Power mains question: wire gauge

In sci.electronics.misc wrote:
> On Thu, 03 Jan 2013 03:23:32 -0500, Spehro Pefhany
> <> wrote:
>
>>On Wed, 02 Jan 2013 22:57:50 -0500, the renowned wrote:
>>
>>>On Wed, 02 Jan 2013 19:11:54 -0800, josephkk
>>><> wrote:
>>>
>>>>On Mon, 31 Dec 2012 16:54:41 -0500, wrote:
>>>>
>>>>>On Mon, 31 Dec 2012 13:50:29 -0800, John Larkin
>>>>><> wrote:
>>>>>
>>>>>>On Mon, 31 Dec 2012 15:08:00 -0500, wrote:
>>>>>>
>>>>>>>On Mon, 31 Dec 2012 12:28:31 -0500, "Michael A. Terrell"
>>>>>>><> wrote:
>>>>>>>
>>>>>>>>
>>>><snip>
>>>>>>>> He said he was going to suggest it to the owner, so who knows.
>>>>>>>
>>>>>>>So why not 500KV? You never know?
>>>>>>
>>>>>>Why not put the compressor where the power is, and run an air hose?
>>>>>>Then we could argue about ths size of the hose.
>>>>>
>>>>>Actually, that's what I plan to do. Put the compressor in the garage
>>>>>and pipe the air downstairs. 4" oughtta do it. ;-)
>>>>>
>>>>>I just have to figure out how much work it's going to be (how things
>>>>>line up).
>>>>
>>>>4" really?
>>>
>>>Of course not. Michael is being silly with his suggestion of running
>>>#6 wire for the compressor. I thought I'd join in. For anything I've
>>>done, 1/2" Type-L copper is fine. That's probably what I'll use again
>>>but it's getting rather pricey.
>>
>>Protectionism at work:-
>>http://www.bloomberg.com/news/2010-...on-china-mexico-made-copper-piping-tubes.html
>>
> Unbelievable. With the housing market in the tank and commodities
> through the roof, what the housing market really needs *more* help
> from UncleS. <sheesh>

it's a tough call as to what sucks more, mexi-narco pipes, chinese copper
plated lead or the government meddling.

 

On 1/3/2013 8:10 AM, John Fields wrote:
> On Thu, 03 Jan 2013 06:40:26 -0600, John S <>
> wrote:
>
>> On 1/2/2013 8:48 PM, josephkk wrote:
>>> On Sat, 29 Dec 2012 11:04:23 -0800, John Larkin
>>> <> wrote:
>>>
>>>> On Sat, 29 Dec 2012 12:20:01 -0600, John Fields
>>>> <> wrote:
>>>>
>>>>> On Fri, 28 Dec 2012 16:05:49 -0800, John Larkin
>>>>> <> wrote:
>>>>>
>>>>>> On Fri, 28 Dec 2012 15:41:08 -0800, DaveC <> wrote:
>>>>>>
>>>>>>> Air compressor 1/2 hp motor rated 220v (2-wire, not 3-phase) @ 15A. Distance
>>>>>> >from load panel ~100 ft (as the conduit runs).
>>>>>>>
>>>>>>> 15A can be handled by 14 gauge, but I'd normally go with 12 gauge due to
>>>>>>> start current.
>>>>>>>
>>>>>>> With such a distance, is it recommend to up-scale the wire to 10 ga?
>>>>>>>
>>>>>>> Thanks.
>>>>>>
>>>>>> #12 is 1.6 mohms/foot. That's 0.32 ohms total. The short-circuit
>>>>>> current from 220 volts is almost 700 amps. A half horse is only around
>>>>>> 400 watts, about 2 amps. I'd use #14.
>>>>>
>>>>> ---
>>>>> The short circuit current through the wire resistance is irrelevant.
>>>>
>>>> It is not. If 700 amps is available, there's a huge margin for the
>>>> startup current for a dinky motor like this one. And plenty of current
>>>> to blow a breaker if needed.
>>>>
>>> No John Larkin, you are full of baloney on this one. I do the wire gauge
>>> for motor starts all the time. I(sc) is NOT used.
>>>>
>>>>> What matters is the stall current through the motor when it's starting
>>>>> up; no doubt the 15A the OP mentioned.
>>>>
>>>> Exactly. It needs 15, we have 700. We don't need #10 wire.
>>>>
>>> Incorrect setup. What is of concern is the drop during motor start. Not
>>> motor run and not wiring fault conditions. The goal is to keep it below
>>> 5% including all other losses to the service transformer. Generally a 2%
>>> to 3% drop during normal operation, and no more than 8% during motor
>>> start, is allowed in the building, all the way to the main service lugs.
>>
>> I'm curious about this. Doesn't a motor draw about 6-10 times FLA during
>> start? If so, wouldn't that cause a 18-30% drop during start if you have
>> a 3% drop normally? Or, looking at it the other way, if you size for 8%
>> starting drop, your normal operating drop would be only 1.3%.
>
> ---
> From the OP's example we have a 240VAC 1/2HP motor with a startup
> current of 15A being fed through 200 feet of #14 AWG wire.
>
> 1HP is 746 watts, so if his motor delivers 1/2HP at the shaft and it's
> 80% efficient it'll be taking about 467 watts from the mains under
> full load.

