# Generator Earthing

B

#### Barry

Jan 1, 1970
0
I have purchased a "top shelf brand" single phase 240volt portable
generator. The manufacturer's instructions instruct me to use an earth
stake..

Why?

I have seen many other people with generators who do not use earth stakes.

I don't understand.... Am I at risk if I don't use one?

What causes the risk?

Any help would be appreciated

S

#### sQuick IEng MIIE $$elec$$

Jan 1, 1970
0
Barry said:
I have purchased a "top shelf brand" single phase 240volt portable
generator. The manufacturer's instructions instruct me to use an earth
stake..

Why?

To cover there own backsides.

I have seen many other people with generators who do not use earth stakes.

I don't understand.... Am I at risk if I don't use one?

What causes the risk?

The risk is a piece of metalwork becomes live, and is not grounded
to the same point as the supply thats making it live.
Any help would be appreciated

sQuick IEng MIIE (elec)

B

#### Barry

Jan 1, 1970
0
Thanks. however I am still a little confused why an earth stake is
necessary. How can the connection of a wire from ground to the frame of the
generator guarantee that the peice of metalwork you refer to is connected to
frame as well?

Sorry for appearing dumb.

S

#### SQLit

Jan 1, 1970
0
Barry said:
I have purchased a "top shelf brand" single phase 240volt portable
generator. The manufacturer's instructions instruct me to use an earth
stake..

Why?

I have seen many other people with generators who do not use earth stakes.

I don't understand.... Am I at risk if I don't use one?

What causes the risk?

Any help would be appreciated

When ever you create electricity there must be a path to earth. With out the
earth ground you run the risk that you circuit breaker will not trip. Ever
notice that every electrical service in your neighbor hood has an earth
ground? If the utility could get away from using them do you not think that
they would quit spending the money? Not earthing the neutral can cause
voltage imbalances to be created. A lot of people just rely on the frame of
the genset to be in contact with the earth... close enough. It takes no time
to drive an minimum 8 foot ground rod flush with the earth and connect it to
the generators frame to the lug provided. (usually)

Make it safe and make your SO's safe. It only takes about 5 milliamps to
kill. Less in some conditions.

I worked for a university and the city folks set 10 20 kw generators on
tires for temp Christmas lighting not one was grounded. I shut them off and
locked them out. The mayor and the president of the university were in the
electric shop the next morning. I explained the safety issues for the public
and the mayor immediately called his people and they installed the required
ground rods. Christmas lights were dark one night. No big deal compared
with making the headlines all over the world. Personally I do not want to
be on TV.

S

#### SQLit

Jan 1, 1970
0
| When ever you create electricity there must be a path to earth. With out the
| earth ground you run the risk that you circuit breaker will not trip. Ever
| notice that every electrical service in your neighbor hood has an earth
| ground? If the utility could get away from using them do you not think that
| they would quit spending the money? Not earthing the neutral can cause
| voltage imbalances to be created. A lot of people just rely on the frame of
| the genset to be in contact with the earth... close enough. It takes no time
| to drive an minimum 8 foot ground rod flush with the earth and connect it to
| the generators frame to the lug provided. (usually)
|
| Make it safe and make your SO's safe. It only takes about 5 milliamps to
| kill. Less in some conditions.
|
| I worked for a university and the city folks set 10 20 kw generators on
| tires for temp Christmas lighting not one was grounded. I shut them off and
| locked them out. The mayor and the president of the university were in the
| electric shop the next morning. I explained the safety issues for the public
| and the mayor immediately called his people and they installed the required
| ground rods. Christmas lights were dark one night. No big deal compared
| with making the headlines all over the world. Personally I do not want to
| be on TV.

At how many points is ground needed? Can this be safely done with a single
solid ground at the transfer switch on a permanently installed generator?

Electrical grounding is always done at a single point at the point of
service or generator. It get a little more complicated when you are working
with a transfer switch. Assuming single phase residential USA. Transfer
switches come in 2 pole solid neutral and 3 pole where even the neutral is
switched. I prefer the 3 pole switches because then the neutral is directed
to the source and is not shared with the other source. Which can be a
bugger to figure out some times.

The ground rod for the generator can be driven local to the generator. Then
you will carry the ground to the other source and tie it together. You will
be creating a supplementary ground system. When either source has a fault
the path will take it back to the ground. Tripping the breaker. If you do
not carry the ground you can have a situation where is can become dangerous.
Try to locate the Soars Book on Grounding at the library,
http://www.ecmweb.com/ar/electric_earth_not_bonding/

Might be a better picture than my words. I just moved, and still have not
unpacked my books.

Section 230 of the NEC is written for grade 22. I have submitted several
times to the NFPA to change the wording so it is not so hard for people to
understand. They have nixed it each time. Oh well I like tilting at
windmills.

