Yay! 50 amp Service upgrade - Done

[lewster]

Originally Posted by markdoane

You don't understand the basics of electrical safety. Please stop before you burn down your trailer.
Also, you should have bought a box with mains breakers, not a mains lug box. You are in way over your head.

YOU ARE WIRING AN RV.........NOT A HOUSE! There Are distinct differences tags you should be aware of before you proceed!!!!!!!!

[perryg114]

I think it would help if we talk about why what he did is wrong and educate everyone in the process. I am learning things as well. We all start out at incompetence and move up from there. Why not propose an an alternate schematic as well. I am going to do what he is attempting to do and I want to understand why one way is right and the other is wrong. If you know why something is the way it is then you are more likely to do it right the next time. Let's help him fix it right.

Perry

[Jammer]

Perry,

The problem with bonding the neutral and ground together in the trailer electrical panel is that it can lead to stray voltage on the shell.

A condition inherent to 120/240v wiring is "unbalanced load," that is, the situation where the load on the two "hot" legs isn't equal. Under these conditions, current flows in the neutral leg, equal in magnitude to the difference between the current flow in each of the hot legs. With RVs a similar situation results when a 30a-to-50a "dogbone" is used, because then the neutral leg carries the sum of the current flow in each of the hot legs (since they're in phase and not really two different legs as would be the case when plugged into a 120/240v, 50a shore power receptacle).

The large current flow in the neutral results in there being some voltage drop between the bonding point and the trailer electrical panel. This can be several volts. If the neutral is bonded to the trailer frame, then a person might get a shock from contacting the trailer frame and the ground at the same time.

While the ground connection does help with this in practice it will carry part of the neutral current and therefore have some amount of voltage drop itself. Ultimately this can create stray voltage for others in the campground.

It is a common fallacy that the neutral and ground wires are interchangeable among DIY electricians. Perhaps this is because, as late as 1980, ranges and dryers were typically grounded through the "neutral" conductor -- the continuation of an emergency measure adopted in 1943 to address the copper shortage during WWII. Or perhaps it is because, in farm and home wiring, ground conductors were undersized until about 1970, so that many electricians would use a neutral wire instead for grounding because it was larger.

In any case, the practice is dangerous, and should be avoided.

As an aside, the U.S. practice of bonding at both the transformer and the service entrance panel poses its own set of problems. A few countries omit one of the bonding points.

[Jammer]

Originally Posted by perryg114

Every electrical box I have seen has both the neutral and ground hooked to the same bus inside the breaker box. There is no other way to do it if you use a standard box.

Most breaker boxes intended for residential use only come with a neutral bus but accept a ground bar that is purchased separately. Most big-box home improvement stores sell ground bars for the breaker boxes they carry.

[Jammer]

Originally Posted by perryg114

Ok so why is it unsafe for the neutral and ground to be connected in a sub panel?

Here is a link I found on what the problem is.

Electric system neutral wire loss leads to shocked homeowner

I need to look at my shop wiring. Looks like I need to separate the blocks and also put in a ground stake.

It depends.

If your shop is fed from the electrical panel in the house, you should have a four-wire feeder. I believe that under most codes the ground stake is then optional although that may vary regionally or depending on year of construction.

If your shop is fed from its own meter, then the neutral should be bonded, and you need a ground stake or some other grounding electrode.

[Jammer]

Originally Posted by yve79

Why would I need two breakers? There is a 50 amp breaker right outside. The original box that I replaced did not have a main breaker either.

In general a main breaker is not required on a sub-panel if there are six or fewer breaker handles in the panel.

I don't believe that a main breaker is important, safety wise, in this situation.

[Jammer]

Originally Posted by TG Twinkie

I haven't used a 50 amp service at a campground, but I think you will find that only half of your panel will be hot. Since I believe it is wired thru a single breaker and not a double pole breaker, which is typically how the 240 volt wiring is done in your home.
The neutral and ground should not be connected together. The neutral should not be bonded to the trailer body. Only the ground should be bonded to the trailer body.

