Mid point ground

To: neon-l@netcom.com
Subject: Mid point ground
From: littlejb@emi.net (Jay B. Little)
Date: Tue, 19 Dec 1995 22:34:31 -0500
Reply-To: neon-l@netcom.com
Sender: owner-neon-l@netcom.com
I have been mid-point grounding all of our installions for the last 7- 8
years. I also insist that all of my installers and service people mid-point
ground.

IT just doen't make sense not to do it. Also it is code. Anytime you can cut
problems in half by doing something simple is smart. Remember the saying
KISS (keep it simple stupid).

Well, let me try to explain mid-point ground installation.  You have to
first make sure that you purchase mid-point ground transformers over 7,500
volt. Lets take a look at a standard 15,000 volt 30ma 110volt primary
mid-point outdoor transformer. There are two lugs for your primary
connections (110 volt). Then there are two bigger lugs usually one on each
end for your High voltage or secondary. Sounds simple so far. There is one
more lug that is not on an insulator. That is your mid-point ground
connection. I have opened lots of cans and always get a chuckle from my
competitors installers when I see the green ground wire tapped to it. It
doesn't probably hurt anything, but that is not its intended purpose. The
transformer will be grounded if it is in a metal can and the can is
grounded, either through the use of EMT pipe or a ground wire screwed to the
can.

As an exmple lets take a sign with individual letters that says GOOD LUCK.
Mount transformer in center of sign. The home runs or high voltage lines
would go from the large ceramic lug to one electrode on the D The other home
run would go to an electrode
on the L. The rest of the sign would be wired in series D to O, O to O, O to
G.  On the other side L toU, U to C, C to K.  The run back to the
transformer The G to transformer and the K to transformer get tied together
in the transformer can an screwed down to the uninsulated lug on the
transformer. Thats it. Now each side of the sign only carries 7,500 volts
and drops lower as it goes from letter to letter, and reaches 0 volts when
it returns to the mid-point ground lug at the transformer. This is why I
stated it cut your problems in half, because it safely dropped your voltage
in half. 

Everyone of us should use the mid-point ground approach. It sure keeps units
from arching.

Hope this helps. And if I did not explain well enough I will try and answer
any questions.


                                  Jay B. Little
                                         Bright Image Signs
                                          Grove Neon Company
                                            Delray Beach, Florida
                                              littlejb@emi.net