Hi,
I have a grounding question again. Please refer to the attached drawing.
At the project we have an overland conveyor of 1km long. At the start of the conveyor we have a 33/4.16 kV 5 MVA transformer substation with its grounding grid designed according to IEEE 80. At the end of the conveyor...
Hi, I am involve in a project where we are running several 3 phase circuits of 33 kV using single phase conductors arranged in a trefoil formation. The cables are installed on a FRP cable ladder which is no good as a grounding conductor. The circuits lengths is around 1000 m, and all of the...
Hi,
Does anyone know if the NEC had any restrictions on using cable joints, tape, or preassembled ones.This is for 33 kV, 500 MCM cable trifoil formation runned on above ground cable ladder and also underground cable duct.The length of the circuit is 1800 m.
I was told that it is not allow and...
Hi all,
I have two underflow pumps (552 kW each, 4.16 kV) for the thickeners in a mining project. For this size of motors I normally use a two 2/0 AWG bare copper cable to ground the motor directly to the earthing grid. In this case we dont have a grouding grid under the motors because of...
Hi,
I am from Chile where we have our own standard for low voltage installations, but since they are not updated since 2003,we normally also follow the NEC as a good practice guide. Article 250 of the NEC states:
250.24(C) For 1000 V or less AC Systems, neutral conductor shall be routed with...
Hi, can anyone explain if IECEx certified equipment can be used in hazardous areas clasified under NEC 2011 code 505. From the code it seems that the marking on the equipment needs to be AEx instead of IECEx. This mean the manufacture of the equipment needs to certified its equipment on the US...
Hi,
I am trying to figure out the following:
- NEC article 392.80(A)(2)(c)state that for single conductors installed in a trifoil formation with separation of 1 diameter between individual conductors we should use table 310.15(B)(17) for ampacity. This table for example gives you an ampacity...
Hi,
NEC 2011, article 630.41 and 392.10 (B)(1)(b) requires for welding cable to be run on a dedicated cable tray.
My question: i have and MCC which supply power to the 63 Amps welding socket, 100 m away. I will use cable tray and conduits to run the cable from the MCC to the welding socket...
Hi,
Anyone knows an standard or document where it states that in a plant is not a good practice to have some local control stations with 120 Vac and others with 125 Vdc?. At the project where I am, it was proposed to have Medium voltage motors with LCS´s control voltage of 125 Vdc and low...
Hi,
Anyone know an standard that define the colours in the lights on LV MCC modules. I mean the lights that indicate Runnign status, ready status, and fault.
Regards,
Hi,
There is any guideline from ieee or from your experience to set the maximum voltage ratio for a distribution transformer? I need to decide if install a 33 kV / 0.4 kV 2 MVA transformer or run a 4.16 kv cable from a 500 m away substation, and install a 4.16 kV / 0.4 kV 2 mva transformer...
Hi, I am trying to understand the NEC 2011 table 430.22(E). I would apreciate if someone can clarify.
From the table I understand NEC classify motors in Continouos duty, intermittent duty, short time, periodic and varying duty. Also each duty is classify in 5 min rated, 15 min rated, 30-60 min...
Hi, I am trying to get my head clear around the following definitions. Can anyone specify the differences between the following devices to control motor in LV assemblies:
Motor controller,
Motor combination starter
Combination motor controller
self protected combination controller
Full voltage...
thread238-214018
Hi,
In the thread 238-214018 Morquea mention a method and rule of thumb to dimention a transformer for motor starting. Basically consist on the following:
Calculate Motor Starting kVA = (FLA of motor)*sqrt(3)*(3 phase voltage)
Calculate SC level at the secondary of the...
Hi,
I am working on some MV drive specifications, the idea is to select the same drive for different applications in the plat. I would like to know what to look for in order to decide if to select a 12 or a 24 pulse drive (18 is not possible since the manufacture is already selected). The...
Hi,
I would like to know if there is any difference in the definition of Arc Proof and Arc Resistance switchgear. To me it sounds the same. I always have understand an arc resistance switchgear as an equipment tested to C37.20.7 or IEC 62271-200. But according to some of my collegues there are...
We are in the process of selecting a grounding criteria for a Dy1 power transformer. We have two alternatives:
1. Use a low resistance grounding of neutral point of secondary. (1500 A)
2. Use a high resistance grounding of neutral point of secondary. (1500 A). (300 or 400 A)
My question is...
Hi,
Can someone give a procedure to correctly size a current transformer to be use in protection ?. I guest it should be something like:
- pick ratio to be below of the nominal current of the system.
- pick accuracy limit factor to be above the maximum fault current.
- pick VA of transformer...
HI,
NEC art 500 states:
"The unique hazards associated with explosives, pyrotechnics, and blasting agents are not addressed in this article.
I want to specify electrical equipment to be install in an explosive and blasting agentes storage above ground (This are explosives for mine...
Hi,
Can someone explain when I should use a CSI (current source inverter) topology for the inverter of the VSD or when to use a VSI (Voltage Source inverter) kind?
Thanks.
