Electrical System Questions

[LiseKen]

Please bear with me as I am a novice learning about my trailer's electrical system. I know it needs work and plan to be safe and conservative in working on it.

I am currently focused on the shore power system. It is a 1977 Boler 1700 with updates to the electrical system.

My shore power plug is shorted out. I want to be sure I get the proper replacement plug, and address the reason(s) it shorted out.

The PO put in a new Power Center. I have the manual, it is a WFCO ULTRA Power Center Model WF-8735P. According to Google it is a 35 Amp Power Center. Although it is an ULTRA not ULTRA III, this online manual looks the same: http://wfcoelectronics.com/wp-conten...tor-Manual.pdf

The shore power plug is a male three prong plug (like a household appliance). The cord is black and says: "Type ST 600V outdoor cord.

Photos attached.

PS: I have seen and am considering the modification of replacing the shore power cord with a shore power plug that others on this site have done. I am not ready to do that yet so plan to stick with a cord for now. I do want to be sure I have the proper cord type and install the correct plug.

[C&G in FL]

Lise, do you have any specific question(s) to ask?


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[LiseKen]

Ha, here's my questions:

Does the fact that my power center is 35 amp mean that I need/can use a 30 amp shore power cord for my Boler?

Is there a possible connection between it shorting out (and looking burnt) and the power center, or other thoughts on why it shorted?

Lise

[C&G in FL]

Originally Posted by LiseKen

Ha, here's my questions:



Does the fact that my power center is 35 amp mean that I need/can use a 30 amp shore power cord for my Boler?



Is there a possible connection between it shorting out (and looking burnt) and the power center, or other thoughts on why it shorted?



Lise

If you look at the main breaker, you should match the shore power cord to that. Your trailer is essentially an electrical circuit with sub-circuits. If the main breaker is 30 amps, it will allow a 30 amp draw without tripping, and you should have a 30 amp rated cord. All that means is that the conductors in the cord are 10 gauge. If this is the case, you will have to put a 30 amp plug on the cord because the plug you have shown is rated at 15 amps and you really shouldn't be pulling more than 15 amps through it; the prongs are relatively thin. When you pull more amperage through a cord than it is rated for, the conductors can heat up to the point that the insulation can melt (and a short circuit could result). This is essentially what happened on Apollo 13. The liquid hydrogen and liquid oxygen tank heaters were upgraded, but the wiring powering them was not. When the heaters were tested long before the flight, the wiring got so hot that the insulation melted. Unfortunately, nobody realized it. During the flight when the tanks were filled with liquid oxygen and hydrogen (explosively flammable) the bare wires sparked causing the explosion.


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[steve dunham]

Originally Posted by LiseKen

Ha, here's my questions:

Does the fact that my power center is 35 amp mean that I need/can use a 30 amp shore power cord for my Boler?

Is there a possible connection between it shorting out (and looking burnt) and the power center, or other thoughts on why it shorted?

Lise

The 35 amps referred to in the description of your converter is the maximum DC amperage that your converter's rectifier is capable of producing . The converter only require 3 to 5 amps of 120 VAC.
The converter is fed from a 15 amp 120 VAC circuit breaker in your distribution panel . The converter changes AC to DC , o
In order to run your 12VDC lights , fan , furnace etc. Cords short out for many reasons - insulation deterioration from age , damage , heat or bad terminations. If your converter has an AC distribution panel ,you could probably upgrade to a 30 amp ,120 VAC service. The size of your trailer's service is determined by the service conductors ampacity , the cord cap you use. the current rating of your converters AC distribution panel ,and the overcurrent protection protecting the service.

[gordon2]

On closer examination it does look like maybe someone put in a 30 amp converter but never upgraded the plug. Who knows what else is substandard. Probably would be safe if you replace the master breaker with a 15 amp one, but now that I look at it again, this is case of "take it to a professional for full inspection."

[Steve L.]

There would be two manuals that I would be interested in. You referenced the user manual. There should also be an installation manual that speaks to installing and wiring the unit. More searching the web should turn one up.

It appears you have 6 DC blade fuses and 3 AC breakers, one of which is a double 30A main breaker. You have two 20A breakers installed. Generally a 20A breaker would support circuits wired with 12 ga. wire (printed on the wire jacket). If it is 14 ga wire the breakers should be 15A, not 20A. The shore power cord looks like the typical shore power cord which means three 10 ga wires (Hot, Neutral and Ground). Given the somewhat amateurish plug job the PO installed, you should visually verify the wire gauge in the shore power cord. Further, I would verify that they followed standard practice in terms on connecting the proper wires to the converter.

It's easy to mix up Hot and Neutral. Similarly, a web search (get 2 or 3 web opinions) as to matching the wire color to the correct plug terminal. Given a 10 gauge wire and a 30 main breaker in the trailer, I'd go with the traditional 3 blade shore power RV plug. Also, they sell inexpensive polarity checkers in the big box stores to check things after you finish.

I would expect that fraying is often from not fixing the wire in the plug with the strain relief plug (they all have them) and/or pulling on the wire rather than the plug when disconnecting.

If all of this is confusing to you then this is probably not something you should practice on. At least not without someone knowledgeable checking your work.