True, but the current will be higher because of power factor.

> 200 feet of #14 solid copper looks like about half an ohm, so we have,
> for the startup case:
>
> 15A--->
> 240AC>---[0.25R]---+ <------+
> | |
> [16R] 233V
> | |
> 240AC>---[0.25R]---+ <------+
>
> Because of the wire resistance, instead of 15A in the circuit we'll
> have 14.55A, and that will drop 233V across the motor.
>
> 233V is 97% of 240V, so there's only a 3% loss in the wire.
>
> In the full load case we have this:
>
> 1.94A--->
> 240AC>---[0.25R]---+ <------+
> | |
> [123R] 239V
> | |
> 240AC>---[0.25R]---+ <------+
>
> so the loss is less than half a percent.

But, that was not what I was curious about. What I want to know is, if
the running current results in a 3% drop, doesn't that result in a 18%
drop when the current goes up 6 times?

 

On 1/2/2013 10:58 PM, wrote:
> On Wed, 02 Jan 2013 19:16:15 -0800, josephkk
> <> wrote:
>
>> On Sat, 29 Dec 2012 16:40:07 -0500, wrote:
>>
>>> On Sat, 29 Dec 2012 13:04:27 -0800, notme<> wrote:
>>>
>>>>> Run several #12s, instead, when needed. It's cheaper.
>>>>
>>>> Pull additional #12s in the future? I've had bad experience pulling
>>>> additional conductors in a conduit with existing conductors.
>>>
>>> Conduit?
>>>
>>>> If I misunderstand your statement, please try again. ;-)
>>
>> Conduit is mentioned in the leadoff post by OP. The cost of putting in
>> conduit almost completely swamps the wire gauge issue.
>
> Agreed, sorta. PVC isn't too bad, though. This whole thing has
> gotten absurd.

Really? S.E.D having an absurd conversation? What's your point?

Rick

 

On 1/2/2013 4:40 PM, John Fields wrote:
> On Wed, 02 Jan 2013 13:08:11 -0500, wrote:
>
>> On Wed, 02 Jan 2013 10:46:18 -0600, John Fields
>> <> wrote:
>
>>>>> it's interesting to note that, in an
>>>>> argument, whenever you come up against the stops because of your
>>>>> limited capability to use logic and reason - which you demonstrate ad
>>>>> nauseam - you always revert to ad hominem.
>>>>
>>>> You're funny, Fields. Too bad you're such an idiot. You don't even
>>>> know that<shift>3 is "#", even though it's right in front of your
>>>> stupid nose.
>
> ---
> See what I mean?
>

You guys are all pretty ridiculous calling each other names and such,
but at least you know how to trim a post. Thanks. It makes it easier
to get through this crap.