TG

It's supposed to be wired as a 240/120v circuit with a double pole breaker, and it usually is, and in most areas that's the way the code says it has to be.

I have heard of various dodgy wiring approaches, such as feeding both sides of a 50a receptacle from a single pole breaker, but have never encountered them in my travels.

[Melody Ranch]

Well, yesterday I thought I was doing OK. The electrical system was done and the next "to do" was being started. I put up a photo to show the new electrical system and my friend TOP sent a note to recheck the ground/neutral connection. Sure enough I had fallen into the same trap of using a standard Circuit breaker box and that suckered me into connecting the neutral and ground to a common buss in that box. This discussion sums it all up...I have the new buss installed. So far not shocked.

[TG Twinkie]

Thanks Jammer. Like I said, I've never used the 50 amp source. Seen the outlet in panels at CG, but didn't pay that much attention.
My guess would be if that the big rigs which require 50 amps went to a place that only had 30 amp and used an adaptor would only be able to use one A/C unit. Again, it's only a guess, since my rig is set up for 30 amps.

[TG Twinkie]

As stated above. An open neutral can be as much of a shock hazard as a hot wire. When a neutral is open, the voltage "stands" at the open connection. If you were to get between the open neutral and the point at which it connects to the neutral buss or earth ground, you would get shocked. If the open neutral wire were to come in contact with the trailer chassis and the chassis was not properly grounded. The trailer would become a shock hazard.
Of course the hot leg to the device would have to be powered. ie the switch closed to a light fixture etc..

[wmarsha]

one of the problems faced by anyone doing electrical work is the decades old usage of the word "ground." Today, there is "earth ground", a "multi-grounded neutral", a "grounding conductor", a conductor "bonded" to a "grounding conductor" or "grounding lug (connector)". My 1985 Airstream had a common neutral and grounding conductor bar. My 2000 has two separate bars; one for neutral conductors and one for grounding conductors-the grounding conductors and the neutral should be entirely separate. When connected to an RV park's pedestal, the RV receives a connection to earth ground via the park's AC system. If a separately derived prime source is used (a generator) then said source should have a driven rod earth ground connection, and the here-to-fore mentioned "sub-panel" in the RV now becomes a main service panel and the neutral of said panel should be bonded to the grounding bar within the panel. Now are you confused?
In DC systems, neither of the two leads required to operate a load are ground conductors, grounding conductors or bonded conductors. There is a battery lead, and a battery return lead. In sophisticated DC circuitry, there is a 3rd conductor which is indeed, a grounding conductor.

The confusion stems from the old(er) usage of 2 wire 120VAC circuitry & 3 wire 240VAC single phase circuitry, and 2 wire dc circuitry. Today, up to date facilities utilize 3 wire 120VAC circuits and 4 wire 240VAC single phase circuitry as well as 3 wire DC circuitry. AND, the extra conductor is a "grounding conductor" not "ground".

These terms (nomenclature) are found in article 100-Definitions of the 2011 National Electrical Code. The term "multi-grounded Neutral" is a Utility Power Source term used to define the neutral conductor in the Utility transmission systems.

[rogerdodger]

To sum it all up, for those of us still confused, can anyone put up a diagram of the correct wiring?

[TG Twinkie]

Just separate the ground and neutral buss'. Then connect the ground buss to the chassis with at least a #6 wire. Do Not connect the neutral buss to the ground buss or to the chassis.

[10Smiles]

OK, here's a picture. The line (red and black) should come in on a 240V bridged circuit as the main breaker (you can keep it on the bus bars, but this gives a bit more protection).


The neutral (white) connects to the "floating" bar, and the ground (green) connects to the bar that is bonded to the panel.

[perryg114]

Ok here is my version. In actuality the 50A breaker is installed in the breaker box and the power comes in with a different hot wire on each pole.

Perry