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Parallel 120VAC / 24VDC Conductors?

  1. Jun 3, 2013 #1
    I have an enclosure that has numerous 18AWG cables running through it. These conductors carry 24VDC which power locking mechanisms throughout a building. The enclosure also has a 10AWG cable run to it carrying 120VAC. This is used to power the 24VDC power supply.

    The electrician wants to bring the conductor carrying 120VAC in from the bottom left-hand part of the enclosure and route it up the side and across the top to hit the power supply. The 24VDC cables will come in from the bottom right-hand part of the enclosure and run along the bottom and up the same side as the 120VAC conductor.

    If we do it this way, we'll have about 2ft where the 120VAC line and the 24VDC lines are in parallel. There is no data communication involved, so I'm thinking the short parallel runs will not have a significant impact on the equipment, but I just want to confirm that before I give the OK.

    I don't know if this matters, but the current on the 120VAC line will be a maximum of 1.9A. The current on the DC lines will be a maximum of 0.5A. The locking device can operate at a minimum of 21.6V (=24+/- 10%). The longest run will give me a voltage of 22V at the locking device after the line loss.

    Any thoughts? Thanks in advance.
  2. jcsd
  3. Jun 3, 2013 #2
    0.4V of margin after line loss seems pretty slim to me. Does this include tolerance of the 24V power supply output? I would be more worried about this than crosstalk from 60Hz over a few feet.
  4. Jun 3, 2013 #3
    In actuality, the power supply will be putting out a bit more than 24VDC, so I wasn't too concerned about the 0.4V margin. 25.6VDC is typical, which would be within the maximum 24VDC+10% tolerance of the lock and would end up being ~23.6V at the lock with my longest run. When I do the figures I typically use 24VDC for all calculations so that I have that built in safety cushion.

    Based on your answer, though, it sounds like you're of the opinion that any impact from the short parallel run is negligible.
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