Iso trafo at sub panel garage studio

[terri faron]

In premises AC power wiring, each of the load conductors (i.e., “line” and “neutral”) normally carry equal currents but in opposite directions at any instant in time. This causes the magnetic fields surrounding each to point in opposite directions but have equal strength, since the polarity of each field is determined by the direction of current flow and the strength (magnitude) of the field is directly proportional to current. This not only causes the conductors to repel each other but it results in a plane of zero magnetic flux exactly midway between them. Consequently, if a third conductor (i.e., safety ground) is positioned along this “zero-flux” plane, no voltage will be induced into it. However, if the safety ground conductor is slightly nearer the “line” or “neutral” conductor, a voltage will be magnetically induced over its length. This voltage is directly proportional to the length of wiring run and, perhaps most importantly, directly proportional to the rate of change of the load current in “line” and “neutral.”

Ground Loops: The Rest of the Story theory's concept...agree it's worth reading

 

[Brian Roth]

Now that we've gone a rabbit hole re. the OP's original question.....

I am curious about so-called "BX" cable. It's has a flexible metal sheath with individually insulated hot/neutral/grounding conductors twisted together in a very regular wind fashion.

For some reason, I thought it was better than "Romex" or random wires pulled through a piece of EMT/conduit pipe.

Bri

 

[shabtek]

In practice we keep low level signal conductors away and perpendicular to ac power...which I think relates to the twisted or not etc discussion, or is the power quality effected in meaningful ways by this inductive interaction?

 

[ccaudle]

Now that we've gone a rabbit hole re. the OP's original question.....

Yes, sorry for my contribution to that. Haven't seen any replies from the OP lately, I think he gave up on getting the problem solved here and wandered off.

I am curious about so-called "BX" cable. It's has a flexible metal sheath with individually insulated hot/neutral/grounding conductors twisted together in a very regular wind fashion.

For some reason, I thought it was better than "Romex" or random wires pulled through a piece of EMT/conduit pipe.

Yes, it is covered in that Fox/Whitlock paper I linked a few posts ago. Figure 6 on page 7 compares different configurations, and BX is about 3x to 6x better than Romex for induced ground noise at power line frequencies, even more around 10kHz.

 

[abbey road d enfer]

Now that we've gone a rabbit hole re. the OP's original question.....

I am curious about so-called "BX" cable. It's has a flexible metal sheath with individually insulated hot/neutral/grounding conductors twisted together in a very regular wind fashion.

For some reason, I thought it was better than "Romex" or random wires pulled through a piece of EMT/conduit pipe.

In most of Europe, power distribution in premises is done with 3-conductor wire, twisted with a pitch of about 8-10 inches, without shielding. So the earth wire, although being very close to the current-carrying conductors, benefits from a very good geometric rejection. It would be interesting to compare with Romex, which also seems to have a pretty good geometry.

 

[JohnRoberts]

I recall working with BX back in the 50s/60s. It was a PIA to cut with a hacksaw. Romex was easier.

JR

 

[HP200CD]

I recall working with BX back in the 50s/60s. It was a PIA to cut with a hacksaw. Romex was easier.

JR

There's a special tool for cutting BX. It holds the cable and applies a hacksaw wheel on a crank. Makes it very easy.

 

[JohnRoberts]

I could have used that tool more than half a century ago...

JR