Rick

 

On Tue, 01 Jan 2013 11:36:28 -0500, wrote:

>t at HD. #10 is "special" and
>>> quite expensive because of it. Anything outside the norm has a
>>> premium attached to it. For example, 12-3 has only 33% more copper
>>> than 12-2 but costs almost double ($120 vs. $70 per 250' roll). And,
>>> 10-2 is $135 per roll, so yes, *DOUBLE*.
>>>
>>> When *was* the last time you bought this stuff? You really need to
>>> get out more and bitch less.
>>
>>
>> Who shops at a big box store when there are electrical distributors
>>all over the place?
>
>Oh, look! Grainger wants $141.10 for 250' of 12/2, TWICE what HD gets
>for it.

It is really strange person that thinks that Grainger or McMaster-Carr are
the low price outfits. Their prices resemble Radio Schmuck versus online.

?-/

 

On Tue, 01 Jan 2013 14:35:53 -0500, wrote:

>On Tue, 01 Jan 2013 13:57:08 -0500, "Michael A. Terrell"
><> wrote:
>
>>
>> wrote:
>>>
>>> On Mon, 31 Dec 2012 19:27:16 -0500, "Michael A. Terrell"
>>> <> wrote:
>>>
>>> >
>>> > wrote:
>>> >>
>>> >> On Mon, 31 Dec 2012 17:45:13 -0500, "Michael A. Terrell"
>>> >> <> wrote:
>>> >>
>>> >> >
>>> >> > wrote:
>>> >> >>
>>> >> >> It doesn't matter what *YOU* have on hand. #12 works just fineand is
>>> >> >> about 1/3 the cost of #10.
>>> >> >
>>> >> >
>>> >> > Do they use lube on you when you buy 10 AWG? It has 50% more copper
>>> >> >per foot. If you pay 200% more per foot, you've been raped. Do whatever
>>> >> >the hell you like, no one else cares.
>>> >>
>>> >> #12 is normal stuff, sold by the pallet at HD. #10 is "special" and
>>> >> quite expensive because of it. Anything outside the norm has a
>>> >> premium attached to it. For example, 12-3 has only 33% more copper
>>> >> than 12-2 but costs almost double ($120 vs. $70 per 250' roll). And,
>>> >> 10-2 is $135 per roll, so yes, *DOUBLE*.
>>> >>
>>> >> When *was* the last time you bought this stuff? You really need to
>>> >> get out more and bitch less.
>>> >
>>> >
>>> > Who shops at a big box store when there are electrical distributors
>>> >all over the place?
>>>
>>> Oh, look! Grainger wants $141.10 for 250' of 12/2, TWICE what HD gets
>>> for it.
>>
>>
>> Gee, I bought a roll of 12/2 with ground two years ago for $25.
>
>That was two years ago. Tell me what you paid last week.
>
>> Sigh. That is THE 'big box' supplier to industry, not a wholesaler.
>
>Grainger?
>
>>They are there to reduce downtime, not be the cheapest source on earth.
>>Also, the prices on their website aren't the same a business pays, it is
>>their full RETAIL. Like any wholesaler, the price you pay depends on
>>the volume of business you do, or a manager who will give you better
>>terms because of the way you do business with them. When I was doing a
>>fair amount of electrical work I had an open account where I bought
>>almost everything by the box/bundle/bag, unlike other customers. They
>>would wait on me first, and gave me 'D' column prices which was their
>>best discount rate. They allowed me to pull my own stock, while they
>>waited on someone else or to look for something that would work, to
>>replace an oddball item I needed.
>
>The point stands. Cost isn't just material. It's volume, as well.
>Expensive commodities sitting on the shelf cost more than those that
>fly off the shelf.
>
>> Do you have a Grainger account? Fastenall? Any industrial
>>accounts? Do you do purchasing for a business?
>
>Get real, Michael. You lost.

Tough chips Keith, Michael is right on this one.

?-)

 

> Why not put the compressor where the power is, and run an air hose?
> Then we could argue about ths size of the hose.

That's the best idea I've heard yet.

Sadly, he had already located the compressor, installed the air lines, hooked
it up before calling me to wire it. He placed it right next to the main
air-user, the mechanic's bays. (It's an auto repair shop.)

