Page 131 - Pipeline Rules of Thumb Handbook

118 Pipeline Rules of Thumb Handbook

windblown dust, and damage from external ice longed submersion at a limited depth, and damage
formation. from external ice formation.
3R Enclosures are intended for outdoor use primarily to 12 Enclosures are intended for indoor use primarily to
provide a degree of protection against rain, sleet, and provide a degree of protection against circulating
damage from external ice formation. dust, falling dirt, and dripping noncorrosive liquids.
3S Enclosures are intended for outdoor use primarily to 12K Enclosures with knockouts are intended for indoor
provide a degree of protection against rain, sleet, use primarily to provide a degree of protection
windblown dust, and to provide for operation for against circulating dust, falling dirt, and dripping
external mechanisms when ice laden. noncorrosive liquids.
4 Enclosures are intended for indoor or outdoor use pri- 13 Enclosures are intended for indoor use primarily to
marily to provide a degree of protection against wind- provide a degree of protection against dust, spraying
blown dust and rain, splashing water, hose-directed of water, oil, and noncorrosive coolant.
water and damage from external ice formation.
4X Enclosures are intended for indoor or outdoor use
Hazardous (classified locations)
primarily to provide a degree of protection against
corrosion, windblown dust and rain, splashing water,
7 Enclosures are intended for indoor use in locations
hose-directed water and damage from external ice
classified as Class I, Groups A, B, C, or D, as defined
formation.
5 Enclosures are intended for indoor use primarily to 8 in the National Electrical Code.
Enclosures are intended for indoor use in locations
provide a degree of protection against settling air- classified as Class I, Groups A, B, C, or D, as defined
borne dust, falling dirt, and dripping noncorrosive in the National Electrical Code.
liquids.
6 Enclosures are intended for indoor or outdoor use 9 Enclosures are intended for indoor use in locations
classified as Class II, Groups E, F, or G, as defined
primarily to provide a degree of protection against in the National Electrical Code.
hose-directed water, the entry of water during occa- 10 Enclosures are constructed to meet the applicable
sional temporary submersion at a limited depth, and requirements of the Mine Safety and Health
damage from external ice formation.
6P Enclosures are intended for indoor or outdoor use Administration.
primarily to provide a degree of protection against Reference NEMA Standards Publications/No. 250-1991
hose-directed water, the entry of water during pro- Used with permission—National Electrical Manufacturer’s Association.

Size portable electric generators

A power plant must be properly sized for the required load. Total motor load = 600 ¥ 3 = 1,800 watts
Electric motors are particularly difficult for portable plants
since they require 2 to 3 times motor nameplate amps or Total other load = 2,100 watts
wattage.
A portable power plant’s surge capacity is limited by engine Total load = 3,100 watts
horsepower and inertia of its rotating parts. Thus, a current
surge of short duration can be supplied by a power plant, but Add 25% for future = 975 watts
a current demand of longer duration such as a heavily loaded
motor starting a high inertia load, can overload the power Total load for sizing power plant = 4,875 watts
plant and possibly damage the power plant and the motor. A
3,450rpm air compressor is a prime example of this type of A generator capable of supplying 5,000 watts continuously
load. will be adequate.
When more than one motor is connected to a power plant,
Example: always start the largest motor first. If the total load is con-
nected to one receptacle on the power plant, be sure the
Load Requirements:
ampere rating of the receptacle is not exceeded.
Electric Heater 1,000 watts
11–100 watt lamps 1,100 watts
Motor 600 watts