Do i need to put C/B before outlet that feeds from step-down transformer?

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I can see a position being taken that you do not if the primary secondary protection is such that 240.21(C) allows the secondary conductors to be protected by the primary overcurrent device but I don't see where that carries over to the device. IMO, you do need to protect the receptacle with an overcurrent device based on Art 210 part II
 
recon1729 said:
[h=2][/h]
Hi, i need to ins. 110V outlet in place that only 380/220V available.So i gonna ins. a 220/110V step-down transformer but do i need to put a C/B before outlet connection?.​


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I think more information is needed.

What ampacity is the 380/220 circuit you are connecting too?

What size is the transformer?

What ampacity do you need at the outlet?

What size conductors are involved?
 
Bob, details notwithstanding, in general terms can you see a situation where an OCP device would not be required on the secondary ? (I'm aware that under the right conditions, 240.21(C) might allow the primary device to protect the secondary conductors but can this be extended to the receptacle outlet ? I found it an interesting question !)
 
augie47 said:
Bob, details notwithstanding, in general terms can you see a situation where an OCP device would not be required on the secondary ? (I'm aware that under the right conditions, 240.21(C) might allow the primary device to protect the secondary conductors but can this be extended to the receptacle outlet ? I found it an interesting question !)
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I am with you, I think there could be a time when that applies.

But as always the devil is in the details.
 
iwire said:
I am with you, I think there could be a time when that applies.

But as always the devil is in the details.
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I'm posting here to learn, not to give an answer.

Set aside code requirements for a moment. Assume that no separate OCPD is required for the secondary conductors.

If the load on the secondary conductors became greater than the rating on the transformer's secondary coil, wouldn't the secondary coil be destroyed before the primary OCPD could trip?


 
(not i-wire but a response)
On a two-wire to two-wire or delta-delta transformer since the secondary and primary currents are proportionally balanced with proper primary overcurrent protection you will prevent secondary overload damage. Since you don't have the same static ratio on a three wire single phase secondary or 4 wire three phase secondary, 240.21(C) will not allow the primary OCP device to protect the secondary.
 
augie47 said:
(not i-wire but a response)
On a two-wire to two-wire or delta-delta transformer since the secondary and primary currents are proportionally balanced with proper primary overcurrent protection you will prevent secondary overload damage. Since you don't have the same static ratio on a three wire single phase secondary or 4 wire three phase secondary, 240.21(C) will not allow the primary OCP device to protect the secondary.
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Thank you, I'll review the sections cited and do a little studying on the electrical theory behind this.
 
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