Understanding the Basics of Electrical Amperage and Wiring for Automotive Lifts

[lurch85]

Im looking into getting an electrician... but it drives me crazy when I don't know why something is done a certain way.

I bought a Bendpak 10000 lb automotive lift. the motor supplied is 220 single phase or 3 phase (i am using single phase)
the motor for 220 single phase is supplied with a white, a black, and a green wire. The instructions call for 10 gauge wire up to this point with a 25 amp circuit breaker (double throw of course)
The wiring calls for 2 wires to be run approximately 14 feet with 14 (fourteen) gauge wire to a switch that is supposedly good for 15 amp.
The only way that i can see this working is with each leg grounding the other lead, that it is actually only considered 15 amp for each wave length (being out of phase for each other)
1. Is this correct in theory?
2. Also, being called 220 single phase... shouldn't this actually be called 2 phase?
I have man more questions.. but this is a good start

 

[Averagesupernova]

Your terminology is a bit off. Why are you bringing wavelengths into this? Without knowing what the 15 amp switch is controlling no one can give much of a comment. It is in fact single phase. This sort of thing has been discussed many times here on PF. A search should turn up something.

 

[wirenut]

Is the switch actuated by a bar across the lift legs, so it will stop the motor if the top of the car hits it?
If so it is a safety switch to prevent lifting the car too high.
The reason for 10 awg wire up to the connection point is for inrush current. If you look at the nameplate of the motor,
the full load amps is probably around 18 to 20 amps.
As for why the switch is rated for 15 amps ? Are you sure it is 15 amps and not 20amps?
A model number or some specs would help.
Also it is a two POLE breaker, not two throw.

 

[lurch85]

So far you both are right on. (I should not post things online when I am totally exhausted and ready to go to bed, I apologize)

Yes, the switch is for a cuttoff switch to make sure the lift doesn't damage the lift or the vehicle.
my understanding is that is cuts off supply to one of the leads and cuts off the ground to the other lead.
I had done a few searches online to try and find out, but nothing really fit (although I did not search this forum directly like I should have)
Actually, one discussion was on exactly this subject and same model even... but the answers given seemed to contradict each other.

The motor is 18 amp.
Model number xpr-10a

Thank you both for your answers.
Hope this helps...

 

[lurch85]

Now that i made such a statement as (the answers given seem to contradict each other... ) here is a link to that discussion

http://www.garagejournal.com/forum/showthread.php?t=113591

 

[jim hardy]

that discussion includes a basic mistake.
Uplift said

You are correct, the reason the switch and wire for the limit switch are rated for 15 amp is because you only have one leg of power running through the switch (1/2 of 30 amp circuit)

which is dead-*** wrong.

Current goes into the motor via one L wire and every bit of it comes back through the other L wire.
Everything should be sized so it's protected by the breaker. Switches included.

Caspian got it right a couple posts later on.

 

[lurch85]

Thank you very much... after that thread in particular, I was very confused...

 

[wirenut]

The safety switch(normally closed) goes in series with 1 leg of the power and 1 side of the motor.
The other leg of power goes to the push button. Nothing cuts off the ground!

 

[wirenut]

@jimhardy I work with 1st-3rd year apprentices(who know everything" 'cuz they just learned it.") who don't believe
that 2 hot legs on a single phase service are still single phase (shouldn't it be 2 phase?). Then try to explain what 2 phase really is, and
watch their eyes glaze over.
After 25 yrs as an electrician I have so many stories.

 

[lurch85]

thinking back I guess maybe I should just use what I know from 2 car batteries in parallel or series knowing that you're either going to combine voltage or amperage but not both. Same theory?

 

[jim hardy]

After 25 yrs as an electrician I have so many stories.

I hope you'll use them here. I've always enjoyed your insightful posts.

old jim

 

[jim hardy]

ps I'm of the opinion that he should run both wires together , not separating them, to both switches.
something in NEC 300 about running wires together to avoid magnetic fields ?

 

[lurch85]

clarification of my above post. this is like having two batteries in series. voltage is combined amperage stays the same. correct theory?

