Wiring size charts, applicable to AC and DC?

[offgriddle]

More powerful HOW?
in what way?
Did they mean a shaded pole 48vAC motor
Would be less powerful than a permanent magnet 48VDC motor?
AC isnt often used below 120V aside from control uses...

Mm Kay:

A) Volt for volt, DC is more powerful than AC as it has constant magnitude and direction unlike AC whose magnitude and direction changes typically 50 to 60 times every second, which makes AC weaker within a given time period. ~ There is no argument that AC of course lends itself better than DC for long distance transmission and distribution.

2) To your question regarding a "Shaded pole 48vAC motor", I will counter your question with a question: What is the capital of Djibouti?

C) This publication by "Machine Design" on "What’s the Difference between AC, DC, and EC Motors?" is informative.

StackPath

4) I do see some 24 VAC stuff around now and then in equipment cabinets and of course doorbell transformers.

 

[Dzl]

Mm Kay:

A) Volt for volt, DC is more powerful than AC as it has constant magnitude and direction unlike AC whose magnitude and direction changes typically 50 to 60 times every second, which makes AC weaker within a given time period.

Can you help me understand what you mean by "more powerful." I understand your line of thinking, I think (that 60hz AC only spends 1/60th of a second per second at its maximum voltage). But a Watt is a Watt, whether we are talking AC or DC right? And a Watt is a unit of power. So how are you defining power here, what are you using the term to refer to, and what is the practical significance to us?

C) This publication by "Machine Design" on "What’s the Difference between AC, DC, and EC Motors?" is informative.

StackPath

I admit to only skimming it briefly but that article is focused on motors, is there a specific piece of information in there that you feel pertains to AC vs DC wiring, or fundamental properties of AC vs DC as it relates to this conversation and/or this forum?

 

[upnorthandpersonal]

You don't compare volt per volt. You compare the DC voltage to the RMS of the AC voltage to be able to do the comparison - and these are developed to compare both since RMS is te DC equivalent. Luckily for us, if you talk about 120V or 240V AC in home use, these are RMS values. If you take a resistive load of 1 Ohm, and a DC and AC voltage of 10V (RMS) the power delivered is the same 10Watt.

You also don't want to mix AC and DC motors, since now you also bring power factor into the mix for your AC voltage while in DC the power factor is always 1. This is why you make the distinction between Watt and Volt-Ampere (VA) as well in e.g. inverters. Besides, AC and DC motors aren't very good animals to compare with wire thicknesses...

@ghostwriter66 See, no math... for now

 

[Dzl]

You don't compare volt per volt. You compare the DC voltage to the RMS of the AC voltage to be able to do the comparison - and these are developed to compare both since RMS is te DC equivalent. Luckily for us, if you talk about 120V or 240V AC in home use, these are RMS values. If you take a resistive load of 1 Ohm, and a DC and AC voltage of 10V (RMS) the power delivered is the same 10Watt.

This is going a little bit over my head. Am I correct in understanding that the takeaway from this should be that nominal AC voltages and DC voltages are comparable, because AC voltages use the RMS ("root mean squared") value which is meant to make comparison between the AC waveform and the DC one-way current comparable?

Or to simplify even further, RMS makes it so laypeople never have to think about any of this when comparing AC or DC voltage and/or power?

 

[upnorthandpersonal]

Yes

 

[offgriddle]

It is a difficult concept no question and everyone in here is struggling with it and I can understand the frustrations for lack of a simple answer.
The RMS calculation is used to calculate the AC equivalent of a DC voltage. Regardless of a calculation that averages a higher AC voltage down to it's lower DC voltage equivalence, (there's a hint right there), DC is more powerful than AC as it has constant magnitude and direction unlike AC whose magnitude and direction changes.
Furthermore, if you turn a light switch on and off many times per second versus just leaving the switch on, more electrons are going to flow if the switch is left on than if the switch keeps being toggled off.

 

[Dzl]

It is a difficult concept no question and everyone in here is struggling with it and I can understand the frustrations for lack of a simple answer.
The RMS calculation is used to calculate the AC equivalent of a DC voltage. Regardless of a calculation that averages a higher AC voltage down to it's lower DC voltage equivalence, (there's a hint right there), DC is more powerful than AC as it has constant magnitude and direction unlike AC whose magnitude and direction changes.
Furthermore, if you turn a light switch on and off many times per second versus just leaving the switch on, more electrons are going to flow if the switch is left on than if the switch keeps being toggled off.