Dave (OP)

 

On Thu, 03 Jan 2013 06:40:26 -0600, John S <> wrote:

>
>> Incorrect setup. What is of concern is the drop during motor start. Not
>> motor run and not wiring fault conditions. The goal is to keep it below
>> 5% including all other losses to the service transformer. Generally a2%
>> to 3% drop during normal operation, and no more than 8% during motor
>> start, is allowed in the building, all the way to the main service lugs.
>
>I'm curious about this. Doesn't a motor draw about 6-10 times FLA during
>start? If so, wouldn't that cause a 18-30% drop during start if you have
>a 3% drop normally? Or, looking at it the other way, if you size for 8%
>starting drop, your normal operating drop would be only 1.3%.

It depends on several variables, including motor size, motor winding
class, number of phases, design of motor start system, and some other
things. Very small motors may start at 2x FLA, some very large (full
voltage start) motors may require 20 to 30 x FLA.

?-)

 

On Thu, 03 Jan 2013 22:01:11 -0800, josephkk
<> wrote:

>On Tue, 01 Jan 2013 14:35:53 -0500, wrote:
>
>>On Tue, 01 Jan 2013 13:57:08 -0500, "Michael A. Terrell"
>><> wrote:
>>
>>>
>>> wrote:
>>>>
>>>> On Mon, 31 Dec 2012 19:27:16 -0500, "Michael A. Terrell"
>>>> <> wrote:
>>>>
>>>> >
>>>> > wrote:
>>>> >>
>>>> >> On Mon, 31 Dec 2012 17:45:13 -0500, "Michael A. Terrell"
>>>> >> <> wrote:
>>>> >>
>>>> >> >
>>>> >> > wrote:
>>>> >> >>
>>>> >> >> It doesn't matter what *YOU* have on hand. #12 works just fine and is
>>>> >> >> about 1/3 the cost of #10.
>>>> >> >
>>>> >> >
>>>> >> > Do they use lube on you when you buy 10 AWG? It has 50% more copper
>>>> >> >per foot. If you pay 200% more per foot, you've been raped. Do whatever
>>>> >> >the hell you like, no one else cares.
>>>> >>
>>>> >> #12 is normal stuff, sold by the pallet at HD. #10 is "special" and
>>>> >> quite expensive because of it. Anything outside the norm has a
>>>> >> premium attached to it. For example, 12-3 has only 33% more copper
>>>> >> than 12-2 but costs almost double ($120 vs. $70 per 250' roll). And,
>>>> >> 10-2 is $135 per roll, so yes, *DOUBLE*.
>>>> >>
>>>> >> When *was* the last time you bought this stuff? You really need to
>>>> >> get out more and bitch less.
>>>> >
>>>> >
>>>> > Who shops at a big box store when there are electrical distributors
>>>> >all over the place?
>>>>
>>>> Oh, look! Grainger wants $141.10 for 250' of 12/2, TWICE what HD gets
>>>> for it.
>>>
>>>
>>> Gee, I bought a roll of 12/2 with ground two years ago for $25.
>>
>>That was two years ago. Tell me what you paid last week.
>>
>>> Sigh. That is THE 'big box' supplier to industry, not a wholesaler.
>>
>>Grainger?
>>
>>>They are there to reduce downtime, not be the cheapest source on earth.
>>>Also, the prices on their website aren't the same a business pays, it is
>>>their full RETAIL. Like any wholesaler, the price you pay depends on
>>>the volume of business you do, or a manager who will give you better
>>>terms because of the way you do business with them. When I was doing a
>>>fair amount of electrical work I had an open account where I bought
>>>almost everything by the box/bundle/bag, unlike other customers. They
>>>would wait on me first, and gave me 'D' column prices which was their
>>>best discount rate. They allowed me to pull my own stock, while they
>>>waited on someone else or to look for something that would work, to
>>>replace an oddball item I needed.
>>
>>The point stands. Cost isn't just material. It's volume, as well.
>>Expensive commodities sitting on the shelf cost more than those that
>>fly off the shelf.
>>
>>> Do you have a Grainger account? Fastenall? Any industrial
>>>accounts? Do you do purchasing for a business?
>>
>>Get real, Michael. You lost.
>
>Tough chips Keith, Michael is right on this one.

