Pulling more than 50 amps ?

Gonna throw my hat in before thread gets closed.

It is known as 120/240 SINGLE SPLIT PHASE & MULTI WIRE BRANCH SYSTEM, 3 "pole", 4 wire.

It is AC (Alternating Current), not DC (Direct Current).

AC allows the POCO to do something that DC can't, efficient power distribution over long distances.

I would recommend folks take a look at the "White paper" from Samlex which has a pretty good explanation of how this works.

Page 1 has a good diagram which may help explain things..

HERE

In a nutshell, L1 and L2 are 180 degrees OUT OF PHASE when referenced to the NEUTRAL.

In other words, if you froze time for ONE CYCLE, L1 would have a positive going voltage and L2 would have a NEGATIVE going voltage.

When the cycle is done, L1 now goes NEGATIVE going voltage and L2 would now be POSITIVE going voltage when referenced to the NEUTRAL.

For 120V you use a SINGLE "Pole" breaker.

For 120V/240V you use a DOUBLE "POLE" breaker (which is TWO Single pole breakers TIED TOGETHER so if one is overloaded BOTH are tripped).

30A 120V RV service uses only a SINGLE POLE BREAKER.

50A 120/240 RV uses a DOUBLE POLE breaker.

In a 50A 120/240 RV each side of the breaker supplies 50A at 120V before it trips (remember though each "pole" delivers a voltage that is the OPPOSITE of the other pole).

From there, things gets much more complex than what can be explained on a Internet forum.

hypoxia wrote:
On an RV that has zero 240 volt appliances is there a reason to have the tied 50 amp breaker instead of two separate 50 amp breakers?

The National Electric Code requires it.

One of the main reasons is so that the socket is completely de-energized when the breaker is switched off, rather than being left--possibly unexpectedly--partly energized and posing a hazard to someone who may be working on it. That's arguably less of a concern when the breaker(s) are nine inches away and in the same enclosure than, for example, when they're on a different floor of a house for the range receptacle, but the concept remains.

It's also best to cut all the power to the receptacle in the event of a fault where, rather by definition, it's not known what may be wrong and how dangerous it is. If a person mowing grass should happen to absent-mindedly chop up your shore power cord, it would be really good to shut off both legs even if only one happened to short out.

(As to whether it's a 100A service of any sort, I'll just ask this: is a semi truck with dual trailers, traveling at 50 mph, really a 100 mph truck because there are two trailers of 50 mph each?)

valhalla360 wrote:
I see a lot of supposed experts talking about amperage without specifying voltage...then calling the guy an idiot.

Without knowing the voltage, you can't answer the question.

Since there are almost never 240v appliances on an RV, we should logically assume the electrician was talking about amps @ 120v. In that case the total amps (regardless of which leg they come in on), can easily exceed 50amps.

Another wrong answer. He specifically said "big rig". And some of the high end rigs do have some 240 vac appliances. And a 240 vac appliance draws current thru the same main circuit breaker as the 120 vac appliances. The only difference is the 240 vac appliance draws current thru both poles of the breaker while the 120 vac appliances draw current thru only one or the other of the poles. So the total current flow thru each pole of the circuit breaker would be the total of the current drawn by the 240 vac appliances and by the 120 vac appliances. How much current is drawn by which voltage is irrelevant. It is the total current thru either pole that trips the breaker whether there are any 240 vac appliances or not.

*grabs another beer and another bowl of chips*

Last call before this one is closed

*grabs another beer and another bowl of chips*

MEXICOWANDERER wrote:
If at home
Go outside
Look at the gauge of cable servicing your drop. 100 or 200 amps AL.

50 Amos demands 6AWG CU. conductor.
It is a mere distance between your transformer and your service drop. Now look at how an RV Park is wired (shudder)

50 amp service does not demand copper conductors. Modern parks are most often wired with 4/0 4/0 4/0 direct burial aluminum with a #2 aluminum ground in a loop feed. (Note that the neutral is not allowed to be undersized in RV park applications). That is up to current code and works just fine.

wolfe10 wrote:
Drawing more than 50 amps on EITHER leg- tripped breakerS. They are duplex/pinned together.

No idea why this topic gets so much attention. BASIC MATH.

Not always pinned together. That can really (trip) your mind when you find one leg of the 50 amp missing and the post has one of the 50 amp breakers tripped.

Electronic Technicians, Electricians, are like artists. Very Very temperamental. You can't get two to agree on how to solder on a connector. :S I taught many techs over the years as well as owning my own electronic service business.

It is amazing how long a discussion like this last. I'm sorry that people get their feathers ruffled easily. There is some amazing talent here on this thread alone.

I'm not indicating that the quoted person here is ruffled. I just happened to digress on my point about the breakers not always being tied together.

TechWriter wrote:

Bobbo wrote:

wa8yxm wrote:

dougrainer wrote:

I read this again. It is worded POORLY. The answer is, YES, THEY CAN DRAW MORE THAN 50 AMPS. But, the 50 amp pedestal handles a TOTAL of 100 amps. Doug

Which wire has the 100 amps on it Doug?

It is 50 amps on L1 and 50 amps on L2. Voila, 100 amps used in the RV. Sheesh, I thought you, of all people, knew this wa8yxm.

Ok, but wouldn’t Neutral wire have to be rated at 100A or higher?

No. The Neutral wire carries the DIFFERENCE between the two legs, not the sum of the two legs. That is the beauty of the 50 amp pole being 120v/240v. If one leg is carrying 50 amps and the second leg is carrying 0 amps, the Neutral is carrying 50 amps. If both legs are carrying 50 amps, the Neutral is carrying 0 amps. I know it doesn't make sense, but that is the way it works.

Of course, that assumes a proper 120v/240v outlet. If both sides are fed off of the same leg so it is just 2 circuits of 120v, with 0v between the two legs, then yes, the Neutral can carry 100 amps. However, that is an improperly wired pedestal.

I see a lot of supposed experts talking about amperage without specifying voltage...then calling the guy an idiot.

Without knowing the voltage, you can't answer the question.

Since there are almost never 240v appliances on an RV, we should logically assume the electrician was talking about amps @ 120v. In that case the total amps (regardless of which leg they come in on), can easily exceed 50amps.

Yes, you must have a tied breaker because the feed for a 50 amp is 120/240 volts. It is a multi wire feeder/branch circuit.