I think I get what you are saying in theory (though I would still like you to define how you are using the term power).

But am I correct in understanding that 120V nominal AC and 120V nominal DC will be comparable (that AC in practice has the RMS calculation baked into it)?

If I switch a 100w light on and off over the course of an hour, it'll use some amount less than 100wh over the course of an hour. But a 100w light bulb on either an AC or DC circuit would have a power draw of 100W and consume 100Wh per hour, correct?

 

[BiduleOhm]

It is a difficult concept no question and everyone in here is struggling with it and I can understand the frustrations for lack of a simple answer.
The RMS calculation is used to calculate the AC equivalent to a DC voltage. Regardless of a calculation that averages a higher AC voltage down to it's lower DC voltage equivalence, (there's a hint right there), DC is more powerful than AC as it has constant magnitude and direction unlike AC whose magnitude and direction changes.

No it's not that difficult. It's actually very simple if you plot the voltages vs time (just imagine the 115 is 120, it's a typo):

The green line is the DC voltage. The black curve is the AC voltage.

See the green area? it's the same as the blue area. That's why the RMS voltage is equal to the DC voltage.

BTW it's the same for current and consequently power.

That's why a resistor powered with 120 V DC or 120 V AC (RMS) will dissipate the exact same power in both cases.

The RMS value is just a tool to ease our lives, if you want you can use the peak voltage (about 170 V for 120 V RMS) to describe your AC voltage but all the usual formulas will be wrong...

NB: the image comes from here: https://physics.stackexchange.com/q...uare-rms-values-when-talking-about-ac-voltage where you can find more info (and maths) on the subject.

Furthermore, if you turn a light switch on and off many times per second versus just leaving the switch on, more electrons are going to flow when the switch is left on than when the switch keeps being toggled off.

Nope, the same number of electrons will flow per unit of time (assuming the current is same in both cases of course). See just above why.

But am I correct in understanding that 120V nominal AC and 120V nominal DC will be comparable (that AC in practice has the RMS calculation baked into it)?

If I switch a 100w light on and off over the course of an hour, it'll use some amount less than 100wh over the course of an hour. But a 100w light bulb on either an AC or DC circuit would have a power draw of 100W and consume 100Wh per hour, correct?

Yes, exactly.

 

[offgriddle]

Can you help me understand what you mean by "more powerful." I understand your line of thinking, I think (that 60hz AC only spends 1/60th of a second per second at its maximum voltage). But a Watt is a Watt, whether we are talking AC or DC right? And a Watt is a unit of power. So how are you defining power here, what are you using the term to refer to, and what is the practical significance to us?


I admit to only skimming it briefly but that article is focused on motors, is there a specific piece of information in there that you feel pertains to AC vs DC wiring, or fundamental properties of AC vs DC as it relates to this conversation and/or this forum?

I included the information on motors in response to another comment about motors, it wasn't intended to make a point regarding the fact that DC passes more current in a given time period than AC.

 

[offgriddle]

[IQUOTE="BiduleOhm, post: 49894, member: 5135"]
No it's not that difficult. It's actually very simple if you plot the voltages vs time (just imagine the 115 is 120, it's a typo):

The green line is the DC voltage. The black line is the AC voltage.

See the green area? it's the same as the blue area. That's why the RMS voltage is equal to the DC voltage.

BTW it's the same for current and consequently power.

That's why a resistor with 120 V DC or 120 V AC (RMS) will dissipate the exact same power.

The RMS value is just a tool to ease our lives, if you want you can use the peak voltage (about 170 V for 120 V RMS) to describe your AC voltage but all the usual formulas will be wrong...

NB: the image comes from here: https://physics.stackexchange.com/q...uare-rms-values-when-talking-about-ac-voltage where you can find more info (and maths) on the subject.



Nope, the same number of electrons will flow per unit of time (assuming the current is same in both cases of course). See just above why.



Yes, exactly.
[/QUOTE]
What would happen to the current comparison if RMS averaging wasn't used and the AC peak did not go above the DC green line?

