There are many such local services in the US. The only services you can
dependably expect are the
120/240 (center tapped) residential service
120Y208 three phase business/commercial service
277Y480 three phase light industrial service
There are many other conventions based on peculiar industries, history
or special applications, but the need to address any other service
should be subject to negotiation with the customer. These applications
are often addressed with local transformers dedicated to the purpose.
Most older 500 volt services have made the transition to 480 volt
(either delta or wye). 600 volt delta is somewhat common and many new
buildings are using multi kV for large motor loads.
All premise wiring systems must be earthed except in very rare
circumstances such as hospitals, cranes, electrolytic cells, or low
voltage lighting. You cannot depend on any convention for either
grounding or phase rotation, except that wye and center tapped systems
use the center as the neutral or earthed conductor. Once a neutral
(grounded conductor) is established, it should be identified throughout
the system by insulation color (white, grey or in special circumstances
light blue), white hardware (silver, chrome rather than brass), tracer
threads, etc. Details of this are addressed in our National Electrical
Code NFPA 70.
Bob Johnson
ITE Safety
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Horst Haug
Sent: Monday, December 17, 2001 9:05 AM
To: Crabb, John; 'Bill Lawrence'; 'EMC-PSTC Forum'
Subject: Three phase delta system in USA
I also learned, that there is a three-phase delta system in USA with 500
Vac per phase.
One phase (L3) is earthed.
Is this system very often used in USA?
Is it correct information, that L3 is always earthed and not L1 or L2.
Horst Haug
