In the 2005 NEC, Section 450.21(A) states that dry type transformers 112 kVA and less must have a separation of 12 inches from combustible material.
There is an exception to the rule that says if a transformer is completely enclosed (with or without ventiallating openings) that the rule does not apply.
So, what constitutes completely enclosed? Is a typical wall mounted transformer in an enclosure where the windings are completely inaccessible due to the insulating materials that the windings are encased in considered completely enclosed?
How about your typical floor mounted transformer where the windings are accessible but housed in an enclosure with removable front and back plates?
Is 450.21(A) only referring to open core, control style transformers? I've never seen an open transformer (no enclosure) larger than probably 5 kVA.
Most of the floor mounted transformers I've installed have a clearance distance listed on the nameplate and with wall mounted transformers you're kind of limited to the clearance you can achieve by the mounting brackets attached to the transformer
There is an exception to the rule that says if a transformer is completely enclosed (with or without ventiallating openings) that the rule does not apply.
So, what constitutes completely enclosed? Is a typical wall mounted transformer in an enclosure where the windings are completely inaccessible due to the insulating materials that the windings are encased in considered completely enclosed?
How about your typical floor mounted transformer where the windings are accessible but housed in an enclosure with removable front and back plates?
Is 450.21(A) only referring to open core, control style transformers? I've never seen an open transformer (no enclosure) larger than probably 5 kVA.
Most of the floor mounted transformers I've installed have a clearance distance listed on the nameplate and with wall mounted transformers you're kind of limited to the clearance you can achieve by the mounting brackets attached to the transformer
