New things on a camping trip that I don't understand.

An UL is just another privately owned entity that actually gets paid by the other entitys that want to use their stickers.

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And your point is?

I still can't find the 80% rule for our 30 amp plugs and receptacles in my NEC book.

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Can any one show me where our RV 30 plugs and receptacles are referenced for 80% in NEC publications. Until so I'm going to go with more internet hooey.

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Suit yourself. 

If you are looking for an explicit statement about 30A receptacle ratings, I'll agree there probably is none.  It's the way electrical ratings in general are done, assuming that average loads are 80% of the peak in most all types of circuits. That "80% average" assumption permeates much of the NEC rules, a major factor in defining the ampacity of wires, number of conductors in a box or conduit, number of outlets on a branch circuit, etc. etc.  And yes, it effects how receptacles and plugs are tested, which in turn carries over to UL testing standards. There are also effects of temperature built into the ratings and not stated on the label.

Electrical ratings are no different than dozens of other ratings that we, the public, use as guidelines.  There are always assumptions behind the ratings, and a test method or procedure for verifying the ratings. Whether the rating is an amp load, an axle or tire weight load, or safe levels of  exposure to a chemical, or whatever. Most people work with a simplified rating value rather than learning the ins and outs of each thing.


I merely offer this as an explanation as to why 30A plugs and receptacle sometimes appear blacked or even melted but the breaker didn't trip. You don't have to accept it. 

sightseers said:

many times (especially on hot days) the whole electrical grid voltage will drop as much as 10 to 15 volts.

because of this if your RV normally draws 30 amps of power at 120 volts,  it will be drawing almost 34 amps if the voltage drops to 106 volts

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If your 30 amp RV exceeds 30 amps the RV's main breaker will trip...

Bill N said:

But would my surge protector cut me off if it got that low?  Also,  I am assuming that if I do use my 50/30 amp converter there will be no problem using the Progressive surge protector either.  See, I am becoming more electrically inclined. I almost hate to admit that I have had my ham radio license since 1975 and even built my own radio (with a lot of help) but my electrical knowledge went out the window from lack of use and all those senior moments.......lol

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Would it make sense just to use the 50/30 adaptor at all times, just in case?  Would it hurt anything in the coach to do so?  I'm interested in this as well.  Why not just use the 50 amp connection all the time on our 30 amp coaches if we have the adaptor anyway?

sightseers said:

because of this if your RV normally draws 30 amps of power at 120 volts,  it will be drawing almost 34 amps if the voltage drops to 106 volts

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With all due respect this is not correct.  The electrical load in your RV consists of both resistive and inductive loads.  Resistive loads (lighting, water heaters, RV refrigerator) obey Ohm's Law  V= IR and, therefore, current flow is proportional to voltage.  So if the voltage drops to 106V the resistive loads will reduce by the factor of 106/120 = 0.88

OTOH inductive loads can increase in the presence of low voltage.  In particular, AC induction motors will draw more current under low voltage.  But this doesn't mean that all motors in your RV will be affected.  Your AC compressor probably will, but the compressor in your residential fridge might well be a DC motor running off of rectified AC and it won't be affected by low voltage.  Nor will the motor in your combo washer since it is a DC stepper motor.

So it's very difficult to say precisely what the current usage of your RV would be at 106V since it will be a combination of the two effects and the mix will vary depending on what devices you are operating inside the RV.

Would it make sense just to use the 50/30 adaptor at all times, just in case?  Would it hurt anything in the coach to do so?  I'm interested in this as well.  Why not just use the 50 amp connection all the time on our 30 amp coaches if we have the adaptor anyway?

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Go ahead - no problem at all, at least not technically.  About the only risk is that some campground staff might get upset because they [mistakenly] think you are putting something over on them, aka "stealing" electricity or some such.

Gary RV_Wizard said:

Go ahead - no problem at all, at least not technically.  About the only risk is that some campground staff might get upset because they [mistakenly] think you are putting something over on them, aka "stealing" electricity or some such.

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I don't understand how they would think I'm stealing electricity.  I've never had to pay a different rate based on whether I was going to use 30 or 50.  Are some campgrounds/parks like that -charge a different rate based on whether you state you will use 30 or 50?

