Power, cat 5, Coax & phone in the same trench? (1 Viewer)

[RavenTai]

Edit, Resolved everything working well.







I am trenching everything to a new building, 100 amp 220v service in 1 1/4" PVC conduit 18" deep, 120' run

In 1" conduit I am going to run 2 RG6, 1 cat5, and a phone line, run is about 150', 100' in the same trench with the electrical, only the cat5 will be live, the rest are for "if I need it" future use, If they ever turn on the DSL back here (fiber was run years ago) the phone would be use for that, the coax for cable tv and internet (if we ever get that) or satelite TV.



I am pretty sure all the low voltage stuff will play nice with each other, the coax is shielded and the other two are twisted pair, what I am not sure on is how much distance I will need from the power line, I am hoping I can just put the low voltage stuff 6" above the power, is soil a better EMi shield than air or does it have the same distance requirements?

 

[Koffer]

when they are running the stuff around here in common trench gas goes on one side of the trench and the rest on the other (phone, cable and electric right next to / on each other .
You'll be fine

 

[Ebag333]

I haven't had problems running phone/coax/cat-5 directly next to power, but I've never done that next to 220 (only 110) and never that long of a distance. Running them 6" apart should be just fine though, as Koffer says.


Hmm, I did find this however...

Cat5 cable run near a 220v power line : lines

Northern Telecom IBDN User Manual contains an Appendix D titled _UTP Separation Guidelines From EMI Sources_. The values are the same as the cabling pathways standard, EIA-569, table 4.8-5.

Minimum Separation Distance from Power Source at 480V or less
CONDITION
<2kVA 2-5kVA >5kVA

Unshielded power lines or electrical equipment in proximity to open or non-metal pathways
5 in. 12 in. 24 in.
(12.7 cm) (30.5 cm) (61 cm)

Unshielded power lines or electrical equipment in proximity to grounded metal conduit pathway
2.5 in. 6 in. 12 in.
(6.4 cm) (15.2 cm) (30.5 cm)

Power lines enclosed in a grounded metal conduit (or equivalent shielding) in proximity to grounded metal conduit pathway
- 6 in. 12 in.
- (15.2 cm) (30.5 cm)

Transformers & electric motors
<------- 40-in (1.02 m) ----->

Fluorescent lighting
<------- 12-in (30.5 cm) ---->

Source: Integrated Building Distribution Network (IBDN) User Manual - Northern Telecom, doc # IBDN-UM-9105, 1991.

 

[RavenTai]

hmm, 100 amps of 220 is 2.2KVA, If I am reading that right that puts me just barely in the 12" group

Reality is I'll probably never actually have 100amps so I should be OK with 6,

thanks for the info, I may make my trench a bit deeper in the morning, maybe put the power at 24" and the data conduit at 12" just to be safe, I was going for 18" as that is the minimum for power service in conduit according to the county,










Edit er wait thats 22KVA, making for 24" acordign to that chart holy crap.

 

[fj40charles]

I would use a 2" PVC conduit. 1.25" conduit is pretty small and you will not have a good time pulling the wires.

 

[kiwidog]

x2 on the 2" conduit.

Thanks jb

 

[retrofive]

Use shielded cat5. Trust me. If you don't trust me then trust my Fluke.

 

[RavenTai]

The 1 1/4 was a PITA, I had to pull it through the straight part than put on the elbows, it was the only size they had enough of to make the run.

I am running regular cat 5, I already have a spool of it.

 

[fj40charles]

The 1 1/4 was a PITA, I had to pull it through the straight part than put on the elbows, it was the only size they had enough of to make the run.

I am running regular cat 5, I already have a spool of it.

I'm sure it was a REAL PITA pulling wires. What size wires did you use for 100amp service?

 

[RavenTai]

The hots are #2, neutral and ground #6, aluminum.

 

[fledglingme]

bite the bullet and pull ALL your low-v wires in at the same time. pulling additional wires after others are already there, makes the job really interesting.( if not impossible) #2 aluminun xhhw is a mite small for 100 amps with 100 foot run.

 

[LAMBCRUSHER]

The hots are #2, neutral and ground #6, aluminum.

Sorry to tell you this now, but, your neutral should be the same size as you current carrying conductors- especially w/ aluminum. #6 al is only rated at 50 amps, the #2 is rated at a hundred. Typically, in Cal, we are supposed to provide a foot of separation from the utilities in a trench. You wont have any trouble sharing that ditch and keeping 6" between them. X2 on pulling ALL the wires at once thru the conduit. I think the #2 al will be fine for the 100 amps- it's the neutral that has me concerned.

 

[RavenTai]

Sorry to tell you this now, but, your neutral should be the same size as you current carrying conductors- especially w/ aluminum. #6 al is only rated at 50 amps, the #2 is rated at a hundred. Typically, in Cal, we are supposed to provide a foot of separation from the utilities in a trench. You wont have any trouble sharing that ditch and keeping 6" between them. X2 on pulling ALL the wires at once thru the conduit. I think the #2 al will be fine for the 100 amps- it's the neutral that has me concerned.

