Slightly OT : dual source grounds

Greetings all!

I've got a panel where, for a variety of reasons, I'm pulling two incoming power sources, a 3-phase 480 VAC circuit and a single-phase 220 VAC circuit. Power draw on each side was too large to make transforming either one to the other practical in this application.

Now, I've got a dual-disconnect and plenty of breakers, so my only concern at this point is grounding. Each circuit has it's own earth ground, and my first inclination is to tie both to my grounding bar. However, I am concerned about creating a huge ground loop if I do this.

Should I connect them or isolate them? Leave one off? Any suggestions on how to proceed?

Thanks!

TM

Dear TimothyMoulder,

Can you give me a single line diagram with sources and examples of load??

Tim. Ground is ground..if both supplies are fed from the same building then both supplies are grounded at the source..if you keep them isolated you could create problems by having a difference in potential between two different grounds..that would not be good. connect them and ground them..its the safe way to go..

Hey Tim, I understand your quandary. Let me ask a couple of questions. Is the ground from each of the sources you quote an equipment ground or a system ground. IE: The 480V 3ph system if it were a Y distribution, could have the neutral grounded. Is the 220V single phase ground required in the power scheme of the equipment? Meaning, is that the center tap of a transformer secondary that happens to be grounded? All of these things are considerations but all in all, darrenj is correct. Ground is ground and only one is really required and if you connect the two ground conductors in your panel at a single point, and if the other ends are a significant distance from your panel, you may indeed run into a ground loop noise problem but if the equipment is just motors and such and not sensitive electronic gear, you will still be ok, but just to make sure, one is all that is necessary.

Thanks guys,

It's all earth ground, no transformers involved, so it looks like I'm probably safe. As long as I'm not letting the smoke out of the building electrical system, I'll cross the noise issue when it comes.

Thanks!

TM

darrenj, ground is NOT ground! That's where the problem of ground loops and loop currents comes from.

However, there is a lot of misconception out there on this subject. When doing power wiring, ground loop noise due to ground loop current is of no real concern.

On the other hand, when doing instrumentation and control wiring, it is highly undesireable to have currents flowing in the ground shields due to these ground currents causing fields that interfer with the low level signals. For these types of circuits, ground currents are to be avoided and the usual grounding practices should be followed---no loops, all grounding done at one point or at least at the transmitting end.