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Old 04-21-2021, 11:30 AM   #1
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50 amp shore power = 50 amp circuit breaker = trouble?

I have a new Forester 3011; my dealer added a second AC, installing a separate outside connection dedicated to the AC. Their instructions were to use the conventional 30A shore power for normal use and add a household (heavy duty) extension cord to the campground 20A outlet for the 2nd AC.

Since I come to the Forester from a 5th wheel, I have a lot of 50A equipment. So I thought I would use the 50A shore power receptacle, my 50A surge protector and one of those 50 to 30/30 wyes: one leg to the camper's normal 30A, the other via a 30/household adaptor to the plug for the second AC. Then I realized that means the camper, wired for 30A, is 'protected' by the 50A breaker on the power post. And unless my dealer included a circuit breaker for the second AC (which I will have to verify), so is that AC. That means 20 amps of potential trouble before a breaker trips -- it is dependent on the unknown quality of the campground's breaker.

I've read a lot of posts on the forum with folks going the 50/30-30 route without issue. Call me paranoid (and maybe it pays to be paranoid when around this much current), but I don't care for that setup. Am I just reasonably paranoid or obsessively so?
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Old 04-21-2021, 11:36 AM   #2
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I wouldn't be too concerned about the main camper as that is mainly the outside cord at risk, your panel should have its own 30A main.

I would be more concerned about the 2nd AC though and add a breaker either where the cable enters or outside where you plug it into the adapter.
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Old 04-21-2021, 11:41 AM   #3
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You are protected by the 30 amp main circuit breaker in the trailer. The second A/C should have it's own power panel with a circuit breaker in it as well, probably a 15 amp circuit breaker. Using a 50 amp to 2x 30 amp adapter is just fine for your use.

https://www.amazon.com/RV-Cord-Adapt.../dp/B073WB5LBY
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Old 04-21-2021, 12:03 PM   #4
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I added my own second A/C unit over the front bedroom and is uses a separate 10/2-G extension cord to supply electricity to it. I also added a 6x6 electrical handy box just inside my front storage area with a push button 20 amp breaker to protect the A/C circuit. In the three years I have had this I have had the 20 amp breaker trip only once, for an unknown reason. I highly recommend that IF you cannot add an additional electrical box with breaker somewhere that you find a competent electrician to add one. I do not depend on the 15/20 amp breaker on campgrounds power pedestal.
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Old 04-21-2021, 12:56 PM   #5
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Either way you described will be fine as long as the 2nd A/C has its own box/breaker.

Your R/V will be protected and limited in current draw to 30a by the main in the R/Vs power distribution box and the 2nd A/C protected and limited in current draw by its own breaker box.
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Old 04-21-2021, 01:19 PM   #6
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As my username implies I'm a Master Electrician and Electrical Contractor. With that said let's look at this from my perspective shall we.
Using the adapters you're talking about that leaves your 30 amp (most likely #10 AWG conductor) connection under the protection of a 50 amp overcurrent device (breaker) an overload do to anything ahead of the RV's main (IE loose connections, broken wire strands etc...) will be protected by a device that is 20 amperes larger than the cord is rated for by the National Electrical Code. I understand your want to use what you already have but remember those items were for am RV rated for a 50 amp feed. My suggestion is to install a 30 amp and 20 amp breaker in a small raintight panel feed from the 50 amp devices and feed the RV and the added A/C from that those breakers in that panel.
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Old 04-21-2021, 01:25 PM   #7
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Old 04-21-2021, 01:31 PM   #8
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Originally Posted by MasterElectrican787 View Post
...an overload do to anything ahead of the RV's main (IE loose connections, broken wire strands etc...) will be protected by a device that is 20 amperes larger than the cord is rated for by the National Electrical Code. ....
I have heard the same exact concerns from other folks knowledgeable about RV electric. That's why I hope I never have to connect our 30-amp R-Pod to a 50-amp pedestal outlet.

Probably won't cause any problems...probably.
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Old 04-21-2021, 03:37 PM   #9
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... an overload do to anything ahead of the RV's main (IE loose connections, broken wire strands etc...) will be protected by a device that is 20 amperes larger than the cord is rated for ...
That was my concern as soon as I thought more about my alternate plan, but others have said that the 30A main breaker in the RV protects it. Is that not the case?

Quote:
20 amp breaker in a small raintight panel
Yep, that's on the shopping/todo list (as if it wasn't long enough already).
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Old 04-21-2021, 04:18 PM   #10
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Originally Posted by dfriedman View Post
That was my concern as soon as I thought more about my alternate plan, but others have said that the 30A main breaker in the RV protects it. Is that not the case?
The only thing that may suffer an overload is the part between the pedestal 50-amp breaker and the RV 30-amp breaker. That's usually the plug, the power cord itself and any wiring or socket at or inside the RV before it hits the 30-amp breaker.

When evaluating risk you need to look at "Likelihood" and "Impact". While the impact might be high depending on where the actual fault is, the likelihood is very small as long as you keep those components in good condition.

My two cents,

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Old 04-21-2021, 04:35 PM   #11
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Originally Posted by 5picker View Post
Either way you described will be fine as long as the 2nd A/C has its own box/breaker.

Your R/V will be protected and limited in current draw to 30a by the main in the R/Vs power distribution box and the 2nd A/C protected and limited in current draw by its own breaker box.
I did the same thing on my last 5th wheel. Never had the first problem. Had several people ask about the second power cord. A real conversation starter.
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Old 04-21-2021, 06:38 PM   #12
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Originally Posted by MasterElectrican787 View Post
As my username implies I'm a Master Electrician and Electrical Contractor. With that said let's look at this from my perspective shall we.
Using the adapters you're talking about that leaves your 30 amp (most likely #10 AWG conductor) connection under the protection of a 50 amp overcurrent device (breaker) an overload do to anything ahead of the RV's main (IE loose connections, broken wire strands etc...) will be protected by a device that is 20 amperes larger than the cord is rated for by the National Electrical Code. I understand your want to use what you already have but remember those items were for am RV rated for a 50 amp feed. My suggestion is to install a 30 amp and 20 amp breaker in a small raintight panel feed from the 50 amp devices and feed the RV and the added A/C from that those breakers in that panel.
This is really good advice ME. Maybe you can expand on this and show an example how it can be done?