 

[HMR]

As an electrical novice, wire sizing has been one of the things I have paid a lot of attention to in my internet research. I have not used scientific data sources for this research, but have relied on "apparently reputable" company sources. Can anyone explain these confusing results?
Item 1: BlueSea.com max 6 ft run 3% V drop 12 AWG has a max amp rating of 25 amp. Voltage not part of equation, only voltage drop.
Item 2: Wirebarn.com 6 ft run 2% voltage drop (cant do 3%) 12 AWG wire has a max rating of 50 amps at 24 V and 25 amps max at 12 v; so here voltage does indeed matter.
Item 3: Rowand.net automotive technician : As an example, charts for amperage ratings of of various sizes wires for 110V AC house current charts are popular and reasonably well-known. On the other hand, the amperage ratings are very different for common/typical 12V DC automotive usage. For example, a 12 gauge wire is commonly rated at 20A for 110V AC home usage, but in automotive 12V DC use 12 gauge wire is commonly used for circuits carrying 60A! A prime example would be the main charging wire from the alternator to the battery and out to the main electrical circuits of the car.
On the surface, it seems to a novice like myself, that there is little uniformity or agreement between commonly available sources on the internet. Does a single authoritative wire sizing chart/calculator/site that most people trust exist? If so, what is it?

 

[BiduleOhm]

What would happen to the current comparison if RMS averaging wasn't used and the AC peak did not go above the DC green line?

You mean if the AC signal was 120 V peak instead of 120V RMS? well, everything would be scaled by the peak/RMS ratio which is sqrt(2) or about 1.4142 so every formula (things like V = I * R) would be wrong by some factor.

 

[kenkoh]

LOL...
The old battle.

To answer your question:

Your wire is rated for 20A for a length maximum 13 ft.

As discussed above, DC is total length of the cable (the + and the -)
AC one length. (as it switches from + to -)

If your total length with DC is longer than 13ft, you are advised to use 10 gauge.

Advised.
For a short distance 12 gauge can do up to 235A fusing current, then the wire will melt. That is with copper.
If you use aluminium, it will melt around 170A

Many wires are OK to get warm, if you can't touch it anymore for a 10 seconds, you better change it to larger gauge!
60, 70 degrees Celsius is no problem for most wires!

Can you tell me where your chart is from?

 

[Dzl]

As an electrical novice, wire sizing has been one of the things I have paid a lot of attention to in my internet research. I have not used scientific data sources for this research, but have relied on "apparently reputable" company sources. Can anyone explain these confusing results?
Item 1: BlueSea.com max 6 ft run 3% V drop 12 AWG has a max amp rating of 25 amp. Voltage not part of equation, only voltage drop.
Item 2: Wirebarn.com 6 ft run 2% voltage drop (cant do 3%) 12 AWG wire has a max rating of 50 amps at 24 V and 25 amps max at 12 v; so here voltage does indeed matter.
Item 3: Rowand.net automotive technician : As an example, charts for amperage ratings of of various sizes wires for 110V AC house current charts are popular and reasonably well-known. On the other hand, the amperage ratings are very different for common/typical 12V DC automotive usage. For example, a 12 gauge wire is commonly rated at 20A for 110V AC home usage, but in automotive 12V DC use 12 gauge wire is commonly used for circuits carrying 60A! A prime example would be the main charging wire from the alternator to the battery and out to the main electrical circuits of the car.
On the surface, it seems to a novice like myself, that there is little uniformity or agreement between commonly available sources on the internet. Does a single authoritative wire sizing chart/calculator/site that most people trust exist? If so, what is it?

I feel your pain, its complicated, and hard for the novice to figure out what's right.

I especially have no idea why wirebarn would have such a big discrepancy between 12 and 24 volts. As to the rest I have some ideas. I think there could be two factors (or more) at play. (1) Different standards (Blue sea and the marine industry uses ABYC/NMEA standards, whereas the Automotive industry would have their own standards body and residential/fixed structures use the NEC in the US) (2) The automotive industry uses chassis grounding, therefore, its possible there calculations will be different as return trip uses the chassis so wire lengths or resistances would be different. I also wonder if item 3 can be explained by voltage drop not mattering much or not being much of a factor in an automotive context. But honestly, I dont know.

