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Old 03-22-2015, 10:28 AM   #91
Mini-Skoolie
 
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Originally Posted by Redbear View Post
Thanks, Mike.

p.s. nat_ster is in Canada. I don't know if the NEC applies as rule there, but best practices should.
You're welcome. One thing to be aware of is that much of the insurance and legal industry in the US is driven by code compliance. So if you choose to build something that does not comply with a building or electrical code, and there's an accident of some sort, your insurance company could refuse to play the claim. I've also heard legal discussions about charging someone criminally if there's injury or death that results from knowing non-compliance. For instance, just last year a young boy was electrocuted by his parent's RV trailer in his back yard. They had been feeling warning shocks for a week prior to the accident, but didn't take it seriously. The trailer was plugged into a broken/rusted receptacle that obviously needed repair. I had a discussion with the local sheriff about charging the parents with involuntary manslaughter, but since it was a small town and the parents were devastated, no charges were filed. However, last year a city electrical worker admitted to not grounding/bonding street electrical boxes properly since they would be constantly resetting tripped breakers. A young girl was electrocuted (died) while walking on the wet street and stepping on the box cover. Of course this admission about not grounding the box on purpose opened up the city for a wrongful death lawsuit in the millions of dollars. Now I'm not trying to scare everyone. But if you build something that you know is unsafe according to code, and loss of life or property damage occurs, you now can become a target. The point is, if you don't like something in the electrical code, then get the code changed, don't just ignore it. I read constantly about electrocution deaths in countries like India simply because there's virtually no electrical inspections and no training for electricians or technicians. I always recommend that you follow all current NEC and RVIA codes (or whatever is required in your own country), and take any warning shocks seriously.
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Old 03-22-2015, 11:31 AM   #92
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Great info, I'm glad Mike himself is now here to answer questions.

A few people here are still Missing a few points I have tried to make.

A wood house has no metal skin or chassis. All grounds are run as conductors back to your breaker box. You have one ground / neutral bond, then the homes ground rod or plate. Two hot 120 volt leads and one neutral connect the transformer to the home distribution panel (breaker Box) No ground wire between the transformer and the distribution panel.

The way my bus is built, there is NO CHANCE of anyone ever touching the metal skin, and a electrical appliance or switch, ect at the same time. I have minimum 4 inches of rigid Styrofoam between me and the skin. We are only running 220 volts, not 600.

My bus is built like a house, not a bus. Forget about the metal skin and chassis, as they are irreverent on this build.

The size of the ground cables installed here in residential homes are small. They will do nothing to protect against lightning.

I have seen what happens to a house when hit directly by lightning. It melted every conductor within the strike zone. The ground wires that didn't melt became hot and started secondary fires.

All electrical was damaged and had to be removed and replaced. No big deal as the house burned half way down anyway.

My practices are safe. I don't mess around. I have valid points.

I'm following all normal wiring practices for a residential home. I just refuse to bond ANY wiring to my metal skin / chassis.

I could not care less about codes for RV's, or campgrounds. Our buses are nothing like a conventional RV. My bus will likely never see a campground. I don't like crowded places.

Later on, if I feel that I made a error not connecting grounds to the chassis, I can always add a connection later.

Nat
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Old 03-22-2015, 12:06 PM   #93
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Originally Posted by nat_ster View Post
Great info, I'm glad Mike himself is now here to answer questions.

The way my bus is built, there is NO CHANCE of anyone ever touching the metal skin, and a electrical appliance or switch, ect at the same time. I have minimum 4 inches of rigid Styrofoam between me and the skin. We are only running 220 volts, not 600.

My bus is built like a house, not a bus. Forget about the metal skin and chassis, as they are irreverent on this build.
Nat
Nat, you should be aware that all metal structures in a house, including furnace ducting, water pipes, etc.... are all required to be bonded to the incoming electrical ground, simply because there's always the possibility of creating a ground fault to that structure. And in your instance it could be possible to electrify the skin of the Bus with nothing more than an extension cord pinched in a door. If that occurs then you will definitely create a hot skin condition. While that won't be dangerous to inside occupants, outside visitors are now at risk. Even when you're stepping in or out of the bus and touching the metal steps and wet earth at the same time, you and your family are at risk of electrocution. In fact, that's generally how RV electrocution victims are killed. This is exactly the same scenario of the chain link fence that electrocuted some high school students in a football field a short while ago. The fence was not properly bonded to the electrical service box (even though it appeared to be grounded) and it's possible that an extension cord with a cut in the insulation electrified the entire fence. But the study is still out on it. And yes, it was only 120 volts AC.

So lets clarify how much voltage is dangerous. The dangerous current levels are generally considered to be - 1mA, threshold of feeling. 5mA is a solid shock that should trip a GFCI. 10mA can be dangerous to those with a heart condition. 20mA is so much current that you can't let go of the energized wire or object. 30mA for more than a few seconds almost guarantees ventricular fibrillation that results in death. Now the human body varies in resistance depending on moisture, etc... but is around 1,500 ohms hand-to-hand or hand-to-foot. A little ohms law hints that just 40 volt AC across a 1,500 ohm load will get you into the 25 mA range, which is so much current that you can't let go, and could kill you if you don't get off of the wire in a few minutes. So I consider 40 to 50 volts AC to be potentially deadly if your hands are wet. If you run the same math with 120 volts you'll see that 120 volts / 1,500 ohms = 80 mA of current which is definitely an electrocution hazard with potential nerve damage in addition to stopping your heart.

