Outbuilding..water in trench [Archive]

Wgoodrich

October 27th, 2002, 11:15 AM

I am picking up that your concern is mostly water in the trench. This UF cable is approved in sunlight, in direct contact with earth and in wet location as well as corrosive location if you use a nonmetallic sheathed cable with UF markings. No problem laying the UF cable directly in the water in the trench. It is expected. However I have a concern of a few Codes you are not meeting.

YOU SAID;
I am running 10/3 UF w/ground out to my shed from a double 30 in my main panel in the house to a 6 place subpanel inside.

REPLY;
225.39.C ilmits a disconnecting means with a 30 amp capacity to a maximum branch circuits of 2 two wire branch circuits. You say you have 6 branch circuits 225.39.D would apply requiring your panel in that garge to be fed with a minimum of 60 amp capacity 6 awg copper or 4 awg aluminum feeder from the house to that detached garage if you have more than two branch circuits in that panel.
If you are using 6 branch circuits then your 30 amp wire is too small for this project. you need to install two hot conductors THWN 6 awg copper or 4 awg aluminum and on 10 awg or larger equipment grounidng conductor with that feeder if you install an equipment grounding conductor with that feeder. YOu must install the equipment grounding conductor with that feeder if you have a metal water pipe or other noncurrent carrying metallic path connecting the two buildings as per 250.32.B of the NEC requirments.

YOU SAID;
When I trenched in my wire I ran it in 1 1/4 PVC

REPLY;
THE 1 1/4 PVC conduit will easily contain your 6 awg wire or your 4 awg wire THWN. Remember to install a wire that has a W in the initials to confirm it to be approved for wet location as required in a trench.

YOU SAID;
about 6"-8" down

REPLY;
PVC conduit is required to be installed a minimum of 18" deep in a trench regardless if scedule 40 or schedule 80 PVC. Your trench is not deep enough.

YOU SAID;
with a 75ohm coax,

REPLY;
This 75 ohm coax is not allowed in the same conduit as the power cables. You must install this 75 ohm cable in a separate conduit from the power cable with a minimum of 6" clearance from the two condiuts involved.

YOU SAID;
when done the PVC was sitting in water not drained by the clay. Is that alright?

REPLY;
No problem as long as your conductor has an insulation with a W or a U in its initials. The W or U says it is approved to be wet.

YOU SAID;
The other question is, on your site you say I should pound a new grounding rod for the shed but in the forums says not to. If I use both a new rod and grounding from the main will that hurt anything?

REPLY;
250.32.A demands a ground rod to be installed. If you did not install a ground rod at that accessory buildings and install your equipment grounding conductor between the two buildings sized as required in 250.32.B.1 as an equipment grounding conductor sized by 250.122 and not a grounding electrode conductor sized by 250.66 then you would be violating 250.32.E. The NEC demands a ground rod at that accessory building regardless of whether there is an equipment grounding conductor installed with the feeder between buildings or not. The concern is to get a faulted current that is in excess of what the neutral conductors can obsorb such as lighteing into the earth as quickly as possible not carry that excessive faulted current into the main dwelling. I am not aware of the forums you are getting advise to not install the ground rod at the accesssory building but you might suggest they study the above rules mentioned that may shed light to them in their interpretations of the NEC, might help them catch up with the current rules of the NEC.

Remember in these forums people are providing what they believe to be accurate interpretations. Many times I have been corrected in my interpretations where I have been wrong in the past. This is the good product of forums to get differing interpretations. Elelctricians are a got to know profession. If questioned on their interpretation they will research on their own to find what they believe to be the NEC true intent. This is very common. No one is perfect when interpreting the NEC not even a person that could study the NEC for TWO LIFE TIMES, still wouldn't be enough time for a person to be without mistakes conecerning the NEC.

YOU SAID;
I know I am supposed to keep the neutral bar isolated from the new box, but I can't seem to find one with a neutral bar and a grounding bar in the same box.

REPLY;
Some panels require you to buy a accessory part that is an added grounding bar. Many panels are designed with a jumper bar connecting two bars one on each side of the panel connected by a removable jumper bar. YOu are expected to remove that jumper bar when separating grounding bar from neutral bar in sub panels and panels in shared service with an equipment grounding bar. Some panels have the jumper bar formed behind the buss bar where the breakers are installed. If you have this panel look on the lower left side for a set of holes to mount an accessory grounding bar that you must buy. If you have the jumper bar connecting two bars together that is exposed and below the buss bar removed by two screws removal then remove that jumper bar connecting the two bars then bond the separated grounding bar to the metal case of the panel and keep the neutral bar up on plastic isolated from that grounding bar and metal case of the panel.

YOU SAID;
Am planning three 15 or 20 amp circuts....1. two lights and a few outlets....2.a few outlets alone on one breaker for a compresser & table saw.....3.outside light and one outlet. Would it be smarter to just buy one GFI double 30 for in the house to cover it all??

REPLY;
The intent of GFIs are to protect each branch circuit on its own separate GFI protective device, not install a main GFI protective device.

I included copies of the NEC concerning the main rule that applies to your concern of the ground rod at the accessory building. Then added a rule that I was concerned about 30 amps where 60 amps is required. Hope they hellp;

COPIED SECTION OF 2002 NEC;

250.32 Two or More Buildings or Structures Supplied from a Common Service.
(A) Grounding Electrode. Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in Part III of this article at each building or structure shall be connected in the manner specified in 250.32(B) or (C). Where there are no existing grounding electrodes, the grounding electrode(s) required in Part III of this article shall be installed.

AND NEW IN 2002 NEC;
250.32
(E) Grounding Electrode Conductor. The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.

THEN MY CONCERN;

225.39 Rating of Disconnect.
The feeder or branch-circuit disconnecting means shall have a rating of not less than the load to be carried, determined in accordance with Article 220. In no case shall the rating be lower than specified in 225.39(A), (B), (C), or (D).
(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or branch-circuit disconnecting means shall have a rating of not less than 30 amperes.
(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.

Hope this helps

Wg