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Old 04-20-2012, 10:01 PM   #1
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Polarity testers disagree.

Hi, today I pulled my trailer forward in my driveway to get a few things done. First thing that I wanted to do was try out my new Orange 30 Amp RV adapter. It seems to make sense that by plugging into the 20 Amp duplex receptacle on my generator and having one 30 Amp type RV receptacle would give the best contact for my shore power cord. [for all practical purposes, I know that I'm not getting 30 Amps] Next was to check for proper polarity. I have two polarity testers and I believe that one of them is wrong. The first one showed a red light and a center amber light; This indicates no ground and reverse polarity. The second polarity tester showed one center amber light; This indicates, no ground. I believe that the second tester is correct; What does your tester read when using a portable generator? And finally, when both of the testers are plugged into a house outlet, they both read correctly. What is your opinion of this?
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Old 04-20-2012, 11:27 PM   #2
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I had one of the yellow ones. It started reading goofy after about a year. I would get inconsistent readings in the trailer, which I know was incorrect. Checked the same circuits with another tester, everything was OK.
Took it in the house, since the wiring is only 12 years old. When I plugged it in to a standard outlet it read goofy again. Plugged it in to a GFI outlet and it tripped the breaker.
I threw it out and bought a replacement.
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Old 04-21-2012, 01:09 AM   #3
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Bob

It is not unusual for the red light to glow at low intensity when there is an open ground or open neutral. Sometimes the amber lights will glow as well. Treat the lower intensity illumination as "off" for determining the situation. Some better quality testers don't do this but most of them do.
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Old 04-21-2012, 03:11 AM   #4
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System ground in Honda Generators

Not sure about the Yamaha, but in the owners manual for the Hondas there is a note about a ground fault error when using polarity testers. This is normal and safe condition (for Hondas). See quote from owners manual, below:

==========

GROUND SYSTEM

Connections for standby power to a building electrical system must be made by a qualified electrician. The connection must isolate the generator power from utility power, and must comply with all applicable laws and electrical codes.

Honda portable generators have a system ground that connects generator frame components to the ground terminals in the AC output receptacles. The system ground is not connected to the AC neutral wire. If the generator is tested by a receptacle tester, it will not show the same ground circuit condition as for a home receptacle.
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Old 04-21-2012, 08:04 AM   #5
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I prefer to use a volt meter. Checking between all three slots in the receptical you should get a voltage reading two of the three combinations.For a 120v 15amp or 20amp outlet,
A correctly wired outlet:
Between the short (hot) slot and the long (neutral) slot should read voltage. Between the hot and ground (round hole) you should get the same voltage. Between the neutral and ground you should not get anything.
A non grounded outlet:
Between hot and neutral you should get voltage.
Between the hot and ground you should get nothing.
Between neutral and ground you should get nothing.
A reverse polarity outlet:
Between hot and neutral you should get voltage.
Between hot and ground nothing.

Between neutral and ground you should get voltage.



For a 120v 30amp outlet the hot and neutral prongs are on the same side as the 15 or 20amp. As your facing the outlet, with the ground on the bottom, the hot is to the right and the neutral is to the left.
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Old 04-21-2012, 08:23 AM   #6
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I always use a meter when I have doubts about what the tester is telling me. I also check to make sure there is a good earth ground on the skin of the trailer. You can do that by checking between the hot side and the skin with a meter. You should read 120 VAC +/-
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Old 04-21-2012, 08:27 AM   #7
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Did you try the plug in circuit tester directly in the wall instead of through the watt meter?

Perry
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Old 04-21-2012, 09:50 AM   #8
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Robert,

Phoenix answered your question. I can't speak about your two testers but both of them are telling you that the generator is not grounded.

Last year my cousin set up his dish on a tripod and ran the cable to the Airstream. It was raining outside and we were watching a ball game. My cousin was getting a static shock whenever he touched anything in the trailer. The strange thing was that I was not getting shocked. I checked the circuit and noticed the no ground. I got my VM meter and noticed a phantom charge of just a volt or two between the ground and the neutral slots in the coach outlets. I was convinced that something was amiss.

After reading the Honda manual, talking to the tech at the shop and reading on line I found that this is normal. Last week I met up with my cousin again and we did the same thing except this time the dish was mounted to this camper and was not touching the ground. No static shock anywhere.
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Old 04-21-2012, 10:07 AM   #9
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Quote:
Originally Posted by Phoenix View Post
Not sure about the Yamaha, but in the owners manual for the Hondas there is a note about a ground fault error when using polarity testers. This is normal and safe condition (for Hondas). See quote from owners manual, below:

==========

GROUND SYSTEM

Connections for standby power to a building electrical system must be made by a qualified electrician. The connection must isolate the generator power from utility power, and must comply with all applicable laws and electrical codes.

