TO: Mike Holt
OF: MIKE HOLT ENTERPRISES
REFER: Power Quality
FROM: Robert M. Maddox DATED: 08/22/2000
to you request on information and ideas on power quality I offer the following
& Information Sources:
(specifically IEEE/IAS) has quite a bit on power quality, however it is sometimes
very deep and would not be for the novice.
is a "Power Quality" magazine (www.powerquality.com).
has articles from time to time.
Common Sense Design & Installation Suggestions:
not design & install to code minimums, do better than that. Naturally it
will not be the least expensive choice.
is most important. Make sure building steel, piping, etc. are well grounded
& tied to the service ground. Make the service ground your central ground
point, if possible.
Remember, grounding is all about establishing a low-impedance
path to ground. Do not be afraid to oversize the ground conductors - the larger
the wire the lower the impedance. On many jobs I have two 750 MCM going out
to the ground rods, etc. & may use grounds sized the same as the conductors
in the feeders.
First, always establish an excellent service ground, not just
two ground rods and forget it. I suggest a resistance to ground not to exceed
same is true on the secondary of 208Y/120V transformers. Try to tie this ground
back to the original service ground.
feeders should have an insulated ground wire (no less than code minimum - some
times a size larger) even if is in a metallic conduit or cable.
not size the service or panels, feeders & OCP to the limit. Oversize &
allow for growth. Take temperature & voltage drops into account.
panel should have a ground bus. All 120V panels should have an IG bus.
branch circuit should incorporate a green ground wire, even if it is in a metallic
conduit or cable.
any sensitive branch circuit loads on panels separate from other loads. Mixing
in lighting, motor and other loads on panel(s) that serve computer and other
sensitive loads are just asking for trouble.
not load computer outlet circuit to the limit, typically 4 to 6 outlets only
per circuit. Use individual neutrals (not shared or common neutral) on these
IG receptacles for computers and related devices. Provide an IG conductor (in
addition the green safety ground) back to an IG bus in the panel. It is best
to carry an IG (in addition to green safety ground) all the way back to the
transformer or service ground.
telephone / data rooms & closets away from transformers, motors, & other
equipment with large magnetic fields.
good high quality surge protection equipment on the service, and branch panels
the telephone company (and all other incoming cabling) a very good low resistance
ground to tie onto. This ground should also be tied back to the service ground.
and inform the owner / tenant what type of service the power company will be
providing (i.e.- underground with a pad mount is much more clean & reliable
than overhead, is it a network transformer, etc.).
simple suggestions will inherently solve most problems before they occur. Any
remaining problems can be dealt with individually. Computer room & telecomm
centers ( with UPS & Generators) typically have engineers and other to select
& guide the installation (if not insist on hiring them)
I hope this helps. I have had very few problems, even when I did not totally
know what the building owner was going to do, when I followed the above suggestions.
End of Memo