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Is there a difference in amount of heat produced on a conductor between AC and DC at the same amperage and voltage?

For example if you ran 50A at 480V through a conductor would the heat produced be the same for AC (60hz) and DC?

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    \$\begingroup\$ Related/duplicate: electronics.stackexchange.com/q/58650/2028 \$\endgroup\$ – JYelton Aug 4 '14 at 22:05
  • \$\begingroup\$ @JYelton - not a duplicate. Elongated conductors experience somewhat different issues than lumped-element resistors. Just look at the difference in answers here and there. \$\endgroup\$ – Chris Stratton Aug 4 '14 at 22:20
  • \$\begingroup\$ @Chris Agreed. Just related, then. :) \$\endgroup\$ – JYelton Aug 5 '14 at 20:33
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Yes... assuming for AC you mean 480V RMS, not peak-to-peak.

The power (in watts) should be:

480V * 50A = 24kW

However if you are measuring 480V AC peak-to-peak, the RMS voltage will be ~340V, in which case the power would be less:

340V * 50A = 17kW

AC voltage and current is continuously variable in a sine wave. Power is calculated using RMS so that it can be compared to DC in a useful way.

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  • \$\begingroup\$ How about AC current too? ;) \$\endgroup\$ – placeholder Aug 4 '14 at 22:17
  • \$\begingroup\$ I'd advise editing the phrase "using RMS - an average", since AC can also be measured as average, or mean (applied to the rectified waveform). \$\endgroup\$ – WhatRoughBeast Aug 5 '14 at 0:17
  • \$\begingroup\$ I asked this question because we do a lot of heat rise testing on large conductors up to 6kA. Usually for anything under 2kA we AC (via a variac and step down transformer setup) whether the application actually uses AC or not. Usually we adjust the voltage based on current and don't really care what the voltage as long as our current is where it's suppose to be. So I was curious if there was difference. So pretty much if I were to pay attention to the voltage when we are testing I would notice that DC voltage is lower that the AC voltage for a give amperage. I was thinking of Peak Voltage btw \$\endgroup\$ – TheColonel26 Aug 5 '14 at 0:38
  • \$\begingroup\$ Thanks for the hints, @WhatRoughBeast and Placeholder. I've edited my answer to clarify a bit. \$\endgroup\$ – JYelton Aug 5 '14 at 20:32
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Yes. DC current will travel through the entirety of the wire -- AC current will tend to move on the outside of the conductor (see Skin Effect). This will cause slightly more ohmic heating in AC than in DC. That's why AC wire is usually stranded while DC wire is usually solid -- more strands = more surface area.

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    \$\begingroup\$ House wiring is AC and house wiring is by code solid in North America I'm not so sure that your "usually" is the usual use. \$\endgroup\$ – placeholder Aug 4 '14 at 22:17
  • \$\begingroup\$ I doubt there is much skin effect in household sized conductors at 60 Hz, but might just start to be noticeable in utility distribution lines. \$\endgroup\$ – Chris Stratton Aug 4 '14 at 22:21
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    \$\begingroup\$ My understanding is that the skin effect doesn't really start causing noticeable issues until you pass 500hz or so. Atleast that's what one of our services techs told me who works on high frequency systems. \$\endgroup\$ – TheColonel26 Aug 5 '14 at 0:46
  • \$\begingroup\$ I thought AC wasn't actually moving down the length of the conductor but vibrating back and forth? \$\endgroup\$ – ACD Aug 5 '14 at 20:41
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If the AC load is reactive instead of purely resistive, then the currents which experience ohmic (conversion to heat) losses in the transmission line include not only the real current which does work, but also the reactive currents.

Because the losses are tangible, industrial customers are billed for reactive power as well as real; for a large facility it is worthwhile to install banks of power-factor correcting capacitors to balance the inductive reactance of motor loads with opposing capacitive reactance, keeping the power on the transmission line mostly real.

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The only thing that is different in ac and dc is frequency. So due to this fact ac repeatedly magnetise and demagnetise the wire elemnt i.e. the dipoles are made to turn again and again .This requires energy. So energy is lost during each magnetisation . Hence energy is lost .

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    \$\begingroup\$ "The only thing that is different in ac and dc is frequency." No, the peak voltage is different. "So due to this fact ac repeatedly magnetise and demagnetise the wire elemnt (sic)". No, copper and aluminium conductors, for example, will not be magnetised. "i.e. the dipoles are made to turn again and again . (sic)" What dipoles? \$\endgroup\$ – Transistor Oct 6 '17 at 15:13

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