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an electrician is telling me that having the 2 conductors (hot and neutral) for a branch circuit from my home Electrical Panel in the same buried conduit will produce less heat because the 2 magnetic fields cancel out.

i think the magnetic fields cancel (ie a current loop probe will show 0 net current) but the heat in each conductor is produced by electron flow and not affected by the other conductor.

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  • \$\begingroup\$ The primary mechanism of heating is resistive losses in the wire. So you are right about that part of it. Also, you shouldn't bury metallic conduit. At least not in my opinion. It is too subject to corrosion when buried in the ground. I doubt metallic conduit would experience much heating due to magnetic fields in the first place. But non-metallic conduit will definitely not. So ultimately, this seems like kind of a thought experiment more than a practical question. \$\endgroup\$ – mkeith Apr 12 at 7:32
  • \$\begingroup\$ There is some difference due to eddies in the conduit itself (if it is metallic). But I doubt it is noticeable on house circuits. Also I don't know if there is some regulation allowing or forbidding this practice. Here in europe we try to keep a branch line bundled for a run, it's easier to manage. \$\endgroup\$ – Lorenzo Marcantonio Apr 12 at 8:04
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It depends on the conduit if it is a conductor or not.

In fact the heat due to magnetic field is not from the cable but on the conduit and it is produced by the eddy currents induced by the magnetic field in the metallic conduits.

That is why in case of metallic conduits cables are arranged in order to cancel the magnetic field.

It is true also for three-phase systems. It is also considered on cable trays.

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  • \$\begingroup\$ My take-away from all these great answers is that 1. yes magnetic field of a single ac conductor in a metal conduit will create eddy current in the conduit which creates heat 2. yes, placing the neutral/hot conductor pairs in same conduit will cancel that eddy effect 3. none the less, the heat produced by a single conductor induced eddy current in the conduit will be negligible compared to the heat from electron flow inside the conductors themselves . please correct me if i didnt summarize well. \$\endgroup\$ – Cool Pontiac Apr 12 at 18:14
  • \$\begingroup\$ It depends on the current, the cable dimensioning, the cable type, the conduit and other conditions in confined space. For high currents cable arrangement is mandatory. In all cases I recommand it . Like norms and standards, if you apply all rules, even if you think that some of them are not related or not significant, you will be on the safe side. \$\endgroup\$ – Paul Ghobril Apr 12 at 18:46
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  • two adjacent wires forward and return will have lower inductance as the mutual coupling reduce EMI and loop inductance somewhat

  • But this only increases apparent power a tiny bit at 1uH/m per wire and has no effect on real power.

  • Putting two lossy distribution lines in the same thermal resistive jacket inside a conduit ought to increase heat rise.

  • yes a loop probe will show 0 current if there is no ground leakage but that is not an indicator or real or reactive power.

  • he may have been taught this for megaVAR industrial sites.

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    \$\begingroup\$ It's taught to Canadian electricians. reduces eddy currents in conduit IIRC possibly mutual inductance problems in packed conduit as well. It's the reason when paralleled conductors are used you put a full set in each pipe rather than use a pipe per conductor set. Still fairly high power levels though. \$\endgroup\$ – K H Apr 12 at 2:54
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You are right.

Heat is produced by electrons flow:

P(t) = R * I(t)^2

R = Rhot + Rneu


Almost all the magnetic flux cancels out and all other appliances are happy.

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