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Open Roads Forum  >  Tech Issues

 > Pulling more than 50 amps ?

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time2roll

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Posted: 08/01/20 12:26pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hell's bells why not use gold? *grin*
Silver is lower cost and conducts better than gold or copper.
Go ahead and have it gold plated for corrosion resistance [emoticon]


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MEXICOWANDERER

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Posted: 08/01/20 12:37pm Link  |  Quote  |  Print  |  Notify Moderator

Point is......

A double standard for RVs. Look what is NEC CODE for an electric stove.

No 6 CU is absurd for 50 amp service.

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Posted: 08/01/20 01:24pm Link  |  Quote  |  Print  |  Notify Moderator

MEXICOWANDERER wrote:

No 6 CU is absurd for 50 amp service.
Not sure what you're getting at here. I just had a #6 Copper 50a service installed at my home.

time2roll

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Posted: 08/01/20 02:01pm Link  |  Quote  |  Print  |  Notify Moderator

If the run is short I believe #8 is fine for a 50 amp connection.
I would not be surprised to see #8 feed the 50 amp connector in the pedestal.

wa8yxm

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Posted: 08/01/20 04:09pm Link  |  Quote  |  Print  |  Notify Moderator

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?


Yes but it is highly technical But I try again:

Assume that between transformer and you is a 2 volt drop each way at 50 amps (At 100 amps that's 4 volts each way)
Now that means 120 volts at the transformer or no-load = 112 full load OUCH that's some serious voltage drop.

Now let's split it to two 50 amp legs. Right away the voltage drop one way goes from 4 to 2.. but wait there's more

IF just one leg is in use we have 2 volts out and 2 back for 116 volts at the RV
But if both legs are in use we have 2 volts out and 2 back for 118 volts at the RV.. Why? Well the 4 volts round trip comes off the 240 volts and that's divided so ..

It means way smaller cables are needed for the same voltage drop

Makes 100% sense

I hope I've explained it well enough but if not.. Pleas ask about the confusing parts and I'll try to clarify.

Alas... THis is what is called "College level" stuff. or intutitive depending on what you studied in college [emoticon]


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Posted: 08/01/20 04:33pm Link  |  Quote  |  Print  |  Notify Moderator

Not sure where you are coming up with amperage for shore power cord. Cord amperage is covered by NEC article 400. Ampacity is Art 400.5(A). #6 is rated for only 45 amps. #8 is rated for 35 amps. NEC allows you to go up to the next standard breaker which is 50 amp.


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Gdetrailer

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Posted: 08/01/20 04:37pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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Posted: 08/01/20 04:43pm Link  |  Quote  |  Print  |  Notify Moderator

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. [emoticon]. 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.

time2roll

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Posted: 08/01/20 05:00pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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Posted: 08/01/20 05:06pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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