50A rigs and wire sizing

[RVnRobin]

A post yesterday about a burnt neutral wire got me to wondering...
If;
A 50A rig has all 120v appliances and loads,
A 120v 10A load will measure the same amperage draw on both the hot side and the neutral side,
A properly wired 50A service will measure 240v from L1 to L2,
And L1 and L2 will each measure 120v to neutral,
50A load max on L1 and 50A max on L2,
The neutral is shared with both,
The load amps from each of the hot lines are additive on the neutral,
Potential load on the neutral wire could max out at 100A.

Question;
Why isn't the neutral wire at least a #2 as per the wire sizing charts?
Wouldn't cords need to be constructed with two #6 for each of the hot lines, one #2 for the neutral, and then the ground?
Is this why we see neutrals frequently have heat damage?

I'm not an electrician. I know rarely both L1 and L2 would run at max. But the amperage charts seem to be pretty clear about what "code" requires.

[Horsedoc]

I have been here for years and for years I have always marveled at how many "right" posts concerning wiring come up.
I have never seen a neutral breaker - not saying there is no such thing, but apparently there are a lot of folks that didn't pay a lot of attention like me.

[LittleBill]

mena661 wrote:
My RV.

and every other residential wiring design

i think our world is a little bit bigger then bob's

[mena661]

My RV.

[red31]

Bob Landry wrote:

Under your scenario, there should only be one breaker for a 30A input since the hot is protected.

Yes and one for 20A, two for 50A



I think wolfie was correct in suggesting the thread be closed!!!

[time2roll]

My home, apartment building, rental houses, workplace, is all wired with a solid neutral and breakers on the hots for split phase (single phase) service.
At the marina I don't know.

[Bob_Landry]

LittleBill wrote:

Bob Landry wrote:


Also, the reason we see so many burned neutral wires, aside from loose connections, is the wire is undersized at installation. Folks, neutral is a current carrying wire. That is why when you go to a breaker panel for a 50A systen, there are three breakers. All current carrying legs have to be protected. If you disagree, tell me where the current flows from to get to the hot wire when a device runs, it's not through ground. In a 50A circuit, the 120V is referenced to neutral. That means that at any given point in the cycle, the neutral has to carry the same amount of current as the hot leg so it has to be the same size wire. Why do you think that when you buy romex or marine wire for AC, the wires for hot(s) and neutral are the same size? It's not because it's easier to manufacture that way, it's because it's required to handle the current load.

well i guess someone had to be wrong, guess its bob

Bob, there are not 3 breakers for single phase 50amp/240v

there is no breaker for a neutral wire, there is no point since the hot side is protected

now on 3 phase 208v, there are 3 breakers but there is also another wire. i think this is where your getting confused

Nope, I guess if someone has to be wrong, it's you. In marine 50A shore power applications, the main breakers are three pole and ganged so that everything opens at the same time. ABYC requires it because neutral is a current carrying leg. Under your scenario, there should only be one breaker for a 30A input since the hot is protected. On the 50A panels that I work with, neutral is switched by a breaker and then goes to a buss that is common for all of the neutrals, but it is on a breaker where it enters and is distributed. Maybe it's different in your world.

[vermilye]

In RVs, most of the burned neutrals are caused by loose wires. Code does require full size neutrals for many applications. The biggest problem causing burned neutrals that I've seen reported is in 3 phase systems carrying lots of harmonic loads. Buildings full of computers have done some damage. NEC article 220.61 describes calculation neutral size. For those interested, this web page might be useful.

[LittleBill]

Bob Landry wrote:


Also, the reason we see so many burned neutral wires, aside from loose connections, is the wire is undersized at installation. Folks, neutral is a current carrying wire. That is why when you go to a breaker panel for a 50A systen, there are three breakers. All current carrying legs have to be protected. If you disagree, tell me where the current flows from to get to the hot wire when a device runs, it's not through ground. In a 50A circuit, the 120V is referenced to neutral. That means that at any given point in the cycle, the neutral has to carry the same amount of current as the hot leg so it has to be the same size wire. Why do you think that when you buy romex or marine wire for AC, the wires for hot(s) and neutral are the same size? It's not because it's easier to manufacture that way, it's because it's required to handle the current load.

well i guess someone had to be wrong, guess its bob

Bob, there are not 3 breakers for single phase 50amp/240v

there is no breaker for a neutral wire, there is no point since the hot side is protected

now on 3 phase 208v, there are 3 breakers but there is also another wire. i think this is where your getting confused

[SolidAxleDurang]

Bob Landry wrote:
..That is why when you go to a breaker panel for a 50A systen, there are three breakers. All current carrying legs have to be protected. If you disagree, tell me where the current flows from to get to the hot wire when a device runs, it's not through ground...

You lost me at the 3 breakers part. I have never seen a neutral breaker.

A properly wired 50 125/250 circuit for an RV (or any other 125/250 appliance for that matter) is fed by a 2 pole breaker - on the L1/L2 hots - that's it.

The neutral - although it does carry current... It is NEVER the source. It is only the return path.

[Bob_Landry]

SolidAxleDurango wrote:

RVnRobin wrote:
I hadn't thought of the effect of phase. Thanks for the info.
So, is it my imagination or do we really see more burnt neutral wires than hot wires? And, why?

It's not phase... Generally all power you are exposed to (at home, and in the RV) is single phase - 3 wire.

L1 and L2 are simply 180 degrees apart on the waveform.

And many people here just can't wrap around that. It's voltage that's 180 degrees out and that doesn't constitute two phase anything.. In a split phase system, voltage and current ar what is shifted out of phase and it's used in large commercial applications to run large motors under a heavy load.

Also, the reason we see so many burned neutral wires, aside from loose connections, is the wire is undersized at installation. Folks, neutral is a current carrying wire. That is why when you go to a breaker panel for a 50A systen, there are three breakers. All current carrying legs have to be protected. If you disagree, tell me where the current flows from to get to the hot wire when a device runs, it's not through ground. In a 50A circuit, the 120V is referenced to neutral. That means that at any given point in the cycle, the neutral has to carry the same amount of current as the hot leg so it has to be the same size wire. Why do you think that when you buy romex or marine wire for AC, the wires for hot(s) and neutral are the same size? It's not because it's easier to manufacture that way, it's because it's required to handle the current load.

[SolidAxleDurang]

RVnRobin wrote:
I hadn't thought of the effect of phase. Thanks for the info.
So, is it my imagination or do we really see more burnt neutral wires than hot wires? And, why?

It's not phase... Generally all power you are exposed to (at home, and in the RV) is single phase - 3 wire.

L1 and L2 are simply 180 degrees apart on the waveform.

[RVnRobin]

I hadn't thought of the effect of phase. Thanks for the info.
So, is it my imagination or do we really see more burnt neutral wires than hot wires? And, why?

[wolfe10]

Wow-- 100% correct replies (initial post incorrect) to a 50 amp wiring question!
Way to go!

Now, can we get this thread closed before "electrically challanged" answers posted?

[Chris_Bryant]

What they said- equal loads on each leg gives a neutral current of zero. This is why a 50 amp outlet *must* be 240 volts.