INFORMATION & REQUIREMENTS ELECTRIC SERVICE - NStar

ARTICLE 802
TABLE 2
Three Phase Motors
Maximum Locked Rotor Current Values in Amperes
This table is based on not more than four starts per hour with
long periods of continuous operation under maximum load
conditions. Contact the NSTAR New Customer Connect Tech
Center where these conditions cannot be met, or where
equipment rating and/or starting characteristics exceed the
following:
A. Equipment with motors rated in horsepower
Rated at
Maximum locked rotor current
208* volts, three phase, 57.5 amps
2 hp or less
2.5 to 19.9 hp 57.5 amps per hp in excess of 2 hp
Over 19.9 hp
Contact the NSTAR Tech Center
B. Air Conditioning or Heat Pump Equipment rated in
btu per hour
Rated at
Maximum locked rotor current
208* volts, three phase, 57.5 amps
20,000 btu/h or less
21,000 – 50,000 btu/h 57.5 amps plus 1.15 amps per
1,000 btu/h in excess of 20,000 btu/h
51,000 – 225,000 btu/h 144 amps plus 1.15 amps per
1,000 btu/h in excess of 50,000 btu/h
Over 225,000 btu/h
Contact the NSTAR Tech Center
ARTICLE 803
803. Motor Protection
A. Protective Devices General
NSTAR strongly recommends that all motor installations
be adequately protected to prevent improper operation,
equipment damage and personal injury which might result
from abnormal conditions occurring in NSTAR’s service
facilities or the customer’s wiring system.
B. Protection Against Single Phase Operation
Three phase motors shall be protected against the
possibility of loss of any phase of the supply circuit.
NSTAR does not provide protection against loss of phase
conditions.
C. Undervoltage Protection
All motors requiring protection against the application of
full voltage at starting, or motors that would endanger life
and/or property by restarting after a service interruption
and a return to normal voltage shall be provided with
undervoltage protection. Such protection devices should
ensure that, with either undervoltage or no voltage, the
motor will be disconnected from the line or the starter
will be returned to the “off ” position.
NSTAR recommends the use of time-delay undervoltage
protection since instantaneous undervoltage protection
may operate on momentary voltage fluctuations.
D. Overload Protection
All motors shall be protected against overload by the
installation of adequate overcurrent thermal protective
devices or their equivalent, which operate to prevent
excessive motor winding temperatures.
* For 480 volts multiply current by 0.435
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