Transformer Power or Control
Transformer Power or Control
(OP)
In sizing primary side protection for a transformer I'm seeing that if this transformer is in a power application the maximum protection allowed is 300% over the full load primary current. Fine.
But then NEC goes on to say if it's used in a control application the maximum primary protection is limited to 500%!
What is the definition of "power" verses "control"?
But then NEC goes on to say if it's used in a control application the maximum primary protection is limited to 500%!
What is the definition of "power" verses "control"?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Transformer Power or Control
xnuke
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RE: Transformer Power or Control
Keith Cress
kcress - http://www.flaminsystems.com
RE: Transformer Power or Control
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Transformer Power or Control
Thanks!
Keith Cress
kcress - http://www.flaminsystems.com
RE: Transformer Power or Control
Bigger transformers tend to be optimized for cost of materials.
Smaller transformers tend to be optimized for cost of assembly.
RE: Transformer Power or Control
RE: Transformer Power or Control
"...In sizing primary side protection for a transformer I'm seeing that if this transformer is in a power application the maximum protection allowed is 300% over the full load primary current. But then NEC goes on to say if it's used in a control application the maximum primary protection is limited to 500%! What is the definition of "power" verses "control"? "
1. In NEC: there is (mention) but [without definition] of "control circuit transformer" with rated current <2A; the maximum primary protection is limited to 500%!. The word "control circuit ..." not " control ..." explains. It is understood that there is a predetermined connected load. There is an initial high inrush of current, until the armature of the relay is sealed....
2. In NEC: there is definition of "Transformer" but not " Power transformer". The former is defined which intended to mean an individual transformer.....". It followed with requirements that is for "power utility" applications, which are different from the "control circuit transformer". Their characteristic/requirement differs, therefore the protection requirements.
Che Kuan Yau (Singapore)