AC power cord length restrictions 1

[SysEng38]

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?

 

[mpparent]

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

 

[Shortstub]

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?

 

[Shortstub]

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

"3-Phase to Single-Phase Current Relationships"

 

[SysEng38]

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.

 

[DanDel]

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.

 

[jbartos]

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.

 

[jghrist]

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.

 

[Lewish]

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.

 

[peebee]

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.

 

[cuky2000]

SysEng38,

For additional reference on extention cord please check the enclose report from the U.S. Consumer Product Safety Commission (CPSC).

http://www.cpsc.gov/cpscpub/prerel/prhtml99/99069.html

 

[busbar]

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.