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    Differance between Manhole and Vault

    Can any one add to the list below as to the differance betw een a manhole and a vault? Thanks 1.A manhole is always underground and the equipment within it is usually submersed in water. 2.Access to the manhole is through an opening from above ground. 3.Manholes are not ventilated. 1.A vault...
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    Standby Generator Sizing for a Fire Pump (long)

    Peebee As others and you mentioned, reduced starting may be one way to reduce the starting current, however, as you may be aware, the fire pump, in the event of emergency, can also mechanically be operated. In that case, regardless of the method of starting, the fire pump will be starting at...
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    Medium Voltage Protection

    Can anyone clarify why the NEC treats the medium voltage (> 600v < 38kv)protection differently as compared to low voltage (<600v)systems? It appears that the code is only requires short circuit protection for medium voltage system (with the exception of motors and transformers) while in low...
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    NEC tap rule

    I believe the 10 feet tap rule comes from the fact that the manufacturers in the past were only capable to extrude the present standard 10-foot length of rigid conduits.
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    Derate cables - solar pickup

    What you need to know is that the ambient temperature is the guideline for the derating. With that said, if a cable is installed within a raceway in outdoor location vs. installed without a raceway would have different ambient temperature, hence a different derating factor. Also what you need to...
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    Conventional current

    There is really no difference between either convention. The convention of - to + has to do with the flow of holes in electronics while the + to - convention is used in power. Regardless of which convention you use, make sure that you follow that convention throughout your analysis.
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    NEC and cable loading in duct banks

    You also need to keep in mind that the Rho depends upon the medium(s) surrounding the cable. In a duct bank there are typically four layers of medium to consider. Each medium has a different rate of heat transfer due to thickness, material and wire size and hence different Rhos. Assuming that we...
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    Ground (earth) Resistance in Low Voltage (&lt;600 volts) System

    I believe we are digressing from the main issue, which is exposure of an individual against &quot;shock&quot; potential due to lightning, line surges or accidental drops of a high voltage line on a low voltage line, if the person is inside or outside of a building. What resqcapt19 says is true...
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    Ground (earth) Resistance in Low Voltage (&lt;600 volts) System

    As mentioned by dpc, the code does mention maximum of 25 ohms resistance to ground limitation for made electrode system. The code goes on to say that if that is the case, you need to supplement it with another electrode installed not less than 6 feet from the first one. Since the code does not...
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    Ground (earth) Resistance in Low Voltage (&lt;600 volts) System

    Can any one tell me when we need to be concerned with the resistance to ground (earth) of a grounding electrode system in an industrial or commercial installation with system(s) operating less than 600 volts? It appears that the NEC is not concerned with it, however, it requires to connect the...
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    US Fire Alarm System Regulations

    the answear to your question can be found in the NFPA 72.

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