I tried suggesting this to an RV owner for her inverter and was met by the "it will be fine" crowd. Everything is fine until something breaks. And that's why safety has to be built in.

One more thing I would add to your suggestion, if you install a second breaker box, it's treated like a subpanel, i.e. you do NOT bond the neutral to ground (or remove the bond if it comes bonded). Your main RV panel is also wired as a subpanel. The N-G bond is required at the RV park's pedestal power box and there can be only one N-G connection at any time.

The only additional N-G bond(s) in an RV should be on your generator or inverter, and these are isolated when not used by transfer switches. These are defined as a separately derived system (SDS).
Generators, converter windings, UPS systems, and solar photovoltaic systems are separately derived systems only when all circuit conductors — including the grounded (neutral) conductor — are independent of the supply conductors.
This somewhat technical jargon is just a way of saying that they are not sharing a connection to the neutral or ground wire. But there are many inverters in RVs that have floating neutrals, and some (cheap ones) don't even have ground pins, and these are not properly addressed by the installer.

See:

https://www.ecmweb.com/content/artic...derived-system
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Old 04-21-2021, 07:18 PM   #13
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Everything is fine until something breaks.
That ought to be printed in big bold letters over the door to every RV!
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Old 04-21-2021, 07:35 PM   #14
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This is really good advice ME. Maybe you can expand on this and show an example how it can be done?
Ideally the 50A breaker would be protecting 6AWG 4 conductor cable from the NEMA 14-50P plug to the enclosure. From there, the L1 and L2 tie into the line side of the breakers (L1 to the 30A, L2 to the 20A or vice versa). Then you'd have 2x 10AWG 3 conductor cables from the load side of the breakers to NEMA TT-30R receptacle. You'd also bond the neutrals together and the grounds together. As noted, these are separate bus bars and are not bonded together (not sure if they make or I'd trust a wire nut for this).

The whole purpose of the breaker is to protect the wire. So if the wire is under specifications for the breaker, you can cause excess heat and thus a possible fire, etc.

I'm not an electrician but this would be my understanding based on the points shown. Keys being that it needs to be a waterproof enclosure which for all of that. That might be the difficult part, but I've honestly never looked for something to do that type of connection.
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Old 04-21-2021, 07:48 PM   #15
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Might be able to make one from one of these and some pigtails.

https://www.ebay.com/itm/23370101924...e43103bacbad10

Then cut a one of these for the pigtails

https://www.ebay.com/itm/37212643171....c101195.m1851

M20 Waterproof Cable Glands should work to seal the cable entrance.
https://www.ebay.com/itm/25436212248...Cclp%3A2334524

The way I read it they should be able to take a cable up to .5 inches.
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Old 04-21-2021, 08:47 PM   #16
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Want a good joke? Search Amazon for "outdoor plug strip"

Apparently these waterproof plug strips do protect some of the internal components... BUT NOT THE PERSON TOUCHING THE CORD!

It's odd that a low cost, waterproof, pigtail circuit breaker device doesn't come up. But there *are* waterproof pigtail GFCI extension cords and there are waterproof surge protectors, but none of what I found have over current protection.

And then there's these contractor "spider" boxes for power distribution on a job site: (hold in to your hat when you see the price). And unless you put a plastic box over it, I wouldn't call it waterproof:

https://www.amazon.com/dp/B00MOGMYI4...ing=UTF8&psc=1
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Old 04-21-2021, 09:32 PM   #17
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...You'd also bond the neutrals together and the grounds together. As noted, these are separate bus bars and are not bonded together (not sure if they make or I'd trust a wire nut for this).
Just to clarify what llamb is saying, you tie power source neutrals together with load neutrals, and you tie power source ground with load grounds -- but there should be no neutral to ground connection.

The term 'bonding' usually refers to neutral to ground bonding and that is already done at the power pedestal (ONCE!).

If a second neutral to ground bond in your RV exists, you risk running some of the neutral current through the chassis of your RV... and that's a bad thing if you're touching the RV.
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Old 04-21-2021, 09:57 PM   #18
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If it is so dangerous to do a 50 amp outlet to 30 amp cord adapter, why don't they put 30 amp breakers or fuses in the adapters? Why isn't it required by electrical code?
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Old 04-21-2021, 11:08 PM   #19
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That's a legitimate question and a major oversight on part of the manufacturers.

It's better if the pedestal has the breakers for each type of outlet. Normally, they do -- until someone comes along with an adapter.

I'll also point out going into your RV, your panel has the right breaker in the load center... that is, if you're using it and not doing an end run to a big appliance. That covers most issues, but not a damaged cord set to your RV.
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Old 04-22-2021, 09:31 AM   #20
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If it is so dangerous to do a 50 amp outlet to 30 amp cord adapter, why don't they put 30 amp breakers or fuses in the adapters? Why isn't it required by electrical code?
I was involved several months ago in a discussion in another forum about how to protect 30-amp RV cords and connections when plugged in to 50-amp pedestal sockets (which seems to be necessary too many times, according to some folks involved in the discussion). We found an outfit online that purportedly had/could fabricate a 30-amp inline breaker that would go between the 50-to-30 dogbone and the 30-amp RV cord, but they never answered any of our inquiries.
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