Replies

1. 
   Steve1 | Mar 18, 2003 02:16am | #1

   around here hydro is buried at least three feet in either direct burial cable or conduit, but phone and cable are just trenched in at 6-12 inches with no conduit

   im no electrician but burying all of them together sounds like trouble to me

2. 
   4Lorn1 | Mar 18, 2003 02:17am | #2

   We usually use 2" PVC for the telecommunications lines. If it seems reasonable we pull in 3 sleeves into this to make it easier to load and change out the various lines. Sometimes the telephone, cable and net people sometimes don't play well together and each wants a separate sleeve.

   The conduit size for power depends on two main factors:

   The size (wire gauge determined by a load calculation), make up (copper or aluminum) and type of conductors (compact or not) and the insulation type used determines the minimum conduit size per the NEC. You may wish to go larger on long runs to make pulling easier.

   The other main factor is what the utility and/or inspectors want. Some want 2-1/2" PVC regardless of the cable size pulled. A few demand 3" others are more flexible. Check with the utility and/or the inspection department.

   There is one more consideration. Upsizing the feed can, assuming you use a lot of power save a bit of money and may also allow for any additions to the house or increased need. Upsizing the conduit size in anticipation of needing a larger feed is cheap and makes upsizing the feed as easy as pulling in new cables. You waste a run of conductors but save the trenching labor and the lawn. If you are sure that the larger feed will be needed it may be cheaper, in the long run, to go ahead and upsize the conductors also. This would save the cost of a second set of conductors.

1. 
   Jeff | Mar 18, 2003 02:29am | #3

   Speaking of up sizing, a question (not to hijack the thread)

   I have a shop with a 2" conduit to it.

   It has 3 no. 6 guage wires (a 50 amp circuit) to it.

   I want to pull an additional 3 no. 2 guage wires in for a second

   larger panal (keeping the first installed for what's on it now).

   Will it work?

   Code say's I have the room in the conduit, but I worry it might be too tight.

   Any thoughts?

   Jeff

1. 
   migraine | Mar 18, 2003 05:12am | #5

   From My previos understanding of the code, and this was a few tears ago, you must run each set of wires in different conduits, not the same.  I believe this is to keep you away from mixing up each set of wires. You shoud also be able to run parrallel feeds and reconnect them in the same box, as lond as the main panel and sub panel can accept hight amperage loads- In other words, you cam run 2 complete sets of small guage wires in place of larger guage wires.  I don't recall what the correct wires sizes are for parrellel wires.  If this isn't correct(Ibelieve it is) someone  my be able to explain it better

1. 
   briank | Mar 18, 2003 08:02am | #6

   use your spellcheck

1. 
   migraine | Mar 18, 2003 06:57pm | #8

   Hey, when in a hurry... that is what you get 

   If you can't read it, oh well

   If you want to criticize some thing, criticize my input, not my spelling

2. 
   LeeSorenson | Mar 19, 2003 12:23am | #9

   Good on you migraine!!!

   I don't know if your answer is correct but I like your response...

   Lee

2. 
   CPopejoy | Mar 19, 2003 05:50am | #10

   First, ART:

   This is between you and the utilities.  In my area, they want 24" between the power and other conduits and will accept 18".  Also as to size, up to 200 feet my poco will run a 200 amp lateral in 2" schedule 40.  Two things they require are steel sweep elbows at the turns (the wire tends to cut through the PVC elbows during the pull) and, where the conduit is above grade, like where it runs up the pole, schedule 80 pvc.

   And Jeff in Vermont:

   I suggest you check out the Code and talk to your local permitting agency/inspector.  The Code prohibits having more than one "service" to a building, for safety reasons.  While the two feeders you're proposing are not services in that they are not supplies from a utility, I strongly suggest that you NOT run two feeders to the building.

   Imagine a firefighter trying to cut power to the building before starting an interior attack--he or she finds one panel, shuts off power, and thinks they're safe.

   Why would you want two separate feeders to the building?

   And if you're going to do it anyway, I suggest that you pull out the existing conductors and pull in all at once.  Too much chance of damaging the insulation, pulling in new when old are in the pipe already.

   Cliff

1. 
   caseyr | Mar 19, 2003 07:19am | #11

   Since I am too deaf to talk to the electrical inspector on his cell phone, getting information from him is a real challenge.  I know I will need his OK before proceeding, but for thinking purposes I am curious about what the situation is for using "smurf" tubing for running electrical underground.  I need to make a long sweeping curve around some oak trees to get to where I am building my shop.  Can't cut down the trees.  I don't know how well sched 80 would work for a continuous 100 foot radius curve.  Smurf would be easy to lay, but I don't know if it is rated for that kind of use. 

1. 
   UncleDunc | Mar 19, 2003 08:31am | #12

   I went Googling and found one site that said the minimum bending radius for PVC water pipe is 300 times the OD, but couldn't find anything addressing conduit.

2. 
   fireball | Mar 19, 2003 03:04pm | #14

   Casey,

   "Smurf tube" or electrical nonmetallic tubing can't be direct buried in earth(NEC362.12(5)).Underground you should use schedule 40,then schedule 80 above grade.You just need a pvc conduit heater"hot box" and the pipe will easily bend to the radius you want.Don't overheat it or the walls will collapse.We often use stell 90's also.

   Barry

3. 
   BillHartmann | Mar 19, 2003 04:37pm | #15

   "Smurf" tubing is the blue corrugated tubing and can't be burried.

