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  • 20"/100# 120sec MR 3'cap #SW P29 Series Low Pressure Cutout Control With Time Delay Relay

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20"/100# 120sec MR 3'cap #SW P29 Series Low Pressure Cutout Control With Time Delay Relay

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Manufacturer: Johnson Controls

Description: 20"/100# 120sec MR 3'cap #SW

Category: Electrical Controls

Sub Category: Pressure Controls

P29 Series Low Pressure Cutout Control
With Time Delay Relay


The P29 combines a pressure
sensing mechanism with a time
delay. A drop in pressure
energizes the time delay relay
which opens a contact after a
predetermined time period.

There are two principal
applications for this control:

1. Chiller Low Temperature
Cutout: Pressure element is
connected to the suction side
of a chiller refrigeration
system and the time delay
relay is wired to the
compressor control circuit.
Prolonged low suction
pressure, such as pressure
caused by a low temperature
condition, will cause the
control to shut down the
refrigeration compressor.

2. Industrial Equipment, Oil
Pressure Lubrication
Cutout: On any electrically
driven machine with a forced
oil system, the pressure
element is connected to the
lube oil system and the time
delay relay is wired in the
control circuit. The control
time delay allows oil pressure
to build up to normal on
start-up or recover from
temporary fluctuations. A
sustained loss of oil pressure
will cause the control to shut
down the machine.

: Use P29
pressure controls only in
normal indoor environments

or outdoors where it is
protected from direct
exposure to weather.


· Heavy duty low profile
pressure elements withstand
excessively high overrun
pressure that may be
encountered in system testing.

· Time delay relay incorporates
trip-free manual reset.

· The timing mechanism (time
delay relay and terminal
board) may be easily removed
and replaced in the field.

· Ambient compensation
minimizes the effect of
temperature variations at the
control location.

· Simple, single pointer scale
indicates cutout pressure.

· Enclosed pressure actuated

· Single unit mounting and
wiring saves installation time
and material.


When the equipment is started,
the time delay heater is
energized. If the gage pressure
does not build up to the "heateroff"
value within the required time
limit, the time delay relay trips to
stop the equipment.
If the gage pressure rises to the "heater-off" value within the
required time limit, the time delay
relay will not trip and the
equipment will continue to run.
The equipment will be shut down
on subnormal pressures longer
than the time setting of the time
delay relay.

Time Delay Relay

The time delay relay is a thermal
expansion device. "Trip-free"
manual reset models are
available with factory set and
sealed 60 second time delay.
The time delay relay is
compensated to minimize the
effect of ambient temperature
variations. Timing is affected by
voltage variations.
For applications using a 208 volt
control circuit, it is suggested that
one leg of the 208 volt control
circuit and a neutral or ground
wire be used to power the 120 volt
circuit of the time delay heater.
When a P29 control is installed on
a 440 or 550 VAC system, use an
external step-down transformer to
provide either 120 or 240 volts to
the pilot and time delay relay
circuits. The transformer must be
of sufficient volt-ampere capacity
to operate the motor starter and
P29 time delay relay.

Replaces Part Numbers: P29NC-38, CARP29NC-38

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