 

[lurch85]

jim hardy... I don't know enough about the theory to understand your post... what would a magnetic field of that type do in that situation?

 

[lurch85]

by the way.. its all wired up and seems be doing well.. 220 volts and no problems...

Thank you all for your help... Now just want to understand better...

 

[jim hardy]

jim hardy... I don't know enough about the theory to understand your post... what would a magnetic field of that type do in that situation?

nothing drastic, probably.
Separating the wires makes a loop that'll act like an antenna. It makes a magnetic field that might perturb sensitive electronics nearby , particularly when starting or stopping that big motor.

i have such a loop in my house that i'll fix when i re-panel the room .
There's one outlet controlled by a three way switch.
I noticed that the touch-dimmer lamps in my living room turn themselves off whenever i switch a capacitive load ( like a computer ) that's plugged into that outlet. Even those fluorescent curly bulbs in an ordinary lamp that's plugged into in that socket will do it. Incandescents and dimmable LED bulbs are okay though.
http://www.mikeholt.com/technical.php?id=powerquality/unformatted/EMIKarl&type=u&title=Power Quality Article

Fields cancel when wiring is correct: Every circuit has two or more conductors. Let’s take the simplest, where there is just a hot and a neutral (correctly called grounded circuit conductor but allow me to use the common term, neutral). The currents in each are traveling in opposite directions. In AC, when one zigs the other zags. The result is that the magnetic field generated by one is canceled by the other. The very small resultant field generated is due to the fact that the conductors are side by side instead of co-axial but it is too small to be detectable in the building spaces. In the case of three or four wire circuits sharing a neutral the magnetic field situation is the same. The resultant of the magnetic fields of the hot conductors is canceled by the magnetic field of the neutral, which is carrying the resultant return current from the hots.

Effects of separation:
So what kind of wiring allows magnetic fields to generate? Any wiring method which allows some or all of the neutral current to separate from its circuit and travel in other paths before joining up again. In other words, when conductors of the same circuit are physically separated.
...
Separation due to wiring error:
How does modern wiring produce elevated magnetic fields? It will not if electricians follow the Code requirement that all conductors of a circuit be run3-way switch wiring:
here's what i think i have in my living room: _jh
3-way switch wiring:
Another common net current situation is set up by incorrect 3-way wiring circuits. When the electrician tries to use two-conductor travelers instead of three, he sets up quite a magnetic field in the room. Essentially, he is using a hot from one junction box to run to one switch and he picks up a neutral from a circuit near the second switch. The result is that the traveler carries only one current at any time, with no canceling current, so the magnetic field is at a maximum. The violation of 300-3(b) is clear when you consider the circuits supplying the 3-way section. One run contains the hot with no returning neutral. The other contains the neutral current but no balancing hot. The simple principle to follow is to make sure that in all parts of the circuit at any time there will be two equal and opposite currents flowing. You can’t achieve that with two-conductor travelers. The only cure is to replace the traveler with a 3-conductor cable and be sure you get your hot and neutral from the same point. Check out 3-way circuit diagrams in books like the NEC Handbook. together in the same cable, raceway, conduit, cord etc.
.....

I don't think it's dangerous to separate them but it might give you some strange symptoms.

 

[wirenut]

@jimhardy The safety switch is just a SO type cord (switch leg) from the point of power connection to the
switch and back. The power to the motor actually comes from the main connection point.

 

[wirenut]

@jimhardy I think in your situation , unless they are on the same circuit, they won't be able to do this very much longer.
I believe they are going to require arc-fault breakers in family/living rooms soon. If it is a neutral from a different circuit
the breaker will trip immediately.
BTW the stories I could tell about "experienced" electricians wiring 3 way switches would make your hair stand up.

 

[Averagesupernova]

Arc faults are already required just about everywhere. Used to be just bedrooms. Then everywhere except the kitchen and bathrooms. Now bathrooms are about the only thing that don't require them. Any finished living space. The rules are getting stricter all the time. Even the garbage disposal/dishwasher require it. The sump pump outlet in the basement even requires a GFCI outlet. It used to be that it was exempt if there was only one outlet and not a duplex plugin. This way nothing except the pump could be plugged in. Now that is out the window. The claim is that nuisance trips are next to non-existent so there is no danger of the sump pump outlet tripping and ending up flooding the basement.

