outlet keeps blowing

[csarm]

I have an outlet (GFCI) that doesn't seem to have a breaker on it. Whenever it blows, it blows the fuse for the entire trailer and I have to go out to the electrical box and replace the fuse. I have been running a heater on that outlet and it was fine for a month or two, and then I charged my computer on the same outlet and the outlet shorted out and blew the fuse for the trailer. I replaced the fuse and power turned back on. Then I ran the heater for about 12 hours and then turned it up slightly and the fuse blew again (without plugging the computer in too). I had been running the heater on that level for months and now it just keeps blowing just after this one thing happend. Any ideas what the problem is?

 

[Bobtop46]

GFCI can get weaker over time and the number of times it trips. You could also have some wire damage from previous overloads.

Might want to open it up inspect for damage and replace with a new GFCI.

 

[Mark_K5LXP]

You're saying the outlet "shorted out" but it's implied that this has happened more than once, so has the outlet actually "shorted" or is that a generic term for an electrical event associated with this outlet? Unless this is an outlet that was installed incorrectly by someone after the fact, it's on a breaker. Might be a useful exercise to test it and identify what breaker in the panel feeds it or exactly what the connection path is.

You didn't say what size fuse is blowing and what kind of trailer it is that's actually using mains fuses. Seems unusual for anything made since about the 1970's. One explanation is the heater is drawing some portion of current along with loads on other circuits and the heater while by itself is not an excessive current, is pushing the fuse over the edge. At no time should a GFI cause fault current much less blow a mains fuse so there is something going on here that will require some critical review of the circuits in place.

Mark B.
Albuquerque, NM

 

[John From Detroit]

Most RV's are not wired for 1500 watt heaters. 750 Watts is usually OK but the way the outlets are designed they can fail at 1500 watts.. Sometimes the failure is... .Very bad.


Now the is more to it. MOST RV's the 120 volt outlets are breaker protected. no fuses. Do not know why your are popping fuses.

 

[Rene T]

An you take a picture of the fuse panel you’re talking about?

 

[DonTom]

Most RV's are not wired for 1500 watt heaters. 750 Watts is usually OK but the way the outlets are designed they can fail at 1500 watts.. Sometimes the failure is... .Very bad.

That is the first time I heard that. Aren't they 15 amp outlets? 120 VAC times 15 amps=1800 watts capable. BTW, I now have a 1500-watt tower heater on right next to me.

IMO, a lot of AC outlets fail because some people unplug items that are drawing a lot of current instead of turning them off first.

-Don- DeRidder, LA

 

[John From Detroit]

That is the first time I heard that. Aren't they 15 amp outlets? 120 VAC times 15 amps=1800 watts capable. BTW, I now have a 1500-watt tower heater on right next to me.

So they appear to be (15 amp) but the nature of the wiring is they can't do that. I'd keep em below 10.. Had to replace one in my RV (thankfully not a "Serious" failure just overheated) and have seen some melted I also installed special outlets for heaters in my RV. they were wired for 20 amps.

the "Punch Down" connectors work great for say telephones or internet cables running a few mA but at 15 amp they overheat not enough contact space.

 

[Mark_K5LXP]

Can't disagree with the position that the stab-on outlets are a latent problem but technically they're a 15A rated device and wired with 14ga wire, protected by a 15A breaker. It's a 15A circuit by every definition. I even found a data sheet for one brand: Speedwire-Manual.pdf

Whether or not one places their faith in the long term reliability of a given device is a separate discussion, but there's more to this than just the outlet. Some fuse upstream is blowing so aside from the inherent reliability of the socket there's something going on that needs addressing.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

The only real limitation on RV 15A outlets is that they typically daisy chain so many on a single branch circuit that you can't get 1500 watts (12.5A) from one outlet without pushing the branch circuit over its 15A limit. Also, 1500 watts is pushing the limit for the power that a 15A branch can continuously supply. A 15A breaker will eventually pop open if it delivers 13-15 amps for more than 30 minutes or so.

