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50A to 30A and 20A Y-adapter...any downsides?

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Post Options Post Options   Quote Pod_Geek Quote  Post ReplyReply Direct Link To This Post Topic: 50A to 30A and 20A Y-adapter...any downsides?
    Posted: 13 Jan 2020 at 3:53pm
So in light of our 195's 12-Amp Inverter breaker (which affects all 120V outlets) I'm considering getting one of these:


It's a Y adapter that plugs in to a 50-amp outlet and supplies both 30 amp and 20-amp female connections.  The 195 would plug in to the 30-amp outlet and I could run an extension cord off of the 20-amp outlet and power a space heater (or whatever) when necessary. Reviews seem to support such a use, e.g., 

Perfect for my RV needs, unable to find at any dealer. Allows me to run my 30 amp RV service and a separate heavy duty line for my after market electric fireplace. Meets some campground "rules" of only using one receptacle per RV space. Massive heavy duty cord, pictures do not do it justice!

Thoughts?
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 7:26am
Yes, one big downside. There is no overcurrent protection on that thing. The only thing limiting current flow is the 50A breaker at the pedestal. So, in the event of an electrical fault, up to 50A can get fed into anything connected to it, with nothing to prevent an electrical fire. IMHO that connector is an accident waiting to happen.
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Post Options Post Options   Quote Pod_Geek Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 9:49am
Originally posted by offgrid

Yes, one big downside. There is no overcurrent protection on that thing. The only thing limiting current flow is the 50A breaker at the pedestal. So, in the event of an electrical fault, up to 50A can get fed into anything connected to it, with nothing to prevent an electrical fire. IMHO that connector is an accident waiting to happen.

Is that any different than using a 50-amp to 30-amp dogbone, which I understand many people do?

FWIW, I do use this Hughes 30-amp autoformer:


The all new Hughes Autoformer 30 amp power boosting autoformer (RV2130SP) has the same performance and reliability of the RV2130 but now has advanced surge protection built in! The unit offers 2,400 Joules of surge protection. As an added feature, the surge / spike protection module is also replaceable. In the event of a massive spike, the surge unit will take the hit ensuring your booster and more importantly, your RV is not damaged.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 10:07am
Conceptually it’s a similar issue but in practice it’s worse than the 50 to 30 dog bone because with the 30A you are feeding your loads through the rpod distribution panel and its circuit breakers, while with the 50 to 15a dogbone you’re going straight to your loads with no overcurrent protection at all other than the 50a breaker at the pedestal. Personally though, I won’t use either dog bone.

The autotransformer provides protection from voltage surges but doesn’t provide overcurrent protection. Only a circuit breaker or fuse does that.
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Post Options Post Options   Quote Pod_Geek Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 10:27am
Originally posted by offgrid

Conceptually it’s a similar issue but in practice it’s worse than the 50 to 30 dog bone because with the 30A you are feeding your loads through the rpod distribution panel and its circuit breakers, while with the 50 to 15a dogbone you’re going straight to your loads with no overcurrent protection at all other than the 50a breaker at the pedestal....

But the R-Pod would be plugged in to the 30-amp female outlet on the Y-adapter just as if it were a simple 50 to 30 dogbone, so I guess I'm confused.  I thought that the distribution panel would limit the current that the 195 sees to 30 amps, based on discussions I've seen related to using 50-amp to 30-amp dogbones.  In fact I recall people indicating that 50-30 dogbones only allow 30 amps at the to pass through anyway, e.g.,

I am a retired electrician and this response is wrong. Your motorhome is protected by a 30 amp breaker in the breaker box, so 50 amps could never end up on the power cord. If it was dangerous they would not sell 30 to 50 amp converters. The box in the campground is rated for 50 amps and that is the most it can deliver, but it only delivers the amount of amperage your motorhome is drawing. Since the motorhome is limited to drawing 30 amps at the most then the cord will never see more than 30 amps.


The only difference is the extra 20-amp female connector that would allow something like a space heater to be plugged in.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 11:17am
You are going to connect an extension cord and a heater to the 20a output of the dog bone, right? The cord and heater are not rated for 50a. Where in that circuit is there overcurrent protection for that extension cord and heater? Answer: there’s not.

As to the quote from the retired electrician, he’s wrong. Lots of things get sold that can be dangerous. There should be a label next to your trailer receptacle that says not to connect it to a circuit which is not limited to 30a. That label is a code requirement, it’s there for a reason. You are violating it if you connect a 50 to 30a dog bone. And yes in the event of a fault you absolutely can flow more than 30a in the cord and the wiring between the receptacle and the distribution panel. Nothing stops that unless the current flow exceeds 50a, at which point the 50a breaker should trip.

You asked if there was a downside so I gave you one. It’s your trailer, you are certainly free to decide to proceed anyway. No need for a debate about it.
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Post Options Post Options   Quote Pod_Geek Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 11:51am
Extension cord would be 12-guage.  Heater draws 7 amps (use it at 1/2 power).  May still be a bad idea.

Originally posted by offgrid

...And yes in the event of a fault you absolutely can flow more than 30a in the cord...

Curious...what type of fault are you referring to?  How common are such faults?

The confusing thing to me is that so many folks on various forums say that it's perfectly ok to power a 30-amp rig off a 50-amp pedestal using the appropriate adapter.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2020 at 12:18pm
12awg is generally good for 20a ampacity.

Current limited faults (which is what we’re talking about here) can be hot to neutral or hot to ground, and can occur when the wire insulation is partially cut or abraded, or from moisture or corrosion at a plug or receptacle. You could also get a resistive (low current) fault combined with the normal load current which can put you over the conductor ampacity limit. I can’t answer regarding how common they are other than to say I’ve seen them more than once both at home and professionally and that a large portion of the electrical code deals with protection from these kind of fault conditions. The code is very strict in requiring all conductors to be protected by a fuse or cb which doesn’t allow that conductor to ever carry more current than its designed for.
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Post Options Post Options   Quote TheBum Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jan 2020 at 12:14pm
I've searched for 50A->30A adapters with built-in 30A circuit breakers but had no luck. Seems like a good business opportunity for someone.
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Post Options Post Options   Quote Pod_Geek Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jan 2020 at 2:49pm
Originally posted by TheBum

I've searched for 50A->30A adapters with built-in 30A circuit breakers but had no luck. Seems like a good business opportunity for someone.

Got me to thinking...

Found this:

Cord Set  In-line GFCI  Voltage Rating 120  Amps AC 30  Color Yellow  Cord Length (Ft.) 2  NEMA Plug Configuration L5-30P  NEMA Receptacle L5-30R  Reset Type Manual  Standards UL 943  CSA


Don't know if the Plug/Receptacle configuration is RV-compatible, however.
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