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DB Fiber optic buried next to DB triplex power cables in a trench - problem?

AlaskanNoob

AlaskanNoob

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Got a 600 foot long trench I'm digging, and first thing going in is a fat 250/250/4/0 triplex power cable. I'm hoping to put a fiber optic cable right next to it in the trench, but some things say the steel jacket of the fiber optic might somehow interfere with the power. Haven't seen anything solid though, nor any distances of separation they should have. Will be a real pain having to partially backfill over the power cable to then add the fiber. This trench is proving sketch enough...

Anybody have any expertise in this area?

Our fiber optic cable is this one: https://www.lanshack.com/6-Strand-C...IG-50125-OM3-Assembly-by-QuickTreX-P8010.aspx
 
There is no reason in the world of physics I can think of that the two cables would cause a problem with each other.

If you were installing a standard Cat5 ethernet cable, I'd be telling you to make sure there's at least 12 to 16 inches of dirt between them and the ethernet line should be shielded.. but fiber optics aren't bothered by EM fields.
 
I have done something similar (OM5 cable in the same pipe as the 4xAWG4 line). No issues. Because its fiber, there is no need to worry about electrical interference.
 
Where did you read that the "metal jacket" would interfere with the power?

The advantage of fiber is they often pull it in the same conduit as the Primary and Secondary Power.

We just had a rural installation done. They removed the primary feed from our transformer can and re-pulled it from the power pole up to the transformer with the new power cable and then ran it with the feeder from the transformer can to the meter where they drilled a hole in the side of the meter box to bring it out to the modem.
 
aenyc said:
I have done something similar (OM5 cable in the same pipe as the 4xAWG4 line). No issues. Because its fiber, there is no need to worry about electrical interference.
Click to expand...

Was your OM5 direct burial with a steel jacket by chance? The things I've seen have said there won't be issue with the fiber with them being close, but that the steel jacket might somehow interfere with the power cable.
 
AlaskanNoob said:
Was your OM5 direct burial with a steel jacket by chance? The things I've seen have said there won't be issue with the fiber with them being close, but that the steel jacket might somehow interfere with the power cable.
Click to expand...

Even simpler.
There is a 2 inch PVC pipe that has both the fiber and the 4AWG strands.
I would not worry about OM5 steel jacket interfering with power. You would need to pass some pretty insane current there to generate enough magnetic field for it to make a difference (ie for the jacket to heat up and melt the fiber)
 
But if the brains here don't think it's an issue, I'm putting it right next to the power cable. I do not want to be driving over that trench any more than I have to. It looks like a 600 foot long grave to me.

Although the power cable to the side that isn't yet installed in it looks pretty nice in forest in the middle of nowhere... Now I just hope I can get it in the trench before a black bear comes to investigate it with it's teeth and claws as they like to do.

forest cable.JPG
 
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The wife just called Discount Low Voltage . com and talked to somebody who said the fiber can't be right next to the power because of the metal jacket. Says he doesn't know the distance it needs to be separated but thinks it's 18"...

He referenced Article 330 of NEC.
 
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up.codes

Metal-Clad Cable: Type MC | UpCodes

Explore a searchable database of US construction and building code. Code regulations are consolidated by state and city for easier navigation.
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What specifically is an issue? The only way to be 100% sure is to talk to someone who has been dealing with this very specific issue. I doubt a sales guy would know.
 
aenyc said:
up.codes

Metal-Clad Cable: Type MC | UpCodes

Explore a searchable database of US construction and building code. Code regulations are consolidated by state and city for easier navigation.
up.codes up.codes

What specifically is an issue? The only way to be 100% sure is to talk to someone who has been dealing with this very specific issue. I doubt a sales guy would know.
Click to expand...

That's what I asked the wife. I said "what problem is this supposed rule trying to avoid?" He didn't say.

There might be a need to ground the fiber optic cable since it has a metal jacket. But, that doesn't mean they can't be buried together I don't think. We're inclined to just put them next to each other and call it good and ground the fiber cable if the electrician thinks that needs to be done.
 
AlaskanNoob said:
The wife just called Discount Low Voltage . com and talked to somebody who said the fiber can't be right next to the power because of the metal jacket. Says he doesn't know the distance it needs to be separated but thinks it's 18"...

He cited Article 330 of NEC.
Click to expand...
Ah.. I'm not an expert in NEC.. but its not a signal or power issue.. its a safety issue if the power cable gets damaged it could electrify the optical cable's shield.
 
I do not pretend to be an expert on NEC specifics, but based on what i saw in 330 it doesnt seem that would even apply as your fiber is a "no voltage" cable.... They have 2 separate rules for <1000V and >1000V, but this whole fiber thing seems to me like its own thing.
I think there are very few people who know NEC applications to these exact parameters. Most licensed electricians have no clue here (NY/NJ) about anything above the most basic.
 