Is that code natioonwide? That is what the electrical suply house sold me for 100 amp service, I would asume they know their buisness but you know what asume does,

The neutral only has to carry the unballanced portion of the load so smaller makes sense to me,

 

[fj40charles]

Is that code natioonwide? That is what the electrical suply house sold me for 100 amp service, I would asume they know their buisness but you know what asume does,

The neutral only has to carry the unballanced portion of the load so smaller makes sense to me,

Best bet is to contact your city to find out the electrical requirements. Many cities have more strict electrical codes than NEC.

I've never heard of the neutral being smaller size. Only the ground wire is smaller than 2 hots and neutral.

Looks like 2 gauge aluminum wire is good for 90 amps at 75 degrees Celsius.

Ampacity Charts

 

[Ebag333]

Looks like 2 gauge aluminum wire is good for 90 amps at 75 degrees Celsius.

Ampacity Charts

Wouldn't it be even less than that, since ground temp is going to be closer to 50-55* C than 75* C?


On the neutral being smaller, I found this which was useful:

It is easiest to understand using a normal house load. Your neutral sizing would start with the answer from your demand load in sizing your house panel minimum size. Then find the load of the A/C unit. This unit uses no neutral load. You can subtract that amount directly from the demand load answer you started from. Then your water heater also if 240 volt electric uses no neutral. If you have a water 240 volt pump it also uses no neutral load. Be careful with these loads concerning nuetral reduction. If you did a demand load calc and you had more than 3 fastened in place loads and used the 25% reduction allowed for more than 3 fastened in place appliances you would be limited how much to reduce on the water heater or water pump. Essentially if you used the 25% reduction already in sizing the hot wires then you can only reduce the neutral size loading by 75% of the water heater or water pump.

The range and dryer uses both 120 volt loads and 240 volt loads thus the reason for the statement of the 70% reduction only on those loads.

Most often an inspector will not react requiring a demand load calculation on a house if the neutral size is only reduced one or two sizes as a rule of thumb. Check with your local inspector for a ruling before you reduce in size without using a neutral demand calculation to do so.

Now the above is related to a house. Notice that SueMarkup quoted that you can not reduce the neutral size smaller than required in 250.66. This NEC rules sizes the minimum grounding electrode conductor for your service. The reason this is stated in the NEC is commonly found in industrial and commercial wiring. Example if you had a machine shop with only lighting and a few convenience receptacles and all other loads are 240 volt motors there would be a large service size required for the hots but having only a few lights and a few receptacles demand very little neutral loading in amps due to all the rest of the shop loads being 240 volt. You can easily find in this type building a 600 amp or lager service but less than 60 amp load on the neutral. Then you can find your neutral demand load sizing to be smaller than 250.66. Then the NEC says do not reduce in neutral size smaller than the required grounding electrode size.

The whole thread has some good info.

http://www.selfhelpforums.com/showthread.php?t=18157

 

[LAMBCRUSHER]

I can't think of the article in the nec, but I would never use a smaller size neutral-in ANY circuit-than the current carrying conductor(s) UNLESS the current carrying conductors were oversized for the overcurrent protection (breaker or fuses) in that circuit. I would always size the neutral AT LEAST big enough to meet the ampicities for the overcurrent protection. I believe I was corrected about ampicity of #2 aluminum. I believe Charles is correct, it is 90 amps for aluminum. #3 copper could also have been used




In this situation, I would ask if you were planning on getting inspection? All may not be lost...is this a separate structure?

 

[RavenTai]

I have a sheet from the county building department showing "service conductor size" as #2 aluminum for 100 amp service. It does not specify neutral sizing one way or the other.

I went back to the electrical supply place today, asked them about the neutral leg, they say the undersized neutral is how its done here, if you want full size neutral you have to special order it. they are not in my county instead the next county over, though there is no other electrical supply in the area so if my county had different rules I would think they would know. I am committed as the run is almost done, just have the last few feet to a new sub panel, It sounds like that is how its done here so as long as the building inspector is happy i'll let it be.

This is a separate building in the sense that it is a sub panel fed from the main panel mounted the power pole,

 

[LAMBCRUSHER]

Good luck!

 

[Koffer]

Thats some weird stuff there
When I did my garage I ran the neutral and the hots all the same size.
When you are running 110v the neutral is the other half of the ckt .

What do they mean that they have to order it ? is it a bare line with no insulation covering ?
I just got the same stuff as the hots and wrapped/marked the ends for the neutral where it stuck out and hooked to the meter, weatherhead and panel with white tape .

I read your sheet as all the conductors are to be 2/0 meaning the both hots and neutral .


Id have them come out and inspect it before you go and bury it

 

[RavenTai]

When you are running 110v the neutral is the other half of the ckt .

Right but 220 loads do not use the neutral, that comes off the size requirements of the neutral.


Also I think but I am not certain tha ballanced 110 loads do not use the neutral either, in other words if I have a 75 watt lamp on one hot leg and a 100 watt bulb on the other hot leg the net load on the neutral from the main pannel to the sub pannel is only 25 watts.

What do they mean that they have to order it ? is it a bare line with no insulation covering?

The 4 wires come pre bundled on a spool you buy the 4 together by the foot. The hots are black the neutral black with a white stripe, the ground green, all 4 are insulated, only bare I have is a #4 for the ground rod and the bares in the romex branch circuits.