Honda portable generators have a system ground that connects generator frame components to the ground terminals in the AC output receptacles. The system ground is not connected to the AC neutral wire. If the generator is tested by a receptacle tester, it will not show the same ground circuit condition as for a home receptacle.

Bob

I got a spare 30a pigtail and re-wired gnd to neutral so the meters read correctly when on the genset.

Bob
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Old 04-21-2012, 10:38 AM   #10
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I had the ground and neutral on the same buss bar in my Avion. Every time I plugged into a ground fault breaker at a campground it would trip. I separated the ground and neutral in the breaker box in the Avion and now I can plug into a ground fault at a campground with no problem. The outlet tester read OK in the trailer wired both ways.
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Old 04-21-2012, 10:51 AM   #11
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Portable gensets under 5 kw with plugs are not required by code to have the chassis ground and neutral bonded together like they are for grid power. That confuses folks with the power checkers sometimes.

i.e. a power checker that shows only one light and an 'open' ground is OK for a plug in genset.

This is related to why your RV circuit box does not bond neutral and chassis ground together. The RV is a sub-panel and the bonding is not done because it would create multiple ground paths which is a safety hazard. Again, see the electrical code.

If you have a permanently installed genset with a transfer switch, that switch will usually take care of proper chassis ground bonding when doing its thing.

Sometimes folks will tie one of the power leads to chassis ground to 'fix' this problem. The lead they bond to chassis then becomes the neutral. That is really not necessary and may even be a bit of an increased safety risk.

That 5kw power level is about 'leakage'. With some testers, you may see a 'ghost' voltage between a hot lead and ground. This is because of induced current and is nothing to worry about until you get to very high power levels.

Notes: 'bond' means electrically connected together. Grounds come in many flavors so I try to use chassis ground to avoid confusion. Earth ground is an entirely different thing and has its own interesting issues. The modern (since the 60's or so) electrical plug ground lug is a chassis ground that connects to an earth ground at one and only one place in a grid powered facility unless very special precautions are taken. That place is also the only point where the power neutral is connected to the chassis ground in grid tied systems.

re: " It was raining outside and we were watching a ball game. My cousin was getting a static shock whenever he touched anything in the trailer." -- watch out and be careful about jumping to conclusions! A static shock is an entirely different thing than the shock you can get from improper wiring. It is one of the things that chassis grounding covers but not neutral to chassis ground bonding. Static shocks can be just due to shoe sole and walking surface differences or it can be because the chassis ground is not connected between the antenna and the rig. Be careful messing with the power leads connections to things unless you really really know what you are doing.
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Old 04-21-2012, 10:52 AM   #12
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Quote:
Originally Posted by ventport View Post
I had the ground and neutral on the same buss bar in my Avion. Every time I plugged into a ground fault breaker at a campground it would trip. I separated the ground and neutral in the breaker box in the Avion and now I can plug into a ground fault at a campground with no problem. The outlet tester read OK in the trailer wired both ways.
You have to have the ground and neutral tied together on the hot side (upstream side) of the GFI for it work correctly. When you plug into shore power [at your house, for example] your camper looks like an extension of any other house circuits. If the neutral and ground is tied together downstream, then the GFI sees current in both of them and trips. You only want current in the neutral leg.

But since a genset it the upstream (hot) end of the circuit, why don't they tie the frame ground to neutral. Is it so that a generator can be tied into a breaker box and not duplicate the neutral-to-ground tie?

Zep
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Old 04-21-2012, 12:05 PM   #13
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You have to have the ground and neutral tied together on the hot side (upstream side) of the GFI for it work correctly. When you plug into shore power [at your house, for example] your camper looks like an extension of any other house circuits. If the neutral and ground is tied together downstream, then the GFI sees current in both of them and trips. You only want current in the neutral leg.

But since a genset it the upstream (hot) end of the circuit, why don't they tie the frame ground to neutral. Is it so that a generator can be tied into a breaker box and not duplicate the neutral-to-ground tie?

Zep
Now that finally makes sense to me thanks, Brian.
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Old 04-21-2012, 12:26 PM   #14
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What do you think of running a ground wire to earth from the generator grounding screw? Is the absence of that ever an issue?

Pat
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