase and the actual ground wire back to the service.
Re: Is this an unsafe practice?#57946 10/24/0507:40 AM10/24/0507:40 AM
If thats what he did then thats not right as the others have said. Two options are to change out the transformer to a 208->24V version or pull a neutral. If the transformer is small which it usually is for control circuits, this might be the cheapest correction.
If he pulled a ground in the conduit (which he probably didnt since he is doing the stunt jumpering the neutral and the ground) and if the ground wire is large enough (#4 or larger) and insulated and it is a metal conduit run, e.g. EMT, IMC, Rigid, then you may retape it white and land it on the neutral strip in the panel. The conduit, per code, is an acceptable EGC. However, the machine specs might require the conductor.
People here are going to hang me for suggesting the last solution
Re: Is this an unsafe practice?#57947 10/24/0508:46 AM10/24/0508:46 AM
I agree with the others. This isn't an acceptable method. The machine should have a neutral or a different transformer installed. Taking a phase and ground to derive 120v is a hack method and could result in many problems down the road, the safety of personnel now and in the future is compromised. There will now be neutral current flowing on the grounding conductor. This is also an NEC violation. Hate to slam another Sparky, but from what you said about the installation, this isn't acceptable.
Re: Is this an unsafe practice?#57948 10/24/0509:36 AM10/24/0509:36 AM
Had a licensed electrician pull the same stunt in my house several years ago. He installed a off-peak control system cabinet that controlled heat storage units, water heater, pool heater, and some baseboard heaters. Anyway, the storage units needed reverse logic (turn power off to the resisters mounted near the thermostats in the boxes to override on-peak condition) so he wired up an 120v coil ice cube relay. The box only contained 240v circuits so there was no neutral. He connected the white from the coil to the cabinet.
When he left, I ran a #14 white throught the 2 foot conduit to the breaker cabinet and provided a proper neutral.
Re: Is this an unsafe practice?#57949 10/24/0506:50 PM10/24/0506:50 PM
Thats an excellent way to kill a plumber the next time a drain pipe is being replaced!I had a machine that was shutting down because the EMT that was the only path to ground fell apart at a joint.They had run A2 from a control relay to the panel ground.