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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Generator Parts and Frequently Asked Guestions


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  #31  
Old 08-16-2010, 10:20:27 AM
armandh armandh is online now
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Default Re: Generator parts and frequently asked questions.

ok here is some thoughts on simple rule of thumb for correct bonding
for typical 120/240 house hold single phase transfer

first remember the earth ground should never be carrying current except during a fault condition.

right now your main entrance panel is probably your point of bonding
It may be able to remain that way but ....
only if your generator CAN operate with an isolated neutral
[4 wires...hot, isolated neutral, hot, earth ground]
and only if the utility does NOT require a meter base with disconnect [new bonding point] or a real transfer switch

given the above you are using manual transfer and manual load shedding

a two wire transfer with interlocking breakers [if allowed by local code]
is possible BUT if you want, or code requires a real transfer switch
it is the first disconnect. or
if the utility or local code requires a meter base with a disconnect
then the bonding point is at that first disconnect in either case there will be 4 wires coming out. Hot, neutral, hot, and earth ground.

then an isolated neutral bus [kit] must be installed or bonding strap or screw removed in the distribution panel so that the bonding at the meter base or transfer switch is the only one.

A two wire transfer is still ok [if code permits] and if the generator can run with an isolated neutral and separate ground [as it still picks up the same bonding point in the meter base or transfer switch]

if your generator can not function with an isolated neutral and must be bonded then a 3 wire transfer is necessary along with a meter base bonded disconnect and the isolated neutral in the distribution panel.

here each separate source has its own bonded power to select from

if you are doing your own isolated neutral install be sure the neutral buss gets only neutral wires and the ground buss gets only the ground wires.

if by now you are totally confused get professional instillation help
this is deadly serious stuff; most anything involving a new meter base or mains transfer switch will require a licensed electrician / permits any way.

automatic transfer is out of my experience/comfort zone

but unless you are getting a whole house generator
and a whole house transfer best left to a professional
you will be setting up an emergency sub panel
[all sub panels must have an isolated neutral]
here 2 or 3 wire transfer will again depend on the generator's
isolation or bonding respectively.
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  #32  
Old 05-17-2012, 10:19:08 AM
Joe Romas Joe Romas is offline
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Default Re: Generator parts and frequently asked questions.

Quote:
Originally Posted by Chainsawman1 View Post
Do you need to use a shunt????
This is one I can answer

Not when you use a CT. I've been looking at some on e-bay like these and the CT is included.
http://ebay.com/itm/Analog-Round-AMP-Meter-Current-trensformer-AC-50A-/150818124465

It does not say but they are about 3" in diameter, I asked
You just run the insulated wire through the CT and it picks up a reading without any electrical connection to it.

Joe
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  #33  
Old 05-17-2012, 02:29:36 PM
Graycenphil Graycenphil is offline
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Default Re: Generator parts and frequently asked questions.

Can you (should you) connect the chassis of your portable generator to a ground rod, when feeding the house with extension cords? If not, why? What is the risk?
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  #34  
Old 05-18-2012, 08:24:17 AM
armandh armandh is online now
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Default Re: Generator parts and frequently asked questions.

Quote:
Originally Posted by Graycenphil View Post
Can you (should you) connect the chassis of your portable generator to a ground rod, when feeding the house with extension cords? If not, why? What is the risk?
feeding appliances in the house or connecting to the house with an illegal back feed????

in every correctly wired case a ground rod to the generator case is advisable
drive one in where the portable generator will sit and use automotive jumper cables. doubling up won't hurt.

if you are running extension cords into the house to feed appliances the generator should have its neutral bonded to the frame
so that the neutral return path will stay near earth [0 volts] [the same for a transfer system where the neutral is transferred]

if you are feeding an interlocked panel where the normal feed is locked off when the generator breaker is on [or other 2 wire transfer]
then the generator neutral should not be bonded to the frame as there is another household bonding point.
this is usually a 4 wire feed hot, neutral, hot, and earth ground

same for an illegal back feed where the main breaker is not interlocked.

[in retrospect] if one is forced by circumstances to do such an emergency back feeding [and it better be to save someones 90 yo mother]
pulling the meter is not a bad idea.

however, a little planning can go a long way to avoid illegal back feeds.
installing a main panel main breaker interlock or...
putting gas or oil fired furnaces on a short heavy plug and cord to an outlet
where there formerly was a switch [now switch and single outlet combination]
makes extension cords workable feeding appliances. [avoiding the house wiring]
as I recall single outlets for permanent appliances are exempt from ground fault requirements.
wells are a little trickier but doable.

during a week long summer outage my 90+ yo mother stayed home
but in the back yard was my 7.2 KW Kohler K-582 powered Homelite
with heavy extension cords feeding a window AC, refrigerator, microwave, and some lighting. [the cable tv was out anyway]
[and by the end of the week a lot of cell areas were out]

in summary
the neutral and safety grounds should never be the same wire and should be bonded together at only one point.
extra grounds generally do not hurt
this may be a problem for some lightning protection situations but
if there is only one bonding point then there is likely no ground loop troubles as
the safety grounds should not be carrying current except during a short fault condition [pun intended]

Last edited by armandh; 05-18-2012 at 10:15:27 AM.
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  #35  
Old 05-18-2012, 11:15:15 AM
Graycenphil Graycenphil is offline
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Default Re: Generator parts and frequently asked questions.