My point is, if you're not prepared to do the electrical math and compare the medical industry shock/voltage tables, then you shouldn't be promoting your own viewpoint and opinion to others. There's nothing special about your bus. It really is an RV as far as the MVA and electrical codes are concerned. Plus I can (and have) set up full scale demonstrations showing why RV vehicle grounding is important to human safety. Again, this isn't my opinion, it's standard electrical engineering theory and practice as well as legal building and RV code.

However, I'll be glad to do a full scale presentation at any bus rally if someone will get a budget together to bring me out. I am a full time audio-electrical consultant/trainer and have day and travel rates. However, the RV industry doesn't seem to be interested in electrical safety for its members, only in selling more vehicles. But if some foundation has a budget for me to attend some rallies, then please put them in touch with me because I'm certainly interested in doing demonstrations.
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Old 03-22-2015, 12:19 PM   #94
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Quote:
Originally Posted by jmsokol View Post
My point is, if you're not prepared to do the electrical math and compare the medical industry shock/voltage tables, then you shouldn't be promoting your own viewpoint and opinion to others.

That's why your here. To clarify in detail right from wrong.

How many milivolts or current does it take to cause electrolysis to my skin and chassis?
This is one more reason I didn't want my electrical connected to the bus skin and chassis in any way.

Mike, you have me 98% convinced to bond my grounds to the buses metal skin / chassis.

Nat
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Old 03-22-2015, 05:27 PM   #95
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Originally Posted by nat_ster View Post
How many milivolts or current does it take to cause electrolysis to my skin and chassis?
Nat
While I'm familiar with Galvanic sacrificial anodes for boat and hot water heaters, I'm not sure of the mechanism you're concerned about for your Bus. Have you or someone you know experienced this type of corrosion? If so, can you provide any details of the circumstances? For instance, I know that the interconnecting point between a steel chassis and aluminum body can have galvanic breakdown, that's built into virtually every RV or bus with an aluminum body and a steel chassis. What and where does this corrosion seem to occur?
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Old 03-22-2015, 06:11 PM   #96
Mini-Skoolie
 
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Originally Posted by nat_ster View Post
Mike, you have me 98% convinced to bond my grounds to the buses metal skin / chassis.

Nat
The thing to be aware of is you only want a single point of bonding the EGC (Equipment Grounding Conductor) to the frame. That allows no AC current to flow through the chassis under normal circumstances. Of course DC current from the house battery and starting systems are a different story. There's no getting around the fact that virtually all vehicles systems use the chassis as the 12-volt return path. I think those DC currents are doing to be magnitudes larger than AC leakage currents that could likely occur.

FYI: Here's a pretty good tutorial of just how galvanic action can occurs between aluminum and steel. Aluminium Corrosion Resistance - Aluminium Design
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Old 03-22-2015, 08:44 PM   #97
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Interesting points.. I had briefly thought about galvanic corrosion and sacrificial anodes, but decided it wouldn't be much of a concern for a bus that doesn't see significant inclement weather driving. Then again, it's potentially cheap protection.

Maybe all vehicles - not just boats - should have them.
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Old 03-22-2015, 08:48 PM   #98
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Originally Posted by jmsokol View Post
The thing to be aware of is you only want a single point of bonding the EGC (Equipment Grounding Conductor) to the frame.
Is this to say that metal device boxes should be grounded by the wiring run, but not touching any of the bus metal? I have my chassis grounded at the buses electrical panel, but I know that at least one of my device boxes is in contact with the bus structure as well. Would this be considered having two bonding points?
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Old 03-22-2015, 08:58 PM   #99
Mini-Skoolie
 
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Is this to say that metal device boxes should be grounded by the wiring run, but not touching any of the bus metal? I have my chassis grounded at the buses electrical panel, but I know that at least one of my device boxes is in contact with the bus structure as well. Would this be considered having two bonding points?
Yes, that's correct. In pro-sound systems double-bonding causes something called ground loop hum. And it can cause GFCI breakers to trip randomly. One way to correct that problem is to use isolated ground receptacles, and leave the metal boxes bonded to the metal of the bus. Now, I think that double-bonding ENG grounds would only add small amounts of circulating ground current under normal conditions that would require the addition of moisture to create corrosion. Still, it's one more thing to consider while troubleshooting grounding systems.
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Old 03-22-2015, 09:13 PM   #100
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Quote:
Originally Posted by jmsokol View Post
Yes, that's correct. In pro-sound systems double-bonding causes something called ground loop hum. And it can cause GFCI breakers to trip randomly. One way to correct that problem is to use isolated ground receptacles, and leave the metal boxes bonded to the metal of the bus. Now, I think that double-bonding ENG grounds would only add small amounts of circulating ground current under normal conditions that would require the addition of moisture to create corrosion. Still, it's one more thing to consider while troubleshooting grounding systems.
Ok, cool.. I'll rectify the situation. The outlets are all GFCI protected and haven't tripped yet, but I'll fix it anyhow.

PS: do isolated ground receptacles all come in orange? White would be nice...
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