Ron and I agree. I was just trying to avoid some of the NEC speak that confuses
people. The point is you only want one bonding point between the neutral and
ground and if the transfer equipment doesn't switch neutral that will be the
jumper in your service panel.
(Separately derived source is NEC speak for a system where the neutral is
switched too so it will have separate bonding jumpers that go with the source).
All the frame grounding will be bonded, no matter what the transfer scheme.
Adding another electrode only insures that the ground on the case is more
closely referenced to the dirt under your feet when you are standing there.
Depending on where you live "ground shift" is more or less of a problem.
Here is the sandbox (Florida) I have seen 35 volt transients across 30-40 feet
For my operations, I have all the gensets wired with the Neutral, Ground,
and both Hot Legs comming out as sperate wires. They then connect to
the Main Transfer Switch where both Hot Legs and Neutral, are switched.
The Neutral and Ground are Bonded at the MAIN 240Vac Panel, which is
where the Grounding Rod is also connected. At the 240/120Vac
Transformer, the Neutral on the 240Vac winding goes back to the Neutral
at the Main Panel, and one side of the 120Vac winding is brought to
the Neutral Buss in the 120Vac SubPanel, which is also Bonded to the
Ground Rod, to establish Neutral and ground for the secondary side
of the Transformer. One Breaker in the 120Vac SubPanel feeds the
Input to my 4024 Trace inverter, which then feeds the 120Vac Inverted
SubPanel, where the Neutral and Ground are not bonded. This is because
the Ground Connection on the Inverter is common to both Input and Output,
therefor the bonding in the 120Vac SubPanel sets the Ground on both
sides of the Inverter. The 120Vac Inverted SubPanel then feeds the
Cabin Subpanel, as well as the ToolShed and GenShed Circuits.
Bruce in alaska
You are connecting this to your home wiring with a transfer switch that
switches only the hot connection. Is that correct?
I used to have a link to a long article that went into extreme detail and
all that, but have misplaced it. Oh well. Anyhow...
If your generator ground is bonded to generator neutral, you MUST use a
transfer switch that switches both hot and neutral, and you MUST ground the
If your generator is not bonded (and no normally available generators are
bonded afaik, but your monster...) then you can switch only the hot and MUST
NOT ground the generator.
The article went on for pages about ground loops or somesuch thing (the
neutral being grounded in two different places). So, my suggestion is that
you find out if you can unbond your generator, since you are unlikely to
find a transfer switch to switch both hot and neutral. There is no need to
ground the generator separately, since it's ground is not connected to
anything except the house ground.
prohibited by the NEC, multiple hot-neutral bonds are quite common. He has
seen the question raised in professional meetings, and the answers were
It seems that some electronic equipment is affected by noise impressed onto
ground, but the problem is overrated.
Second hand information from a "professional electrician"... geez, when I
see some of the work done in the past on my house by professional; my 23a
water heater was run with #12 on a 30a breaker, a multiwire circuit was all
on the same leg, etc.
A bond implies no -middle man- sort of load between two conductors.
The gentleman meant to say ground to neutral connections.
The guy doing your wiring should have been fired. A number twelve wire
suitable for house wiring is usually rated for 20 amps. Heating loads
have to use no more than 80 percent of the wire 'ampacity.
So, his number 12 was good for only 16 amps in this situation.
a 30 amp (#10) wire would have barely met the legal requirements (.8 X
30 = 24)
"The day Microsoft makes something that doesn't suck is
probably the day they start making vacuum cleaners."
I wonder if the water heater woudl be considered a 'continous load'
like a houses heating, but it does make sense even without the
derating, #12 shouldn't be used on a 30am breaker.
I'm guessing it was a typo.
tom @ www.FindMeShelter.com
I am sure that he is referring to multiple bonding points to the neutral.
Your supposed to do it once at the service. The neutral is a "grounded
current carrying conductor" Having it grounded/bonded in more than one place
just increases the probability of something going wrong. Does it happen you
bet, is it correct. NO
If you ground to your service, best in my opinion. Use the same size ground
wire as your service. You are creating an "supplemental ground" for the
service. Any ground conductor smaller than the ground for the service could
create a weak link in the grounding. Bonding to the metallic piping systems
is required. This may not be a problem if you are able to come off of the
ground bar in the service. Assuming that the metallic piping systems are
Personally I like and use only switched neutral transfer panels. Solid
neutral switches are available and a little cheaper. I have had to many
problems with sensitive electronics over the years. If my customer insists
then they find someone else to do the job. Almost all that have in the past
have come "crawling back" for me to fix it AFTER the damage was done. They
are very careful not to discuss or complain about price.