MurphyGuy said:
Ah.. I'm not an expert in NEC.. but its not a signal or power issue.. its a safety issue if the power cable gets damaged it could electrify the optical cable's shield.
Click to expand...

That makes sense to me. But I think we're okay with taking that risk. The power cable would have to be damaged at the spot that the fiber cable just happened to be touching it, I would think. In a 6-9 foot trench filled with sand. Seems like a manageable risk to me.

Then again, I am clueless. And we have earthquakes frequently. And frost heave although it shouldn't get down that far and the soil is pure sand down there so good drainage.
 
AlaskanNoob said:
That's what I asked the wife. I said "what problem is this supposed rule trying to avoid?" He didn't say.

There might be a need to ground the fiber optic cable since it has a metal jacket. But, that doesn't mean they can't be buried together I don't think. We're inclined to just put them next to each other and call it good and ground the fiber cable if the electrician thinks that needs to be done.
Click to expand...

Ground the cable? If its in the ground, its already grounded is it not? (If its direct burial, or does it have additional insulation on the sheathing?) Again its a fiber cable that carries no current, but with so many regulations these days, i guess the bets are off. The only people who would know for sure is someone like the Telco who deal with it every day.
Personally i see no electrical/interference issues.
 
aenyc said:
Ground the cable? If its in the ground, its already grounded is it not? (If its direct burial, or does it have additional insulation on the sheathing?) Again its a fiber cable that carries no current, but with so many regulations these days, i guess the bets are off. The only people who would know for sure is someone like the Telco who deal with it every day.
Personally i see no electrical/interference issues.
Click to expand...

It does have sheathing outside the metal, so it's not touching the ground. But I don't see that possible grounding issue as a reason why the two cables can't be next to each other.
 
Had to read this again.

So no, there is no interference issue but you can't have a conductor in the the same raceway. The metal armor is conductive so you would have to use the non-metallic armored cable.

Now with that said, you're not in conduit so I don’t know what the rule is for Alaska.

I would tell you though, put the fiber in conduit. Its going to get damaged if you don't.

Also ask @timselectric see if he knows
.
 
AlaskanNoob said:
That makes sense to me. But I think we're okay with taking that risk. The power cable would have to be damaged at the spot that the fiber cable just happened to be touching it, I would think. In a 6-9 foot trench filled with sand. Seems like a manageable risk to me.

Then again, I am clueless. And we have earthquakes frequently. And frost heave although it shouldn't get down that far and the soil is pure sand down there so good drainage.
Click to expand...
Don't lay them right next to each other.. put in an inch or two of dirt/sand, then lay down the other cable. You maintain a lot more safety that way.
 
Checkthisout said:
Had to read this again.

So no, there is no interference issue but you can't have a conductor in the the same raceway. The metal armor is conductive so you would have to use the non-metallic armored cable.

Now with that said, you're not in conduit so I don’t know what the rule is for Alaska.

I would tell you though, put the fiber in conduit. Its going to get damaged if you don't.

Also ask @timselectric see if he knows
.
Click to expand...

It's direct burial fiber cable with a steel jacket that is causing all this annoyance, so if that doesn't keep it from getting crushed without conduit, so be it. I'm not adding 600 foot of conduit for a direct burial, steel jacket, fiber optic cable that is supposed to not need it.
 
AlaskanNoob said:
It's direct burial fiber cable with a steel jacket that is causing all this annoyance, so if that doesn't keep it from getting crushed without conduit, so be it. I'm not adding 600 foot of conduit for a direct burial, steel jacket, fiber optic cable that is supposed to not need it.
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Point taken BUT

If your soil is glacial till like ours (lots of river rocks) then I would bite the bullet and ruin conduit.......get the 20' sticks from a professional supply house to make it easier............It's only 30 sticks!

All the new power installs around here require 3" conduit for the feeder. No more direct bury!
 
AlaskanNoob said:
That's easy enough to do. I can do that with a shovel without going back and forth with the excavator and risking collapsing the trench.
Click to expand...

Yeah. So you can bury the fiber well above the power. It need not be so deep so long as you're not driving on it.
 
Checkthisout said:
Point taken BUT

If your soil is glacial till like ours (lots of river rocks) then I would bite the bullet and ruin conduit.......get the 20' sticks from a professional supply house to make it easier............It's only 30 sticks!

All the new power installs around here require 3" conduit for the feeder. No more direct bury!
Click to expand...

Our soil is straight up sand. Rocks are very rare. Clay on top for a foot or two, then pure sand.
 
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