240V vs 110V Wire gauge

[shillamus]

I hate to ask such a dumb question but I am stuck on the subject

For 50 Amps 110V service the correct wire gauge would be 10 gauge 2 wire

per: http://www.powerstream.com/Wire_Size.htm

Is it a true statement that For 50 Amps 240V Service the amps would be 25 amps per line (L1,L2) so that 14 Gauge 3 wire would be acceptable???? Or do L1 and L2 wires need to carry 50 amps and be 10 gauge also???

Thanks for helping.

 

[pattenp]

50A is 50A regardless of voltage. #6 is needed for 50A.

That chart you linked does not follow NEC building wiring amp limits.

 

[dave89iroc]

in terms on residential 220/240ACV(single/split phase), same wires sizes apply

3 phase can vary, as can DCV

 

[dave*99]

I hate to ask such a dumb question but I am stuck on the subject



Is it a true statement that For 50 Amps 240V Service the amps would be 25 amps per line (L1,L2) so that 14 Gauge 3 wire would be acceptable???? Or do L1 and L2 wires need to carry 50 amps and be 10 gauge also???

Thanks for helping.

All of this statement is false.
For 240VAC service a 2 pole breaker is required. The legs L1 and L2 are effectively in series. So a 50A service uses a 2 pole 50A breaker and the wire is sized to carry 50A. That would be 6 gauge wire.
If you used a 3 wire service it could supply 50A on either leg to neutral so you could draw 50A at 120VAC.
The neutral conductor in this case carries the difference in current between L1 and L2.

 

[shillamus]

Thanks for the replies and shared responses

Is there a link that anyone can share for NEC amp loads by wire gauge? is this the ampacity of the wire??

Is this a better table?

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

 

[ishiboo]

Thanks for the replies and shared responses

Is there a link that anyone can share for NEC amp loads by wire gauge? is this the ampacity of the wire??

Is this a better table?

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Yes and no. I don't mean to be rude but a lot of things go into using some of the more complex tables. For general homeowner use I would recommend:

 

[simpler=better]

http://www.electrician2.com/calculators/wireocpd_ver_1.html

http://www.electrician2.com/calculators/rf_calculator.html

I like to follow the 60*C column, yes when piped the wires can technically be used at 75*C or 90*C but it bothers me that I would design a system to let wires heat up like that, especially when wire is so cheap.

 

[sberry]

I don't have a good table handy but don't much care for that either. Its not bad but leaves an impression that every 20A circuit needs to be sized for 20A, it is very conservative and worth making a note it is for 110V.
Not every piece of wire over 50 ft needs to be upsized on general circuits and many or maybe more accurately most come thru a 14 cord and 15 plug or supply a calculated load.

 

[ishiboo]

I don't have a good table handy but don't much care for that either. Its not bad but leaves an impression that every 20A circuit needs to be sized for 20A, it is very conservative and worth making a note it is for 110V.
Not every piece of wire over 50 ft needs to be upsized on general circuits and many or maybe more accurately most come thru a 14 cord and 15 plug or supply a calculated load.

I absolutely agree, but with the limited electrical knowledge demonstrated, it provides a somewhat guesswork-eliminating way to size a circuit.

 

[sberry]

http://www.electrician2.com/calculators/wireocpd_ver_1.html

http://www.electrician2.com/calculators/rf_calculator.html

I like to follow the 60*C column, yes when piped the wires can technically be used at 75*C or 90*C but it bothers me that I would design a system to let wires heat up like that, especially when wire is so cheap.

While this is true it may have a 15 or 20 breaker it doesn't mean there will be that applied load. I have hundreds of ft of 14 with a 15 A breaker, 1 amp, 2 A, some even a whopping 4 or 5. If I am designing a system that truly has a 20A load then it is accounted for.

 

[Norcal]

http://www.electrician2.com/calculators/wireocpd_ver_1.html

http://www.electrician2.com/calculators/rf_calculator.html

I like to follow the 60*C column, yes when piped the wires can technically be used at 75*C or 90*C but it bothers me that I would design a system to let wires heat up like that, especially when wire is so cheap.

The ninety degree column is only used for derating it cannot be used otherwise. The sixty degree column must be used with NM cable.

 

[LXCam]

in terms on residential 220/240ACV(single/split phase), same wires sizes apply

3 phase can vary, as can DCV

Amperage in relation to wire size is a constant no matter what the applied voltage or system configuration. there are some applications where conditions allow for varying sized conductors verses over current protection is allowed, but not in a residential application. Your best and safest bet OP is sizing your wire by the last table posted using the 60c column.

 

[theoldwizard1]

Changing the subject slightly ...

Most residential wire has insulation rated for 300V. Industrial use wire is typically at least 600V.

Some insulation is rated for "high" temperature, but I think that has more to do with the ambient temperature and I do not know how that affects the charts. XHHW or XHHW-2 is pretty common and I don't think there is much upcharge over THHN/THWN.

 

[Norcal]

NM cable is rated for 600 volts, in some areas 12/3 NM is used for 480 3 phase while I do not like the idea, that is just my opinion.

 

[dave*99]

Changing the subject slightly ...

Most residential wire has insulation rated for 300V. Industrial use wire is typically at least 600V.

