Generator Parts and Frequently Asked Guestions

[cornbinder89]

Originally Posted by armandh

to make the whole bonding issue simple.........
correct bonding makes it impossible for a point of failure in the return path to create a hazardous condition.

]

OK, to a layman, I am haveing trouble following this. I know your not supposed to have more then one bond point.... But, again to a layman, when you open your breaker panel in your house, you see all the nuterals and grounds tied to the same strip. I'm haveing trouble grasping the concept that more is worse then one. If the gen was grounded, the house or other end user grounded with a seperate ground rod, why is this more dangerous then a single ground point with both the nuteral and grounds connected? If I understand why it helps make sure I do it right all the time.
It seams with a single bonding point, a single failure would lead to no grounding and a "floating" nuteral... Am I wrong?
A transfer sw without a nuteral switch could back feed the grid if the ground is lost (do I at least have this correct?) and as such nuterals should be disconnected from the grid when back up power is used... But why the issue of a single bond point?
HELP!!

[BTPost]

Chainsawman, No, a CT (Current Transformer) does not need any electrical connection to the measured circuit. It uses Inductive Coupling to sample the Current thru the wire run thru the center of the CT.

cornbinder89, You are not the only one confused by this part of the NEC, Many Electricians, Electrical Engineers, and Electrical Inspectors are also in the same boat. Neutral/Ground Bonding is NOT the real issue here. That is well understood, by almost all. It is when you add a Backup, or Alternate Source, of power to your system, that things get complicated. This issue has only been part of the NEC for the last 15 years and only really became relevant since the issues were documented after all the Y2K Backup Gensets were installed, Tested, and found wanting. Also the introduction of GFI Outlets and Breakers, in the last two decades, has complicated the issue significantly. There are MANY different ways to accomplish this type of connection, but to do it Safely, and where there are minimum chances for a Single Point Failure causing, problems, that persist because a Breaker or Fuse doesn't Trip, is a complicated issue, and that doesn't even get into the Gound Loop part of the Issue. The NEC in this area is just now getting to the point where it is fairly stable, on this issue, as terms like "Separately Derived Source" definitions, have been in the NEC for a few years, and are taught in ALL Apprentice Courses. My buddy sits on the NEC Board that writes the code, and teaches NEC to Inspectors, Electricians, both Master, and Journeyman, as well as the Apprentice Courses, and he insists that this section of the NEC is the least understood, and most miss-applied Section.

[cornbinder89]

Do you have a good source that does help explaine it? Looking at how my house is wired, I already see things that I doubt are to code. I am thinking about adding a transfer sw (at least my main disconnect is on the yard pole, so easy to make it a full transfer.). I want to have a full understanding of what should be, before tackleing what is!

[Jim Rankin]

http://www.ecs.umass.edu/ece/hollot/...DS06/ESD_2.pdf

A 2.12 MB PDF file that shows grounding and bonding for both transformers and transfer switches as well as equipment grounding and ground fault interrupting devices.

[Chainsawman1]

Hey armandh....(SHIPMATE)
I dont remember any CT Meters in the Navy.
I dont even think we cared how much power we used.
But I know we used loads of it. Did I miss something?
I do remember we had to go light up san francisco when PG&E croaked.

[Chainsawman1]

1-Q: How many amps will it take to kill you?
A: Female, 50 miliamps for 2/10 of a second,for male, 75 miliamps for 1/2 of a second will send heart into ventricular fibrilation.

2-More than 6 ma current passes through your heart shall KILL you.

[armandh]

and simple E=IxR tells you that lowering the contact resistance with water or increasing the voltage will increase the current

using a large gen to feed several transfers would require doing it much like a large building distribution

bonding at the generator
overload protection for the feed to each transfer
bonded disconnects at each meter base
transfers that have neutral transfer
and isolated neutral distribution panels after the transfer


or transfer only the largest panel and provide several small emergency runs
to emergency transfer and sub panels in outbuildings.


as to why
here in MO a kid got killed climbing on to a boat dock
the 3 wire hookup became hot when the neutral got loose

there must be independent earth ground and neutral returns to the bonding point. deadly situations exist when conductors fail and the current seeks an alternate return path through you

incorrect bonding/grounding provides that alternate route.

[Fred M.]

It may be slightly off topic, but how about adding a link to one of Walmart's new boxes:

<http://www.walmart.com/catalog/product.do?product_id=12568628&findingMethod=rr>

Fred

[Chainsawman1]

Now that is the only electric box that I dont want!!!
You dont get a meter or big switch or even a little green light.

[Chainsawman1]

I was even thinking about why people dont use a rubber mat 6000 volt..
To stand on.