AC Relay?

You've got it, use the 12v setup. Try this relay:

Because of the inductive nature of a motor load, relays/contactors are rated by current and by hp. The relay above is 25 amp, but only 1 hp. I'd guess that your 15 amp compressor is 1 1/2hp. In which case, this relay would be better:

Bob

Such relays are called contactors and are a dime a dozen.

An ordinary contactor for air conditioners would work fine. They run on 24 VAC like thermostats.

I don't believe you're allowed to run low-voltage signal lines in the same conduit with power, if that's what you're considering.

Mark, you're making us guess too much. What is the rated horsepower of your motor? Is the 15 amps at 115 or 230 volts (i.e., do you need a single pole or two pole relay)? Are you or do you want to use the buried #14 wire for any other purpose, now or in the future? (seems a waste to use it up for a low current control line.) Is there any other signal connection to the workshop, like telephone? Is the "buried" 14-3 direct burial without a conduit or inside a conduit? How big a conduit? How are you going to get the air to the house? Is the compressor receiver emptied after each period of use or left under pressure? (Might be handy to use pneumatic control if you are running a new air line.)

Actually, I'm not sure there is a prohibition against running control wires in the same conduit as power conductors. There are issues about low voltage lines being terminated in the same box as power lines. Check your local code. Lots of options. No particular need to provide a transformer for low voltage control unless you want to.

awright

Imprudent to speculate in favor of risk.

Remote-control circuits less than 30 volts are "Class 1".

(1) In a Cable, Enclosure, or Raceway. Class 1 circuits and power supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.

My understanding is you need a separate physical path for low-voltage signals versus power. You can't run them together through, for example, an underground conduit.

Think about it. If this wasn't prohibited, you'd have every computer geek in the world fishing Ethernet cable through power conduits in old buildings. Sooner or later you'd be shorting out the ungrounded network sockets with AC power.

Since he has 60 amp service out there, I'd guess the 14/3 was once for lighting only and has since been supplanted as a power source for the shop. If so, then it's up for grabs for remote control.

Tom made a good point: with X10 a number of loads in the shop could be remotely controlled over the single 14/3 line. I don't know if there are any X10 load modules that will directly handle 1.5 HP, but they could certainly operate a contactor.

Yes,.,google on the term "contactor"

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

That's a "Class 1 Power-Limited Circuit." A "Class 1 Remote-Control and Signalling Circuit" is limited to 600V, but has no power limit.

Doesn't that last statement contradict the NEC quote above it? Unless there are some very recent changes I'm not aware of, as long as the control circuit is associated with the power conductors, and all the conductors are rated for the highest voltage present in the raceway, it's permitted.

The voltage and functional association requirements take care of this.

Ned Simmons

What is X-10?

D>

your cat5 likely has a pair of unused wires (iirc, normally ethernet uses 4 wires only), you can easily use those with some simple off the shelf parts to turn your compressor on. it is an easy one evening project.

It modulates a small current onto the power lines . At the other end ( receiving end ) ,

its demodlated and controls stuff , like turns on big expensive contactors ....

Its old tecnology . In Ham radio ( KC7CC ) , there are some big complaints , but i know better , so i ignore em .

" Our cows dont give as much milk under power lines transmitting X-10 signals .."

Thinking about it .... 60hz power lines are dangerous , but not X-10 !!

BTW Just got a new pocket PC , GP2X , gotta hook a USB HDD , and USB-Mouse and, and .... It has USB Host , so it can Surf the web , ,,, boots Linux .. $200 .

_________________________________________________________

mark wrote:

It modulates a small current onto the power lines . At the other end ( receiving end ) ,

its demodlated and controls stuff , like turns on big expensive contactors ....

Its old tecnology . In Ham radio ( KC7CC ) , there are some big complaints , but i know better , so i ignore em .

" Our cows dont give as much milk under power lines transmitting X-10 signals .."

Thinking about it .... 60hz power lines are dangerous , but not X-10 !!

BTW Just got a new pocket PC , GP2X , gotta hook a USB HDD , and USB-Mouse and, and .... It has USB Host , so it can Surf the web , ,,, boots Linux .. $200 .

_________________________________________________________

mark wrote:

You're not making any sense.

Nobody has shown that 60Hz power lines are dangerous.

What the FARK are you talking about? Why would the government care?

You're wrong about that too.

I'm trying to think of a PDA I've owned that I couldn't use USB with. I can't.

What's your point & goal in posting, exactly?

Good question. Problem is that werty won't be able to answer. Others may able to do a diagnostic but......

I wonder if he is rambling about BSR X-10.

I was going to suggest a "Psychic Relay" but not everybody can get those to work reliably.

Matters not. We consider a 24 VAC contactor or the like with no overcurrent protection on the signal circuit, necessitating a power- limited source.

No. While you could run a dedicated power circuit (for an air compressor or other hard-wired appliance) and control (alone) in the same conduit, you could not run a 24 VAC control line in the conduit that happens to also supply, say, a sub-panel for a detached shop. In short, you need a conduit or buried cable or whatever separate from any other power lines to the building, if there are any others.

Typical low-voltage cable does not carry a 600V rating, nor is there overcurrent protection on the control circuit.