Presumed RF Interference

That is already half of a solution:

Go for fiber. That is imune to both ground and RF problems. Avoid
ground connections between the equipment.

Replace ethernet with fiber. Break serial lines with optical isolators.

Yes, fiber will solve ground loop problems. And this smells like
a ground loop issue. But at this juncture, I don't have enough
specifics to recommend ma$$ive changes.

Cut the ground wire in your power cords but ground the equipment directly
to a metal frame.

I would NEVER tell a client to do this.
That could easily kill someone.

Avoid ground loops: Between two computers you have a ground connection
via the powerline ground. Connect them via RS-232 and you have a second
connection via the RS-232 ground. If your power ground is bad then you
might run amperes through the RS-232 ground that results in Volts, more
than your signal level, maybe.

I don't recall mention of RS-232,. but yes, this is the classic
example of ground loops.


The safety purpose of the ground cord is to cause a short circuit in
case line voltage energizes the case, in which case the breaker will
trip. If you cut that wire, the metal frame frame can become hot;
unless it's firmly grounded itself, there will be a potential between
it and ground. Along comes the next well-grounded person to touch it
-- poof!

Even if the frame were grounded properly, that's a local ground, which
may differ in potential from the breaker box's ground. The neutral
wire in the circuit is tied to ground at the breaker box, which means
there could be a potential difference between it and the frame. That
also creates a potential shock hazard, though presumably not that great.

What might be useful -- ask an EE, not me -- is a circuit with an
isolated ground. In that case, the ground wire from the power plug is
routed all the way back to the breaker panel, and isn't connected to,
say, the local electrical box that the cord is plugged into. I've seen
computer equipment wired that way in the past.

The isolated grounds are definitely a recommended idea for telco/server
rooms... Perhaps an array of them depending on the size power feed we're
talking about. I'm assuming it's a sizeable UPS that runs your telco and
data equipment (or small server room). The irritation, if you haven't done
this step already, is that adding a TRUE isolated ground after you've
already built your building and room is not exactly a cheap thing to do.

Especially in nice metal framed buildings that like to have a tendency of
becoming the nearest path ground themselves. But I agree that it's
certainly something as a worthwhile "first path" to look into!


PS. I agree it's not good business practice to kill your clients!

In the US, the NEC code states that the only place a neutral and a ground should be bonded together is in the primary service entrance facility or where the neutral is created. All subpanels will have isolated grounds and neutrals. If you have three phase service and use a delta (wye without the neutral) to wye transformer to create the neutral, the neutral will be bonded to ground inside the transformer cabinet. Eliminating the neutral is typically done to save money when converting 277/480V to 120/208V (no neutral means a reduced conductor count inside the conduit so smaller conduit can be used since the extra copper for the neutral is eliminated on the input side.) All grounds must be connected to the first metal box or conduit they touch. If you are using plastic boxes with Romex, your grounds will go all the back to your subpanel ground bar which will not meet the neutral until the main breaker panel. More often in a datacenter environment or a commercial facility, the wiring will be BX under a raised floor or BX or EMT with THHN overhead. Either way, the ground is connected inside the outlet box and wired directly back to the breaker panel. The bonding in the box is to ensure there is no voltage potential carried on any metal conduit. My NEC book is at the office now and I'm home, but I'm pretty sure everything I have stated from memory is accurate.


Tellurian Networks - The Ultimate Internet Connection | 888-TELLURIAN | 973-300-9211
"Well done is better than well said." - Benjamin Franklin

Yes, I believe that that's correct, though I'm not going to dig out my
copy of the NEC right now, either. I chose to leave out the part about
separate panels.

    --Steven M. Bellovin,