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rohit1

06:52AM | 06/20/05
Member Since: 06/02/05
7 lifetime posts
Bvelectrical
Hello,

I am installing outdoor outlets and would like to know the advantages/disadvantages of using #12 wire vs. UF wire to install under the lawn.

Should either be placed in PVC or can the be placed without PVC conduit.

Thanks.

tshea1

07:23AM | 06/20/05
Member Since: 05/03/05
79 lifetime posts
PVC conduit with #12 wire including the green (for grounding) is acceptable. Burial depth is 18".

Direct bury wire #12 UF is also acceptable. Burial depth is 24". IF using Column 4 of NEC Table 300.5 you may reduce burial depth to 12" if the circuit is rated 120 Volts or less with Ground Fault protection and maximum 20 Amps.

That means it you GFCI protect the wires you can bury them 12" deep.

As for the receptacle boxes: You will need to provide a means of support besides the piece of PVC conduit. If you use UF cable I recommend sleeving the conductor into the box to prevent damage to the wire.

What looks nice is mounting the box on a 4"x4" pressure treated post, with the top cut on an angle away from the outlet, or 4 bevel cuts, sunk into the ground about 18". The top of the post is above ground by about 12".

If you do not GFCI the wiring going to the outlets, then install a GFCI receptacle and feed thru to the next, or a GFCI at each location.

Don't forget to install the in-use covers. These are commonly called bubble covers.

If in doubt, contact a licensed electrical contractor in your area.

rohit1

07:27AM | 06/20/05
Member Since: 06/02/05
7 lifetime posts
Thanks for the info.

The feed coming from the house is 15 amp and GFCI protected. I have few questions.

1. Can the 7 outlets/light be on this 15 amp or does it need to be upgraded to 20 amps.

2. Which is better the UF or another cable.

3. IF GFCI protected, can either cable be used at 12" depth without PVC?

4. If I put GFCI on all 7 outlets would I face false trips?

Thanks for your help

tshea1

07:43AM | 06/20/05
Member Since: 05/03/05
79 lifetime posts
The feed coming from the house is 15 amp and GFCI protected. I have few questions.

1. Can the 7 outlets/light be on this 15 amp or does it need to be upgraded to 20 amps.

You should be OK as long as the "plug in" equipment does not total over 15Amps. Obviously (hopefully) the breaker will trip.

2. Which is better the UF or another cable.

UF is the best bet for residential direct buried cables.

3. IF GFCI protected, can either cable be used at 12" depth without PVC?

YES Only UF

4. If I put GFCI on all 7 outlets would I face false trips?

Are you saying to install a GFCI receptacle at each location or a single GFCI at the first outlet then continue?

Either method is OK. You may experience some false tripping if you only use 1 GFCI receptacle by the house. This is attributed to many things--voltage drop, humid conditions, capacitance in the wire, among a few.


Billhart

07:50AM | 06/20/05
Member Since: 04/25/05
1916 lifetime posts
#12 wire just defines the size of A WIRE. Does not denote anything about the type of insulation or the usability for any application.

The size of the wire depends on the load and the lenght of run.

UF is a type of cable; IE wires and a sheathing, designed for direct burial applications. It is availbe in different sizes and number of wires.

If you run conduit you need to use wire approved for wet locations. THWN is most common. Check the spools at the borg. While the sign might say THNN they are often dual marked with THWN.

If you run UF you can use conduit, but you don't want to. Too hard to pull and you need to use relatively large size to met the "conduit fill" spec.

However you do need to protect the cable where it is exposed. Run PVC conduit to under ground then just lay the cable in a trench.

In either case for homes you need to be 18" deep.

tshea1

09:38AM | 06/20/05
Member Since: 05/03/05
79 lifetime posts
Thanks Bill for catching some of the nuances and minor details that make a proper installation.

Billhart

10:20AM | 06/20/05
Member Since: 04/25/05
1916 lifetime posts
First of all before you start call you state utility locator service. It will be listed in the fron the phone book under Call before you Dig.

Different names like First CAll, Dig Safe, Dig Rite, etc. If you can't find it call any local utility and they will give you the number.

But they only locate utilities for their member companies. They won't show you things like a line to a yard light/post light, irrigation pipes or wiring, or down spout drain pipes. Or in my case the water and sewer for the very small city that I am in.

And then make a map of where you ran these line(s) and store it someplace that you will can find it again. And update the changes on the panel circuit schedule (and if it is now blank now is the time to start). One day you will be glad that you have done this.

But we both made minor errors. I stated that either one has to be 18" deep (excluding the GFCI case), but UF needs to be 24", only PVC can be 18" without GFCI.

And you indicated that the 12" GFCI exception was only for UF cables, but unless they changed it from 99 NEC that exception includes any legal wiring method.

And if it is run with UF 12" deep get some PT strips, old water pipe, rebar or something and lay it over the top of the UF, specially if this runs under a flower bed or near foundation plantings.

It is easy to cut through UF with a sharp shovel. DAMHIKT!

rohit1

10:27AM | 06/20/05
Member Since: 06/02/05
7 lifetime posts
Thanks a lot for the info.

To summarize:

The sheathed electrical cable feed comes from the panel via a GFCI protected outlet. I can now run UF cable without PVC at a 12" depth to all the outlets.

It would not matter if all the outlets are GFCI or standard since there is one GFCI it goes through in the basement. And yes, I will call OneCall!

I hope I got that right.

1. Why is UF better in this situation?

2. Should I put the UF in PVC where it is in plant beds or leave it as is both under lawn and plant beds.

Thanks


Billhart

10:46AM | 06/20/05
Member Since: 04/25/05
1916 lifetime posts
Better is relative.

While PVC conduit is easy to work with there are other details and technics such as know the number of bends that you have and how to fish wires.

I prefer PVC it because it is more adaptable in that you can repull wires and the like. But for a simple run to a remote outlet UF is probably simpler.

Yes, for protect in the garden area you can just cut straight sections of PVC and slide over the UF. Don't glue it because you don't want the PVC solvents to get on the UF.


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