I work at a facility that manufactores metal working equipment. We are currently building two cnc machines that require servo motors and in turn a 10 kva transformer. Originally we used fuses that were to small, ACME told us to use larger fuses, which is fine now. The customer argued that there was something wrong with putting larger fuses in, normally we would agree. But which is best because the in rush is so high?
10 kva transformer which is best? fuses or circuit brea
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Re: 10 kva transformer which is best? fuses or circuit brea
What voltage are we discussing (primary and secondary)?
Properly sized, fuses or circuit breakers will protect the transformer adequately.
What size did you have in there originally?
What voltage are we discussing (primary and secondary)?
Properly sized, fuses or circuit breakers will protect the transformer adequately.
What size did you have in there originally?
Re: 10 kva transformer which is best? fuses or circuit brea
It is of my opinion that with the limited information that you have provided a specific answer is dificult to give.
To start out with, as a rule of thumb, you can expect the inrush of a 150degC 10kva dry type transformer to be about 20x the FLA. This increases for 115degC, 80degC, and K-factor transformers.
Also, the instantaneous or magnetic trip value or highest adjustable trip value is 10X the breaker rating.
Then the question is if the OCPD used, either fuse or breaker, will allow the transformer to be energized with out tripping or blowing. Also, is it the maximum rating that is allowed by the NEC for the specific installation.
You didn't say if it was a single with a two or three wire single phase secondary or three phase with a 3w or 4w secondary which will determine if secondary protection is required and the primary protection rating. Another consideration is if secondary protection is provided and how far is the primary protective device is located from it.
Table 450.3(B) shows the latitude that is provided when 240.21 (3) Taps Supplying a Transformer (primary plus secondary not over 25 ft. long.
It is of my opinion that with the limited information that you have provided a specific answer is dificult to give.
To start out with, as a rule of thumb, you can expect the inrush of a 150degC 10kva dry type transformer to be about 20x the FLA. This increases for 115degC, 80degC, and K-factor transformers.
Also, the instantaneous or magnetic trip value or highest adjustable trip value is 10X the breaker rating.
Then the question is if the OCPD used, either fuse or breaker, will allow the transformer to be energized with out tripping or blowing. Also, is it the maximum rating that is allowed by the NEC for the specific installation.
You didn't say if it was a single with a two or three wire single phase secondary or three phase with a 3w or 4w secondary which will determine if secondary protection is required and the primary protection rating. Another consideration is if secondary protection is provided and how far is the primary protective device is located from it.
Table 450.3(B) shows the latitude that is provided when 240.21 (3) Taps Supplying a Transformer (primary plus secondary not over 25 ft. long.
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