Another long electrical run

Discussion in 'Electrical Forum discussion & Blog' started by Stan the Man, Nov 19, 2016.

  1. Stan the Man

    Stan the Man New Member

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    May 6, 2016
    OK the more I read, the more confused I get.. I'm putting in a 2 ton heat pump unit with a max breaker size of 25 amps,.. minimum circuit amps of 14.7.. My circuit run is about 70 feet one way.. I was thinking of pulling #8ga. , but now wonder if #10ga. will work.. Suggestions??
     
    Last edited: Nov 19, 2016
  2. Stuff

    Stuff Well-Known Member

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    HVAC wiring has different rules. You are allowed to use 14 gauge since HVAC conductor size is based on the MCA and independent of breaker size. 14 gauge copper is technically good for 20 amps here so it is already oversized. That being said I would still go with 10 due to length causing voltage drop/power loss. 14 gauge would be like having an extra 80 watt light bulb turned on at the same time. 12 would be 50 watt. 10 would be 30. Finally 8 would only get you down to 20.
     
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  4. WorthFlorida

    WorthFlorida The wife is still training me.

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  5. Stan the Man

    Stan the Man New Member

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    Humm,.. so this is what I see.. #10 will go 30 amps at 50ft but 20 amps at 100ft.. and somewhere else I have seen it stated that #10 will only handle 15 amps period.. Voltage drop doesn't look like a concern.. Wow,.. like I said,.. the more I look, the worse it gets.. Not to mention people arguing over who is right.. I'll just look to see what is feeding the unit in my house, and use that in my shop..
     
  6. Reach4

    Reach4 Well-Known Member

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    Say whaaat?

    ?????? What is going through your head? You seem to be agitated for no understandable reason.
    How did you come up with that course of action? Voltage drop is additive. It is not the smallest wire in a circuit that determines voltage drop.
     
  7. Stan the Man

    Stan the Man New Member

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    Looking around at different blogs and so called help sections, yes, there are people that seem to feed on those of us that don't know everything.. I wasn't referring to anyone here..
    I used a voltage drop calculator to see the drop is not worth talking about..
    http://www.powerstream.com/Wire_Size.htm Look at power transmission for #10 wire,..
    My course of action is determined from the fact my house hasn't burned down yet, and my newer system is no doubt more efficient so,..
     
  8. Stuff

    Stuff Well-Known Member

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    OK. I'll bite and argue. Why do you need 10 gauge conductors for a 14.7 amp air conditioner circuit? Are you saying that the NEC exception for air-conditioning and refrigeration equipment doesn't apply?
     
  9. Reach4

    Reach4 Well-Known Member

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    I am not checking your numbers, but did you remember that the wire is a round-trip?
     
  10. Stan the Man

    Stan the Man New Member

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    May 6, 2016
    Unless I missed something, the calculator asks for one way and shows round trip.. So no argument, I know enough to know, I don't know,.. Give me a few,..I'll be back :)
     
  11. WorthFlorida

    WorthFlorida The wife is still training me.

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    Having the compressor and circuit breaker being 70 ft away form each other is quite common. Many large homes are built with the A/C and electric panel on opposite sides of the home. After you put in all the bends it adds up. My 220 volt pool pump has 110 ft of conduit before it goes up the wall to the panel. Running 26 years and never a problem with 12 gauge. I have a smart meter as do most of the country now has and my meter reads 240 volts. If the resistance drops it a few volts, you'll never notice it.

    The purpose of the link reference was to find the resistance and voltage drop. The calculator states to put in the distance for "one way". It then gives the results for the "loop". For most single family homes 10 gauge is used for AC compressor and air handler (for the electric heating elements), water heaters and electric dryers. The compressor and air handler do take two different circuits. Electric ranges takes a larger wire. Electric Range - 220 - 240 volt, 60 hertz, properly grounded circuit with 40 amp breaker or fuse protection with #8 gauge wire. With a 50 amp breaker, # 6 gauge wire is required.

    As far as the chart is concerned do not use this table for max current loads. It does not apply to your situation.
    http://www.eevblog.com/forum/beginn...ng'-vs-'maximum-amps-for-power-transmission'/

    Use this chart and reference the column for "up to 3 cores. read the foot notes.
    http://www.engineeringtoolbox.com/wire-gauges-d_419.html
     
    Last edited: Nov 19, 2016
  12. Stuff

    Stuff Well-Known Member

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    You need to be careful with those tables referenced as they are for engineering system design, not code enforcement. They get used by guys designing submarines as well as washing machines.

