Pulling more than 50 amps ?

[TechWriter]

Our park electrician says that some of the big rigs with 3 ACs and electric everything can sometimes draw more than 50A from a 50A pedestal.

Truth or BS?

[hypoxia]

valhalla360 wrote:
I've yet to come across one of these rigs that have 240v appliances. I'm sure they exist but kind of like hen's teeth

Mine has a 240 VAC Dryer but no hens teeth. The AquaHot uses both sides with two 2000 watt elements but they are 120 VAC elements so I guess that doesn't count.

[Gdetrailer]

wa8yxm wrote:

Gdetrailer wrote:

You however cannot "combine or connect" L1 and L2 together because they are out of phase (one positive and one negative going). Adding two voltages out of phase CANCELS the voltage and in this case creates a huge short and the result would be zero volts.

Though you are correct. 100% and that was a good post I will comment on this paragrapy.
Wrong point of view
When we talk about "Combining" we mean one leg is fed to the OUTLET so there is L-1 and L-1 not L-1 and L-2
You were looking at it from the other side. You are correct that if you try to hook L-1 to L-2 smoke fire and sparks (or tripped breakers) will ensue.

But some "Cheater Parks" only run one leg to the box or so I'm told.

The key is "so you been told"..

There is no way ANY park which has a 50A 120/240 socket could have connected only ONE hot to both L1 and L2 terminals in the box and have been "legal". That would have had to be an pirate connection, I think you have been told a few "tall tales" from folks who don't understand how the mysteries of electric work.

Why?

Simple, using only one of the split phases can easily overload the NEUTRAL wire on your shore cord and even the campgrounds own Neutral.

That would never have passed the POCOs inspector and the POCO REQUIRES ALL connections to the grid to be INSPECTED before any power is applied.

The split phase setup allows one to use the same size neutral wire as the hot phase (L1 and L2). This is because the voltage and current on the L1 and L2 are 180 degrees. The same thing as the voltage, the current on L1 goes up when the current on L2 goes negative. That has the effect of canceling out the current seen on the neutral.

To visualize this you would have to imaging having only a purely restive load like say two 120V 100W incadescent bulbs wired in series. The voltage and current are evenly divided and flowing only on L1 and L2 and zero current would be flowing on the neutral (balanced circuit).

Now, if one of the 100W bulbs were to be replaced with a 50W bulb, you would have an unbalanced circuit and because you have the neutral the 100W bulb still pulls 100W and the 50W bulb pulls 50W and the neutral will have 50W on it..

In your example, using only one of the Split phases two 100W bulbs are in parallel and the neutral carries full 200W. Very easy to overload the neutral.

Combining L1 and L2 on the shore power socket would mean the Neutral would now see a potential of a 100A worth of current (basically paralleling the TWO 50A breakers) , that is going to cause fires. Campground would end up being liable and on the hook for burning down someones RV..

Now, if you are talking those portable "cheater boxes" where you use a 30A 120V and 20A 120V plug in to the shore power, 30A and 20A add up to 50A and will not overload the neutral.. Those CAN use the SAME phase or L1 and L2 but in most more modern parks you WILL run into issues with the 20A plug in having a GFCI which will most likely not like that setup and be a tripping issue.

[enblethen]

Yes, a rig could draw more then 50 amps if you combine the two legs. If the rig actual draws more then fifty the rig's 50 amp main should trip. The rig electrician is referring to could be wired incorrectly.
Design of the rig should be done in such a manner as to prevent this from happening.

[BB_TX]

valhalla360 wrote:

BB_TX wrote:

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.

I've yet to come across one of these rigs that have 240v appliances. I'm sure they exist but kind of like hen's teeth (maybe with rock band buses or some other specialized system but so far from common as to be a wild leap to assume he was talking about rigs actually using 240v power)...so not really relevant other than in a pedantic sense that it's possible.

The vast majority of RVs...even the big ones with 3 air/con units use no 240v devices.

You are also presuming the issue being discussed. You assume, it's about tripping the breaker at the pedestal. He could just as easily be talking about the larger system where they stay under 50amp per leg and when you have many rigs doing similar things, it stresses the upstream system. Or they could have simply been talking about the utility bill and how many KWH the park has to pay for. We don't know the specifics of what was discussed or how the OP translated that into the original post.