 

[Gary RV_Wizard]

I have an outlet (GFCI) that doesn't seem to have a breaker on it. Whenever it blows, it blows the fuse for the entire trailer and I have to go out to the electrical box and replace the fuse.

You have an actual fuse in your outside power box? As opposed to a circuit breaker? What size (amperage) fuse and is it the one for the outlet the RV's shore cord is plugged to? An description of the power set-up on your campsite and your RV's power needs (30A, 50A, etc) would be helpful.

Just to be clear, you are saying the GFCI in the outlet does NOT trip. What are the circumstances that cause the outside fuse to blow, e.g. some electrical appliance plugged in or ???

 

[Mark_K5LXP]

A 15A breaker will eventually pop open if it delivers 13-15 amps for more than 30 minutes or so.

If it does, there's something wrong. Residential breakers are rated for continuous operation at a nominal 40C ambient temp. If it trips at rated current then ambient is higher than that, a poor connection is raising the breaker temp, or the breaker is bad. There is no end to the variations of time delay and instantaneous trip combinations of breakers available but every time-current curve I've looked at there are zero trip conditions at or below rated current. My bet is that if a circuit is tripping after a long delay it probably is overloaded.

Mark B.
Albuquerque, NM

 

[garyb1st]

So for us non-engineering types who never heard of Stab-on outlets or Punch down connectors and have no idea of how to determine if the wiring is adequate to handle current a space heater what do we do?

We've used our 1500 watt space heaters for years. Prefer them over the propane furnace and usually they're on for hours. So far no indication of any failure.

 

[DonTom]

If it does, there's something wrong.

Yep, and internet searches agree. I found several places that give a spec something like this:

"Does a 20 amp breaker trip at exactly 20 amps? Actually, a 20 amp breaker must trip at a sustained current of 27 amperes (135 percent) at less than one hour, and at 40 amperes (200 percent of wire rating) in less than 120 seconds—"

-Don- DeRidder, LA

 

[SeilerBird]

So for us non-engineering types who never heard of Stab-on outlets or Punch down connectors and have no idea of how to determine if the wiring is adequate to handle current a space heater what do we do?

We've used our 1500 watt space heaters for years. Prefer them over the propane furnace and usually they're on for hours. So far no indication of any failure.

Don't waste your time worrying about stab on outlets or punch down connectors. What you are experiencing is normal. I was a union electrician during the 70s and 80s in southern California and personally installed thousands of stab on outlets. Southern California is prime earthquake territory and yet there has never been a problem with stab ons not working properly. They are used because the ones that have screw terminals would take several hours of electricians time more per house. If there would be any problem with this type of outlets it would have been discovered a long time ago and steps would have been taken to correct the problem. Your space heaters will cause no problem.

 

[Mark_K5LXP]

how to determine if the wiring is adequate to handle current a space heater

If the wiring was conscientiously installed to code you don't have to give it a second thought. It's not 100% foolproof as there can still be conditions that can cause problems but generally the end user shouldn't need to review any circuit they plug stuff into, that's what codes and inspections are for. If it's a 15A socket then the user can reasonably expect to get 15A. The basics of that is this circuit will have a 15A breaker, something less than 50 feet of 14ga copper wire and a 15A receptacle. So that would be your inspection criteria if you're wondering about what you have. Per code you can have more than one receptacle on a circuit so it's possible to overload the breaker with multiple devices, so knowing all the powered equipment on a given circuit is up to the user. Worst case there though will be the breaker trips and you find out immediately what was being powered and no longer is. Inherent durability and reliability of the receptacle over time and cycles is a separate issue. Ideally one has an awareness of a "loose" plug or one that gets warm during operation but not everyone is, and sometimes bad things happen.

Mark B.
Albuquerque, NM

 

[DonTom]

A 15A breaker will eventually pop open if it delivers 13-15 amps for more than 30 minutes or so.