    I think that what confuses all of this is that there are multiple answers: what will work, what is NEC compliant (can vary by year), what someone thinks is NEC compliant, what is local code compliant, what the individual inspector requires, what is optimal (performance per $, ease of installation, aesthetics).

    Also - Most residences have 240/120 volt single split-phase service while most a/c condensers are spec'd to work with 208 volts so even with severe voltage drop they will still run without issue.
     
  13. WorthFlorida

    WorthFlorida The wife is still training me.

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    Just this past week I installed a new 2 ton AC unit for my already sold home (as luck would have it), label reads 208v-230v. FYI...for Stan the Man at my church where I work and maintain everything, the building is 208v three phase. Most taps on the 24 volt transformers are on the 208v for the 10 AC units. Right from your first question you were concerned about the distant with voltage drop. There is no worry here if you think it will hamper your setup.
    LOL
     
  14. Stan the Man

    Stan the Man New Member

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    Ok sorry,.. I looked again.. If I use 80 ft as a conservative figure(and i'm probably closer to it),.. Voltage drop on #10 is less than 2%.. (by the calculator) My units state a max voltage drop of 2%, so ok.. But as far as ampacity, one chart has #10 at 15 amps and another has it at 52 amps!! What is going on here?? What am I missing??
    The compressor unit lists M.C.A. 14.7, M.O.P. 25, RLA 10.9 and LRA 62.9.. While the air handler lists M.C.A. 27 amps, and M.O.P. 30 amps. Yes this is a 208/230V 1ph system.. I don't want to be on the edge of safe.. This is all so frustrating.. Can someone please explain what the heck am I supposed to go by?? Oh and I looked to see what was in my house,.. Looks like multicore #8 and #6.. Geez..
     
  15. Reach4

    Reach4 Well-Known Member

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    Stuff and WorthFlorida speak accurately.

    If you buy and run #6 for this purpose, and admit it, you would be safe from wire overloading but you would not be safe from being scoffed at. However that would be nothing compared to saying that you are distressed that you found inconsistent information on the internet. On the other hand, it could be that you are applying inapplicable info. For example, 52 amps in a car for #10 would not be high at all.
     
  16. Stan the Man

    Stan the Man New Member

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    well,..I guess I got my answer
     
  17. DougB

    DougB Member

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    When in the peak of a high demand, the line voltage may drop, thus increasing the amps required. So $#10 may be a good choice - besides what's a couple of bucks? #6 - you could arc weld.
     
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Let's assume the device really needs a certain amount of power. Then, look at the equation for power: power=volts*amps. But, then look at the Volts=amps*resistance, another fundamental formula. You can do some algebra and come up with power=amps^2* resistance. Changing the resistance or the volts or the amps will change the amount of power available. A smaller wire=higher resistance.

    The codes are written to limit both the voltage drop and the heating of the wiring. What a wire can 'handle' is different than what is safe, especially long-term. Throw in some connections along the way (screw terminals, or wire nuts, etc.) and each of those is not perfect - they add some resistance. The heating/cooling cycling can affect things, too, and if you haven't torqued things down properly, cause a screw to loosen, raising the resistance considerable. So, workmanship comes into play, as well.

    Almost any device will come with installation instructions that dictate what the minimum gauge wire is required along with the associated protection device (typically a circuit breaker). You do not have to guess at this...the instruction manual will tell you what is required. You can always use a heavier gauge wire if you wish, up to the ability of the device to accept it (usually only applies to things like screw terminals - wire nuts don't care as long as they are adequate for the wire(s) used).
     
  19. Stan the Man

    Stan the Man New Member

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    May 6, 2016
    I'm not an HVAC tech,.. I have heard/read so much conflicting info, and gotten so many half answers its mind numbing.. MOP is 25 and 30 amps,.. I'll be pulling #8 with the appropriate breakers..
    Thank you for all your input..
     
  20. Reach4

    Reach4 Well-Known Member

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    I hope it was nothing that I said. I think all of the suggestions and comments pointed to #10 being safe and effective, or maybe even #12.

    I found Stuff's info on heating and cooling wire to be very interesting and new to me.
     
    Last edited: Nov 21, 2016
  21. Stan the Man

    Stan the Man New Member

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    Its more, "Me not knowing", and I have other things adding to my frustration.. I know guys that are HVAC.. They went the other way.. #6.. My house has what looks like #6,.. I couldn't tell from the quick look I did but its large.. Everything I saw, read and was told didn't seem to add up..
    I realize that's a different/bigger system, just everything seemed strange to me at that point.. And when someone said HVAC doesn't play by the same rules, and there are different situations, well, that made it worse.. Pulling #8 will not hurt a thing, and I will feel better about it.. The right breakers and I know I'm ok..
     
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