Now you should know that anything dealing with electricity is controlled by standards...the manufacturers make the parts to specifications set forth by relevant standards for their customer base locations...just ask your supplier which codes they comply to and any certifications they have...
I've been reading the IEC 60137, ANSI/IEEE C57.19.00 and C57.19.01 standards and haven't found anything about standard dimensions. The only one I saw that has some standardized dimensions was the IEC EN 50386 standard for "DIN" type bushings (see image)
The North American manufacturers H-J, Kennaloy and Warco (see image) do not follow the same dimensions for the same bushings classes, which leads me to think that in the US there is no standardization in this regard (dimensions).
IEEE standards (and I assume IEC also) don't specify dimensions for bushings, as they don't for most other electrical apparatus. That is determined by each manufacturer based on meeting the electrical performance parameters specified by IEEE. That's why you can't just interchange various manufacturers' bushings or other items in most cases where mechanical/dimensional fit is of concern.
What is it that you are trying to do, find a replacement that fits a specific bushing that you can't get from the OEM (original equipment manufacturer)?
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To get the right answers, first you need to ask the right questions.
I am a member of the transformer bushing study commission of the Brazilian Association of Technical Standards. The Brazilian Standard specifies requirements for bushings based on IEC 60137. In addition to meeting the performance requirements of this Standard, "Brazil" type bushings called "NBR" bushings have, in addition, standardized dimensions that facilitate interchangeability.
The last revision of the Brazilian Standard included the "ANSI/NEMA" type bushings and the idea of my post was to know if there are some standardized dimensions so that it is necessary to propose the inclusion in the Standard at an opportune moment.
Your explanation was very helpful and I can understand that standard dimensions are not established for ANSI/NEMA bushing types, perhaps just the hole sizes and thread types given by NEMA.
One might gain a speedier insight by ringing <...bushing...> manufacturers directly, and talking to them.
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