Hots and neutrals run in separate metal raceways

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jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
I saw it yesterday and sorry I don't have a picture for you but tell me what you think of this:

A 4" square metal box near a circuit panel. A pair of metal flex raceways with 3-4 ungrounded conductors in one, and two neutrals in the other. Both use a duplex MC connector to enter both the panel and the 4" square box. This is how the 3-4 branch circuits are fed from the panel.

What are the issues here? I recall something from school about having the hot pass through one metal circle while the neutral passes through a different one. But that was a decade ago and I haven't run into any similar situation since then.

Is it EMFs or harmonics or something like that?
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
I know it's late on a Friday night, so I'll come back later to check out the replies. I'm mostly wondering if this is an NEC thing, or if there are inherent dangers here.

What should I say to convince the customer that it needs to be fixed?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If the cable sheaths are ferrous, there will be inductive heating of them resulting in wasted energy. At the current levels that would be in these small cables there is no real danger of enough heat to cause any real problems.
It is a code issue. See 300.3(B) and 300.20
 

kwired

Electron manager
Location
NE Nebraska
There would also be an increase in total impedance of the conductors especially during a ground fault which may increase the operation time of the overcurrent device.
 

Electric-Light

Senior Member
The magnetic fields don't cancel out and CRTs are EXTREMELY sensitive to the field. There was a day when big screen CRTs even had a switch in the back to set which way the TV is facing to compensate for natural magnetic field.

In one of the houses I lived in, there was a 3-way circuit with separated hot and neutral in the wall behind my monitor. Whenever that light (300W chandelier) was turned on, I would see waves in my monitor.

There isn't any household electrical item that is anything near as sensitive to magnetic field as CRTs though.
 

Strife

Senior Member
I remember about a service call I did one time (when computer monitors were CRT). Customer complained that one of the monitors kept flickering.
After hrs of scratching my head I finally figured out what it was.
The conduit feeding the fluorescent fixtures in the office was installed in the wall, right behind that monitor.
So, yeah, I'd agree that nothing is as sensitive as CRT's.

The magnetic fields don't cancel out and CRTs are EXTREMELY sensitive to the field. There was a day when big screen CRTs even had a switch in the back to set which way the TV is facing to compensate for natural magnetic field.

In one of the houses I lived in, there was a 3-way circuit with separated hot and neutral in the wall behind my monitor. Whenever that light (300W chandelier) was turned on, I would see waves in my monitor.

There isn't any household electrical item that is anything near as sensitive to magnetic field as CRTs though.
 
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