Transformer windings protection under 600v
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Primary ocp can be responsive to secondary short circuits but is not always responsive to secondary overcurrent caused by? PP294
an unbalanced condition
Transformer "charging current" for smaller transformers is what compared to the ampere rating of the transformer? PP298
Proportionally larger for the ampere rating of the transformer
The overcurrent device prtecting the primary of a transformer may be located where? PP300
But must do what?
May be located at other than than the tranformer, but must....
protect the primary windings (T450.3B) and the conductors (240.4)
According to 240.21(C)1 of the 2008 NEC, the transformer secondary is not permitted to be protected by the primary ocpd unless it is one of the following transformer connections. PP310
- single-phase, 2 wire, single-voltage secondary
- Delta-Delta, 3 phase, 3 wire, single-voltage secondary
When primary protecton includes sencondary protection, what must be used? Controls what? PP311
Transformer ration, and controls the size of the conductors used on the secondary of the transformer.
The basic rule for feeder taps on transformers (240.21) states that the OCPD is required to be connected where? PP313
Where the conductor recieves its supply
Tap rules allow what? PP313
Exceptions that allow the tap to not have an OCPD at the point where the conductors recieve thier supply
The length of a tap is from what to what? PP314
Secondary conductors are sometimes refered to as tap conductors? T/F PP 315
from the feeder to the OCPD, and not the transformer
What rule is the only rule that permits secondary conductors to land directly onto main lug only-type switch boards or panelboards. pp316
The 10ft tap rule as it pertains to the 10ft secondary conductor rule
regarding fire pumps, what type of overcurrent protection is allowed on the secondary of the transformer? PP327
None. Primary ocpd only
Note 1 on table 450.3(B) for OCPD for primary and secondary conductors for transformers under 600v allows rounding up to the nearest OCPD and what for conductor ampacity?
rounding down for conductor ampacity
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