Kind of related, I have an electric log splitter, which I plug into the (3 wire)dryer outlet. I should probably connect that too a ground rod too? If it were a 4 wire dryer outlet, would the ground be less important? Is there any reason not to ground the splitter?
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  #36  
Old 05-18-2012, 02:07:08 PM
Power Power is offline
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Default Re: Generator parts and frequently asked questions.

This has been discussed many times in the past. Contrary to common thinking, The correct answer is if the generator only supplies cord and plug, it should not be grounded Grounding a generator supplying cord and plug greatly increases the risk of electrocution.

If it is connected to the house electrical system, It must be bonded at the panel, and should NOT be bonded at the generator. Installing a ground rod is generally wrong. The only time to install one would be if the generator is a primary suply in a separately derived system.
Here is the OSHA article again

oshaprofessor.com/Portable%20Generators%20and%20OSHA%20Co...

OSHA FactSheet excerpts

Major Causes of Injuries and Fatalities
• Shocks and electrocution to users from
improper use.
Safe Work Practices
• Maintain and operate portable generators
in accordance with the manufacturer’s use
and safety instructions.
• Always plug electrical appliances and tools
directly into the generator, using the appliance
manufacturer’s supplied cords. Use
heavy-duty extension cords that contain a
grounding conductor (3-wire flexible cord
and 3-pronged cord connectors).
• Proper grounding and bonding are a means
to prevent shocks and electrocutions.
• Use ground-fault circuit interrupters (GFCIs)
as per the manufacturer’s instructions.
Grounding Requirements for Portable
and Vehicle-mounted Generators
Under the following conditions, OSHA
directs (29 CFR 1926.404(f)(3)(i)) that the
FactSheet

frame of a portable generator need not be
grounded (connected to earth) and that the
frame may serve as the ground (in place of
the earth):
• The generator supplies only equipment
mounted on the generator and/or cord and
plug-connected equipment through
receptacles mounted on the generator
,
§ 1926.404(f)(3)(i)(A), and
• The noncurrent-carrying metal parts of
equipment (such as the fuel tank, the internal
combustion engine, and the generator’s
housing) are bonded to the generator
frame, and the equipment grounding conductor
terminals (of the power receptacles
that are a part of [mounted on] the generator)
are bonded to the generator frame,
§ 1926.404(f)(3)(i)(B).
Thus, rather than connect to a grounding
electrode system, such as a driven ground
rod, the generator’s frame replaces the
grounding electrode.

Safe Work Practices
• Never attach a portable generator directly
to the electrical system of a structure
(home, office or trailer) unless the generator
has a properly installed open-transition
transfer switch.
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  #37  
Old 05-18-2012, 02:13:31 PM
Graycenphil Graycenphil is offline
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Default Re: Generator parts and frequently asked questions.

How does grounding the generator increase the risk of electrocution?
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  #38  
Old 05-18-2012, 04:35:42 PM
armandh armandh is online now
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Default Re: Generator parts and frequently asked questions.

I disagree but here is the reasons for/against


against bonding a generator in the field:

if the hot and neutral are floating any contact with a conductor will have no return path, thus no shock hazard.
this assumes all the other equipment plugged in have no earth to neutral or hot leakage


for bonding and grounding a generator in the field:

static charge build-up in the generator could exceed the insulation value of a hand tool causing a high voltage static shock or damage to electronic components.
ungrounded generators could be like filling a gas can on a plastic bed liner.


best practice for a generator in the field [IMHO]

a grounded generator a bonded neutral and ground fault breakers on/in all outlets.
[see 4 th and 5th bullet points above]

[but it is your butt and your choice]


a third option would be grounded generator frame and high Z bonding with ground fault outlets

since ground fault interrupts measure the hot and neutral current tripping when they are unequal
they will work with or without bonding; but only if used separately
[two items plugged into the same ground fault in a floating system, one faulted to n, one to hot=no trip]
this along with a gas discharge or MOV from the n to ground to prevent static build up
might be an improvement on either choice.

Last edited by armandh; 05-19-2012 at 06:33:14 AM.
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  #39  
Old 05-18-2012, 06:29:17 PM
Power Power is offline
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Default Re: Generator parts and frequently asked questions.

Read the articles and look at the pictures.

---------- Post added at 06:29 PM ---------- Previous post was at 06:21 PM ----------

Well, Armandth I used to ground portables in field for the reasons yu state, until I was told OSHA does not want them grounded, and new NEC indicates best to float them. There is an exception for over 5KW for possible static build up, but the experts claim not an issue under 5 kw.
If there is an issue, and the unit conforms to OSHA and the National Electric Code, the risk of litigation should be minimized. If the unit has a ground rod or other ground, the legal boys surely will point out it is not in compliance with codes and try to stick it to the owner, no matter the good intentions.
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  #40  
Old 05-18-2012, 08:03:18 PM
Graycenphil Graycenphil is offline
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Default Re: Generator parts and frequently asked questions.

I still don't see how groundinng the generator can be more dangerous. Won't having it connected to a ground rod eliminate the possibility of you getting the shock if anything goes wrong when you are touching the frame? And wouldn't the same be true with my electric log splitter? Is there any way it would be more dangerous wth the ground?
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