Question 1, why the minimum nominal thread diameter must be large than 3.5mm
for screw type? Should the size of protective wiring terminal provided to
comply with 2.6.1 e), f), g) be large than 3.5mm for screw type? 3.0mm is
not OK?
Please refer to the requirements from UL 60950-1.
The cross section area of a steel screw of 3.5 mm dia. is 9.6 sq. mm.
Since the conductivity of copper is about ten times that of steel,
this roughly corresponds to the conductivity of the 1mm copper wire
required for the same 10 amp application. I believe for pillar or stud
type applications, the electrical connection is expected to depend upon
direct surface contact rather than through the screw shaft. For screws
of this size, there is also concern for mechanical robustness.
Note the requirement (up to 10A) is screws must be 3.5 mm or larger,
not screws must be larger than 3.5 mm.
Question 2, why green-color, hexagonal head/nut is needed for permanently
connected equipment? How about this requirement is accomplished in fact?
In the US, green has been traditionally used to identify earth
connections.
As this was internationalized, the color green with yellow stripe became
the
international identification of earthing conductors (some countries made
use
of solid green for other purposes). US codes expect clear identification
of
connections and specify these three identification options for earthing
conductors because miswiring could lead to shock risk. These electrical
code
requirements are reflected in the ITE standard.
In the US, screws are commonly available for this application with a
combination slotted and hex head with green plating or chemical coating
(not paint) for use by electricians e.g. Raco Cat. No. 973. Most ITE
manufacturers choose the IEC 60417 No 5019 label option.
Question 3, what is “two-hole compression-type connectors”? when is the
“two-hole compression-type connectors ” needed? Do you think “two-hole
compression-type connectors” is needed for all end-product?
Please see the requirements from “Telcordia Technologies Generic
Requirements GR–1089–CORE Issue 3, October 2002”.
This is a crimp terminal with an extended tongue containing two holes
instead
of one. The use of two screws provides redundant connection and prevents
loosening the screw by tugging on the wire to rotate the terminal. This
requirement is not typically applied to small products. However, this
requirement is a customer demand, not a national standard. Therefore its
application is different from company to company. You need to actually
go to
each of your customers (telephone companies) and confirm their need or
not for
compliance with this requirement. Refer to Dave Lorusso’s discussion on
this
subject at www.lorusso.com.
Bob Johnson
ITE Safety
From: [email protected]
[mailto:[email protected]] On Behalf Of Zhang Guoqing
Sent: Monday, February 23, 2004 10:32 PM
To: [email protected]
Subject: questions for earthing terminal
Hi, all,
I have some questions for earthing terminal, could you give me some
suggstions?
Zhang Guoqing
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