Bullshit.

 

On Thu, 03 Jan 2013 21:22:23 -0800, josephkk
<> wrote:

>On Tue, 01 Jan 2013 11:36:28 -0500, wrote:
>
>>t at HD. #10 is "special" and
>>>> quite expensive because of it. Anything outside the norm has a
>>>> premium attached to it. For example, 12-3 has only 33% more copper
>>>> than 12-2 but costs almost double ($120 vs. $70 per 250' roll). And,
>>>> 10-2 is $135 per roll, so yes, *DOUBLE*.
>>>>
>>>> When *was* the last time you bought this stuff? You really need to
>>>> get out more and bitch less.
>>>
>>>
>>> Who shops at a big box store when there are electrical distributors
>>>all over the place?
>>
>>Oh, look! Grainger wants $141.10 for 250' of 12/2, TWICE what HD gets
>>for it.
>
>It is really strange person that thinks that Grainger or McMaster-Carr are
>the low price outfits. Their prices resemble Radio Schmuck versus online.

So show us your numbers instead of more diarrhea of the mouth, as is
your normal MO.

 

On Thu, 03 Jan 2013 21:01:11 -0500, rickman <> wrote:

>On 1/2/2013 4:40 PM, John Fields wrote:
>> On Wed, 02 Jan 2013 13:08:11 -0500, wrote:
>>
>>> On Wed, 02 Jan 2013 10:46:18 -0600, John Fields
>>> <> wrote:
>>
>>>>>> it's interesting to note that, in an
>>>>>> argument, whenever you come up against the stops because of your
>>>>>> limited capability to use logic and reason - which you demonstrate ad
>>>>>> nauseam - you always revert to ad hominem.
>>>>>
>>>>> You're funny, Fields. Too bad you're such an idiot. You don't even
>>>>> know that<shift>3 is "#", even though it's right in front of your
>>>>> stupid nose.
>>
>> ---
>> See what I mean?
>>
>
>You guys are all pretty ridiculous calling each other names and such,
>but at least you know how to trim a post. Thanks. It makes it easier
>to get through this crap.

Buy a scroll wheel.

 

On 2013-01-05, <> wrote:
> On Thu, 03 Jan 2013 21:01:11 -0500, rickman <> wrote:

>
>>You guys are all pretty ridiculous calling each other names and such,
>>but at least you know how to trim a post. Thanks. It makes it easier
>>to get through this crap.
>
> Buy a scroll wheel.

They don't make them that that go fast enough to deal with the sewage
you produce


--
⚂⚃ 100% natural

--- news://freenews.netfront.net/ - complaints: ---

 

On 5 Jan 2013 02:27:57 GMT, Jasen Betts <> wrote:

>On 2013-01-05, <> wrote:
>> On Thu, 03 Jan 2013 21:01:11 -0500, rickman <> wrote:
>
>>
>>>You guys are all pretty ridiculous calling each other names and such,
>>>but at least you know how to trim a post. Thanks. It makes it easier
>>>to get through this crap.
>>
>> Buy a scroll wheel.
>
>They don't make them that that go fast enough to deal with the sewage
>you produce

You lefties are always projecting your inadequacies.

 

On 1/6/2013 12:22 PM, wrote:
> On Sat, 05 Jan 2013 17:19:21 -0600, John Fields
> <> wrote:
>
>> On Sat, 05 Jan 2013 17:25:02 -0500, wrote:
>>
>>> On 5 Jan 2013 02:27:57 GMT, Jasen Betts<> wrote:
>>>
>>>> On 2013-01-05, <> wrote:
>>>>> On Thu, 03 Jan 2013 21:01:11 -0500, rickman<> wrote:
>>>>
>>>>>
>>>>>> You guys are all pretty ridiculous calling each other names and such,
>>>>>> but at least you know how to trim a post. Thanks. It makes it easier
>>>>>> to get through this crap.
>>>>>
>>>>> Buy a scroll wheel.
>>>>
>>>> They don't make them that that go fast enough to deal with the sewage
>>>> you produce
>>>
>>> You lefties are always projecting your inadequacies.
>>
>> ---
>> You pretend to be part of the right, yet wallow in self-indulgence.
>
> You're fuckin' whiner, just like a lefty.