B

#### Barry

Jan 1, 1970
0
Thanks SQLit,

I can see that a 1phase unit needs an earth stake now. Is that because one
end of the winding is connected to the frame of the genset and the other end
is the active?

If this is the case do I need to use an earth stake with a 3 phase gen set
connected in Star if the earth and neutral are internally bonded ie

Is the star point on the 3 ph genny always at 0 potential?

M

#### Mark or Sue

Jan 1, 1970
0
SQLit said:
When ever you create electricity there must be a path to earth. With out the
earth ground you run the risk that you circuit breaker will not trip. Ever
notice that every electrical service in your neighbor hood has an earth
ground? If the utility could get away from using them do you not think that
they would quit spending the money? Not earthing the neutral can cause
voltage imbalances to be created. A lot of people just rely on the frame of
the genset to be in contact with the earth... close enough. It takes no time
to drive an minimum 8 foot ground rod flush with the earth and connect it to
the generators frame to the lug provided. (usually)

I disagree with what you say here. In many ways, systems would be safer if they weren't grounded.
You'd have to touch two wires to get shocked instead of just one. The reason utility wires are
grounded is because of lightning and the possibility of a very high voltage wire falling onto a
lower voltage one. A breaker won't trip on an earth ground fault at normal voltages because the
resistance of the earth is too high -- you must bond the grounding system to the neutral in order to
trip a breaker through the equipment grounding wire. However, once a system is grounded, then you
need to keep grounding everything connected to it or else you could still be shocked. An isolated
generator generally is immune from most of these risks. A bunch of long extension cords or christmas
lights could be susceptable to lightning, but that is all. An equipment grounding (really bonding)
wire that goes back to the generator neutral would also be very helpful if metal equipment is
plugged in.
Make it safe and make your SO's safe. It only takes about 5 milliamps to
kill. Less in some conditions.

I worked for a university and the city folks set 10 20 kw generators on
tires for temp Christmas lighting not one was grounded. I shut them off and
locked them out. The mayor and the president of the university were in the
electric shop the next morning. I explained the safety issues for the public
and the mayor immediately called his people and they installed the required
ground rods. Christmas lights were dark one night. No big deal compared
with making the headlines all over the world. Personally I do not want to
be on TV.

Weren't these portable generators (even though they are big they were temporary weren't they)?
Aren't these exempt from ground electrode requirements?

I suppose you want me to ground my car too? And the 12V to 120V inverter I plug into it?

G

#### Gary P. Fiber

Jan 1, 1970
0
When ever you create electricity there must be a path to earth. With out the
earth ground you run the risk that you circuit breaker will not trip. Ever
notice that every electrical service in your neighbor hood has an earth
ground? If the utility could get away from using them do you not think that
they would quit spending the money? Not earthing the neutral can cause
voltage imbalances to be created. A lot of people just rely on the frame of
the genset to be in contact with the earth... close enough. It takes no time
to drive an minimum 8 foot ground rod flush with the earth and connect it to
the generators frame to the lug provided. (usually)

Make it safe and make your SO's safe. It only takes about 5 milliamps to
kill. Less in some conditions.

I worked for a university and the city folks set 10 20 kw generators on
tires for temp Christmas lighting not one was grounded. I shut them off and
locked them out. The mayor and the president of the university were in the
electric shop the next morning. I explained the safety issues for the public
and the mayor immediately called his people and they installed the required
ground rods. Christmas lights were dark one night. No big deal compared
with making the headlines all over the world. Personally I do not want to
be on TV.

You sure it is not the green wire that carries the fault current to
circuit breaker which makes it trip and not the earth connection.

Basically the earthing of every service entrance allows the electric
company to have a nice low impedance path back to their ground
reference. They provide a ground about every 1/4 mile on the pole
line. They actually use every one of the service entrance grounds to
help provide a lower earth impedance path.

What amazes me if earthing was so important; and you can't get a earth
ground rod resistance of less than 25 ohms you drive a 2nd rod; if it
is still higher than 25 ohms its ok to stop there according to the
NEC. So I could drive two rods 6 feet apart, end up with 100 ohms to
ground and that would be fine with the NEC and inspectors.

I doubt unless the voltage is high enough like over 600 volts any
fault current is going to overcome earth resistance to blow a breaker.

Section 250.4(A)(5) says the Earth is not an effective Fault Current
Path.

I work on a floating bridge, there are no ground rods there, though
concrete is a pretty fair ground. The transformer secondary X0 is
bonded to the equipment grounding conductor in the P1 panels.
Otherwise the earth ground floats I have no trouble blowing breakers
on the bridge. Now if I remove the equipment grounding conductor I'd
bet i would have a terrible time blowing the breaker.

