Electrical question: 2 fuses operate together in parallel?

[dirtdivaca]

So while trying to troubleshoot power draw issues in our trailer, we discovered that two fuses seem to be running in parallel (or in series) as I think is the proper technical term? :@

In our 2014 R-vision travel trailer, we found two interior lights and power awning all tied into Fuse #1 and Fuse #10 in our fuse box. If you remove one of the fuses, the power to these items still works. It is not until you remove both fuses that the power is disabled. They are 15 amp fuses, so my question is this a safety issue? We are concerned that by running in series, they might be drawing 30 amp power and the wiring is not 30 amp (as we believe) and the fuses are not 30 amp. Is this a standard design done on Travel Trailer? :h We are also concerned that this might be fire safety hazard since the fuses won't trip properly if there is oversurge of power due to parallel design. I'm not EE so I apologize for posting a newbie question.

Unfortunately the Mfgr is out of business and we're not sure if this is a design flaw or not? Dealer doesn't have justification to charge to our extended warranty to look into this since we don't have a "failed" item to claim on it.

Anyways, I would love to get some input on if this is OK and why would mfgr do this? As we understand it, the power awning doesn't need 30amps to operate. Or does it?

Thanks much!

[Byrogie]

Glad you got that problem fixed...
Not hard to see why they went out of business.

[dirtdivaca]

DrewE wrote:
Does the fuse panel have lights that illuminate when the fuses are blown? ...If the fuse is blown and there is some load on the circuit, a handful of milliamps can flow through the LED, limited by the resistor and the impedance of the load, and it illuminates. If there's no load on the circuit, then the LED won't illuminate but the load side of the fuse connection will float up to about 12V.)

Good to know but they did test the wirings outside of the fuse box and that's how we determined there was still current flowing. They tested voltage coming on a "negative" wire so we knew there was something causing a short in the wiring. Which was now found to be attributed to extra wire in the thermastat area. :S I'm not sure what the mfgr guys were smoking when they built our trailer but they did worst shoddy job on our ducts, plumbing and now wiring.

[dirtdivaca]

IT'S FINALLY SOLVED! 🙂

"The consensus is that the manufacturer added a power wire to the thermostat, that is unnecessary and is causing a power loop back through the ceiling lights."

After everything they've torn apart to find the culprit, this was the issue. I'm glad we finally found the fix and now they can remove this extra wire and put trailer back together. I'm wondering :h if other R-vision trailers have same issue that were built around this timeframe (Jan/Feb 2014)?

Anyways - thanks all for your contributions and ideas! I'll keep you posted if anything else changes.

[DrewE]

Does the fuse panel have lights that illuminate when the fuses are blown? Those will cause stray voltages on the output terminals with the fuse pulled when measured with a voltmeter. If the dealer isn't familiar with that, I would start thinking about going to another dealer for servicing....

(Those little lights are nothing more than LEDs with appropriate dropping resistors in parallel with the fuse. If the fuse is not blown, it shorts out the LED and it does not light. If the fuse is blown and there is some load on the circuit, a handful of milliamps can flow through the LED, limited by the resistor and the impedance of the load, and it illuminates. If there's no load on the circuit, then the LED won't illuminate but the load side of the fuse connection will float up to about 12V.)

[dirtdivaca]

westend wrote:
I'd bet a doughnut that the awning is powered by the light circuit even though it has it's own fuse location. If the Mfg's guys wired the awning from the light circuit, when you remove a fuse, there will still be power available through the other circuit.

The first place I would look would be the outside scare light fixture to see if the awning motor's power wire is attached to that fixture.

Hmm, you bring up a good point! I'll pass it along. I wasn't aware that awning might have it's own inline fuse if I understand you correctly. If you're right, I'm getting you a dozen donuts!

[westend]

I'd bet a doughnut that the awning is powered by the light circuit even though it has it's own fuse location. If the Mfg's guys wired the awning from the light circuit, when you remove a fuse, there will still be power available through the other circuit.

The first place I would look would be the outside scare light fixture to see if the awning motor's power wire is attached to that fixture.

[dirtdivaca]

Just wanted to update the post, we still don't have a solution and dealer is still troubleshooting. Here's their response on what we've found so far:

"The problem is far beyond fuse 1 & 10. When we pulled all of the fuses fuse posts 2,4,6,7,8, & 12 all had 12volts, fuse 5 had 7.5volts. We pulled the fuse block out and checked the back side for corrosion or something that would have created this very strange connectivity. The fuse block is fine. This leads us to believe that there is something in walls or floor that could be causing this."

They dropped the underbelly and checked all areas where they did duct replacement work as well as in area behind fuse box where our drawers were not secured with screws (from mfgr). As final attempt, they swapped convertor and problem still exists. We are now at stage where they need to start pulling the walls down to visually inspect the wires. Ugh...such a bummer.

I was also able to contact Monaco RV and request diagrams on the trailer which I just rec'd -yay! I'm hoping we will be able to narrow down areas to troubleshoot. I'll update once I have more details.

