gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
151102-0727 EST
HSB_007:
Post #8 from you.
Post #1 from you.
Post #5 from you.
Post #6 by GoldDigger.
Post #8 by you.
With my experimental setup of two #14 Romex cables lashed together over a 12 ft distance and running 10 A 60 Hz thru one cable (this obviously means shorting one end and feeding the other from an adjustable voltage transformer with a current meter in series) , and shorting one end of the second Romex cable and placing a 75 ohm load at the opposxite end, results in a voltage of 2.45 mV across the 75 ohm resistor from magnetically induced voltage in the second Romex cable. For your 10,000 ft application this might mean a maximum ballpark estimate of 2.5 V.
I believe the parallel arrangement of this experiment provides the maximum magnetic coupling between the two cables. You have twisted pairs in your cable and thus coupling could be less, and there are differences in wire spacing. You have a statistical problem and probably should try some experiments on possibly 1000 ft of your cable. You also have to determine the thresholds of operation of your different loads.
Your individual currents are much lower than 10 A, but there is some composite flux vector at the wire pair of interest that you must estimate from the sum of all the magnetic fields of the various pairs.
As an alternative use DC instead of AC.
.
HSB_007:
Post #8 from you.
I believe we are now concerned with a 3000 meter cable, about 10,000 ft. Also #18 wire in this post, 6.39 ohms / 1000 ft at 20 C. Post #13 has #16 wire and 0.33 A. #16 copper is 4.02 ohms / 1000 ft at 20 C.I collected some more information to see if one could look further and provide some help into figuring out if there will be a problem of inductive coupling at a distance of 3000 meters.
Post #1 from you.
I would not call a horn or strobe an instrument. At what voltage does it fail to pull-in (start to work)? At what voltage does it drop-out (quit working if already started)?We have an instrument that requires 120 V ac to work and we mandate that the conductors length from control room (safe area) to the instrument do not exceed 1000 ft (305 meters).
Post #5 from you.
Apparently a very low data rate. Is a single pair uaed for both power and control, or just a signal to activate the device?The situation I have is a multi-pair cable (12 pairs) each one of them is of the same signal type, 120 Vac digital output serving horns and beacons.
Post #6 by GoldDigger.
With a signal level of 120VAC I think that you are really talking about powering the horns and beacons rather than just supplying a control signal to turn them on and off with the power provided by another circuit.
But in any case, there is no specific distance at which a problem will suddenly appear.
If the devices will work just as well on 100VAC as 120VAC and will not operate at an input of 20VAC, then it is very unlikely that there would be any crosstalk problems even at 1000 feet.
You are much more likely to get a problematic voltage drop in that length of wire from the wire resistance than a problematic stray voltage from coupling.
Post #8 by you.
The loop DC resistance of #18 copper for a 10,000 ft one way distance at 20 C is about 2*64 ohms or 130 ohms. If a horn is 10 W at 120 V, then current is greater than 0.08 A. Assume a current of 0.1 A, then loop voltage drop is about 13 V neglecting inductance. What is the threshold current to operate a horn?1- Multi-pair (12 pairs)
2- All conductors are in the same cable and will serve the same purpose (power and control Beacons and Horns through 120 V ac).
3-We are complying with IEEE 518 when it comes to spacing with other adjacent signals. In this case, there is enough spacing on the same cable tray between this multi-pair cable and adjacent ones (about 6 inches from signal level 2, and 8 inches from signal level 4).
4- Twist: 60 mm
5- Conductor: Circular copper,7 strands minimum; tinned per ASTM B33
6- Conductor size: 18 AWG
7- Primary Insulation material: thermoset cross-linked polyolefin, temperature rating 90 C.
8- Primary insulation voltage: 300 Vac.
9- Primary Insulation thickness: 0.38 mm
With my experimental setup of two #14 Romex cables lashed together over a 12 ft distance and running 10 A 60 Hz thru one cable (this obviously means shorting one end and feeding the other from an adjustable voltage transformer with a current meter in series) , and shorting one end of the second Romex cable and placing a 75 ohm load at the opposxite end, results in a voltage of 2.45 mV across the 75 ohm resistor from magnetically induced voltage in the second Romex cable. For your 10,000 ft application this might mean a maximum ballpark estimate of 2.5 V.
I believe the parallel arrangement of this experiment provides the maximum magnetic coupling between the two cables. You have twisted pairs in your cable and thus coupling could be less, and there are differences in wire spacing. You have a statistical problem and probably should try some experiments on possibly 1000 ft of your cable. You also have to determine the thresholds of operation of your different loads.
Your individual currents are much lower than 10 A, but there is some composite flux vector at the wire pair of interest that you must estimate from the sum of all the magnetic fields of the various pairs.
As an alternative use DC instead of AC.
.