vermilye
Oswego, NY, USA
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Quote:Regarding your statement "In a split phase generator (120/240V) there is a neutral and bonding of the neutral to the generator frame is required by both the NEC & OSHA", could you by any chance point me to the article that says the split phase generator has to be bonded, but doesn't also require the grounded conductor in a 2-wire system? When I first started looking at this in the 2005 NEC it was easy to find, but I'm having a hard time with the 2008 and 2011 editions Wish I could help, but I'm working from a 2005 code book - If I keep butting in on these discussions I suppose I should break down & buy a new one, but since retiring I don't use it all that much. I'm not clear on what you mean by "but doesn't also require the grounded conductor in a 2-wire system" As far as I know, the definition of a neutral requires a split phase system & a 2 wire, 120v system doesn't have a neutral so any rules for neutrals don't apply.
A discussion of bonding/grounding of portable generators at the Mike Holt Forum may shed some light on the bonding/grounding question. It also points out that even among electricians there is quite a bit of confusion...
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john&bet
North Vernon,in.
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I also think there is a huge difference between inverter based generators and the old fashioned contractor style generators and how the might affect this issue. To date I have not been able to get a complete understanding of how the inverter style are built, wired and work to my satisfaction. I do not own any type of generator. If anyone has a web site I could go to to help me I would appreciate it. Thanks.
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ExRocketScientist
Laurel, MD
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MrWizard wrote:this issue "bonding a portable generator" was discussed ad nausea for weeks in the 3000w Chinese generator forum
with the same results as here
it boils down to the bare facts
that unless you have a driven earth ground and bond Both and the generator frame to grd and rv frame to grd ( against code)
bonding the generator frame makes the rv frame part of the electrical circuit and subject to voltage potential above zero volts earth grd
I will never bond the "supposed" neutral of a 120v portable generator to the generator frame
I would rather be exposed to a capacitance of 60v low current in milliamps than a 120v shock from the generator output
real example here: many times I have used generator powered drills or saws or welder on the RV
if the tool failed and shorted out worn wiring , bad switch etc.. it would be a capactive effect of 60v
with the neutral bonded the voltage between hot and frame is 120v
remember your rv sets on tires, unless connected to shore power the frame is not earth bonded, and even then people get tingled or shocked between bare grd and door handle or steps
WHY. ?
because of voltage difference, improper or in Complete earth bonding on the circuits mean the bonded frame is Not at zero volts
bonding the 'neutral' to generator frame, without providing a solid secure buried earth grd per NEC specs for the generator frame, is not a good idea
your opinion may vary
That is why I have been saying "bond/ground" meaning both. Otherwise, look at the drawings OSHA has that explains how you can get fried. If you are going to run your tool off of a GFCI, you want bonded and earth grounded. If you aren't going to use a GFCI, you are, as you point out, better off not having any bonding or earth grounding.
Assuming you put wood blocks under all of your stabilizers etc. (or they have a perfect coat of paint on the bottom) your RV can be at a higher potential than the ground. We have had some reports here of people being shocked because their unit was sitting at a storage facility under a power line. In that case, there is a constant source of charge. Barring that, as soon as you touch some metal on your RV, you will bring the potential of the RV to that of the ground you are standing on. It is like dragging your feet on the carpet in the winter time and then getting shocked when you touch a door knob.
Aside from sources of charge like being under a power line, the only other case I know of where you would get more than that momentary "static shock" is when touching a helicopter that is hovering -- but I think this is limited to the Navy when they have to winch a helicopter down onto the deck in heavy seas (they actually have a special pole for hooking the cable to the bottom of the helicopter to keep the guy on deck from getting fried).
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Wayne Dohnal
Bend, OR.
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At a high level, the inverter generators are pretty simple. The motor drives a 3-phase alternator. The motor and alternator are physically integrated so there doesn't have to be a discrete flywheel with its associated size, cost and weight. The alternator can be fairly low cost because there's no need for it to produce a pretty waveform. The AC is then changed to DC, with a 3-phase switching regulator in-between. The regulator uses thyristors, the same devices used in light dimmers. The resultant DC level is in the 170 volt ballpark, the level needed for the peaks of a 120 volt sine wave. The control circuitry runs the engine at a somewhat higher speed than needed for the current load on the generator, allowing for the switching regulator to make instantaneous adjustments to handle small load changes seamlessly. A large load increase of course needs the engine to be spooled up, a fairly slow process. The 170 volt DC level then powers the inverter that produces the nice quality 120 volt AC output. The inverter may or may not have parallel operation capability, depending on the generator make and model. The generator's inverter is simpler than an inverter with a 12 volt input. The 12 volt inverter actually has 2 inverters, the first to convert the 12 volts to about 170 volts, and the second to produce the AC output. The inverter generator doesn't need this first inverter because the higher voltage DC is already available.
From listening, most people tend to assume an idling eu2000i is running at a few hundred RPM. Its low speed idle is actually 3,000 RPM. The higher power inverter generators tend to have bigger engines that run at lower speeds, which partially explains why an eu3000i is quieter than an eu2000i.
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ExRocketScientist
Laurel, MD
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john&bet wrote:I also think there is a huge difference between inverter based generators and the old fashioned contractor style generators and how the might affect this issue. To date I have not been able to get a complete understanding of how the inverter style are built, wired and work to my satisfaction. I do not own any type of generator. If anyone has a web site I could go to to help me I would appreciate it. Thanks.
I don't know about a web site, but I can give you some insight into the difference. It helps to understand old cars, so we won't be confused by the incorrect terminlogy used today. So lets go back to the 1950s. A car had a battery and used 12volt power for various things. Nothing new right? That power needed to be replaced. So there was a device on the car that generated 12volts DC (direct current). The key thing is it produced direct current, which is exactly what the 12volt system and the battery needed. The problem with them is they had to have brushes in them in order to produce direct current. This caused a high failure rate. So we get on into the 60s and instead of putting generators on the cars, they put alternators. These could be made brushless, but they produced alternating current. This had to be converted to direct current for the 12 volt system in the car and the battery.
Fast forward now to today and look at your RV. What you are trying to produce is 120 volts AC. Well what you need is an alternator. That is what you have on the typical "contractor generator". It is a brushless alternator hooked to an internal combustion engine typically turning at 3600 RPM to produce 120 volts AC at 60 Hz (the frequency will be dependent on the RPM of the motor).
Well we know that we can produce 120 volts AC from a 12 volt DC battery with an inverter. In fact, by doing so, the amount of amperage we draw is a funtion of how much amperage we have to produce. We control the frequency of the output AC current through the inverter electronics.
Well, why not supply the 12 volt power to the inverter using a generator we took off of an old 1950s car that we connected to a nice little internal combustion engine? Hence is born the inverter style generator. The way the eco throttle works goes back to what I said about the inverter. The required amperage in is a function of the amperage out. So when you don't need a lot of amps, you don't have to have high RPM on the engine.
Honda, when they came out with this took it a step further. These little single cylinder 4 stroke air cooled engines need a flywheel in order to operate. Typically, the magnetos for the ignition will be built into the flywheel. Well Honda used the generator as the flywheel -- yes thats right; unlike the contractor generator where the alternator bolts to the engine, on the Honda inverter generator, the generator is actually part of the engine. This eliminates some extra bearings, eliminates weight, reduces coupling vibration, and thus reduces mechanical noises.
Hope that explanation helps.
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