 

[wirenut]

@Averagesupernova I realize the current code calls for them, but in Buffalo NY, they are enforcing the 2008 code.
Most towns around here are using '08 (or '11 codes if you're lucky).
I have a high water alarm on my sump. It texts me if it goes off.

 

[psparky]

I wire everything 2 phase...haha...what's wrong with that?

Single pole breaker: Single phase. Line to neutral. One bus bar to neutral. Neutral is always tied to ground in panels. On an oscilloscope you will see one sinusoid, hence the name single phase.

Double pole breaker: Single phase line to line. One bus bar to another bus bar. Bus bars are either 120 degrees (3 phase) or 180 degrees out of phase. (Single phase panel) On an oscilloscope you will see one sinusoid, hence the name single phase.

Three pole breaker: Three phase line to line to line. One bus bar to another bus bar to another bus bar. All are 120 degrees out of phase. On an oscilloscope you will see THREE sinusoids...hence the name three phase.

These rules apply to three phase panels or even your standard 240/120 volt single phase residential panel. (Except you can't get three phase out of a single phase panel...unless you use an awkward converter).

 

[jim hardy]

@jimhardy The safety switch is just a SO type cord (switch leg) from the point of power connection to the switch and back.

Ahhh okay, so long as it goes to switch and back...

 

[jim hardy]

@jimhardy I think in your situation , unless they are on the same circuit, they won't be able to do this very much longer.
I believe they are going to require arc-fault breakers in family/living rooms soon. If it is a neutral from a different circuit
the breaker will trip immediately.
BTW the stories I could tell about "experienced" electricians wiring 3 way switches would make your hair stand up.

indeed.
I found the utility room here is wired with 2 wire "Romex" no ground.
Fortunately i'll be re-paneling that room too. Local lumberyard had a sale on modern EM with ground so i stocked up.

<start rant>
i dread arc-fault breakers, don't want them.
"Newer> and "Better" are not synonymous.

Did you know there's a move afoot to dump the present US DTV format (8VSB) in favor of some European standard ?
Another 200 million TV's for the landfills .

Windows has conditioned a generation to accept useless overcomplexity and needless frustration and change for change's sake.

But that's a social problem not a physics one. I'd best not get started on that tack.

Blame Gates, not Bush.

<end rant>

 

[dlgoff]

Did you know there's a move afoot to dump the present US DTV format (8VSB) in favor of some European standard ?

What the ...

 

[rbelli1]

Did you know there's a move afoot to dump the present US DTV format (8VSB) in favor of some European standard ?

Do you have any references for this? It seems a bit tin-foil hatty.

BoB

 

[jim hardy]

i ran across several articles surfing one night.

Tonight these are the first two that popped up

http://www.cedmagazine.com/articles/2012/07/capital-currents-digital-television-30

http://www.tvnewscheck.com/article/74105/ofdm-seen-key-to-blanket-ota-coverage

http://www.cedmagazine.com/articles/2014/02/capital-currents-tv-broadcasting-%E2%80%93-the-next-generation

it's not coming up real soon

will try to recover those references.

keywords 8vsb ofdm should be fruitful

 

[jim hardy]

slideshow at
http://btsgold2014.unitbv.ro/uploads/presentations/Bill_Hayes_BTSGOLD2014.pdf http://www.tvtechnology.com/article/ofdm-based-%E2%80%98futurecast-atsc--proposed-by-lg-zenith-and-harris-revealed/221693atsc 3.0 as i understand is heading toward different modulation scheme, OFDM, and is not backward compatible.

fortunately it's not a "real soon" thing.

 

[rbelli1]

Thanks for the information.

I do believe we've hijacked this thread though.

BoB

 

[jim hardy]

Indeed, sorry for the hijack. i was on a rant, as indicated.if you're interested here's a tutorial on 8VSB
http://www.theonlineengineer.org/TheOLEBLOG/8vsb-a-tutorial/
over and out on that topicold jim