   You could use liquid tight flexible non-metalic. But I think that just using the ridgit would be better. Get one stick and see how much it will bend. If that is not enough then you can heat and bend it.

2. 
   Jeff | Mar 19, 2003 02:53pm | #13

   Hi Cliff

   Problem around here is that we don't have inspectors for residential

   housing only a very few and far between for commercial.

   They usually leave it to the electricians to do it right.

   The wires would all go thru one panal in my shop, so no problem with

   the local fire chief (I might add that he helps me with my construction projects and knows my place well.)

   My electrician friend said it would probably work fine, but also

   wanted to just put one feed in and remove the old completely.

   He asked the same question, why?

   Right now, I have a 100 Amp panal and a 50 Amp panal connected

   together, with a #6 feed (50amp) feeding boths panals from the main

   house.

   Up to now, I only used the panals to give me enough breaker space, as

   I like to wire direct to my equipement and each wall with alot of

   outlets to prevent any chance of overload.

   I've recently upgraded to a large cyclone dust collector and a 5hp

   cabinet saw.

   If my compressor kicks in with everything running, I will probably

   pop the main breaker. I've been careful up to now, but feel that

   I don't want this problem.

   Since I have 2 panals, I can do one of 2 things.

   Pull in a 100 amp feed for both, or pull in a 100 amp feed for 1 panal and keep the 50 amp for the other.

   Seems to me that I have less chance of overload on future upgrades

   and improvements with the extra amperage.

   Can you see any real problem with this? Any reason I shouldn't do this upgrade. The only catch in the whole thing is I don't want to

   dig up and re-bury my underground pipe.

   Your thougts or anyone's would be greatly appreciated.

   I have a few months till I do this (the snows still thick on the ground here and its not worth the hassle till it melts.)

   Anyone?

   Jeff

1. 
   BillHartmann | Mar 19, 2003 04:44pm | #16

   You can have upto 6 main disconnection in the building as long as they are in the same area, so that is not a problem.

   But, without checking it, I think that you can only have one circuit from the house to the outbuilding. Similar reasoning that you want to make sure that power if off when working on it.

   Here is what I would suggest. Pull out the existing wire and size the replacement for 150 or even 200 amps. Keep the current pannel setup, but change feed breaker in the house to 100 amp.

   That gives you an immediate upgrade.

   Then if you need more power in the future you can either replace the 100 amp pannel or add a new 200 amp pannel. Use the new pannel to feed both the 100 amp and the 50 amp (separatelty), plus any new circuits. Then you can replace the house breaker with the appropriate 150 or 200 amp.

3. 
   Megunticook | Mar 18, 2003 04:08am | #4

   Art,

   I just buried my utilities 850 feet, and here's what I did based on NEC and local power company requirements:

   Power is in 2 1/2 inch conduit. This must be at least 12 inches from other communications conduits in the same trench (note--I ran primary to a transformer because of the distance--the required distance for secondary is 6 inches, I believe). Must be at least 36 inches deep.

   Phone and cable each have their own 2 inch. You could put them together, but it makes pulling and maintenance easier if they're seperate. There is no distance requirement.

   Be sure to talk to your power company before making any final decisions.

   Ed

4. 
   kbd | Mar 18, 2003 12:56pm | #7

   Art,

      Just buried my utilities for the same reason. All inspected, 110 feet.  200 amps. 2.5 inch pvc for electrical, and two 1 inch pvc's for phone and cable. All in same trench, next to each other, minimum 2 feet deep. They had to be surrounded by sand with yellow caution tape on top of sand. Have no interference on phone, have yet to hitch up cable.

5. 
   C1802362 | Mar 22, 2003 12:13am | #17

   Thanks everyone for the info - Art

1. 
   TooManyTools | Mar 22, 2003 02:57am | #18

   Got a similar question.  I'm putting #2Cu THHN in 1-1/2" conduit 65' to my garage.  I'd like to put a 3 way #12j switch leg in to control a yard light on the garage from the house.  Can I legally put it in the same conduit.  NEC fill table say it is ok.

   Edited 3/21/2003 8:27:42 PM ET by JANATION

1. 
   CPopejoy | Mar 22, 2003 05:55am | #19

   Yep.

1. 
   4Lorn1 | Mar 22, 2003 06:12am | #20

   yes. Other conductors can be added but...

   Don't forget to derate the conductors for the number in the conduit and also remember that the neutral and hot have to follow the same path. So your going to have to add at least two "current carrying conductors. This is two plus the number already in the conduit. The derating factor for 4 to 6 conductors is 80%. So the conductors are only allowed to carry 80% of the rated ampacity.

   This could mean, depending on the situation, that you have to up size the existing conductors which might mean that there will no longer be enough room in the conduit. The specifics determine the outcome.

   All of this assumes that there are not any portions of the conduit that go through areas at raised temperature. This could lead to the dreaded double derate of doom.

1. 
   UncleDunc | Mar 22, 2003 08:16am | #21

   So if you think you might ever want to add more conductors, put in 6" or 8" pipe right from the start.

2. 
   MajorWool | Mar 22, 2003 09:26am | #22

   Might be easier to use an X10 switch in the house to control the garage light. Just need to be sure that both are on the same leg for optimum reliability. X10 is the nutz for some of these problems, and for problems where wire pulls are difficult.