[Joe Romas]

Besides the overheated 15 amp plug and the breaker situation all those yellow wire nuts stand out like a sore thumb to me. Get them connected properly.

Start with a 30 amp RV extension cord and cut the female end off and hook it to your panel properly.
Here's a 25' one for $30 with a molded end.
30 Amp Extra Heavy Duty RV Extension Cordset - 25' - Furrion I30ER25-SB - Electrical Cords - Camping World

Some owners worry about propane lines being a hazard. I lean more toward sloppy electrical work.

Joe

[Franswa]

from the picture of the plug with hand as reference the wire size might be adequate....I say "might" but can't be sure just looking at a picture....

it might just be that the plug shown, under the weight of the heavy cord worked its way loose (half on, half off) a bit from the receptacle and it started arcing, causing heat...could have been bumped loose too....the fix could be as simple as getting a 30A plug (rounded plug with wire coming out at 90 degrees...hanging straight down in actual use)....and using an adapter when you want to plug it into a 15A receptacle like an outside plug at your house.....

the rest of the wiring is a mess (sorry)....all those wires ought to be secured and if wire nuts are used AT ALL they should at least be very well taped up (wire nut and a couple inches of wires running into it) to eliminate vibration.

but there's so much going on there with loose wires all over the place that the suggestion of having the whole thing looked at by an RV or boat tech is a good one IMO

[LiseKen]

Thanks for all the insight and opinions! Other ideas welcome.

Steve L: The installation instructions are included in my manual, I will need to search and see if I can find them online.

All Others:

I did cut a piece of the shore power cord and the burnt plug and have it ready to take in to determine the gauge of the wire. A quick Google search on the printing on the cord leads me to believe it is between 6 and 18 gauge....ha!

Before I bought the Boler I used a polarity tester on the outlets and they were wired correctly.

I think I would prefer to replace the plug end with a 30 amp rated plug/cord for now and see how it works for me.

I already had calls into a couple electricians to take a look at all that wiring and help me decide what needs to be done. Yes, that hatch was a mess when I opened it, I just closed it right up while I dealt with new tires/bearings/brake cleaning!

So far i have had no luck finding someone willing to work on the electric. My husband handles basic household electric stuff, but feels this is out of his expertise. Unfortunately our local RV shop is not the type to give opinions or encourage a learning do-it-yourselfer.

My to-do list for other things is long, so I will continue on those things as I explore getting professional help for the electrical.

Lise

[LiseKen]

Franswa - your suggestion is great--I had not yet thought about getting a boat tech to look at it! I have been trying to figure out who would know about both 110 and 12 volt--duh--it's called "shore power" for a reason!

I'm in Seattle, so boat places abound. New plan for tomorrow...thanks!

Lise

[Steve L.]

Cables designed for trailer tow applications, the cable that connects the trailer to the tow vehicle, has two wire gauges and as many as seven wires (left, right, brake, backup, running and positive for battery charging, negative for ground. a six wire cord, which I associate with older trailers and European trailers, doesn't carry a wire for the backup lights.). The positive and ground are usually heavier than the wires for the lights and brakes.

The shore power cable is a different cable and should have only three wires of all the same gauge.

Buying a premade shore power cord and cutting off the female end is a good idea and one I've used for assorted wiring projects. As mentioned, the wiring on the trailer seems pretty sketchy. This would be a good time to spiff it up.

[Joe Romas]

On my Bergman 7 pin cable there are THREE sizes of wires

Plus and Minus charge lines are 10 gauge,
Brake wire is 12 gauge
Lights are 14 gauge!

Joe

[Steve L.]

Originally Posted by Joe Romas

On my Bergman 7 pin cable there are THREE sizes of wires

Plus and Minus charge lines are 10 gauge,
Brake wire is 12 gauge
Lights are 14 gauge!

Joe

I expect you're right. I did my post from memory this morning. Didn't do a check like I should have. But the point I wanted to make is the two cables are different and one of them has multiple gauges. If the shore power cord had multiple gauges then the previous owner really messed things up.

[steve dunham]

When I was working as an electrician ,when we rewired homes we were required to repair / replace any wiring that was obviously hazardous , illegal or unsafe. This led to a lot of problems
Many times it meant tearing out the wiring done by the homeowner and reinstalling it properly . The further you dug into the wiring the more you found things that were wrong.. I once filled a 2 yard dumpster with homeowner wiring I had to rip out. This led to arguments over the bill and on several occasions ended up in court.
If I was an electrical contractor , I would avoid working on your trailer because there is no way to estimate the cost or how much of the wiring needs to be replaced. In many instances , it is cheaper to rip it all out and start from scratch. A licensed contractor does not want to stick his neck out and face future liabilities.
We often got calls where people did their own wiring and wanted us to hook it up in the panel and certify that the wiring was safe and to code. We would refuse to comply with their request .

[LiseKen]

Steve makes sense contractors would not want to get into amateur wiring, and that's what mine is looking like.

I believe I've found a boat electrician who has worked on trailers before and is willing to take a look.

Thanks all for the advice and input. I am looking forward to cleaning up my trailer wiring and learning more about it in the process.

I take safety pretty seriously and share Joe's opinion about the relative dangers of propane and electricity. I've lived with/around propane with few troubles, but have seen enough electrical fires and other mishaps to give me a healthy respect.