Gerald Newton wrote:

"Gerald Newton" wrote in message
...

"Vern Heiler" wrote in message
. ..

Thanks to all. It makes me feel better about writing them up having a
better knowledge of why.


Of equal importance to not bonding the neutral or grounded conductors on
the load side of the service is the importance of having a main bonding
jumper installed at the building service. Without the main bonding jumper
a short to ground will not trip the circuit breaker in many cases. I have
found main bonding jumpers missing in several inspections.
Let me give you a real life example that happened a Chena Hot Springs
Resort near Fairbanks, Alaska in about 1990 that almost got me killed.
A competent(?) master electrician had wired an 8 plex and I was performing
the final inspection. There was no rough in inspection since we don't
have State building permits here and I was the State Inspector. The
building was supplied from a generator at 240/120 volts located about 600
feet from the building through an underground service lateral.
While preparing to write my inspection report I laid my metal tablet on
the Kitchen range of one unit. As I picked it up I accidentally placed my
other hand on the adjacent metal sink and received a jolt. I said what
goes here? I got my meter out of the car and checked and found 120 volts
between the range and the metal sink. Holy, mcMoley, I had just inspected
the crawl space and literal wrapped myself around metal pipes while
crawling around. I went to the service panel and checked there and again
there was 120 volts from ground to the neutral. The ranges had been
grounded using the neutral or grounded conductor and not the equipment
grounding conductor as now required. I had the master electrician come
over to the open service panel and asked him for a short piece of wire. I
used the wire to temporarily short the neutral bar to ground and whammo, a
20 ampere circuit breaker popped. That 20 ampere circuit breaker fed a
small water pump in the crawl space. We went to it and found that the
cover had pinched a hot wire to the metal ground placing all the metal
water pipes in the building at 120 volts to whatever. We went back to the
panel and sure enough the main bonding jumper was missing. It was just a
green screw that made the neutral bus bond to the panel metal can and
equipment grounding conductor.
There was a ground rod and it was bonded to the metal pipes and to the
equipment grounding bus in the service panel. Without the main bonding
jumper the fault current had to go through earth all the way to the
generator building to trip the circuit breaker and the ground resistance
was simply too high. The result was there was 120 volts potential between
every range and every metal sink in the entire building. The conclusion
of this is to never assume anything about the main bonding jumper. It is
the first thing I learned to look for when performing an inspection.
Luckily, I lived to tell this story.

I should have added that the service lateral from the generator was three
wire with no equipment grounding conductor.


Many people probably don't know a major function of a ground wire is to
cause enough current to flow when hot faults to ground to trip a
breaker. This requires the neutral-ground bond at the service to give a
low resistance path back to the transformer. If not bonded, the current
flows through the earth back to the transformer. The resistance will
very likely be too high to trip breakers.

--
bud--