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  • Users: rwilsond
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  1. rwilsond

    NEC vs. UL

    Sometimes there are inconsistent requirements for manufacturers, between the NEC and UL standards. Presently, I'm looking at requirements for manufacturing luminaires, and see some grounding requirements in the NEC, are stricter than those of the UL. For example Article 410.18 states that...
  2. rwilsond

    Combined Neutrals

    Here's an oddity I came across. An electrician was called to a house, because of lights flickering. He came to believe there was an open in the neutral of a 2-wire branch circuit. But he was unable to locate and correct the open. So, he jumpered the neutral to the neutral of another 2-wire...
  3. rwilsond

    VFD's & IEEE Std 519

    I'm involved in the selection of VFD's for some large AC motors (up to 450HP). The spec that was given to the supplier imposes the requirement that these VFD's "shall meet all requirements of IEEE Std 519". I have IEEE Std 519 ("Recommended Practices and Requirements for Harmonic Control in...
  4. rwilsond

    Grounding in Control Panels

    Section 409.60 of the 2005 NEC refers to "Multisection industrial control panels", but there is no definition. What would be an example of a Multisection industrial control panel? Would it be multiple sub-panels in a common enclosure? Also, the second sentence of 409.60 seems ambiguous. Is a...
  5. rwilsond

    UL, SCCR, and the NEC

    Section 440.4(B) of the 2005 NEC requires that the Short Circuit Current Rating (SCCR) be included on a visible nameplate for "Hermetic Refrigerant Equipment" having multiple motors or combination loads, when supplied by an OCPD of more than 60A . A major industrial HVAC equipment manufacturer...
  6. rwilsond

    Ground in Bus-Duct

    A large 1 MVA, Delta-Wye transformer supplies a 480V, 3-Wire MCC via a bus-duct. The 20-foot length of bus-duct contains NO ground-bus, and no neutral, and the enclosure is NOT Listed for grounding. The transformer secondary, and the Ground-Bar inside the MCC, are both connected to the...
  7. rwilsond

    Article 409 and Tap Rules

    A particular 480V Industrial Control Panel in a "Supervised Industrial Installation" is fed from a large (say 2000 kVA) transformer, without any type of OCPD on the transformer's secondary side, and without a Main CB inside the panel. Instead, the 15-foot long tapped supply conductors terminate...
  8. rwilsond

    Circuit for Oversized Transformer

    Assume a balanced connected load of 25 kVA on the secondary of a 45 kVA, 3-phase, 480-208/120V transformer. Does the NEC prohibit less than that of the transformer's primary rating for sizing wiring and CB? For example, can a 45A CB, and 50A ampacity wiring be used to supply the transformer's...
  9. rwilsond

    NEC Demand Factor for Hotel Hairdryers & Coffee Makers

    For a large existing hotel two new circuits will be added to each guest room to eliminate nuisance CB trips caused by too many coffee pots and hairdryers. These new circuits will feed only one receptacle each per room (one for a hairdryer & one for a coffee pot). New panels & transformers will...
  10. rwilsond

    Demand Factor Dilemma

    For a large existing hotel two new circuits will be added to each guest room to eliminate nuisance CB trips caused by too many coffee pots and hairdryers. These new circuits will feed only one receptacle each per room (one for a hairdryer & one for a coffee pot). New panels & transformers will...

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