From the OP:

Our park electrician says that some of the big rigs with 3 ACs and electric everything can sometimes draw more than 50A from a 50A pedestal.

A very simple statement regardless of the intent behind it. And that simple statement is absolutely true, at least until either the park 50 amp breaker trips, or the RV 50 amp breaker trips. And the voltage being used is entirely irrelevant. Doesn't matter whether the RV has any 240 vac appliances or if they are all 120 vac.

Boggles my mind that this has turned into a 9 page (an counting) debate about an "idiot electrician" making a very simple and very true statement and everyone turning that into their own personal interpretation as if they know more about what he was referring to than the electrician himself.

[valhalla360]

BB_TX wrote:

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.

I've yet to come across one of these rigs that have 240v appliances. I'm sure they exist but kind of like hen's teeth (maybe with rock band buses or some other specialized system but so far from common as to be a wild leap to assume he was talking about rigs actually using 240v power)...so not really relevant other than in a pedantic sense that it's possible.

The vast majority of RVs...even the big ones with 3 air/con units use no 240v devices.

You are also presuming the issue being discussed. You assume, it's about tripping the breaker at the pedestal. He could just as easily be talking about the larger system where they stay under 50amp per leg and when you have many rigs doing similar things, it stresses the upstream system. Or they could have simply been talking about the utility bill and how many KWH the park has to pay for. We don't know the specifics of what was discussed or how the OP translated that into the original post.

[Bobbo]

DrewE wrote:

Bobbo wrote:

DrewE wrote:
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?)

Incorrect analogy. The correct analogy is "is a semi truck with dual 50,000 pound trailers a 50,000 pound load or a 100,000 pound load?"

Trailer "L1" has 50,000 pounds, trailer "L2" has 50,000 pounds. The receiving destination (the RV) gets 100,000 pounds delivered.

Pounds of load moved in the trailers would be more nearly to watts, I believe, rather than amperes. A 240V 50A circuit (split phase or not) certainly delivers twice the power as a 120V 50A circuit, but it does not deliver twice the current. In both cases, you're getting your 50 Coulombs per second. Similarly, the dual trailer truck is doing twice the work per unit time as a single trailer truck, and so delivering twice the power to moving the load; but, of course, it is not going twice as fast.

Yes. If you think the average RVer needs the technical details of how electricity works to understand the power limits of his rig. If he is OK without the technical details, my analogy gives him those limits in a way he can understand. That is why it is called an "analogy."

[wa8yxm]

Gdetrailer wrote:

You however cannot "combine or connect" L1 and L2 together because they are out of phase (one positive and one negative going). Adding two voltages out of phase CANCELS the voltage and in this case creates a huge short and the result would be zero volts.

Though you are correct. 100% and that was a good post I will comment on this paragrapy.
Wrong point of view
When we talk about "Combining" we mean one leg is fed to the OUTLET so there is L-1 and L-1 not L-1 and L-2
You were looking at it from the other side. You are correct that if you try to hook L-1 to L-2 smoke fire and sparks (or tripped breakers) will ensue.

But some "Cheater Parks" only run one leg to the box or so I'm told.

[MEXICOWANDERER]

There really isn't a simple comparison. Because learning wrong will confuse someone as to why there is a big problem when neutral is lost.

Or how can a neutral be sized with the same gauge as L1 and L2? "AC FOR DUMMIES ?"

Do people have an aversion to learning? Maybe it's like me and computers not understanding idiotic sounding jargon.

Finding the easiest to learn book about AC power basics ?

[DrewE]

Bobbo wrote:

DrewE wrote:
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?)

Incorrect analogy. The correct analogy is "is a semi truck with dual 50,000 pound trailers a 50,000 pound load or a 100,000 pound load?"

Trailer "L1" has 50,000 pounds, trailer "L2" has 50,000 pounds. The receiving destination (the RV) gets 100,000 pounds delivered.

Pounds of load moved in the trailers would be more nearly to watts, I believe, rather than amperes. A 240V 50A circuit (split phase or not) certainly delivers twice the power as a 120V 50A circuit, but it does not deliver twice the current. In both cases, you're getting your 50 Coulombs per second. Similarly, the dual trailer truck is doing twice the work per unit time as a single trailer truck, and so delivering twice the power to moving the load; but, of course, it is not going twice as fast.