Bill N said:

................
One question to the electrician types.  Since I have a 30 amp coach I usually have a choice of a 50 amp or 30 amp outlet at most campgrounds.  If the 30 amp looks to be rather damaged (black around one leg) can I use my 50-30 amp adapter without problem?  That presupposes that the 50 amp outlet is in decent condition.  Sounds like a stupid question to me because why else would they make such an animal.

Bill

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A bit of confusion for me here.... the 50 amp receptacle is actually (2) 25 amp circuits providing 240 VAC (isn't it?) So if you plug a 50/30 adapter into the 50, wouldn't you probably only get 115 VAC/25 Amp from this safely?  ???

_Rusty_ said:

A bit of confusion for me here.... the 50 amp receptacle is actually (2) 25 amp circuits providing 240 VAC (isn't it?) So if you plug a 50/30 adapter into the 50, wouldn't you probably only get 115 VAC/25 Amp from this safely?  ???

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No, the 50 amp receptacle is 50 amps at 240 VAC hot to hot (12,000 watts max), or 50 amps at 120 VAC hot to neutral (6,000 watts max). The 30 amp adapter only connects to one hot leg and the neutral though, so it potentially has 50 amps available, but the RV 30 amp main breaker restricts the usage to just 30 amps (3,600 watts max).

Very educational thread for this non-electrician.
I've often wondered how an RV park is powered, full up with 100+ motorhomes on a hot summer day, presumably each one near amperage capacity.

The NEC has an entire section (Chap 5, Sect 551) devoted to RV's and RV park wiring, Bob. Along with the other pertinent parts of the NEC, it sets the minimum standards for load calculations, wire sizes, breakers, site wiring, percentage of 30 and 50 amp outlets, etc. Older parks that were built to lower standards are where you're more likely to run into low voltage situations under the load conditions you described.

Gary is spot on with his 80% statement for full load. That applies to all electrical load centers that I am aware of. Does not matter if it is in your house, business or factory. If you want it code, full circuit load should be no more than 80% of branch circuit rating it is connected to.

Most circuit breakers are of the time delay type. They will handle an overload for a period of time. This is to prevent unnecessary tripping and still protect the circuit. Some might handle up to 4 times their rating, for a very short period of time, like starting a motor. The less the overload, the longer the time before tripping. Some might handle 2 times their rating for 30 seconds.

If you are pulling 100% rating, it is getting warm and you are inviting a trip out, unless it is in a cold environment.

Bill N said:

One question to the electrician types.  Since I have a 30 amp coach I usually have a choice of a 50 amp or 30 amp outlet at most campgrounds.  If the 30 amp looks to be rather damaged (black around one leg) can I use my 50-30 amp adapter without problem?  That presupposes that the 50 amp outlet is in decent condition.  Sounds like a stupid question to me because why else would they make such an animal.

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Be careful with your 50 to 30 amp adapter.  I had one that had the molded black rubber plug and socket, it's 30 amp end got just as hot as when I plugged the RV cord into the park's 30 amp outlet.  Apparently the rubber doesn't do a very good job of supporting the socket's 30 amp pins and when it gets warm it releases compounds that degrade the contacts.

Or at least that's my best guess.

I replaced it with a Camco adapter that has the yellow hard plastic ends with white inserts around the pins and it works much better, staying cool under the A/C load.

The yellow Camco 30 amp plugs are also a good choice if your molded rubber shore power plug shows signs of heat damage.  Just be sure to trim back the cord until you see bright, undamaged copper.

Lou Schneider said:

Be careful with your 50 to 30 amp adapter.  I had one that had the molded black rubber plug and socket, it's 30 amp end got just as hot as when I plugged the RV cord into the park's 30 amp outlet.  Apparently the rubber doesn't do a very good job of supporting the socket's 30 amp pins and when it gets warm it releases compounds that degrade the contacts.

Or at least that's my best guess.

I replaced it with a Camco adapter that has the yellow hard plastic ends with white inserts around the pins and it works much better, staying cool under the A/C load.

The yellow Camco 30 amp plugs are also a good choice if your molded rubber shore power plug shows signs of heat damage.  Just be sure to trim back the cord until you see bright, undamaged copper.

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Thanks Lou.  I have both of those items but have not yet installed the new plug (carry it as a spare to be installed when needed)  That will be my next project as the current plug has a pin that always needs to be cleaned.