West Marine has one of the clearest explanations I think: https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

 

[HMR]

Dzl: thanks for the very reasoned response. Its interesting that the West Marine Table you reference pointedly states that its for 12 V systems only. That leads one to think that the same table for 24 V or 48 V systems would be considerably different. So again, voltage matters?

 

[Sgt Raven]

More powerful HOW?
in what way?
Did they mean a shaded pole 48vAC motor
Would be less powerful than a permanent magnet 48VDC motor?
AC isn't often used below 120V aside from control uses...

Well a Alternator makes AC, but is quickly converted to DC in it's output.
But I know, that is not what you were talking about.

 

[offgriddle]

Peak to peak, be it 1 volt or 1 million volts, DC is going to pass more electrons in a given point of time than AC will in the same given point of time.
The Wizard of RMS

 

[Sgt Raven]

Dzl: thanks for the very reasoned response. Its interesting that the West Marine Table you reference pointedly states that its for 12 V systems only. That leads one to think that the same table for 24 V or 48 V systems would be considerably different. So again, voltage matters?

How often is 24V-48V DC used in a marine setup? IDK. They may say 12V because their source has not tested it in a 24V-48V system.
Just a SWAG on my part.

 

[ghostwriter66]

As an electrical novice, wire sizing has been one of the things I have paid a lot of attention to in my internet research. I have not used scientific data sources for this research, but have relied on "apparently reputable" company sources. Can anyone explain these confusing results?
Item 1: BlueSea.com max 6 ft run 3% V drop 12 AWG has a max amp rating of 25 amp. Voltage not part of equation, only voltage drop.
Item 2: Wirebarn.com 6 ft run 2% voltage drop (cant do 3%) 12 AWG wire has a max rating of 50 amps at 24 V and 25 amps max at 12 v; so here voltage does indeed matter.
Item 3: Rowand.net automotive technician : As an example, charts for amperage ratings of of various sizes wires for 110V AC house current charts are popular and reasonably well-known. On the other hand, the amperage ratings are very different for common/typical 12V DC automotive usage. For example, a 12 gauge wire is commonly rated at 20A for 110V AC home usage, but in automotive 12V DC use 12 gauge wire is commonly used for circuits carrying 60A! A prime example would be the main charging wire from the alternator to the battery and out to the main electrical circuits of the car.
On the surface, it seems to a novice like myself, that there is little uniformity or agreement between commonly available sources on the internet. Does a single authoritative wire sizing chart/calculator/site that most people trust exist? If so, what is it?

PLEASE do not confuse the AMP Question that you are asking with everything these guys are talking about in this thread ..... I have an EE degree and they lost me after POST #5 ...

To make it easy I have attached probably a chart that you should just print out and save ... this is the chart we use .... YES there may be slight differences between what certain manufacturers recommend but overall - like my grandmother told me -- when in doubt - go BIGGER ...

DC AMP WIRE CHART

The ONLY thing you need to stay away from is Copper-clad aluminium wire ... aka CCAW or CCA ... it is a POS electrical conductor composed of an inner aluminium core and outer copper cladding ... I just hate that junk for soooo many good reasons ...

PS - also don't get to wrapped up in the aurguments you are going to hear about solid vs stranded vs fine stranded ... at the distances you are talking about get what you can most easily work with .... AND do whatever you can to either get UV shielded cable or put the cable in the automobile electrical cable flex hosing ... The sun is the number one killer of RV cables ...

 

[Sgt Raven]

DC AMP WIRE CHART

The ONLY thing you need to stay away from is Copper-clad aluminium wire ... aka CCAW or CCA ... it is a POS electrical conductor composed of an inner aluminium core and outer copper cladding ... I just hate that junk for soooo many good reasons ...

Going slightly off topic here. I worked for a large scrap metal corporation and hauled many a drop box from PG&E yards. I would say I hauled 4 times as much scrap aluminum wire as I did copper wire. Maybe even more than that. In their big yards, we would have three 20' drop boxes for aluminum wire and one 20' box for copper. Then we would have another box for scrap steel, too. Most of the power wire supplying electricity to California is aluminum wire.