At least your rants are short (I mean all of you). Thanks, makes it
easier to breeze through the muck.

Rick

 

On Fri, 11 Jan 2013 11:37:45 -0500, rickman <> wrote:

>On 1/6/2013 12:22 PM, wrote:
>> On Sat, 05 Jan 2013 17:19:21 -0600, John Fields
>> <> wrote:
>>
>>> On Sat, 05 Jan 2013 17:25:02 -0500, wrote:
>>>
>>>> On 5 Jan 2013 02:27:57 GMT, Jasen Betts<> wrote:
>>>>
>>>>> On 2013-01-05, <> wrote:
>>>>>> On Thu, 03 Jan 2013 21:01:11 -0500, rickman<> wrote:
>>>>>
>>>>>>
>>>>>>> You guys are all pretty ridiculous calling each other names and such,
>>>>>>> but at least you know how to trim a post. Thanks. It makes it easier
>>>>>>> to get through this crap.
>>>>>>
>>>>>> Buy a scroll wheel.
>>>>>
>>>>> They don't make them that that go fast enough to deal with the sewage
>>>>> you produce
>>>>
>>>> You lefties are always projecting your inadequacies.
>>>
>>> ---
>>> You pretend to be part of the right, yet wallow in self-indulgence.
>>
>> You're fuckin' whiner, just like a lefty.
>
>At least your rants are short (I mean all of you). Thanks, makes it
>easier to breeze through the muck.

Instead of incessantly whining, you could just ignore me. No, you
lefties are too stupid to do that.

 

On Jan 2, 10:57 pm, wrote:
> On Wed, 02 Jan 2013 19:11:54 -0800, josephkk
>
>
>
>
>
>
>
>
>
> <> wrote:
> >On Mon, 31 Dec 2012 16:54:41 -0500, wrote:
>
> >>On Mon, 31 Dec 2012 13:50:29 -0800, John Larkin
> >><> wrote:
>
> >>>On Mon, 31 Dec 2012 15:08:00 -0500, wrote:
>
> >>>>On Mon, 31 Dec 2012 12:28:31 -0500, "Michael A. Terrell"
> >>>><> wrote:
>
> ><snip>
> >>>>>   He said he was going to suggest it to the owner, so who knows.
>
> >>>>So why not 500KV?  You never know?
>
> >>>Why not put the compressor where the power is, and run an air hose?
> >>>Then we could argue about ths size of the hose.
>
> >>Actually, that's what I plan to do.  Put the compressor in the garage
> >>and pipe the air downstairs.  4" oughtta do it.  ;-)
>
> >>I just have to figure out how much work it's going to be (how things
> >>line up).
>
> >4" really?
>
> Of course not.  Michael is being silly with his suggestion of running
> #6 wire for the compressor.  I thought I'd join in.  For anything I've
> done, 1/2" Type-L copper is fine.  That's probably what I'll use again
> but it's getting rather pricey.
>
>
>
>
>
>
>
> > How big it that compressor, 500 kW?  Does it go over 3000'?
> >Not that i am all that expert but that is the size of compressor and the
> >run length i saw last time i saw one plumbed at 4".  And that one was done
> >by an expert.

Well I'm not interested in being quarrelsome but would you mind
explaining why you would use copper piping for air lines. Copper has
gotten more pricy rather than recently pricey so it would seem to be
rather a waste to use it for air. Help me out here. What am I
missing?

