Mercede Electric Co.

Lester, PA, United States

Mercede Electric Co.

Lester, PA, United States
SEARCH FILTERS
Time filter
Source Type

Mercede F.,Mercede Electric Co. | Mercede J.N.,Mercede Electric Co.
EC and M: Electrical Construction and Maintenance | Year: 2011

The guidelines followed in the selection and coordination of branch circuit overload and short circuit protection of low-voltage motors are presented. Motor branch circuit overload protection is provided by a thermal overload relay with melting alloy heaters, while branch circuit short circuit protection is afforded with a motor circuit protector or dual-element fuses. The knowledge of the maximum starting amperes of the motor is necessary to properly select motor branch circuit short circuit protection. The maximum starting current not only accounts for the locked rotor current, but also considers the possible asymmetrical offset of the starting current waveform. The safe stall time should not exceed 20 seconds for a standard NEMA Design B motor with class B or F temperature rise. The motor branch circuit overload protection is provided by a thermal overload relay with three melting alloy heaters, and the motor branch circuit short circuit protection is afforded by a motor circuit protector.


Mercede F.,Mercede Electric Co. | Mercede J.N.,Mercede Electric Co.
EC and M: Electrical Construction and Maintenance | Year: 2011

Some issues affecting the results of arc flash calculations under the IEEE Std 1584 method are discussed. Arc flash calculations were performed for three different values of available 3-phase, short circuit MVA of the utility supply, such as 100MVA, 10MVA, and 1MVA. The results of the calculations show increasing incident energy levels for decreasing available 3-phase, short circuit MVA of the utility supply. Under the IEEE Std 1584 method, arc current is calculated from the bolted 3-phase, short circuit current with an empirically derived equation, showing that the arc current decreases with decreasing available 3-phase, short circuit MVA of the utility supply. Arc flash calculations were also performed for two types of primary fuses for the system such as 10A, class K, and 10A, class T. The results show an increase in the incident energy level from 6.19 J/cm2 for the class K fuse to 16.9 J/cm2 for the class T fuse, necessitating an increase in the Hazard/Risk Category.


Mercede F.,Mercede Electric Co. | Mercede J.N.,Mercede Electric Co.
EC and M: Electrical Construction and Maintenance | Year: 2011

An understanding of some of the misconceptions of arc flash labeling and the tragic consequences of non-compliance is presented. The first include no notification or violation concerning the field-labeling of electrical equipment for arc flash hazard risk. The counterargument says that in the event of an electrical accident at your facility, the absence of field-labeled electrical equipment is cause for an OSHA violation. Regarding the responsibility to field-label the electrical equipment for arc flash hazard risk it is said that even if contractors perform all of the electrical work, owner is held liable in the event of an electrical accident if the electrical equipment in question is not field-labeled for arc flash hazard risk. For a misconception that inexpensive generic warning labels can be applied to the electrical equipment to meet the requirement it is defined that in the event of worker injury due to an electrical accident at your facility, generic labels could be cited as cause for the accident.


Mercede F.,Mercede Electric Co. | Mercede J.N.,Mercede Electric Co.
EC and M: Electrical Construction and Maintenance | Year: 2011

This article has considered the requirements to select the ratings, characteristics, and settings of the phase overcurrent and ground-fault protective devices of a low-voltage unit substation. Due to space limitations, this presentation is brief; therefore, the reader should refer to IEEE Std 242-2001 (IEEE Buff Book) for further understanding of this important topic.

Loading Mercede Electric Co. collaborators
Loading Mercede Electric Co. collaborators