Is there an NEC provision that requires the fuses/cb on devices (panelboards mostly) downstream of a transformer to just total the same as the transformer secondary current? I have always thought that these OCP's are sized and limited to no more than six (6) times the transformer available secondary current.
OCP Downstream of a Transformer
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ron
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Re: OCP Downstream of a Transformer
NEC-2002 Table 450.3(A) Note 2
NEC-2002 Table 450.3(A) Note 2
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Re: OCP Downstream of a Transformer
Or, as applicable, 450.3(B).
I can't imagine where you might have gotten the notion that you could set up "protection" that did not protect. If each breaker allowed the transformer's full rated secondary current to flow, and if there are six such breakers, and if the transformer was therefore supplying six times its rated current, then what would stop the transformer from smoking?
Or, as applicable, 450.3(B).
I can't imagine where you might have gotten the notion that you could set up "protection" that did not protect. If each breaker allowed the transformer's full rated secondary current to flow, and if there are six such breakers, and if the transformer was therefore supplying six times its rated current, then what would stop the transformer from smoking?
Re: OCP Downstream of a Transformer
Thanks for the info.
To Charlie B: It is not like that at all. Who said I was in the process of doing that kind of protection? For one thing, the transformer is not capable of supplying six times its current rating. Secondly, what is the use of the protection upstream? But thanks for helping.
Thanks for the info.
To Charlie B: It is not like that at all. Who said I was in the process of doing that kind of protection? For one thing, the transformer is not capable of supplying six times its current rating. Secondly, what is the use of the protection upstream? But thanks for helping.
charlie
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Re: OCP Downstream of a Transformer
I am a little confused by this thread so if this doesn't make sense, please forgive me.
The transformer must be protected on its primary and maybe the secondary side so it doesn't get smoked. See Section 450.3 as Charlie and Ron already mentioned. It may also be protected on the secondary side by the use of 240.21(C) provisions which are required to protect the conductors.
If the transformer is sized properly and all the rules for overcurrent protection are properly applied, its not going to get smoked.
I am a little confused by this thread so if this doesn't make sense, please forgive me.
The transformer must be protected on its primary and maybe the secondary side so it doesn't get smoked. See Section 450.3 as Charlie and Ron already mentioned. It may also be protected on the secondary side by the use of 240.21(C) provisions which are required to protect the conductors.
If the transformer is sized properly and all the rules for overcurrent protection are properly applied, its not going to get smoked.
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