Limited-service controllers (LSC) are used
as fire pump controllers within defined limits and restricted
performance. LSCs are permitted in fire protection
applications in instances where cost is a major factor and, if
not permissible, would most likely result in the decision not
to have any fire pump. They have been used in some nursing
homes, day care centers, larger private homes, and similar
small premises. LSCs were added to NFPA 20 Standard for the
Installation of Stationary Pumps for Fire Protection after
a serious fire in Chicago more than 40 years ago where
testimony showed that the loss of life could have been
lessened had a fire pump been placed in service.
Limited-service controllers were designed for these small
premises, limited to 600 V, 30-hp maximum and were intended to
be used with limited-service pumps. Their use must, on a
case-by-case basis, be permitted by the authority having
jurisdiction (AHJ).
Paragraph 10.7.1 of NFPA 20 (2003) states
"that the limited service controllers, consisting of
automatic controllers for across-the-line starting of
squirrel-cage motors of 30 hp or less shall be permitted to be
installed where such use is acceptable to the authority having
jurisdiction." Further, there is an appendix item,
paragraph A.10.7, which states: "The authority having
jurisdiction can permit the use of a limited-service
controller for special situations where such use is acceptable
to said authority." In many instances, the AHJ has need
for factual information to aid in making his decision, which
this article is intended to address.
The designs of the fire pump controller and
LSC have changed over the past forty years. For example, fire
pump controllers are now available for all horsepower and
voltage combinations served by the LSC.
NFPA 20 mandates, among other things, that
motor protection provided by fire pump controllers be of the
non-thermal type, be immediately re-settable and that it
provide short-circuit and locked-rotor protection only (no
overload protection). These requirements are tempered for the
LSC so that it performs more like a specialized industrial
motor controller than a fire pump controller. Motor protection
for the LSC is permitted to be of the thermal type that may
require cooling time in order to be re-settable. Locked rotor
overcurrent protection for the LSC is addressed in paragraph
10.7.2.1 of NFPA 20 (2003)—"the locked rotor
overcurrent protection shall be permitted to be achieved by
using an inverse time nonadjustable circuit breaker having a
standard rating between 150 percent and 250 percent of the
motor full-load current." This may produce performance
considerably different than the desired and required 8–20
seconds locked-rotor current tolerance time before tripping
that is unique to fire pump controllers.
Thus, under certain circumstances, the
limited-service controller may trip too quickly to adequately
start a distressed pump, take too long a time to reset under
fire conditions, or protect the motor from damage. AHJs, in
making their decisions, must also realize that the LSC does
not contain an isolating switch, which is required in fire
pump controllers. Thus, if service on the thermal-magnetic
circuit breaker is required, loss of fire protection may be
prolonged since often the LSC is connected directly to utility
power.
NEMA recommends that AHJs consider the
above facts in their decisions to permit limited service
controllers to provide fire protection.
Bruno Goupil, Torna Tech Inc.,
Saint-Laurent, QC H4M 2Z2 Canada; Craig Miller, Hubbell
Industrial Controls, Inc., Archdale, NC 27263; Douglas
A. Stephens, P.E., Firetrol ASCO Power Technologies,
Cary, NC 27512; Richard Schneider, Joslyn Clark
Controls, Inc., Lancaster, SC 29721-0945; Russell
Anderson, Metron, Inc., Denver, CO 80223; Tony
Kranendonk, Eaton Electrical, Inc., Burlington, ON L7N
3H8 Canada; William F. Stelter, Master Control Systems,
Inc., Lake Bluff, IL 60044 |