--
Tom Horne

 

On Jan 3, 9:32 am, SoothSayer <> wrote:
> On Thu, 03 Jan 2013 08:10:27 -0600, John Fields
>
>
>
>
>
>
>
>
>
> <> wrote:
> >On Thu, 03 Jan 2013 06:40:26 -0600, John S <>
> >wrote:
>
> >>On 1/2/2013 8:48 PM, josephkk wrote:
> >>> On Sat, 29 Dec 2012 11:04:23 -0800, John Larkin
> >>> <> wrote:
>
> >>>> On Sat, 29 Dec 2012 12:20:01 -0600, John Fields
> >>>> <> wrote:
>
> >>>>> On Fri, 28 Dec 2012 16:05:49 -0800, John Larkin
> >>>>> <> wrote:
>
> >>>>>> On Fri, 28 Dec 2012 15:41:08 -0800, DaveC <> wrote:
>
> >>>>>>> Air compressor 1/2 hp motor rated 220v (2-wire, not 3-phase) @ 15A. Distance
> >>>>>> >from load panel ~100 ft (as the conduit runs).
>
> >>>>>>> 15A can be handled by 14 gauge, but I'd normally go with 12 gaugedue to
> >>>>>>> start current.
>
> >>>>>>> With such a distance, is it recommend to up-scale the wire to 10 ga?
>
> >>>>>>> Thanks.
>
> >>>>>> #12 is 1.6 mohms/foot. That's 0.32 ohms total. The short-circuit
> >>>>>> current from 220 volts is almost 700 amps. A half horse is only around
> >>>>>> 400 watts, about 2 amps. I'd use #14.
>
> >>>>> ---
> >>>>> The short circuit current through the wire resistance is irrelevant..
>
> >>>> It is not. If 700 amps is available, there's a huge margin for the
> >>>> startup current for a dinky motor like this one. And plenty of current
> >>>> to blow a breaker if needed.
>
> >>> No John Larkin, you are full of baloney on this one.  I do the wiregauge
> >>> for motor starts all the time.  I(sc) is NOT used.
>
> >>>>> What matters is the stall current through the motor when it's starting
> >>>>> up; no doubt the 15A the OP mentioned.
>
> >>>> Exactly. It needs 15, we have 700. We don't need #10 wire.
>
> >>> Incorrect setup.  What is of concern is the drop during motor start..  Not
> >>> motor run and not wiring fault conditions.  The goal is to keep it below
> >>> 5% including all other losses to the service transformer.  Generally a 2%
> >>> to 3% drop during normal operation, and no more than 8% during motor
> >>> start, is allowed in the building, all the way to the main service lugs.
>
> >>I'm curious about this. Doesn't a motor draw about 6-10 times FLA during
> >>start? If so, wouldn't that cause a 18-30% drop during start if you have
> >>a 3% drop normally? Or, looking at it the other way, if you size for 8%
> >>starting drop, your normal operating drop would be only 1.3%.
>
> >---
> >From the OP's example we have a 240VAC 1/2HP motor with a startup
> >current of 15A being fed through 200 feet of #14 AWG wire.
>
> >1HP is 746 watts, so if his motor delivers 1/2HP at the shaft and it's
> >80% efficient it'll be taking about 467 watts from the mains under
> >full load.
>
> >200 feet of #14 solid copper looks like about half an ohm, so we have,
> >for the startup case:
>
> >          15A--->
> >240AC>---[0.25R]---+ <------+
> >                   |        |
> >                 [16R]     233V
> >                   |        |
> >240AC>---[0.25R]---+ <------+
>
> >Because of the wire resistance, instead of 15A in the circuit we'll
> >have 14.55A, and that will drop 233V across the motor.
>
> >233V is 97% of 240V, so there's only a 3% loss in the wire.
>
> >In the full load case we have this:
>
> >          1.94A--->
> >240AC>---[0.25R]---+ <------+
> >                   |        |
> >                 [123R]    239V
> >                   |        |
> >240AC>---[0.25R]---+ <------+
>
> >so the loss is less than half a percent.
>
>   That is right on the mark.
>
>   It was always fun to un a 100 foot extension cord to a construction
> work area and run a device like a circular saw or such.  Then try it with
> two 100 foot cords together for 200 feet.  It (the difference) is very
> noticeable.
>
>   Most of those cords are #14 at those lengths (or they'd better be), but
> at the price difference for raw wire and a buried run, I'd say that
> dropping to #12 or eve the #10 run was not an improper suggestion,
> considering it was going to be a permanent install, and the device being
> powered may not be, and wiring a service outlet is what we are doing.
>
>   So, yes, as you illustrate, #14 is sufficient, even good, considering
> what I have seen houses and such wired with.
>
>   At 200 feet away, and not knowing if the device will be the only item
> being powered, I would at least examine the cost tables for the job using
> #10, #12 and #14 Thhn, no conduit.
>
>   As far as the conduit goes though, if one gets small diameter PVC, and
> all the fittings, no 200 foot pull needs to be done.  The segments and
> fittings can all be fed down the wire bundle and build the conduit in
> place right on the wires, then bury the finished run.

