×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AC power cord length restrictions

AC power cord length restrictions

AC power cord length restrictions

(OP)
I am trying to provide ac power to a chassis unit that is located 800' away. In this unit, I have four linearly regulated DC power supplies. I am considering in using an AC power cord to supply power to my power supplies. What is the length restriction for using ac power cords in the outdoors? Do I need driver amplifiers for my application?

RE: AC power cord length restrictions

I would reconsider your position on the use of a cord.  I don't recall any length restriction, however, being that it's 800' long(?!), I would definitely recommend a permanent solution like pipe and wire to a location nearby(within say 10'), and then you can run a cord if so desired.  If you're in the US, you should check article 400 of the NEC, because it gives specific uses of cords in that section(400.7 & 400.8).

Mike

RE: AC power cord length restrictions

SysEng38,

1) What is the total power, in Watts, or VA, that you are tryng to supply, 800' away?

3) What is the required voltage?

3) Have you thought about splitting the 4 units up, and suppling them with a 3-ph/4-wire circuit?

RE: AC power cord length restrictions

T100,
For a related topic, see thread 278-44947,

   "3-Phase to Single-Phase Current Relationships"

RE: AC power cord length restrictions

(OP)
mpparent:

I am working in the US. My application is to remotely turn on power supplies at a distance of 800'. The supplies are located near an AC outlet, however, it is cumbersome to have to plug and un-plug an ac power cord. The ac outlet is located on a pier and I am on a cliff that is located 800' away.

Shortstub:

Here are my answers:
1) 70 watts
2) 120 Vac at 800'
3) No, I have not--it seems involved. The supplies have to be co-located and housed in a weather-tight enclosure. My application is to remotely turn on the supplies. I would like to have a 'toggle switch' that is 800' away. I am trying to avoid making many trips to this enclosure and turn on the supplies.

RE: AC power cord length restrictions

SysEng38, are you asking if you need driver amplifiers for your AC supply? If you don't usually do this kind of work (Power) refer to a qualified person. An 800' run of extension cords is not a practical wiring method.
First, the load must be determined, and the voltage drop for this load must be calculated for this distance at the load's voltage (in a professionally installed wiring method). If the voltage drop is excessive (and it almost certainly will be), you may need oversized conductors or the use of a higher voltage for the 800', and then transformation down to your load voltage.

RE: AC power cord length restrictions

Suggestion: The permanent or temporary nature of this installation needs to be determined. It makes a difference from safety standpoint. Temporary installations accepts cords. The proper size of the cord is needed, e.g. #12AWG, however, this would assume that there is a regular load with acceptable voltage tolerance plus minus 5% or so and no motor loads with high inrush currents.

RE: AC power cord length restrictions

If I understand your situation correctly, there is AC power at the load, but it is inconvenient to get to the load to turn it on and off.  I would consider a radio controlled switch for the load.  If there is a phone at the load, you could get an X10 switch that can be controlled by telephone (see http://www.attr.com/x10/a5005.htm).  You might find something at Radio Shack that could be used.  

Running an 800 ft cord, especially when part of it is on a pier, would be out of the question.  It would be dangerous and there would probably be too much voltage drop.

RE: AC power cord length restrictions

You might also consider a power-line modem.  At the refinery in Anacortes, WA there are several which control pumps, down on the pier, at a distance of some 1500 feet.

RE: AC power cord length restrictions

Conductor length is limited by voltage drop.  Voltage drop calcs depend on conductor size, type, and arrangement, conduit type, and load current.  The calcs are not rocket science, but I agree that you should get an engineer or at least a sharp designer or electrician to work with you on this.

Another way to achieve hard-wired control would be to use a control relay or contactor to switch the loads.  That way only a very small control-power current would have to traverse the 800-foot wiring run and voltage drop would become much less of an issue.

I agree that radio or phone might be more convenient and possibly cheaper.

RE: AC power cord length restrictions


Something like a 24VDC "ice cube" relay [P&B KRP?] with small DC power supply may do the job.  Consider 2-pair 24AWG telecomm cable:  One pair to switch the realy coil and one to send back a contact closure.
  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources