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Richard Cummins
Electrical Manager
Lectrus Corporation
(832) 295-1200
Richard Cummins is Electrical Manager for Lectrus Corporation (formerly Metal Systems), a Chattanooga-based industry leader that engineers and builds fully-integrated, electrical equipment centers, operator centers and custom enclosures for the power, oil & gas...more»»
Emergency Lights in NJ
Posted by tommy from manahawkin, NJ, US on May 15, 2009
Where can I find out info on placement of emergency lights in NJ?
According to the New Jersey Division of Codes and Standards, the 2008 National Electrical Code was adopted with technical amendments on April 6, 2009 (N.J.A.C. 5:23-3.16). Therefore, please reference NEC Article 700.15.
480 V Open Delta Service
Posted by Antonio from Denver, CO, US on May 14, 2009
Is there limit on how big a motor you can serve with a 3-phase, 480 V, open delta service from a two phase distribution line (without adverse effect to motors or other large 3 phase loads)? Transformer size not being an issue, can you serve a 50 hp or 100 hp or 500 hp motor without cutting its life due to voltage unbalance?
Thank you.
An open Delta system is typically not a 480 system. It is normally a three phase system with power limitations because only two transformers are used. It has two 120 VAC legs and one 208/240 VAC leg measured to ground. Phase to phase measures 208VAC so you have a balanced system. The open delta system can only deliver 87% of the rated power of the two transformers. Example: If the two transformers are 25KVA each you would have 87% of 50 KVA or 43.5 KVA of power to use in your facility. The other calculation associated with the open Delta is to base the calculation on a three transformer system even though you are only using two transformers and multiply by 58%. Example: 25KVA x 3 = 75KVA x .58 = 43.5KVA of usable power. This is a balanced system so it should not affect the life of your motors.
MC Cable
Posted by Peter from Marshfield, WI, VI on May 14, 2009
For a hospital-grade mc cable, what do we do with the “bare ground” wire?
When you strip the sheathing back for termination before installing the connector on the sheathing, wrap the extra ground around the sheathing in the natural grooves of the MC cable on one end. On the other end, terminate the extra ground to the device with the equipment ground conductor. This helps give a better ground to the MC cable since (by code) you can not consider the sheathing of MC as a ground like you can a conduit.
Proper Installation in Wet Locations
Posted by Milan from Cedar Rapids, IA, US on May 14, 2009
Are raintight emt fittings allowed to enter above live parts on Nema 3R enclosures?
Typically, no. It is recommended that a rain tight hub (from either Myers or TNB) be used above the live parts.
Current Transformer
Posted by jerry from griffith, IN, US on May 14, 2009
What is a current transformer and what is it used for?
According to www.electric-find.com, a current transformer is a transformer used in instrumentation to assist in measuring current. It utilizes the strength of the magnetic field around the conductor to form an induced current that can then be applied across a resistance to form a proportional voltage.