In North American Practice the electrical codes forbid assembling
conduit around wire. The conduit must be built as a complete assembly
and then you pull the wire from pull point to pull point.

--
Tom Horne

 

On Sun, 13 Jan 2013 18:15:07 -0800 (PST), Tom Horne
<> wrote:

>On Jan 2, 10:57 pm, wrote:
>> On Wed, 02 Jan 2013 19:11:54 -0800, josephkk
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> <> wrote:
>> >On Mon, 31 Dec 2012 16:54:41 -0500, wrote:
>>
>> >>On Mon, 31 Dec 2012 13:50:29 -0800, John Larkin
>> >><> wrote:
>>
>> >>>On Mon, 31 Dec 2012 15:08:00 -0500, wrote:
>>
>> >>>>On Mon, 31 Dec 2012 12:28:31 -0500, "Michael A. Terrell"
>> >>>><> wrote:
>>
>> ><snip>
>> >>>>>   He said he was going to suggest it to the owner, so who knows.
>>
>> >>>>So why not 500KV?  You never know?
>>
>> >>>Why not put the compressor where the power is, and run an air hose?
>> >>>Then we could argue about ths size of the hose.
>>
>> >>Actually, that's what I plan to do.  Put the compressor in the garage
>> >>and pipe the air downstairs.  4" oughtta do it.  ;-)
>>
>> >>I just have to figure out how much work it's going to be (how things
>> >>line up).
>>
>> >4" really?
>>
>> Of course not.  Michael is being silly with his suggestion of running
>> #6 wire for the compressor.  I thought I'd join in.  For anything I've
>> done, 1/2" Type-L copper is fine.  That's probably what I'll use again
>> but it's getting rather pricey.
>>
>>
>>
>>
>>
>>
>>
>> > How big it that compressor, 500 kW?  Does it go over 3000'?
>> >Not that i am all that expert but that is the size of compressor and the
>> >run length i saw last time i saw one plumbed at 4".  And that one was done
>> >by an expert.
>
>Well I'm not interested in being quarrelsome but would you mind
>explaining why you would use copper piping for air lines. Copper has
>gotten more pricy rather than recently pricey so it would seem to be
>rather a waste to use it for air. Help me out here. What am I
>missing?

A reasonable alternative.

 

On Jan 13, 11:19 pm, wrote:

> >Well I'm not interested in being quarrelsome but would you mind
> >explaining why you would use copper piping for air lines.  Copper has
> >gotten more pricy rather than recently pricey so it would seem to be
> >rather a waste to use it for air.  Help me out here.  What am I
> >missing?
>
> A reasonable alternative.

I've seen the pipe fitters install hundreds of feet of black iron on
jobs with a lot of air in use such as assembly lines. What is wrong
with that? Is it too expensive to install to be cost effective? I
have been out of the big job work for over a decade now.

--
Tom Horne

 

On Sun, 13 Jan 2013 21:02:19 -0800 (PST), Tom Horne
<> wrote:

>On Jan 13, 11:19 pm, wrote:
>
>> >Well I'm not interested in being quarrelsome but would you mind
>> >explaining why you would use copper piping for air lines.  Copper has
>> >gotten more pricy rather than recently pricey so it would seem to be
>> >rather a waste to use it for air.  Help me out here.  What am I
>> >missing?
>>
>> A reasonable alternative.
>
>I've seen the pipe fitters install hundreds of feet of black iron on
>jobs with a lot of air in use such as assembly lines. What is wrong
>with that? Is it too expensive to install to be cost effective? I
>have been out of the big job work for over a decade now.

Black iron is incredibly expensive and impossible to work with.