Electrical Problem

[Sg6923]

I took my 3625RT 5er out last weekend to the same campground we've gone to for years. I hooked the 50 amp cord up and went in to run the slides out. I noticed smoke rolling out if the microwave. I ran out and shut it off, unplugged the microwave and plugged the camper in again. I went in and checked the voltage meter I keep plugged in the 120V outlet. It was all the way over and pegged out on the right and getting very warm. The fuse box switches were in the ON position. The repair center gave a quick look with a 30 amp plug and said my fridge, microwave and AC wouldn't work. All the 12 volt systems seem to work.

Does anyone know what the heck happened? The host.checked the box at the campground and said voltage was okay.

I unplugged and came home.

Thanks,

T-man & Sugar

[Herk7769]

This is a classic "Open Neutral"
This results in 240 volts in the camper.

Most likely since the campground checked out ok, the problem is either in your power center or the back of the 50 amp cord socket (or gang box).

[MIKE44460]

If I was the camp ground I too would of said, I'm good here, must be your equipment. You may be looking at a big expense. I would of had someone check their power before you pulled out. I carry an amp probe and meter and will check voltage before I plug in.

[MIKE44460]

Herc, what does a neutral have to do with 240AC?

[DDC]

I would imagine this is why some of us use a Surge Protector with Voltage Protection although if the fault is in the tailer it would not help either.

[Sg6923]

Thanks for the info. Pretty sure he's on the up and up. I watched him check it and others around that we're hooked up. It had the same readings as the others. Thanks.

[pmsherman]

Originally Posted by MIKE44460

Herc, what does a neutral have to do with 240AC?

A 50A connection should be similar to the power coming into your house. You probably have three wires: a neutral, and two hot wires. You get 120V between each hot wire and the neutral. If you measure between the hot wires, you'll discover that you have 240V. This is caused by the two 120 hot lines being out of phase with each other. A ground is generated by connecting the metal fuse/circuit breaker box to a water pipe which is buried in the ground. (Interesting question - what about new houses using plastic pipe? They'll require a grounding rod system to meet electrical code standards.) Since your motor home doesn't have a buried metal water pipe to provide a ground, the campground needs to provide one for you. This creates the four pronged 50A outlet.

If the neutral line is disconnected at the campground connection and you have an active electrical device connected to each of the hot lines, then 240V will appear across the two devices. If both were 100W bulbs, you could get away with this but when the devices have different wattage ratings, the current flowing in the device with the higher wattage rating will be greater (and can be much much greater) than the designed rating of the device. This was the cause of the smoke you saw.

When you connect your campground hookup, two devices are usually immediately powered up; the refrigerator and the converter. It's very likely that they are on different hot lines of the 50A circuit and could cause this problem. If you have a TV with "instant on", it also starts drawing power as soon as the AC appears at the plug.

Understanding how AC power works and knowing how to use a meter that lets you check each "circuit" in a 50A outlet will prevent this problem. When I check an outlet at a campground, I check each hot line to neutral for 120V, check across the hot lines for 240V, then check for voltage between neutral and ground. If no voltage between neutral and ground, I check the resistance between neutral and ground to verify that they're bonded together somewhere before the outlet. The neutral line is normally grounded at the power company's transformer that converts the (usually) 3Kv supply line to the lower voltage supplied to the campground. A large campground is more like a housing subdivision and may have multiple transformers and ground points. Bad connections at power poles can have interesting effects on outlets in one area of a park but not in others.

Phil

[MIKE44460]

Phil, if you don't have a nuclear reactor in your basement, you should. Thanks for a very informative reply. Something I will do, for sure, from now on.

[Herk7769]

Phil's reply was perfect. Thanks were sent (and sent again here).

If the neutral fault is in your camper (at the main circuits), it is possible to have an issue at the power center in your camper that would not show up at the pole. 240 VAC could still appear across some circuits depending on how the power center was wired, if the white neutral came loose at the common buss. The connection between the two "hots" would then be through the ungrounded "neutral" buss.

The damage will be the same; just the campground would have an "out."

[pmsherman]

Originally Posted by MIKE44460

Phil, if you don't have a nuclear reactor in your basement, you should. Thanks for a very informative reply. Something I will do, for sure, from now on.

