1. A system comprising:
a channel nut comprising a threaded bore, at least two channel rails, and a flat top surface;
a rail assembly; and
a channel nut tool comprising:
a metal shank having a first end and a second end;
a molded plastic handle formed on said first end of said shank;
an end piece formed on said second end of said shank comprising a socket fitting and a ball lock release aperture;
a first socket comprising a threaded shaft connected to a socket body, and a ball lock; and
a second socket comprising a threaded bore configured in a socket body, and a ball lock.
2. The system of claim 1 wherein said threaded shaft comprises no more than 1 turn of thread.
3. The system of claim 1 wherein said shank comprises at least one extendable telescoping member.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A protective relay for an induction motor, having known operating parameters including known overload thermal current limits, comprising:
a circuit for measuring the input current to the motor;
a first program function for establishing a first thermal threshold value for a start condition of the motor;
means for determining a representation of the thermal condition of the motor during the start condition thereof;
a comparator for comparing the start condition thermal representation with said first thermal threshold value and for producing an output signal when said first thermal threshold value is exceeded by said start condition thermal representation;
a circuit for establishing a second thermal threshold value for a run condition of the motor, the second thermal threshold value being different from the first thermal threshold value, wherein the circuit for establishing a second thermal threshold value includes a selected time constant which is used to calculate a time-current curve combining the start and run time-current curves resulting in a substantially continuous time-current curve;
means for determining a representation of the thermal condition of the motor during the run condition thereof; and
a comparator for comparing the run condition thermal representation with said second thermal threshold value and for producing an output signal when said second thermal threshold is exceeded by said run condition thermal representation.
2. A system of claim 1, wherein the protective relay allows the user to set the time constant for a particular motor.
3. A system of claim 1, wherein the time constant is calculated using the equation:
TDR
\u2061
R
1
R
o
\xb7
I
L
2
\u2061
(
T
a
–
T
o
)
\u2062
where
\u2062
TDR
=
1
R
1
R
\xb7
6.25
\xb7
T
a
T
a
–
T
o
\xb7
TD
ln
\u2061
6.25
6.25
\xb7
(
SF
)
2
and
\u2062
R
1
=
locked
\u2062
\u2062
rotor
\u2062
\u2062
electrical
\u2062
\u2062
resistance
\u2062
\u2062
R
o
=
running
\u2062
\u2062
rotor
\u2062
\u2062
electrical
\u2062
\u2062
resistance
\u2062
\u2062
I
L
=
locked
\u2062
\u2062
rotor
\u2062
\u2062
current
\u2062
\u2062
T
a
=
locked
\u2062
\u2062
rotor
\u2062
\u2062
time
\u2062
\u2062
with
\u2062
\u2062
motor
\u2062
\u2062
initially
\u2062
\u2062
at
\u2062
\u2062
constant
\u2062
\u2062
temperature
\u2062
\u2062
T
o
=
locked
\u2062
\u2062
rotor
\u2062
\u2062
time
\u2062
\u2062
with
\u2062
\u2062
motor
\u2062
\u2062
initially
\u2062
\u2062
at
\u2062
\u2062
operating
\u2062
\u2062
temperature
TD
=
the
\u2062
\u2062
time
\u2062
\u2062
needed
\u2062
\u2062
to
\u2062
\u2062
reach
\u2062
\u2062
trip
\u2062
\u2062
temperature
\u2062
SF
=
service
\u2062
\u2062
factor
\u2062
\u2062
(
threshold
\u2062
\u2062
temperature
)
\u2062