[dirtdivaca]

D.E.Bishop wrote:
My first question would be are the wires identical? It's hard to tell in the photo, are both white or are they different colors?

The pic is not from my trailer, that is another poster just showing an example. It doesn't represent my scenario or situation. The awning as one of the options included in the trailer build so not sure if I'd say it's aftermarket. Until I have access to my trailer, I can't troubleshoot or take pics but if I get a chance, I will do so. Thanks!

[DrewE]

BFL13 wrote:
IMO there is no "short"--the pos touching the neg. Fuses are not blowing and wires are not melting. It does seem the pos of one is touching the pos of another. Can't tell about the neg side, but often that is "common" anyway.

I think your confusion is more semantic than anything.

A short just means two things are connected together directly, most commonly things that shouldn't be connected together. Those two things don't have to be power and ground, though that's certainly one common situation where the word is used. Obviously in this case it's not shorted to ground, but to another positive line somewhere.

An open is the opposite of a short--some connection that is disconnected, most commonly one that is supposed to be connected.

[D_E_Bishop]

I don't think this is going to be an easy fix or even trouble shoot but here is what I'd do, disconnect the batteries, remove the fuses and using your multimeter, check for continuity between the load sides, it would seem that would be the case, now disconnect the wires and check the load side of the fuse, probably no continuity, that rules out a short between the two circuits on the board. Now comes the really fun part, check the two load side wires, should be '0' ohms or shorted. My first question would be are the wires identical? It's hard to tell in the photo, are both white or are they different colors?

If ten is the awning and a different color from one it is after build most likely, beg, borrow, steal or buy a fair to middling signal tracing devise and hook it up and start following the wire for the awning. To make sure you're following the correct wire start at the load and work back to the fuse. If the awning wire is a different color than the lights, it probably is an after market item and the wire may not be in the factory loom.

One step I forgot is to disconnect the wires at the load, the lights and the awning and check for continuity between the wires.

[BFL13]

IMO there is no "short"--the pos touching the neg. Fuses are not blowing and wires are not melting. It does seem the pos of one is touching the pos of another. Can't tell about the neg side, but often that is "common" anyway.

The DC fuse panel should say what fuse 1 and 10 are for. What is the individual and total draw of whatever they are for? He says only two lights and the awning are affected. There must be more things on the two circuits?

15a of lights would be only five 3 amp lights, so there must be more light circuits. It seems the awning is tapped into both positives and has a neg somewhere. Or else both positives are touching (wrongly) and the awning is tapped into one of them?

The question seems to be what would happen if the OP turned on all of whatever is really on the 1 and 10 circuits at once. Can anything bad happen other than blowing a 15a fuse (or two)? Can he melt any wires? How?

Is the "short" people are talking about a short that could happen like that screw into the frame going through a pos wire, but there is no short now? If that did happen, isn't that what the 15a fuse is for? Why isn't that enough?

Both positives that are touching are individually fused to 15a and I ASSume are the right gauge wires for 15a circuits. Negs all in common say, but they don't matter AFAIK.

I am not saying it is safe for sure as is, but I have not understood what the problem could be as explained so far 😞 Thanks.

[RJsfishin]

2 positive wires connected together in not a "short", its just a bigger wire.
A "short circuit" is a shorter direct path to ground (neg)
And if such a thing happens, either fuses blow, or wires smoke.
If that's wrong, oh well.....

[dirtdivaca]

Joe417 wrote:
What Old-Biscuit and doughere said. You have a short between the two circuits. Remove one fuse and each circuit is still protected up to 15 amps until you find the short.

Thanks Joe - it seems based on all the feedback we have rec'd, it seems we do have a short. We have not done any customizations or screwed anything into the walls. As newbies, I've been too nervous without knowing what is behind the walls, I've been using the 3M adhesive hooks in our trailer.

Thanks to everyone (I LOVE THIS GROUP!) for responding and confirming that we are not crazy and have the same concerns as we do. I'll have the dealer follow up with diagnostics and once we learn more details, I'll be sure to update my post so others can learn from this. Thanks again!

[Joe417]

What Old-Biscuit and doughere said. You have a short between the two circuits. Remove one fuse and each circuit is still protected up to 15 amps until you find the short.

Each of the circuits is protected up to a maximum of 15 amps. The load on each circuit may only be maybe 3 amps but the designer calculated the wire can handle 15 amps so he fused it at 15.

With two 15 amp fuses in parallel (outputs shorted) it would theoretically require a 30 amp load before blowing a fuse (both would blow). But, if you pull 29 amps through one side of the shorted pair, the fuses may not blow. 29 amps in that single wire may not be a problem, but what is the safe limit for the wire used in either of the circuits.

The chances of pulling too much current is low but removing one of the fuses until you resolve the issue is on the safer side.

Might think back to any mods you made to the camper to help resolve the short, such as hanging a picture or a shelf with a screw.

A couple of years ago, I found a screw running directly through the middle of the #10 wire that supplies generator power to our transfer switch. The screw held an aluminium support brace which was in the basement and was isolated from all human contact. But, it was potentially a problem.

Might need to find your short to alleviate potential problems.