Not a new one or one in good condition. A 15 amp breaker should NOT pop at 15 amps. Anything over that is time vs. current, but all should be fine with a 15 amps breaker with a continuous 15.000 amp load continuous for years, under normal conditions.

I get to correct you again?

FWIW, my RVs all have 20 amp breakers to the outlets, but all go to more than one outlet.

-Don- DeRidder, LA

 

[Lou Schneider]

Don't waste your time worrying about stab on outlets or punch down connectors. What you are experiencing is normal. I was a union electrician during the 70s and 80s in southern California and personally installed thousands of stab on outlets. Southern California is prime earthquake territory and yet there has never been a problem with stab ons not working properly. They are used because the ones that have screw terminals would take several hours of electricians time more per house. If there would be any problem with this type of outlets it would have been discovered a long time ago and steps would have been taken to correct the problem. Your space heaters will cause no problem.

There's a difference between residential "stab on" outlets and the one piece junk that's installed in RVs and doesn't meet code in any fixed application.

If the outlets in your RV have a one piece faceplate they use single point puncture connections to the feed wire, where the wire is laid in the back of the outlet and a V shaped knife blade pierces the insulation of the wire. The wire is held in place when the plastic back cover is snapped into place and provides continuous pressure to hold the wire in the knife jaws. Both of these can be compromised by heat buildup deforming the back cover and loosening and the connection.

Residential stab-on recepticles only use metal to hold the wire in place. The wire is pre-stripped and then inserted into a shark-bite style fitting that grabs onto the wire and self-tightens when the installer pulls back on the wire. This is much more robust than the connection in the RV style outlet. Additionally, residential outlets are installed in electrical boxes that provide positive rigidity to the connections instead of relying on the integrity of a snap on plastic cover to hold things in place.

In short, the outlets in most RVs are the bare minimum that will sort of do the job and are allowed only in the "temporary" RV setting. By the way, the NEC specifies a maximum of 80% of a circuit's maximum rating for "continuous loads" of over 3 hours duration. So a 1875 watt heater running for more than 3 hours overloads the outlet.

 

[DonTom]

. So a 1875 watt heater running for more than 3 hours overloads the outlet.

Just because it does NOT meet the code, it doesn't mean it is overloaded. NEC specs are overly cautious and yes, they use 80% for safety reasons.

When the CB trips, or when wires melt, or get overly hot, etc, that means you're overloaded. 99% of capacity isn't going to hurt anything in normal conditions yet such is 19% above the NEC spec. 100% capacity means exactly that, 100%, not 80%. The 80% is just some arbitrary value some paranoid group came up with to have a safety fudge factor.

-Don- Giddings, TX

 

[Kirk]

Aren't they 15 amp outlets? 120 VAC times 15 amps=1800 watts capable. BTW, I now have a 1500-watt tower heater on right next to me.

A 1500 watt heater at 120V will draw 12.5A. At 110V it would draw 13.6A. But, as Lou has pointed out in most cases in either an RV or a house a single circuit breaker will supply several outlets and so the circuit breaker sees the combined total load of everything on that circuit. If the RV is 30A it probably has only 1 circuit for all of the outlets. Most 50A RVs will have two outlet circuits.

The 80% is just some arbitrary value some paranoid group came up with to have a safety fudge factor.

That is not correct. Any circuit breaker actually has at least 3 designed trip points. There will be a long time trip which is usually around 80% of the marked rating. There is also a short time trip setting and that is typically 110 - 120% of that rating and the instantaneous trip point is typically 3 - 5 times the rated set current and sometimes even higher. For those who want to learn more about circuit breaker design, UNDERSTANDING TRIP CURVES

 

[DonTom]

At 110V it would draw 13.6A.

Has 110VAC been used anywhere in the USA in the last 50 years? Even under that 14 amp load?

-Don- Giddings, TX