Having two sources of power is not rocket science. It is problematic when
incorrectly installed. If you land on a solid neutral block, you will have a
the possibility of current traveling to your generator while it is off.
Switching the neutral with the phases assures that the generator will be
completely isolated when not being used.
I do not know exactly what the code says, but I do know what makes sense
from a safety perspective. The neutrals of all circuits should be
connected to ground at ONLY one place - in your main service panel. There
must be no grounding of neutrals in sub panels. Ranges etc. connected to
sub panel circuts should use a 4 pin connector (hot, hot, neutral, ground).
The ground wire from your main panel may be connected to multiple grounds
and it's best if these are close together. Two grounding rods are
frequently used for a lower resistance ground path and better reliability.
Do not ever use a pipe as a ground. The water supply line may be PVC or
may be changed to PVC at some time in the future and you would have no
Since a good ground is so important, use the gauge wire required by code or
larger, protect it where required and never allow a splice in it. Use only
the best quality U/L approved grounding clamps and be sure all contacting
surfaces are clean and tight.
All of this applies to your generator too. For best safety, if your
generator is outside, it should be physically close to your system ground.
If the code requires anything less, it should be changed.
The US NEC requires that any underground water piping that is ten feet
or more in length shall be used as a grounding electrode. That is not
optional. No matter how authoritative a posting recomending against
this sounds it is bad advice for anyone who's work is governed by the US
If the underground water piping were too short or non conductive the
code would require that any interior metal water piping that is likely
to become energized be bonded to the service equipment enclosure, the
grounded conductor at the service, the grounding electrode conductor
where of sufficient size, or to the one or more grounding electrodes
used. That connection is required regardless of whether there is any
underground metal water piping present. Most Authorities Having
Jurisdiction (AHJs) consider any metallic water piping that supplies
water to any electric appliance as likely to become energized and
although most AHJs will except the Equipment Grounding Conductor (EGC)
of the electrical equipment attached to the piping as the bonding means
for interior gas piping they will not except an EGC as the bonding means
for water piping. For water piping the bonding conductor must comply
with 250.104 of the US NEC which requires it to be sized exactly the
same as an Grounding Electrode Conductor (GEC).
[250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used.
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in
direct contact with the earth for 3.0 m (10 ft) or more (including any
metal well casing effectively bonded to the pipe) and electrically
continuous (or made electrically continuous by bonding around insulating
joints or insulating pipe) to the points of connection of the grounding
electrode conductor and the bonding conductors. Interior metal water
piping located more than 1.52 m (5 ft) from the point of entrance to the
building shall not be used as a part of the grounding electrode system
or as a conductor to interconnect electrodes that are part of the
grounding electrode system.
250.104 Bonding of Piping Systems and Exposed Structural Steel.
(A) Metal Water Piping. The metal water piping system shall be bonded as
required in (1), (2), (3), or (4) of this section. The bonding jumper(s)
shall be installed in accordance with 250.64(A), (B), and (E). The
points of attachment of the bonding jumper(s) shall be accessible.
(1) General. Metal water piping system(s) installed in or attached to a
building or structure shall be bonded to the service equipment
enclosure, the grounded conductor at the service, the grounding
electrode conductor where of sufficient size, or to the one or more
grounding electrodes used. The bonding jumper(s) shall be sized in
accordance with Table 250.66 except as permitted in 250.104(A)(2) and
(A)(3).] Copyright 2002 the National Fire Protection Association.
Failure to follow the electrical code that is enforced as law in your
area can void your fire and liabilty insurance if that failure results
in an otherwise insured loss. It is considered a legal obsurdity to
attempt to insure against the cosequences of the insureds own unlawful
act. Insurance contracts are "contracts of utmost good faith." That
means that all parties to the contract must scrupulously obey the law in
all matters that could affect any other party to that contract. To fail
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