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!

[mike-s]

BFL13 wrote:
Fuses are supposed to be sized for the wire's ampacity per AWG. If the wires to the fuses are proper for 15a DC fuses, then isn't that ok?

A 30 A circuit should have 10 ga wire, which is uncommon in RVs. And, if "the wires to the fuses are proper for 15a DC fuses," that doesn't mean they're proper for 2x 15 A fuse in parallel (~30A fuse).

[BFL13]

EDIT--warning! I don't have a clue, and am just asking, so don't ASSume nothing is wrong just because I am wondering about it!

Fuses are supposed to be sized for the wire's ampacity per AWG. If the wires to the fuses are proper for 15a DC fuses, then isn't that ok?

If somehow more amps are drawn than that, then a fuse should blow, perhaps they would both blow. As it is they are not blowing and everything works.

Is there really a safety issue here at all? It does look like "they" tapped in the awning with the lights (or vv) somehow looking for a pos and neg to connect to, and somehow got into two circuits for the pos side.

On parallel fuses, note that some inverters have twin wires for pos and neg (four wires total) If you use one fat AWG wire for the pos you can put say a 300a fuse on that OR use two thinner AWG wires and put a 150a fuse on each wire.

If one wire went, all the current would go on the other wire and blow the 150 amp fuse on it

[dirtdivaca]

Rolling Condo wrote:
A possible scenario would be where the power awning requires more amperage than one wire can carry. Therefore they have doubled up on the wiring, each wire would carry half of the load. From your description there are in parallel and not any shorts as the fuses would blow.

But if it required more amperage, why does it still continue to work if I disconnect one of the fuses? It seems it would require both fuses to be connected at all times to operate the power awning. I was told the awning doesn't require more than 15 but maybe I need to find the specs for that awning to confirm. Maybe I'm missing something.

[Rolling_Condo]

A possible scenario would be where the power awning requires more amperage than one wire can carry. Therefore they have doubled up on the wiring, each wire would carry half of the load. From your description there are in parallel and not any shorts as the fuses would blow.

[wa8yxm]

I have heard of fuses being wired in parallel but about the only place I have heard of it is in high amp converters. 60 or more amps will often have 2 or 3 (2 for 60 3 for more) in parallel as Reverse Polarity Fuses.

On a fuse panel your situation indicates a short.

[Old-Biscuit]

dirtdivaca wrote:
Good suggestion Doug - we will look into that!

The trailer is not accessible at this time so I don't know how many wires are connected, I'll have to find out or get to trailer one of these days. (it's offsite). If my memory serves me correctly, there is only one wire to each fuse which is why we are concerned that they must be crossed or connected somewhere else? :h Wouldn't that be a bad design?

More likely wires are 'shorted'.....pinched together/stapled together

Not good no matter how but doubt it is 'by design'

[RJsfishin]

You already verified that all of it will fun on 15 amps, so why not get rid of the 2nd fuse, and change the remaining one to a 20 amp, and be done w/ it.
Or seperate them into 2 15 amp circuits and be done w/ it.
The last thing I would do is letting some unknown electric wannabees in there and really screw things up. You sound perfectly capable of doing this very simple little job yourself. And besides that, warranty probably won't cover it anyway because they usually won't fix what ain't really broke.

[dirtdivaca]

Good suggestion Doug - we will look into that!

The trailer is not accessible at this time so I don't know how many wires are connected, I'll have to find out or get to trailer one of these days. (it's offsite). If my memory serves me correctly, there is only one wire to each fuse which is why we are concerned that they must be crossed or connected somewhere else? :h Wouldn't that be a bad design?

[doughere]

Until you get it fixed, I'd leave one fuse out.

Doug

[Old-Biscuit]

How many wires are connected to each FUSE terminal......
Fuse #1 and Fuse #10???

Are there more then ONE on each?

[dirtdivaca]

RoyB wrote:
My 12VDC Power Distribution panel where the fuses are located has two fuses off to themself which are the REVERSE POLARITY fuses...Maybe this is what you are seeing like shown here with the two red 40A fuses...
Roy Ken

Unfortunately, we are not looking at RED 40A fuses. (I'm not sure we have those inside.) We are looking at TWO BLUE 15A fuses. I think we have like 12 or 13 of them and when we went down pulling them out to see what items were connected (as part of resolving a power draw issue) we discovered that until you remove Fuse #1 and Fuse #10 (in our box) then the power awning and two interior lights stop working....but if you only pull one Fuse and leave the other connected, they still work.

[RoyB]

My 12VDC Power Distribution panel where the fuses are located has two fuses off to themself which are the REVERSE POLARITY fuses...

Maybe this is what you are seeing like shown here with the two red 40A fuses...


Google Image

Roy Ken

[dirtdivaca]

DrewE wrote:

What you're describing definitely does not sound normal or correct. I would guess that the lights and the awning were meant to be on separate circuits but somehow the positive lines got connected together somewhere.

Yes exactly what we are concerned about. The dealer doesn't seem to think it's an issue so I'm trying to gather more information so we can present case for warranty claim.

[dirtdivaca]

Thanks, we bought this trailer new and the company went out of business right after we purchased it (ugh). The power awning was part of the package option from the mfgr. It sounds like this needs to be addressed so I'll bring it up again and look into our extended warranty. Based on your responses, it sounds like this is an issue. Thanks guys!

[DrewE]

There are times when fuses are used in parallel, usually because it's less expensive than getting a single larger-capacity fuse. One common example is the main ("reverse polarity") fuses on converters, which are often two or three fuses ganged in parallel. I don't think it's ever a best practice, but it can be an acceptable one under the right conditions.

What you're describing definitely does not sound normal or correct. I would guess that the lights and the awning were meant to be on separate circuits but somehow the positive lines got connected together somewhere.