Bill

I think it is common for 30 amp plugs in RV pedestals to be burned or poor condition before you ever plug in. Many times the park owner is not even aware of the fact. It is only called to their attention when the customer does not have any electricity.

Many RV'ers are not even aware that their 30 amp RV is probably pulling near and many times over 30 amps. Under these conditions, the 30 amp pedestal receptacle starts to deteriorate rather rapidly and begins working on your RV male plug itself.

Neal said:

Many RV'ers are not even aware that their 30 amp RV is probably pulling near and many times over 30 amps. Under these conditions, the 30 amp pedestal receptacle starts to deteriorate rather rapidly and begins working on your RV male plug itself.

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If a 30 amp RV is pulling more than 30 amps more than momentarily, then the onboard 30 amp main breaker has failed closed. An extremely rare occurrence. Even pulling anything much over 24 amps (80%) for an extended period will typically trip the breaker.

NY_Dutch said:

If a 30 amp RV is pulling more than 30 amps more than momentarily, then the onboard 30 amp main breaker has failed closed. An extremely rare occurrence. Even pulling anything much over 24 amps (80%) for an extended period will typically trip the breaker.

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All breakers get old wear out after a while, the more they get tripped,  the weaker the get, I've had an Amprobe on circuits before and watched them trip well below their limits.

usually they fail in the open position and won't reset.

It's true that breakers can wear out, some brands/grades faster than others, but in my opinion this is a vastly overrated source of problems. A worn breaker or GFCI should be far down in the list of possible faults, yet RV and Homeowner DIY sites are continually flooded with "change the breaker" advice whenever somebody mentions a tripped breaker.  Is it just Wishful Thinking, hoping that the breaker is faulty rather than there really being a short or overload?  Most often a breaker or GFCI trips because it is doing its job, detecting an overload or ground fault as it was designed to do.  However, breakers can be affected by loose wires and poor fit to the power bus, or even the temperature within the load center box.  Low voltage can also cause a tempoarary increase in amps, pushing a marginal circuit past the breaker amp limit.

I mean this to be helpful, but maybe it's just a rant over a personal peeve. I doubt if people are going to stop swapping breakers and GFCIs every time they get a fault, just because I said so...

Gary RV_Wizard said:

.  Low voltage can also cause a tempoarary increase in amps, pushing a marginal circuit past the breaker amp limit.

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several years ago I was working a problem on a really large multi-million dollar stadium LED display one summer day.  I was trying to find out why all the C/B components inside were melting (inside the air conditioned cabinets) . As I monitored the voltage and amperage every time a large message flashed on the board, I watched the voltage dip to 104/5 VAC.

after it had damaged many 1000's of expensive LED cards in the board... all it took the fix it, (after they had to verify with their own meters what I was telling them)  was to have the power company put it on a higher transformer tap.
As it had it's own in ground power transformer it was very interesting to watch from a distance as they switched the trans tap with long fiberglass poles, a very dangerous procedure.

after that we had true 120 volt power even under max loads and no more problems.

ever notice more breakers pop in the summer time,  heat equals resistance, resistance reduces voltage, lower voltage increases amperage, increased amps creates more heat... and it just keeps on going. 

as summer time demand goes up,  voltage goes down.    they are called Brown-outs around here.

I remember, one time, the park service panel main breaker tripped shortly after 3 of us pulled in and connected. After checking the load and for loose connections, we set a fan in front of the open panel so that we all might have some electricity for the night.

Gary RV_Wizard said:

  Most often a breaker or GFCI trips because it is doing its job, detecting an overload or ground fault as it was designed to do. 
I mean this to be helpful, but maybe it's just a rant over a personal peeve. I doubt if people are going to stop swapping breakers and GFCIs every time they get a fault, just because I said so...

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an  issue I had  GFCI breakers...

At the Staples center in L.A. we put in these 2 big 250 foot tall TV screen type LED boards.  each one had this brand new type really cool massive $10k 480 volt LCD readout GFCI breaker that controlled all the power from the mains.  This was mandated by code for "outdoor electrical devices".

Every time the message changed on the screens it instantly changed the power consumption rate,  and that GFCI would trip off... thinking there was a short.

After we showed the inspector what was happening,  it was replaced with a regular breaker.  a $20k mistake for the city of L.A.