| Author |
Message |
doctor al
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 11:16 am: | |
I've got a small problem that maybe someone can guide me in the right direction. I noticed the other day that the bus would tingle me in the damp. obviously feeding electric thru the ground.(not good) Not a jolt, just tingle. I checked to make sure that no neutral (white) wires were hooked to the ground strip. none were.not sure where to start troubleshooting. Any ideas?
Thank You in advance, Alex |
Jim and Myrna Lawrence (Daffycanuck)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 12:14 pm: | |
Get yourself a small circuit tester...110 volt type that has the 3 indicator lights on it. Plug it into each receptical....it will tell you if it is an open ground etc...
Happened to me once and traced it to the landline connection, not my bus. I now check every landline connection I connect to before connecting. |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 12:22 pm: | |
Al,
Unplug all your loads and turn off all your circuit breakers first, then see if the problem goes away. If it does, turn things on one at a time until the problem returns -- this should help you to isolate the problem. Sometimes a ground/neutral fault in an appliance can cause this.
Also, you may want to connect a voltmeter between your coach chassis and a good ground on the shore, which will give you a more positive (and less tingly) indicator of what is happening than the touch-test.
Beyond that, I would need to see the wiring layout for your coach to provide more specific guidance.
-Sean |
doctor al
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 4:28 pm: | |
Give that daffycanuck a cigar. I have the 3 light circut tester. never occurred to me to check the recepticle I was plugged into. After all, it's at my house:-)
You were right on the money...open ground. fixed the plug, and no more tingle.
Thank You, Alex |
doctor al
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 4:31 pm: | |
Oh yes, thanks Sean, I took your advise and hooked the voltmeter to the earth and bus.waaayyy better than tingle. LOL
I've now added these pieces of equipment to the bus tool box. will never hook at a campground without checking first. |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 14, 2005 - 11:04 pm: | |
Al,
Fixing the open ground on the receptacle forces your coach chassis and ground to be at the same potential, therefore no more tingle.
It's probably still worthwhile, though, to find out what was "heating up" the chassis in the first place...
I would deliberately open the ground on the shore line, replacing with the voltmeter as I suggested earlier, then unplug/disconnect things until you find out what's dumping current to ground.
If nothing else, this problem will cause campground GFI's to trip when you plug in. At worst, it can be dangerous.
FWIW.
-Sean |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 15, 2005 - 2:03 am: | |
Sean, if ground is open circuit, the "Y" capacitors in most line filters will force enough current into the ground lead to make you tingle. Usually not enough to hurt you but it'll make you jump.
If Doc has most anything electronic plugged in that has a built in line fiter prior to a switcher, it'll happen even if everything is up to par. So he may have absolutely nothing wrong. This drives audio guys with hum NUTS.... All it is is a couple of .001 caps in series between hot and neutral, with the CT hooked to ground. tries to drive ground to 60 volts. Pretty much industry wide standard although I never liked the idea (I'm a studio engineer sometimes)...but it does get rid of common mode stuff when things are "right"... |
ChuckMC9 (Chucks)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 15, 2005 - 10:11 am: | |
Gary, for some reason I find this interesting. If you feel like typing could you cover what you said above in a different way?
Are you saying that an amplifier, for example, will be trying to filter out certain noise/frequencies and drive that 'excess' to ground to dispense with it?
And if if the ground is open, it's being driven back into the amp, for example, which causes the dreaded 60 cycle hum, rather than being shunted into the earth?
Web site for an overview of this? |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 15, 2005 - 11:20 am: | |
Gary,
You are absolutely correct. I should have been more clear that this did not *necessarily* mean anything was broken.
Turning off circuits until the tingle went away would reveal what appliance was causing the issue, and if, as you say, it's something with a filtered supply, then no worries.
If it were me, I'd want to know for sure what it is.
Incidentally, capacitors in my inverter preclude me from ever plugging into a GFI circuit. (Different issue, I know, but annoying.)
-Sean |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 15, 2005 - 11:51 am: | |
Chuck, sorry I got into electronic speak a little bit, because I knew Sean knew what I was talking about. Electronically it's a pretty simple subject but if you don't know electronics, it probably sounds like a foreign language, and it is!!
Let's see....
In most electronic devices, TV's stereos, etc, the power supply inside is a switcher these days. This means that instead of a hunky heavy copper-iron transformer of the 60's, there are a bunch of tiny lightweight electronic parts that do the same job of creating internal supply voltages for the device. But they do it in a different way, much less expensive and much lighter. For example, this is why microwave ovens of today weigh about 1/4 what they did in the 60's -80's, and why you can have 1000 watt stereo amplifiers that don't weigh 200 pounds.
In doing their job, switchers create a lot of RF energy that if left untamed, would be seen by the outside world as horrible RF interference. So they need to have filtering devices built in to make sure this doesn't happen.
