Rolling of coiling of Cable, NEC VIOLATION?

[mivey]

It is my understanding that even if 'out balance' all the current going one way matches all the current going the other way, there would be no magnetic field created.

With large gauge service cord comes large currents and often people choose to push the ampacity of these cords 'because they are temp' IMO this is where you get heating from.



I agree.

I agree with you and your agreement too. You have not only doubled the heat dissipation space you get the crossing gap space mention...makes sense.

Now about the figure 8: I've never tried it. Will this work good with small wire like extension cords? Will the bundle play out nicely even if you pick it up and move it around?

I have peeled off a huge pile of fishing line into a pile and was able to reel it back up with no knots (don't touch the pile!). A have also seen huge buckets of yarn in factories piled into big bins and they come back out untangled (no messing with the stack there either).

 

[nakulak]

I'm sure that inductive coils have been inadvertantly created by unknowing individuals, but I am also sure that it would be a freakish accident. coiling the cables, but leaving adequate separation between them would be a safe bet (no mutual induction). transformers, after all, are just expertly coiled wire, with a metal core inserted.

 

[Johnmcca]

Try the figure 8 with a garden hose to see how it works. It does keep the kinks out.

 

[SAC]

It is my understanding that even if 'out balance' all the current going one way matches all the current going the other way, there would be no magnetic field created.

With large gauge service cord comes large currents and often people choose to push the ampacity of these cords 'because they are temp' IMO this is where you get heating from.



I agree.

From a electromagnetic point of view, about the only thing that would occur here would a slight increase in inductance. Given the relatively low number of coils, the relatively large diameter, and the opposite and equal flow of the current in the two conductors, I'd say the electromagnetic effects would be negligible - particularly with respect to any heating effect on the conductors themselves. I'd agree that some other factor was more likely at work here, and the concentration of conductors and lack of airflow due to the coiling would seem to be a more likely cause of overheating than any of the electromagnetic effects.

 

[realolman]

Seems to me you could almost calculate the heat.

I can't believe inductance would have much effect.


What we need is a guy from Texas.

The kinda guy who would do a ground rod shell experiment; to set this up and try it.

Too bad we don't know any body like that.

 

[brian john]

We have infrared coiled cables and induction is a REAL ISSUE the, while the straight portion of the cables were fine at full load, the cables in the coil had elevated temperatures that exceeded the insulation ratings.
Oh and I threw a quarter in the coil and had a JW pick it up, his watch went bonkers (technical term) and did not keep accurate time after that (so he told me)

 

[mivey]

We have infrared coiled cables and induction is a REAL ISSUE the, while the straight portion of the cables were fine at full load, the cables in the coil had elevated temperatures that exceeded the insulation ratings.
Oh and I threw a quarter in the coil and had a JW pick it up, his watch went bonkers (technical term) and did not keep accurate time after that (so he told me)

Were the cables individual phases or did it include the current in both directions?

 

[SAC]

We have infrared coiled cables and induction is a REAL ISSUE the, while the straight portion of the cables were fine at full load, the cables in the coil had elevated temperatures that exceeded the insulation ratings.
Oh and I threw a quarter in the coil and had a JW pick it up, his watch went bonkers (technical term) and did not keep accurate time after that (so he told me)

If you put a clamp on ammeter around a cable containing both the grounded and ungrounded conductors of a circuit, it will read zero as the equal and opposite currents cancel the magnetic fields of each other. Zero net current gives you zero net magnetic field. It doesn't matter how many loops you have, you won't get any significant inductive effects. That why the NEC requires (in general) both the grounded and ungrounded conductors of a circuit to pass through the same opening in an enclosure - to eliminate the inductive effects on the material of the enclosure.

Furthermore, heating due to induction is caused by currents being induced in a conductive material by the magnetic field of some other current carrying conductor. This induced current then operates on the resistance of the material to cause heating. In circuit analysis there is a thing called "Kirchhoff's current law", which basically states that there is a conservation of current. What this means in this case is that the current through the loops of the cable cannot be greater than the current through the straight part of the cable. Since current working through the resistance of the cable is what causes heating, the same amount of current causes the same amount of heating, regardless of the part of the cable being considered - straight or coiled.

I think instead what you were experiencing was a lack of heat dissipation in the coiled section, compared to what was occurring in the straight section. This lead to the higher temperature in the coiled section.

 

[brian john]

Were the cables individual phases or did it include the current in both directions?

These were three separate cables 4/0 Locomotive cable three separate coils

 

[SAC]

These were three separate cables 4/0 Locomotive cable three separate coils

That would explain the "bonkers" part, but not the heating through self-inductance part.

 

[Power Tech]

I agree with you and your agreement too. You have not only doubled the heat dissipation space you get the crossing gap space mention...makes sense.

Now about the figure 8: I've never tried it. Will this work good with small wire like extension cords? Will the bundle play out nicely even if you pick it up and move it around?

I have peeled off a huge pile of fishing line into a pile and was able to reel it back up with no knots (don't touch the pile!). A have also seen huge buckets of yarn in factories piled into big bins and they come back out untangled (no messing with the stack there either).

Yep, 150' anchor rope in and out of the bucket, all day. Don't touch it.