Gary K8IZ
Washington State Resident
Registered Linux User # 312991

B

#### Ben Miller

Jan 1, 1970
0
When ever you create electricity there must be a path to earth. With out the
earth ground you run the risk that you circuit breaker will not trip.

What breaker are you referring to? If you are talking about the facility
breaker, how does a grounding electrode affect it?
Not earthing the neutral can cause
voltage imbalances to be created.

How? Where would the imbalance be?
Make it safe and make your SO's safe. It only takes about 5 milliamps to
kill. Less in some conditions.

For external contact with the skin, it takes a lot more than 5 mA to kill. 5
mA is in the "mild pain" range, but not fatal.

Ben Miller

S

#### SQLit

Jan 1, 1970
0
SQLit said:
When ever you create electricity there must be a path to earth. With out the
earth ground you run the risk that you circuit breaker will not trip. Ever
notice that every electrical service in your neighbor hood has an earth
ground? If the utility could get away from using them do you not think that
they would quit spending the money? Not earthing the neutral can cause
voltage imbalances to be created. A lot of people just rely on the frame of
the genset to be in contact with the earth... close enough. It takes no time
to drive an minimum 8 foot ground rod flush with the earth and connect it to
the generators frame to the lug provided. (usually)

Make it safe and make your SO's safe. It only takes about 5 milliamps to
kill. Less in some conditions.

I worked for a university and the city folks set 10 20 kw generators on
tires for temp Christmas lighting not one was grounded. I shut them off and
locked them out. The mayor and the president of the university were in the
electric shop the next morning. I explained the safety issues for the public
and the mayor immediately called his people and they installed the required
ground rods. Christmas lights were dark one night. No big deal compared
with making the headlines all over the world. Personally I do not want to
be on TV.

answer to the masses, everyone is entitled to an opinion. If you disagree
with me, OK attack me, but do not confuse the issue for the people who are
asking for help. I try to reduce technical questions to something that the
guy next door can handle. A lot of the time the answer is hire a qualified
contractor. That is another subject. This is an open forum, all can voice
there opinion. Let us leave it at that and not attack each other, we all
know what an ass hole is..

Lets try to be a little more applicable to the question
MARK,,,, your comments should be left to people that UNDERSTAND the issue.
I have worked on and installed non-grounded electrical systems. I WOULD
NEVER recommend them to an residential customer. Your opinion is considered
and rejected for this application.
Lets try and answer the questions at hand, not take the average guy into
territory that is way un - charted for the average guy.

We are here to help each other, I for one have learned alot in the
newsgroups.

my thoughts alone all negitative email should come to me
not the group.

M

#### Mark or Sue

Jan 1, 1970
0
SQLit said:
answer to the masses, everyone is entitled to an opinion. If you disagree
with me, OK attack me, but do not confuse the issue for the people who are
asking for help. I try to reduce technical questions to something that the
guy next door can handle. A lot of the time the answer is hire a qualified
contractor. That is another subject. This is an open forum, all can voice
there opinion. Let us leave it at that and not attack each other, we all
know what an ass hole is..

Lets try to be a little more applicable to the question
MARK,,,, your comments should be left to people that UNDERSTAND the issue.
I have worked on and installed non-grounded electrical systems. I WOULD
NEVER recommend them to an residential customer. Your opinion is considered
and rejected for this application.
Lets try and answer the questions at hand, not take the average guy into
territory that is way un - charted for the average guy.

We are here to help each other, I for one have learned alot in the
newsgroups.

my thoughts alone all negitative email should come to me
not the group.

My answer wasn't meant as an attack. I'll give an opposing view to anyone, so don't take it
personally....

Since we're here to help each other, comments should be aired in the open. The OP asked what was
that a breaker won't trip without a ground rod and comparing it to a distribution system that is
hundreds of miles long. I could agree that a ground rod may help a GFCI trip, but no one stated if
GFCI's were on the generator.

We can all have opinions, but here is what the NEC says:

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be grounded and
shall be permitted to serve as the grounding electrode for a system supplied by the generator under
the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected
equipment through
receptacles mounted on the generator, or both, and
(2) The non-current-carrying metal parts of equipment and the equipment grounding conductor
terminals of the receptacles are bonded to the generator frame.

Now if you want to power your house with this generator through a transfer switch, then you would be
required to ground it and I would agree that it is a good thing. But I think you over reacted to

So for the "average guy", why is an ungrounded portable generator unsafe? I can think of a few
answers of why it may not be good for the generator, but none dealing with safety.

B

#### Barry

Jan 1, 1970
0
Thank you all for your replies.I look at this newsgroup from time to time
and must say that it is refreshing to be able to read the different
opinions that you guys have. I don't understand most of it but it is still
enjoyable.

Thanks

S
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