I'm setting up a trailer pad at home and will be running service to a load center for the trailer and additional power to back yard area (about 100'). My only question to resolve is the proper way to set up the ground at the load center pedestal. I'll be setting up a 50 amp 240v service using this panel https://www.amazon.com/gp/product/B00A8FQUYW/
If I read the comments below by these experienced electricians correctly then
I should bury an additional ground conductor (ECG) i.e. a 4-4-4-4 and not bond the neutral to ground at the load center but connect ground of load center back to the main service panel with the additional conductor.
I wonder if in additional to that it would be prudent to set a ground rod at the pedestal and tie that to the same unbonded ground of the load center as well. Or is that overkill or simply ill advised?
If you have some experience with this issue would appreciate your thoughts.
Jim, Take a look at 551.76. RV Pedestals SHALL BE GROUNDED by a
continuous EGC run with the feeder conductors for the pedestal row.
551.76 (C), The neutral SHALL NOT be used as an EGC. Having said all of this, ground rods at each pedestal would not be required, however
after much investigation, in California for some reason, the AHJ wants
ground rods at each pedestal and NO EGC run with the feeders. No
matter which method is used, the neutral is not grounded or bonded at
the pedestals.Name: Wayne Foster Email: hurk27@attbi.com Location: Indiana Title:
Electrician In Trade Since: 1976 Registered: Jan 2002 Total Posts: 768
posted November 15, 2002 at 01:12 AM Edit/Delete Message "the
AHJ wants ground rods at each pedestal and NO EGC run with the
feeders. No matter which method is used, the neutral is not grounded
or bonded at the pedestals."Talk about a dangerous setup if a appliance were to go to ground the
earth would not provide a low enough impedance path to trip a 5 amp
breaker!!! and the whole RV would be hot to earth!! could you imagine
what would happen if a elderly couple touch the door and fell dead.
guess whoo they would go after? the installer not the local AHJ.80.29 Liability for Damages. Article 80 shall not be construed to affect the responsibility or liability of any party owning, designing,
operating, controlling, or installing any electric equipment for
damages to persons or property caused by a defect therein, nor shall
the _____ or any of its employees be held as assuming any such
liability by reason of the inspection, reinspection, or other
examination authorized. “`
Best Answer
The answer is "electrician in trade since 1976". In 1976 a 3-wire groundless connection was legal. Certainly not today.
Even a 1976, a separate neutral and ground wire was an improvement. He made it sound like the AHJ would prohibit it, seems unlikely.
Today, belt and suspenders is mandatory. All sub panels must have ground and neutral brought separately, with separation in the sub panel. And then, an outbuilding or other off site location needs a separate ground rod.
And unless the ground rod tests to 25 ohms, it needs two ground rods. Unless you have the equipment, testing is more expensive than driving a second ground rod.
If you're in conduit, use THWN or XHHW. It's cheaper.
if the conduit run is continuous, don't choke cable down it, use individual THWN or XHHW conductors. Your neutral can be smaller and your ground can be much smaller.
For instance I just priced 2/2/4/6 in XHHW and it was $120 for 100 feet. I don't see any 2/2/2/4 URD or anything out there at that price.
Mind you I got these prices by calling my local electrical supply house: trying to buy wiring on the Internet doesn't really work. Too many prices are sucker prices, or lowball but "gee, we're out of stock but thanks for joining my email list" prices, and then there's shipping to contend with. There is also junk imported from far-east places that use US wire sizes. You don't want that. US big-box stores don't have any selection. Proper electrical supply houses aren't online, these things have a very low price-to-weight ratio, so selling online is a fool's game.
Why URD is not a good fit for feeder
Feeder, service lateral and distribution are three separate and different things. Your location is on your side of the meter, which makes yours feeder.
Power companies follow a completely different and more liberal code. They are allowed to use AA-1350 aluminum, it was designed for power transmission and distribution after all! URD is intended for distribution (pole to pole) or service lateral (pole to demarcation point which is before the meter) and that is abundantly clear:
Now if you selected this cable because of these wild ampacity ratings like 120A for #4, that doesn't work at all. You need to use NEC rules for determining ampacity. For instance #4 Al has the same ampacity as #6 Cu, only good for a 60A subpanel.
So why does groundless 2/2/2/4 URD exist? For service laterals for three-phase wye service, hot-hot-hot-neutral, either wye or wild-leg delta. Why does Home Depot sell it? Because it sells. Given how bad their help is, I'm sure a lot of what they sell is misapplied, or wasted when the inspector catches it.
Also, the cable does not have a ground wire. People look at the yellow striped smaller wire and go "that's the ground because yellow is kinda like green". No, it's the neutral. It's legal to remark #4 or larger wires, so it would need to be marked with green tape to make it a ground, and a hot conductor would need to be re-marked with white tape to be neutral. I bet almost nobody does that.
A fair bit of googling reveals many claims that URD is not legal inside any home. The claims are that NEC doesn't mention URD so it's not a proper wiring method. That does make sense.