It doesn't require a nuclear reactor. What got me started was the standard college preparation high school program I went through:
4 years math
4 years english
4 years history, social studies, government
4 years sciences
4 years gym
2 years foreign language
2 years mechanical drawing
1 years freehand drawing
2 years machine shop
1 semester each - woodworking, foundry, commercial printing, tinsmithing

Round that off with a stint in the military, a couple of college degrees, a 45 year marriage, two independent adult children, a 50 year interest in amateur radio (including climbing a 100' tower and helping install a repeater antenna on another that was hot with 50kw of RF energy), a lifelong interest in photography and astronomy, 35 years as a DIY homeowner (painting, woodworking, carpeting, plumbing, wallpapering, electrical work, masonry, and tree removal), 25 years as a member of the National Ski Patrol, and over 20 years of IBM selling my IT skills by the hour and I figure that by now I have the beginnings of a fairly well rounded skill set.

Phil

[Sg6923]

Most excellent info; better than I had hoped. I haven't heard from service yet but will update when I hear if the thread is still around. At least I'll have general knowledge when they start explaining what happened.

T-Man

[Sg6923]

I forgot to mention that the host verified voltage exactly as described at my post and a couple surrounding posts. He did not check neutral to ground. I'm definitely getting a voltage meter to verify before connecting. Thanks again guys.

T-Man

[Herk7769]

Were you there when he checked the 50 amp plug and how did he check it? Did he just tell you it was OK?

The voltage must be checked from each hot to neutral (not ground).
Both legs must read 120VAC. An "open" on this check will show 220 inside the camper on some circuits.

If the hots are checked to GROUND (not neutral) it will "appear" to be OK, but it may not be if the neutral wire is corroded or broken.

Read the attached discussion on campground power.

[Sg6923]

One side measured 119.8 and the other 119.7. He did check to what I assume was the neutral; the bottom center hole in the plug. I watched him do it.

T-Man

[Mark and Linda]

Herk, thanks for the pdf file. I have downloaded another one into my laptop for future reference. Thanks for all the info....

[Timex]

Great info there Herk!
Next question, say you're on vacation, pull into a site, run your tester and it shows a problem with the pedstal.
Or, after you hook up and over a period of time, problems with the power source occurs. Hopefully, the campground can fix the problem quickly or move you to another site.
Or, you pull in after check in and there is no one to call.

Guess you boondock for the night!

[jimh]

there may have been nothing wrong with the campground wiring. it could have been a worn neutral contact in the socket. results is as described above. a test of the outlet before u plugged in may not have picked up on this. as far as ur camper is concerned, same results.


one thing that i got corrected on here awhile back was the difference between neutral and ground. if they were tied together in the trailer, the ground should have corrected the problem. it isn't code to do it that way. u don't want to tie them together in the trailer. u want that protection between u and the appliance.

[pmsherman]

You can eliminate damage from worn or broken neutral connections by spending the $$ to replace all of your individual circuit breakers with GFCI breakers. Grounded appliances with leakage current (hot to ground) will, unfortunately, trip the GFCI breaker and not be usable. If GFCI breakers aren't available for your AC distribution box, you'll need to find a box that accepts them. Combined AC/DC breaker/fuse boxes could be a lot harder to replace than AC only boxes.

GFCI breakers are one of the solutions for protecting outlets in older homes that don't have ground wires in each outlet. If your state/county/municipality requires upgrading bathroom and kitchen wiring to include GFCI protection; it's a lot cheaper to add a couple of GFCI breakers instead of running wire through finished walls.

GFCI breakers work by measuring the current flow through the hot and associated neutral wires. If the current flow differs my more than a few milliamps (ma) then the breaker trips. This will prevent current flows between the two hot AC input lines.

Phil

[cfsoistman]

Originally Posted by Sg6923

One side measured 119.8 and the other 119.7. He did check to what I assume was the neutral; the bottom center hole in the plug. I watched him do it.

T-Man

The plug on the right is for 50 amps. Yes the bottom prong is the neutral while the two near the center are the load and the top round prong is the ground. The other plug is for 30 amps. As you're looking at this plug the prong to the right is the neutral and the other is the load while the round is the ground. Just for a reference if anyone needed it.

[Sg6923]

Thanks for the visual. I'm going to spring for the surge protector. Although I think the problem is within the camper, as yet unknown, it just makes sense to not take risks. The protector is a bit pricey but worth it for piece of mind.

T-man