Description
2.1 Overview - applications and portfolio
3VA molded case circuit breakers with UL and IEC certification
14 Manual, 01/2019, L1V30435333-01
Aspects of the UL market - Low-voltage systems in the USA
This chapter is an excerpt from the document "The secrets of UL". You will find the complete
document under
(
http://w3app.siemens.com/mcms/infocenter/dokumentencenter/ce/Documentsu20Brochures
/e20001-a820-p305-v2-7600.pdf).
Low-voltage systems in the USA
The usual system configurations in the USA are very different from those found in Europe.
Unlike in the IEC, there is a corner-grounded delta system in addition to the solidly grounded
wye system, which is very similar to the TN-S system. In the USA / UL / NEC, all voltages
that occur in the respective system configuration are always specified (see table below).
When devices are selected, very close attention must be paid to which system configuration
is present at the location of use and the system configuration for which the individual devices
are approved.
The main configurations in industry and in non-residential buildings are 3-phase networks
with 240 V and 480 V, as well as 3- and 4-conductor systems with 480Y/277 V. In residential
buildings and in office spaces of industrial and non-residential buildings, the single-phase
system with 120/240 V can also be commonly found.
1)
Y describes the "Solidly grounded circuit". The value "Y" indicates the voltage between the
phases (e.g. 480 V), and the value behind the slash indicates the voltage between the phase and
the grounding or the neutral conductor (e.g. 277 V with 480 V voltage between the phases).
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