can somebody explain the pysics behind

amakarevic · 11-01-2011, 01:44 PM

when conductor (wire) travels more vertically, why does it get hotter and needs more insulation (MC for going between floors) than when it goes more horizontally? i'm just curious in the physics behind this phenomenon.

thanks

AllanJ · 11-01-2011, 02:03 PM

The wire heats up as current flows through it, the greater the number of amperes the more it heats up.

Air around the wire cools it down, the air moves upwards as it warms up by the wire. (warm air rises)

The vertical wire the same air moving vertically tends to follow the wire so the warmer air it gets it doesn't cool the wire higher up as quicklyu compared with a horizontal wire where different air moves upwards all along the length of the wire.

Then the air transfers the heat to other things like the subfloor or top of the stud cavity above.

I think that the effect of cooling on a vertical wire versus a horizontal wire makes little if any differnece in terms of having to use fewer amperes than the wire normally calls for (called derating); I think you do not have to derate because the wire is hung vertically. In other words the original question is for scientific purpose only, those doing electrical work can ignore it.

amakarevic · 11-01-2011, 02:13 PM

thanks. makes sense.

jimmy21 · 11-01-2011, 03:34 PM

never heard this before. makes sense though. If your wires are getting hot, there is a problem

Yoyizit · 11-01-2011, 04:08 PM

Quote:

Originally Posted by amakarevic

when conductor (wire) travels more vertically, why does it get hotter and needs more insulation (MC for going between floors) than when it goes more horizontally? i'm just curious in the physics behind this phenomenon.

thanks

Does not make sense according to my mental image of the setup and what I understand about radiative, convective and conductive heat loss.

Can you provide specifics - temps, distances, other factors?

jimmy21 · 11-01-2011, 10:13 PM

heres what i picture. But i don't believe it has any real world application because wires shouldn't be warm in the first place

The warm air on the vertical wire stays around the wire, while the horizontal wire the air moves away

11-01-2011, 01:44 PM	#1
amakarevic Member Join Date: Apr 2007 Posts: 2,083	can somebody explain the pysics behind when conductor (wire) travels more vertically, why does it get hotter and needs more insulation (MC for going between floors) than when it goes more horizontally? i'm just curious in the physics behind this phenomenon. thanks

11-01-2011, 02:03 PM	#2
AllanJ Member Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 6,775	can somebody explain the pysics behind The wire heats up as current flows through it, the greater the number of amperes the more it heats up. Air around the wire cools it down, the air moves upwards as it warms up by the wire. (warm air rises) The vertical wire the same air moving vertically tends to follow the wire so the warmer air it gets it doesn't cool the wire higher up as quicklyu compared with a horizontal wire where different air moves upwards all along the length of the wire. Then the air transfers the heat to other things like the subfloor or top of the stud cavity above. I think that the effect of cooling on a vertical wire versus a horizontal wire makes little if any differnece in terms of having to use fewer amperes than the wire normally calls for (called derating); I think you do not have to derate because the wire is hung vertically. In other words the original question is for scientific purpose only, those doing electrical work can ignore it. __________________ The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded. Last edited by AllanJ; 11-01-2011 at 06:38 PM.

11-01-2011, 02:13 PM	#3
amakarevic Member Join Date: Apr 2007 Posts: 2,083	can somebody explain the pysics behind thanks. makes sense.

11-01-2011, 03:34 PM	#4
jimmy21 liscenced electrician Join Date: Jul 2008 Location: Oregon coast Posts: 945	can somebody explain the pysics behind never heard this before. makes sense though. If your wires are getting hot, there is a problem

11-01-2011, 10:13 PM	#6
jimmy21 liscenced electrician Join Date: Jul 2008 Location: Oregon coast Posts: 945	can somebody explain the pysics behind heres what i picture. But i don't believe it has any real world application because wires shouldn't be warm in the first place The warm air on the vertical wire stays around the wire, while the horizontal wire the air moves away Attached Thumbnails

can somebody explain the pysics behind