In one common aspect of the filtering scheme, manufacturers connect a tiny capacitor from hot to ground, and another identical one from neutral to ground. These are called "Y" capacitors. As long as ground is intact, no biggie, but if it's lifted these capacitors now appear, electronically, to be in series with the center tap between them hooked to ground.
If ground is hooked up as it should be, the result is a tiny amount of current "pumped into" ground through these capacitors on every cycle of the 60hz sine wave. That is an artifact of the real reason for them, which is to bypass any really high frequency interference to ground.
What happens when ground is disconnected... the two capacitors now act as a "capacitive voltage divider" and they try to bring the ground lead up to 60 volts (half of line voltage), and they often do just this. Since the current they can supply is limited by their (small) capacity, it is not dangerous but it can make you tingle, and often does. If measured, it's only a few tens of microamps which is not necessarily dangerous, just annoying.
I suppose that if you actually plugged enough devices with Y capacitors into a circuit with a bad ground connection, they could gang up on you to the point that you could possibly get shocked enough to cause bodily harm... An interesting flaw to a supposedly perfect system...
Since you asked about the audio aspect, it's a bit to digest, I'll see if I can make it simple...
Picture an audio amplifier and a CD player... also to be very clear, let's think "professional" studio stuff that has three prong plugs instead of two prong plugs. (Most home stuff is two prongs these days, so for them this discussion isn't as applicable, although the problem still exists...too deep to get into on a bus board)
The amplifier and the CD player are both plugged into a power strip. Both are grounded thru the 3rd pin on the power plug. So far so good. Now connect the audio cable between the two... ok, what you've just done is create a ground loop... if you follow... CD player has a ground in the audio cable that goes to the amplifier, which has a ground in it's power cable going to the power strip, which then has a ground in the power cable going back to the CD player. A little circle.
As long as this is all you have and it's hooked up correctly, it'll probably sound ok.
So here you have these little capacitors pumping a tiny bit of 60hz into ground. No problem as long as ground is intact. But disconnect the power ground and now you have these little capacitors pumping 60hz (and any RF) into the only ground left in the system, the audio cable! This is where that really annoying 60hz buzz comes from in many audio systems.
This same thing happens is systems with only two wire plugs but again, too deep to get into on a bus board... but I hope the example I gave is clear enough. It's just the tip of a giant iceburg in the audio industry.
...So, the above being a gross oversimplification, I hope I made it understandable... it's the subject of much black magic, and an audio engineer's biggest nightmare. I know, I used to be in that biz....
|
Brian Brown (Fishbowlbrian)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 16, 2005 - 2:15 am: | |
Wow, Gary, thanks. I never cease to learn stuff just lurking the boards. Hats off to you and other gurus sharing your knowledge. It's much appreciated!
BB |
Phil Dumpster
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 16, 2005 - 8:50 am: | |
Surge supressors can also do it.
Surge supressors use a variable resistance device that looks like a disc capacitor, called a MOV (Metal Oxide Varistor). These change their resistance depending on the voltage across their terminals. At low voltages they have a very high resistance, and above a device's rated voltage they drop to a low resistance.
Most supressors have three of these where power enters the device, one between line and neutral, one between neutral and ground, and one between line and ground. If the ground connection is left to float, a voltage divider is created through the MOVs which can bring the ground line potential to half the line voltage. Because of the high resistance of the MOV at less than its rated voltage, the current available is very low, but it is enough that you could feel it.
These days, many solid state electronics have surge supression built in, which is one of the reasons why they carry a warning about plugging into only a grounded outlet.
As in the past, I still recommend that you never connect AC house electrical ground to chassis vehicle ground. You're only asking for trouble if you do. |
ChuckMC9 (Chucks)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 16, 2005 - 10:35 am: | |
Gary, thanks a lot for your trouble! The last knowledge I had from similiar subjects was back in the day of those hunky heavy copper-iron transformers. I vaugely remember ground looops and those issues, and it's good to revisit. |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 16, 2005 - 1:00 pm: | |
Phil,
Some surge suppressors can, indeed, create this situation.
However, I need to take exception to this statement:
"I still recommend that you never connect AC house electrical ground to chassis vehicle ground."
A connection between the main AC ground and the chassis is required by code at the main electrical distribution panel. Omitting this connection can be extremely dangerous.
The connection is required to ensure that any hot circuit accidentally coming into contact with the vehicle frame does not make the entire frame "hot" and thus render it a shock hazard to touch.
Remember that the vehicle frame is otherwise isolated from earth ground. Even a direct short of, say, the main 30a or 50a shore feed to the vehicle frame would go undetected. A person standing on the ground (or worse, holding something metal connected to the shore power system) who then touches the vehicle could complete a circuit and be subject to fairly high current, a potentially fatal situation.
So I have to say that whatever trouble you think might be created by making this required connection, it is not worth the safety risk to avoid it.
-Sean |
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