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Three Phase Service Entrance
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Three phase service entrances are mainly commercial and industrial. The layout of such systems are typically more efficient, and cost effective than residential single phase systems. Of course they end up using different front end devices and panels in the installation, because they are all different.




Types of Service Entrances


Three phase (4 wire system) 'Y' or Wye
- 120/208 (light and power w/neutral)
-347/600


Three phase (3 wire system) 'Delta"
-240/480,600V
-no neutral
-ungrounded



Permit and Inspections
Nova Scotia power must approve plans for a three phase service entrance. This is done by obtaining a permit, submitting plans for approval, and scheduling inspections. The information can be obtained on their website.


Service Entrance Capacity
-exceed 320A than it must be a three phase service at either 120/208 or 347/600 volts
-normally 400A requires three phase 347/600 volts
-120/208 or 347/600 are limited to 600A but higher amperage services are available. Please note that commercial installations routinely install 600 volt services with up to 3200 ampere ratings.



Meter Sockets
Single Meter Layout (200A or less)
-meter does NOT require disconnect
-comes before switch or panel
-does NOT have CT or PT

Single Meter Layout (200A plus)
-located after main disconnect
requires metering cabinet and meter base
-requires CT's

*CT's are used to step down current in order to properly measure usage (power)
-they are needed after 200A
-two types 'donut' and 'bar type'
-primary marked 'H1' and 'H2'
-secondary marked 'X1' and 'X2'
-must be grounded
-subtractive polarity for added safety

*PT's are used to step down voltage in larger than 600A systems to the CT's
-must be grounded
-subtractive polarity
-often require primary fuse protection




Conductors in Parallel
-usually 250A and over
-reduction of cost
-ease of installation
-can be run in one conduit or...
-two in one and, one conductor plus the neutral


Color Coding - 4-036 CEC
Red, Black, Blue



Procedure for Conductor Selection
1. Determine Load
2. Is it continuous or non-continuous?
3.If continuous is equipment rated for continuous use?
4. Apply derating factor 8-104 (4) or (5) considering the wire method
5. Select a conductor. Can 8-106(1) apply? This is the 5% rule.
6. Select an O/C device to 'match' the conductor


Underground Installations
(12-012 CEC) (Table 53)
*apply with diagrams from B4-1,B4-2,B4-3,B4-4
*and tables D8B through to D15B