Distance Low voltage needs to be from High voltage

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hcbenz

Member
At a job I am working at the electrician says the distance that seperates high voltage and low voltage is 3 inches. I say at least 12. Who is right or are we both wrong? And what is the distance to pass inspection.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Re: Distance Low voltage needs to be from High voltage

Well, what are we talking about here? What voltage is high voltage, where is the wiring and what kind. What kind of low voltage wiring and where is it being installed?

-Hal
 

hcbenz

Member
Re: Distance Low voltage needs to be from High voltage

The high voltage is regular 110 120. The low voltage is rg6 cat5 22/4 22/8 ect. It a residental dwelling.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Re: Distance Low voltage needs to be from High voltage

All can be run through the same holes if you wanted to. There is no NEC restriction on spacing.

That said, you may want to maintain some spacing because of hum and noise from the 120V wiring and some LV wiring though I have never seen this to be a problem. Certainly not with coax and twisted pair.

-Hal
 

RRich

Member
Re: Distance Low voltage needs to be from High voltage

The separation from "line voltage" depends on a couple of things, both of which depend on your desire to be better than required and how sure you want to be that induction won't be a problem!
The two things to consider are (1) is the wire/cable running parallel? maintain at least 12" . crossing perpendicular or diagonally? at least 3" and for as little length as possible. No code that I'm aware of, but you won't be sorry.
 

tom baker

First Chief Moderator
Staff member
Re: Distance Low voltage needs to be from High voltage

"The high voltage is regular 110 120. The low voltage is rg6 cat5 22/4 22/8 ect. It a residential dwelling"
Keep in mind the NEC does not define high and low voltage. To a POCO, 120 is low voltage, to a fire alarm tech, 120 is high voltage.
There is no NEC requirement for separation, NM cable is a wiring method, the same are EMT. If there is no separation for EMT, then the same for NM cable.
However separation is required for proper performance, not in the same stud bay and cross at right angles.
 

brannen

Member
Location
Charlotte, NC
Re: Distance Low voltage needs to be from High voltage

I believe the 12" horizontal and 3" /90 degree perpendicular seperation are EIA/TIA standards and not NEC.
 

johnj

Member
Re: Distance Low voltage needs to be from High voltage

NEC 725.55 covers most of the requirements of what your asking.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Re: Distance Low voltage needs to be from High voltage

He is talking about separation of wiring within walls and ceilings of a residential building. 725.55 covers separation of conductors and communications wiring in raceways, enclosures and manholes.

Not exactly the same thing.

-Hal
 

macmikeman

Senior Member
Re: Distance Low voltage needs to be from High voltage

I could easily be wrong once again on this but but back when I was an apprentace I was taught that the door bell wiring (two cunductors twisted around each other, no sheath) could not be run thru the same holes as the nm and needed to be seperated by two inches. Now I cannot find any code reference so I am not really sure if this is right or wrong.
 

hurk27

Senior Member
Re: Distance Low voltage needs to be from High voltage

By macmikeman: I first went to work down in Fort Myers Fla. I wonder if it was a Lee county requirement.
Back in the "70's" I worked for B&R electric off pondsetta west of US41. I worked on the 2, 10 story condo's at the north end of the old US 41 bridge.

Small world :D
 

macmikeman

Senior Member
Re: Distance Low voltage needs to be from High voltage

Hurk, I was with Three D electric, and later Claude Jansen Electric over in Cape Coral, then last for Sun Electric which I think is the only one still going of the three. I graduated from Cypress Lake High School.
 

steved

Senior Member
Location
Oregon
Re: Distance Low voltage needs to be from High voltage

In motorhomes the 12V wiring is required to be separated from the 110V wiring by at least 1/2", except where they cross.

NEC section 510-10(c)(3).
 
Re: Distance Low voltage needs to be from High voltage

Originally posted by hcbenz:
At a job I am working at the electrician says the distance that seperates high voltage and low voltage is 3 inches. I say at least 12. Who is right or are we both wrong? And what is the distance to pass inspection.
As a software engineer, this is one I *can* chime in on...

Parallel runs of video / data lines should maintain at least a 12" distance to avoid interference bleeding in from the 120/240 circuit runs.

Perpendicular runs are fine, but if you can maintain a 3" distance when going perp to higher voltages the better.

...
The problem is not a regulation of any kind but the fact that both RG-6 Quad shied - as well as any inferior type of coaxial - and any type of unshielded twisted pair (UTP) do not resist the hum that higher voltages give off.

The net result is an increase in attenuation on your video or data lines. On video lines it's often so negligable that you cannot notice it - UNLESS it is for an HDTV run then you'll see a very fast degredation of signal if you don't maintain the distances.

In data networks, on 100 Mbps systems, if you're less than 12" you might notice that you're only getting 70-90 Mbps. However, if you were to run that parallel through the same holes, you may find some of the longer runs only get 10-40 Mbps.

This is because the digital data signals are being lost because of the interference and being forced to be resent from whatever originated the signal.

--
Hope that helps,

R. Joe Reich
 

GENEM

Member
Re: Distance Low voltage needs to be from High voltage

The 2" separation probably comes from the NEC requirement for IS wiring although it would not apply to any thing else. Just a thought.
 
800.52 Installation of Communications Wires and Cables

(A) Separation from Other Conductors

(2) Other Applications
Communication wires and cables shall be separated at least 50mm (2in) from conductors of any electric light, power, Class 1, non-power-limited fire alarm, or medium power network-powered broadband communication circuits.

Exception No 1: Where either (1) all of the conductors the electric light, power, Class 1, non-power-limited fire alarm, or medium power network-powered broadband communication circuits are in a raceway or in metal sheathed, metal clad, non-metallic-sheathed, type AC, or type UF cables, or (2) all of the conductors of communications circuits are enclosed in raceway.
 

rjmeitner

Member
The NEC requires 2" separation (or a barrier), as previously noted. EIA/TIA used to have specific spacing requirements but I believe these have been removed from the more recent versions and replaced with general language along the lines of keep far enough separation to minimize e-m interference.
 
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