Some insulation is rated for "high" temperature, but I think that has more to do with the ambient temperature and I do not know how that affects the charts. XHHW or XHHW-2 is pretty common and I don't think there is much upcharge over THHN/THWN.

NM-B which is the most common residential wire, is rated for 600V

 

[dave89iroc]

Amperage in relation to wire size is a constant no matter what the applied voltage or system configuration. there are some applications where conditions allow for varying sized conductors verses over current protection is allowed, but not in a residential application. Your best and safest bet OP is sizing your wire by the last table posted using the 60c column.

regaurding amperage, yes, but if you add in the voltage change,same amount of work, size changes

if you double voltage, you only need half the amperage for the same work, wire is sized for amperage

 

[theoldwizard1]

NM cable is rated for 600 volts, in some areas 12/3 NM is used for 480 3 phase while I do not like the idea, that is just my opinion.

Learn something new everyday !

 

[shillamus]

Thanks all again for the discussion in regards to my inquiry.

I am not an electrician by trade, but find myself assisting others.

I am convinced that 3 Gauge is a suitable size wire for 100 amp service. I have much to learn about wire types..


The current requirement (which is only in discussion and not in installation) is running 100 amp service from the property main about 150 ft to the shop

I recently saw 100 amp service wired with 14 ga...wow

 

[drw315]

I don't have a good table handy but don't much care for that either. Its not bad but leaves an impression that every 20A circuit needs to be sized for 20A, it is very conservative and worth making a note it is for 110V.
Not every piece of wire over 50 ft needs to be upsized on general circuits and many or maybe more accurately most come thru a 14 cord and 15 plug or supply a calculated load.

This is how fires happen, folks. 20A circuits need to be sized for 20A because that's how much current could flow through the system without tripping the breaker. It's all fine and dandy with your "1A applied load" you calculated for - until something shorts/arcs and you now have 17A running through your wiring designed for your "1A applied load." Whoops, there goes the garage/house!

Oh, and you did the work yourself and didn't get it inspected? Best of luck with the insurance company.

 

[wyliesdiesels]

This is how fires happen, folks. 20A circuits need to be sized for 20A because that's how much current could flow through the system without tripping the breaker. It's all fine and dandy with your "1A applied load" you calculated for - until something shorts/arcs and you now have 17A running through your wiring designed for your "1A applied load." Whoops, there goes the garage/house!

Oh, and you did the work yourself and didn't get it inspected? Best of luck with the insurance company.

Actually a short would be a lot higher than 17a. Were talkin hundreds for split seconds...

 

[drw315]

Actually a short would be a lot higher than 17a. Were talkin hundreds for split seconds...

Haha, I knew someone would correct me, and I'm glad. You're right. Shorts would be protected by the SCPD (breaker), and I obviously pulled 17A out of my shorts.

Yet the point remains. Protecting a circuit with a 20A breaker, but not wiring for 20A is asking for problems. There are a million ways the current in a circuit could exceed the original "calculated load." Wiring for what you think the maximum load would be is a risk you simply don't take in a residential situation.

The weak link in a circuit should not be the wiring. That's the entire purpose of installing breakers/fusing. Telling a novice DIYer "not to worry" about something like this could get someone killed - literally.

 

[wmchurch]

Something people constantly struggle with is the purpose of the breaker. It's there to prevent a fire. It does that by preventing the current draw from exceeding the capacity of the breaker. It's only able to do it's job when the wire it's protecting is rated for the capacity of the breaker or higher.

My guess with the 110/220 confusion is the idea that you can have a motor wired for 110 that draws 10 amps, wiring that same motor for 220 draws 5 amps. It's simply because the voltage is doubled, the overall wattage is the same. 110*10 = 1100W, 220*5 = 1100W.

Most people here probably know this, but I think it's helpful for those who don't.

 

[wyliesdiesels]

Something people constantly struggle with is the purpose of the breaker. It's there to prevent a fire. It does that by preventing the current draw from exceeding the capacity of the breaker. It's only able to do it's job when the wire it's protecting is rated for the capacity of the breaker or higher.

My guess with the 110/220 confusion is the idea that you can have a motor wired for 110 that draws 10 amps, wiring that same motor for 220 draws 5 amps. It's simply because the voltage is doubled, the overall current is the same. 110*10 = 1100W, 220*5 = 1100W.

Most people here probably know this, but I think it's helpful for those who don't.

Actually, its the wattage aka power thats the same. Amperage/current is halved or doubled depending on which way youre going with the voltage...

 

[wmchurch]

Heh, yup. That's absolutely right.

Got to love it when I screw up my own attempt to set something straight.

 

[alfredeneuman]

Haha, I knew someone would correct me, and I'm glad. You're right. Shorts would be protected by the SCPD (breaker), and I obviously pulled 17A out of my shorts.
.

The correct term for a circuit breaker is OCPD, "Overcurrent Protective Device", rather than SCPD

 

[drw315]

The correct term for a circuit breaker is OCPD, "Overcurrent Protective Device", rather than SCPD

Sure, but I was referring to a short circuit condition. Therefore, the SCPD is the same as the OCPD - the circuit breaker.

An OCPD is also a SCPD; it protects against short-circuit current as well as over current.