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Discussion in 'The Club House' started by jca1, Jun 1, 2011.
If so I have a question.
I think JD is electrical.
I am not an Electrician, but I play one on the Interwebz.
What's the question? I had to learn the hard way when I remodeled the house.
Fire away, maybe we can help.
I am no electrician, but I work in the power field and I have close to 20 years in the Ohms/Amperes/Resistance field.
I don't know electrical code for any area, as I have never had to have an official inspection on my work, but I know the basics.
If I can help, or if I can contact someone who can, I would be happy too.
What's the question brother??
I electrocuted myself once... does that count?
AC? or DC? or both?
I'm trying to understand AC voltage drop.
I have 6AWG copper wire (4) running 160' to my wife's outdoor kitchen.
I want to run a new 8000btu 7amp window AC, a small 2.5amp fridge/drink cooler thing, one (maybe two later) 2.7amp stand mixers, occasionally a small microwave, and now a 16 amp oven.
I have enough amps with a 60amp circuit but someone else told me voltage drop may be a problem cause the outdoor kitchen is 160' from the house.
jca, try this:
American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies
I can't speak for house voltage and my experience/advice should be taken as anecdotal (NOT SCIENTIFIC just my experience) at best.
My experience is as an AGE mechanic in the Air Force. We use portable diesel/jet powered generators to provide power to aircraft. 150' of line pushing 120VAC @ 400HZ @ 80 Amps will drop to about 115VAC at the end of the cable. Take that up to 200 Amps and you will be at 105VAC which on our equipment is a problem. For that reason we try to stay under 100' cable length. Also moving a cable over 100' long is crazy difficult.
I don't know if the fact that we are pushing a larger amperage changes the voltage or if it's the % of maximum potential power that causes the change in voltage so your mileage may vary.
/I hope I have thoroughly confused everyone
Looks like a little over 3% drop. Is that acceptable?
The biggest problem you will probably run into is when one or more of the motors kicks on. That's when the draw is at it's most.
A 3% drop is not that much but take this example - if you are only providing 20 amps and your equipment needs 15 amps, the breaker is only going to give you 80% of that 20 amps - 16 amps total. That would be too close in my opinion. Anyway you could install a sub panel at the kitchen and feed each appliance with it's own circuit?
The #6awg is feeding a sub panel.
Misread the previous post. JD covered it very thoroughly. Sorry.
You will DEFINITELY have a problem due to voltage drop, but most units have a voltage threshold that will allow low voltage down to 115AC of even 110AC with some units.
More importantly you will have a heat problem because any of the units that you have mentioned have what's called Locked Rotor Current, or Cold Cranking Amps.
Motors, no matter the size or quality, need an initial "in-rush" of current, in the form of higher amps, sometimes as high as TEN TIMES their operating amps.
More expensive, higher end, elite units will use what is called a "Pre-Conditioner" or a "Soft Start" to get their motors going with less "In-Rush" current, but by use of a capacitor that loads over time (trickle charging).
Most household units don't have that feature, so while your 7 amp AC is rated at 7 amps, it might actually need 35-40 amps just to get it working.
When you add the LENGTH of the "cable" (it's only wire when it's in the air, cable is what you put in the ground) you run into extra amps generating TONS of extra heat on the lone cable that you have running that distance, which will DEFINITELY overload your breaker, and that is with that one, lone unit running by itself.
<<<<<<<<<<<<<<< CAUTION >>>>>>>>>>>>>>>>>
The following advice is merely an opinion and may not be entirely legal depending on WHO provides your power service!!
That type of distance?
With what what you have planned?
I would split your incoming service from the road, after the meter, but right before your house panel, run some 4/0 cable to a sub panel with 4 or 5 dedicated breakers in the external kitchen. Then wire the kitchen as you would any other room in the house.
That will alleviate your problems brother.
You trying to turn me into french toast or something? Good lord man! I'll fry myself
If I run a 15 amp circuit to a window AC in my house it too will have to survive that LRC draw. How does the length of the cable make it any worse?
Please explain....I'm learning here, so be slow and clear like you're talking to a dummy.
Wire, any electrical conductor, has resistance. In that, I mean it resists current flow much like a 1/2" hose inhibits water flow compared to the same length hose that is 5/8".
The larger the wire, the lower the resistance. Try to picture a series of resistors in series, kind of like a string of Christmas lights. The longer the string, the more current it draws. The same applies to any conductor you run electricity through. If you want to make a longer run, you have to increase the current carrying capabilities, ie.; wire size.
I was telling you what I would do. Your pull the meter, the power on the house side is down. You splice in with a welded or other mechanical connection and run the 4/0 through some conduit or direct bury out to the extended kitchen. Plug into a new panel, main breaker off on the kitchen panel, plug your meter back in and power up the house.
You ever play that kids' game where you put like 6 straws together, end to end, and try to drink your soda from like 5 feet away? You know how hard you have to "suck" to be able to get soda through that length of straw??
Think of that in reverse.
Or, if it makes it easier, visualize this:
You have a 5 gallon bucket filled with water. You have a piece of hose that is 12 inches long and a funnel on one end to dump the water into.
When you dump the water, it comes out the end of the 12" hose pretty much as fast as you pour it in. You have good flow, you have good pressure and can even cap the end and "spray" it.
Now, same scenario, but your hose is 40 feet long. You dump and dump, but what finally comes out the other end is a trickle.
The difference? You have surface area that the water must pass through.
Before it was able to max out the interior diameter of the hose and press through with the 12" hose.
With the 40 foot hose you don't have the pressure to max out the interior diameter, so it trickles out the end.
With electricity, the further you go from the source, you are adding "draw" which is what your electronics need to start or run, the more surface area, the more heat electricity generates. The more heat it generates on the cable (or wire) the more RESISTANCE increases.
The more resistance, the less voltage is getting to your end source, thus a lack of voltage readings and available amps to draw from.
Does that make sense?
Yes, but I'm slow. I thought I could have a voltage drop of 5% per NEC and I have just a little over 3%. I have a 60 amp breaker but a 42amp load +/-.
When the AC compressor starts that surge will be like a millisecond right? Just like it is with any other motor. I was under the impression it was not necessary to figure in the LRC because it was just a momentary surge and the breakers are even designed withstand that for a second. It seemed like your first reply was focusing on the LRC of the AC.
Maybe what you are saying is that the current flowing through the cable under normal load is going to generate heat above the 75C the cable is rated for?