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Ask Our Instructors

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Feel free to submit questions regarding electrical safety, maintenance or engineering. We will post the questions and answers as we receive them. When your answer is posted we will send you a quick email to let you know.

Is there a requirement to have a device available to pull someone off an energized source in the event of a mishap? If so, where do I get the specifics as to what is it suppose to be made of, etc.? Lloyd J.
Is it necessary to ground the cable armor of armored cable? Do we need to ground both ends of the armor of the cable or just one end? What will be the different effects if we ground one end and both ends?
Is there a basic difference between meggering the insulation of a conductor (parallel sets of 500 KCM) and resistance testing the insulation? Farinas
What are some good safety precautions when doing battery maintenance?
What does the NEC® say about doors to electrical equipment rooms?
When hi-potting equipment what are the recommended safe distances from the high potential lead for medium and high voltages? -Mike B.
Is there a written safe procedure for removal or insertion of MCC buckets on energized motor control centers. About all one can find anywhere is information saying de-energize the motor control center etc. This is not possible in 24/7, 365 day/yr operating plants such as nuclear and/or chemical plants. - Dorazine
What are the differences between 2 conductors that are the same size but one is flexible and the other is solid?
I have to test an 11/0.4 KV 1,600 KVA Dyn11 Transformer, therefore what are the tests standard procedure for the Tr. - Ahmed K.
To test a 6.6 kV trailing cable, what is the best rating on a megger to test it? Will the best be 7.5 kV or 5 kV megger? Will a 10 kV setting on the megger damage a 6.6 kV cable? What are the time periods to test a cable with a Megger? - Gwylem J.
When a transformer is rated at 500KVA,11/0.433KV and its ampacity is 25/666.7, at the Primary and Secondary respectively, Does it mean the ampacity at the secondary side(666.7) is for Red phase,Yellow phase and Blue phase respectively or is for Red,Yellow and Blue combined? - Evans A.
Does poor earthing system causes high meter reading and hence increases the tarrif? - Evans A.
When do you apply 90deg. cable THHN, on Table310-16?
Also, the Lightning Protection System, is it connected to Bldg Grounding System or is it Isolated? - Gerzan A.
We are installing Local Control Panels in Material Handling Systems. The environment is wooden dust. The area is considered Class II, Div.2 Our Local Control Panel , have NEMA 4x Enclosure and all push buttons, lights are explosion proof NEMA 7. Is this ok ? Do we have to provide cast copper free aluminum casing with explosion proof pushbuttons? There is considerable cost difference and weight of assembly? Can you please give guidance?
We're installing grounding studs on the load side bus of breakers which is in metalclad switch gear. The breakers are racked out, and we have open points on our getaway line switches, some up to 3/4 mile away, which are tagged and grounded. We have been told we are protected by the grounds on the line so we can go on and work on the switchgear bus to install the ground studs without using any PPE. Are we safe to do this work this way and when does equipotential grounding come into effect? - Jerry C.
I am a volunteer aboard a decommission coast guard cutter - the ship is under going some restoration work to get her sailing again. I have been tasked with meggering the drive motors - I think I understand the basic premise of Meggering but how is it performed and why. I believe Megger deals with the quality of the insulation for the windings and that I need to check from the windings to the motor house using some type of high voltage low amperage tester. Is that correct and is there a design and function book / manual you can recommend for me to read about meggering thanks - Scott F.
We are using a Megger DET4TD2 ground tesing device to test all of our ground rods on Asphalt Plants. Do we test them with no electrical current active? We generate our current; 3ph, 480 to 600 volts depending on the plant. We tested an active ground (600v) and got a reading of 167 ohms but the meter gave us three check marks and no warnings. The device came with no chart, is this ok and is there literature i can find to support your answer? - Mike M.
I have (3) 5000v 1/0 wires feeding a motor underground in conduit about 50ft in length. If I meg between the wires @ 1000v what readings can I expect if the wire is good or bad? - Ron W.
What are the proper procedures for static grounding on aircrafts? What type of meter is best to use? - Oscar E.
When doing insulation resistance testing on a 16 AWG, 950' run, what values should I look for? - Luis D.
What are the precommissioning tests prescribed for equipment in 220,110,66,33,KV Stations? Equipment: Power transformer, C.Ts, P.T.s, Relays, Battery, Breakers, 11 KV Switch gear, Capacitor Banks etc. Do you have any books on the subject? - Kolaki
Where or how can I obtain more information on color coding on electrical wires and fiber optics? -Avee
While testing the insulation resistance testing (meggering) of motors and generators, we isolate the connected electronics (like AVR) and control systems. Is there any published standard/guideline that states this requirement in black and white. -Agoram M.
1. What are the benefits of, and how does one write Switching Procedures for 2300, 4160 and 12,000 volt distribution systems for plant maintenance situations? 2. How does one determine where to place Safety Grounds on de-engerized 2300, 4160 and 12,000 volt distribution systems for plant maintenance situations? -John C.

 

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