I should be on the lake right now.

 

[Power Tech]

Have seen cord smoke on a coil with too many temp lights. It was fine after it was uncoiled.

On a ladder, I look down to see a cord explode. Loud bang, right in the middle with no one around.

 

[Rick Christopherson]

My understanding is when cable is coiled, especially large gauge service cord with more than one conductor under one jacket the cord will heat up due to magnetic field generated this effect is increased when the load per phase is out of balance. I cannot find a written ref. to this or a code section to site.

This stems from an old wive's tale, and it still has quite a few firm believers, obviously including the inspector for the OP. Even if these were individual conductors, there is virtually no heating effects from induction.

The cord reels are a completely different situation with a completely different cause. These are very prone to overheating when not fully uncoiled. The reason also has nothing to do with induction, but is simply because they are in a confined tight coil, and the heat from the inner coils cannot be dissipated, as they are thermally insulated by the outer coils.

 

[e57]

I have peeled off a huge pile of fishing line into a pile and was able to reel it back up with no knots (don't touch the pile!). A have also seen huge buckets of yarn in factories piled into big bins and they come back out untangled (no messing with the stack there either).

I do it with cat5 all the time - just need to come back up in the same relitive direction - and NEVER let the end of the cable get near the pile. Another fun one is a traffic cone inside a trash barrel.

 

[ohmhead]

Well look at this picture inside the steel tower of this 300 foot crane on our job site its rolled up ho so cord 400 amps 3 ph 480 v coiled & raped around a wooden 6x6 post inside frame of crane it doesnt melt but it does get hot .http://i611.photobucket.com/albums/tt195/stringking/000_0012.jpg

This is one of three tower cranes


It will not melt the insulation but if the ground is not a good connection it will start to heat up .

But we are not exceeding the temp of the insulation so no one ever unraps these.

Yes Brian you are correct in your post it will create a field in the core thats why we roll up on wood if its on the tower crane metal frame you have a big issue with heat on the frame .

If you take a small conductor thats ampacity is exceeded and hook it up 208 volts single phase to a load and dont unrap it it will burn the ground becomes a core and eddy currents are induced seen this once on a job a roll of romex hooked up to a temp service 14.2 at 30 amps melted the roll so bad you could not pull it apart .


Sorry for the picture ill take another monday .

 

[iwire]

Well look at this picture inside the steel tower of this 300 foot crane on our job site its rolled up ho so cord 400 amps 3 ph 480 v coiled & raped around a wooden 6x6 post inside frame of crane it doesn't melt but it does get hot .http://i611.photobucket.com/albums/tt195/stringking/000_0012.jpg

This is one of three tower cranes


It will not melt the insulation but if the ground is not a good connection it will start to heat up .

That make no sense at all. What does a 'ground' have to do with heating.

 

[ohmhead]

Well take a look at this http://i611.photobucket.com/albums/tt195/stringking/article_1_2007_sharlon_7.gif


I was taught in school that phases will cancel out each other .

But iam not sure today if thats true with what i feel and have seen if the crane power cable is ungrounded it runs hotter than grounded.


Eddy loop currents flow but have no way to go to ground the ground is now a coil .

Eddy currents flow in a emt conduit with a single phase meaning one conductor of one phase no others .

But were rolling up a cable on a tower crane this is not a normal way of installing power i see magnetic effects here .

 

[SAC]

So what you mean is literally a "ground" - a conductor at ground potential. It is in the proximity of a coil of one phase of a multi-phase circuit. The "ground" is not the current return path of the circuit of the ungrounded conductor. So the current in the ungrounded conductor is inducing currents to flow in the grounded conductor, causing it to be heated. That sounds very plausible. If all phases of the circuit were grouped together we wouldn't expect that to happen. It doesn't really matter if it is grounded or not - even an electrically isolated conductor would be heated. That's how induction furnaces and induction stoves work - like the pictures you linked to.

 

[ohmhead]

Well SAC i can only give what i see at work let me ask a question if i may .

The cable is 500 mcm 4 conductor cable cord type and the ground conductor is just a bond from main service to the 400 amp switch service at the tower .


There is no neutral needed this feeds two transformers in the nest above if the ground is not attached the cable gets hot .

If the ground conductor is completed with a solid connection on both ends then the cable is at normal temp .

Can eddy currents in the loop coiled cable and a magnetic field by the coiled cable create and induced heat in the ground not attached just like in the iron core of a transformer ?

And can the coiled cable create a field by its self and create induction heat in the metal frame making a much higher level of generated heat ?

Iam interested i always thought eddy currents went around in a circle in a metal material why does the ground connection matter the ground wire is stranded kinda like a transformer laminated iron core iam trying to understand this ?

Is this like a secondary of a transformer by the phase conductors in the cable there all in the same jacketed cable ?

 

[SAC]

If I understand correctly, that would be a situation that would worry me.
The cable that is coiled has three phases, and EGC? If the EGC is not connected the cable gets hot, but if it is connected, it doesn't? ASAP I'd take an amperage reading on the EGC while it is connected. It sounds as if there might be something wrong with the load and the EGC is carrying unbalanced current - and maybe the frame of the crane, too.