[Gdetrailer]

Reisender wrote:


Wow. I actually understood that...and that’s sayin something. :). Thanks dude.

🙂

Glad that explanation was helpful to you..

Looks like the thread however has gone off the rail and destroyed a few trucks along the way on the last couple of posts.. :E

[time2roll]

I see two trucks approaching each other at 50 miles per hour to meet at the depot exactly between them. Depot manager says the load is closing in at 100 miles per hour yet each truck is just going 50. Is he right?

[Bobbo]

DrewE wrote:
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?)

Incorrect analogy. The correct analogy is "is a semi truck with dual 50,000 pound trailers a 50,000 pound load or a 100,000 pound load?"

Trailer "L1" has 50,000 pounds, trailer "L2" has 50,000 pounds. The receiving destination (the RV) gets 100,000 pounds delivered.

[Reisender]

time2roll wrote:

Reisender wrote:
Side note. For Our Tesla you can dial it right back to 8 amps with 120 or 240 volts. Kinda handy in power sharing situations. Not the case with our leaf that runs flat out at 27 amps all the time.

Yes the LEAF maximum rate is controlled by the charging cord it is connected to. LEAF will most certainly charge at slower rates down to the 6 amp minimum of the charging standard.

Ah yes. Poor explanation on my point. We have a Juicebox that can be wifi controlled down to 8 ish amps. Good catch. On the leaf it’s done on the EVSE (cord). On the Tesla it’s done on the car.

[time2roll]

Reisender wrote:
Side note. For Our Tesla you can dial it right back to 8 amps with 120 or 240 volts. Kinda handy in power sharing situations. Not the case with our leaf that runs flat out at 27 amps all the time.

Yes the LEAF maximum rate is controlled by the charging cord it is connected to. LEAF will most certainly charge at slower rates down to the 6 amp minimum of the charging standard.

[Reisender]

Gdetrailer wrote:

Reisender wrote:
In practical terms on a 50 amp pedestal you can draw 40 amps st 240 volts continually. We have an electric car and we sometimes do that.

Real world experience. Visiting a friend with a Newell with three AC’s, all running as well as a bunch of other things. Our Electric vehicle hooked up to his pedastal via a Y connector off the box pulling16 amps at 240. No problem.

Yes, 40A at 240V is correct and possible, that is 9600W draw.

50A at 240 is 12,000W.

However, what most folks seem to miss is a RV "50A" connection IS actually a COMBINATION connection, it is a 120V/240V connection, it has a NEUTRAL which allows for not only 240V appliances but 120V appliances also.

This means you can use a combination of 120V AND 240V appliances on this connection.

Pure 240V ONLY devices do not need and are not wired for the Neutral.

Home water heaters, deep well water pumps, heavy duty air compressors, high BTU home A/C units typically fall into the category of 240V ONLY.

Your high amperage car charger is is using BOTH the hot legs (L1 and L2) and not the neutral so it is subject to BOTH of those breakers limits which is 50A or 12,000W and would fall into the pure 240V only category.

Now, for 120V loads, you use only ONE of the Lines coming in (L1 OR L2) PLUS THE NEUTRAL and you can draw a max of 6,000W at 120V (50A).

With 50A 120/240 service you actually have the same as TWO 50A at 120V (6,000W) power feeds. In reality you could say that for 120V appliances you actually you have up to 100A of capacity (12,000W).

You however cannot "combine or connect" L1 and L2 together because they are out of phase (one positive and one negative going). Adding two voltages out of phase CANCELS the voltage and in this case creates a huge short and the result would be zero volts.

Typical RV 50A 120/240 will put MOST of the loads on the L1 "leg" and very few loads on the L2 leg. L2 on the RV is often reserved for the second or third AC unit.

It is done this way to allow a 50A RV to hook up to a 120V ONLY 15A-30A pedestal and have MOST of the RV get power although at very limited amperage of course.

Wow. I actually understood that...and that’s sayin something. :). Thanks dude.

Side note. For Our Tesla you can dial it right back to 8 amps with 120 or 240 volts. Kinda handy in power sharing situations. Not the case with our leaf that runs flat out at 27 amps all the time.