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 > Pulling more than 50 amps ?

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Bobbo

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Posted: 08/01/20 07:07pm Link  |  Quote  |  Print  |  Notify Moderator

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.

* This post was edited 08/01/20 07:29pm by Bobbo *


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Posted: 08/01/20 07:38pm Link  |  Quote  |  Print  |  Notify Moderator

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?


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Gdetrailer

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Posted: 08/01/20 09:11pm Link  |  Quote  |  Print  |  Notify Moderator

Reisender wrote:



Wow. I actually understood that...and that’s sayin something. [emoticon]. Thanks dude.



[emoticon]

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.. [emoticon]

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Posted: 08/02/20 12:30am Link  |  Quote  |  Print  |  Notify Moderator

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.





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Posted: 08/02/20 02:59am Link  |  Quote  |  Print  |  Notify Moderator

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 ?

wa8yxm

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Posted: 08/02/20 05:45am Link  |  Quote  |  Print  |  Notify Moderator

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.


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Bobbo

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Posted: 08/02/20 07:10am Link  |  Quote  |  Print  |  Notify Moderator

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."

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Posted: 08/02/20 08:19am Link  |  Quote  |  Print  |  Notify Moderator

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.


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BB_TX

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Posted: 08/02/20 09:15am Link  |  Quote  |  Print  |  Notify Moderator

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.

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Posted: 08/02/20 11:02am Link  |  Quote  |  Print  |  Notify Moderator

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.


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