Interesting experiment video - eddy currents

[PetrosA]

I came across this earlier and found it interesting since it's in our code as well to not run conductors through individual holes in a steel enclosure without cutting a notch between them to mitigate the effects of eddy currents. According to this guy's finding, there is no appreciable rise in temperature in the metal between the holes even at 125A. I will feel much better now about retrofitting 3" pancakes with individual KOs for K+T onto old, loom enclosed wires

 

[don_resqcapt19]

I came across this earlier and found it interesting since it's in our code as well to not run conductors through individual holes in a steel enclosure without cutting a notch between them to mitigate the effects of eddy currents. According to this guy's finding, there is no appreciable rise in temperature in the metal between the holes even at 125A. I will feel much better now about retrofitting 3" pancakes with individual KOs for K+T onto old, loom enclosed wires
...

The rules in the Canadian Electrical Code for this issue don't apply unless the current will exceed 200 amps.

 

[mbrooke]

Good vid!

 

[K8MHZ]

Very good video!

Thanks!

 

[K8MHZ]

Now I would like to see the same done with the Line in one hole, the Neutral in another and then passing to the load.

As good as the vid was, it still does not replicate what we may see in the field.

 

[petersonra]

wouldn't the magnetic fields of the two wires be 180 degrees out of phase in such a configuration? that might well be cancelling out some of the inductive heating that might otherwise happen.

 

[kwired]

wouldn't the magnetic fields of the two wires be 180 degrees out of phase in such a configuration? that might well be cancelling out some of the inductive heating that might otherwise happen.

As they also would be if the two conductors passing through enclosure wall were line-neutral or line-line and the enclosure housed the load, or even just passed the load on through other holes in the enclosure. You have an inverted 1 turn core/coil for each conductor penetration here, cut slots between the holes and you have made it only one hole with multiple conductors through the core and if you have equal and opposite polarity from all conductors or all three phases for a three phase load the net flux on the core is zero.

 

[GoldDigger]

There are two potential sources of heating in the metal. One is eddy currents, whose source is not particularly clear and which would be more significant in non-ferrous cases. I do not consider those to be a large problem.
The other is hysteresis losses from the alternating magnetic field. Those losses will be greater the thicker the ferrous metal is, and for a thin gauge case and low (~100A) current may not be a real problem either. John's experiment certainly supports that.
For short circuit currents, on the other hand, both the choke effect limiting the fault current and the heating effect can be more noticeable.

P.S.: The current in the two wires, and therefore the heating effect, will be exactly the same for the situation he shows as for the situation where the load is inside the box. The only difference is in the voltage on the insulated wires passing through the two holes, and I do not expect that to influence the results in the slightest way.