NEC 240.21(C)(1)

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Eewomb

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I have a transformer I am trying to determine meets this provision in the code for omitting secondary protection. Its a 480/240 to 240/120 transformer with 2 hots and a GND on the primary side and 1 hot, a neutral, and a GND on the secondary side. I think this scenario is not sufficient for this rule because of the neutral coming off the secondary but i am not sure. Any insight would be greatly appreciated!
 
Sounds like a "two-wire/two-wire" arrangement and, provided it meets the remaining criteria of 240.21(C)(1) (ratio, etc.) , it qualifies for rbeing protected by primary.
 
electrofelon said:
Does that section intend the number of wires you are using, or the number of wires the transformer has (whether you use the CT or not)?
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This is the question i am wrestling with. The exact wording is "Conductors supplied by the secondary side of a single-phase transformer having a 2 wire (single voltage) secondary" I am still new to NEC so i am not 100 sure if this situation works
 
Eewomb said:
This is the question i am wrestling with. The exact wording is "Conductors supplied by the secondary side of a single-phase transformer having a 2 wire (single voltage) secondary" I am still new to NEC so i am not 100 sure if this situation works
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From your description, you have 2 wires and a single voltage on the secondary. 240.21(C)(1) would allow protection of the secondary conductors by the primary OCPD.
 
Eewomb said:
I have a transformer I am trying to determine meets this provision in the code for omitting secondary protection. Its a 480/240 to 240/120 transformer with 2 hots and a GND on the primary side and 1 hot, a neutral, and a GND on the secondary side. I think this scenario is not sufficient for this rule because of the neutral coming off the secondary but i am not sure. Any insight would be greatly appreciated!
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You have a three wire secondary. You cannot use 240.21(C)(1).

"Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single-voltage) secondary"
 
dkidd said:
You have a three wire secondary. You cannot use 240.21(C)(1).

"Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single-voltage) secondary"
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He has the two secondary coils connected in parallel, it is being used as a single voltage secondary.

If he had the secondary coils connected in series he would have 120/240 volt three wire secondary system.
 
kwired said:
He has the two secondary coils connected in parallel, it is being used as a single voltage secondary.

If he had the secondary coils connected in series he would have 120/240 volt three wire secondary system.
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I dunno. Paralleling doesn't alter the fact that the secondary is NOT a 2-wire, single voltage secondary. The fact that the secondaries can be connected in series OR parallel seems to defy the description.
 
LarryFine said:
I dunno. Paralleling doesn't alter the fact that the secondary is NOT a 2-wire, single voltage secondary. The fact that the secondaries can be connected in series OR parallel seems to defy the description.
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I'm in agreement with kwired and others. If you have two of your wires coming out of the secondary then you have a two wire secondary. If you have a single voltage secondary then you have a single voltage secondary. It doesn't matter how many leads the manufacturer puts in the make up box.
 
In practice, I agree with you. Strictly speaking, however, the secondary is made up of more than one winding, with four wires emerging from the core. Whether those individual wires are hidden or exposed doesn't alter that we're talking about a 2-winding secondary that can be configured for more than one voltage (as well as a primary with the same configuration).
 
LarryFine said:
In practice, I agree with you. Strictly speaking, however, the secondary is made up of more than one winding, with four wires emerging from the core. Whether those individual wires are hidden or exposed doesn't alter that we're talking about a 2-winding secondary that can be configured for more than one voltage (as well as a primary with the same configuration).
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And how you configure the windings determines whether you have a two wire, single voltage secondary or not and whether or not you can use primary only protection.

We just had a big argument a month ago about if a box being outside makes it outside or not. This is in the same category. When you have a two wire secondary then you have a two wire secondary and nobody will convince me otherwise.
 
ActionDave said:
I'm in agreement with kwired and others. If you have two of your wires coming out of the secondary then you have a two wire secondary. If you have a single voltage secondary then you have a single voltage secondary. It doesn't matter how many leads the manufacturer puts in the make up box.
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So in your opinion, if I have a tranny with a single winding and a center tap but dont use it, or a two winding connected in series (and dont use the midpoint I just made), are those the same for purposes of the code article in question and can I call both of those two wire secondaries because of how I am using them?
 
electrofelon said:
So in your opinion, if I have a tranny with a single winding and a center tap but dont use it, or a two winding connected in series (and dont use the midpoint I just made), are those the same for purposes of the code article in question and can I call both of those two wire secondaries because of how I am using them?
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Yes, I would call that a single voltage secondary.
 
dkidd said:
OP didn't say that. You are speculating.
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The OP said he has two secondary coils. He also said he is using the transformer as a single voltage 2 wire secondary.

One might speculate that he is connecting the coils in parallel, but he could connect them in series and also have a single voltage 2 wire secondary.
 
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