1-Voltage, 2-Wire Secondary

[Jerramundi]

Stuck in a semantic argument w/ myself and require a little bit of clarification...
I'm trying to discern whether or not the following transformer would qualify as a "single voltage, two wire secondary" (see diagram below).

Clearly there are four wires coming off the secondary and the option to wire the secondary for multiple voltages (120V and/or 240V).

I should probably just stop here and acknowledge that this is NOT a "single voltage, two wire secondary," but in an attempt to justify possibly avoiding secondary overcurrent protection and save on cost, my brain does the following...

Per the wiring diagram below, I will be wiring X1 to X3 and X2 to X4 to produce the single voltage of 120V. Leaving the transformer enclosure will be only two wires and a single voltage, which makes me think I could make the argument that these conductors ARE a "single voltage, two wire secondary."

Then I loop back around mentally and remind myself to be honest about the fact that there are actually four wires coming off the secondary and multiple voltages available, even if I am ultimately creating a "single voltage, two wire secondary."

Which is it? Is my initial notion correct about this not being a "single voltage, two wire secondary" or do my semantic games fly? haha.

 

[Hv&Lv]

I would say if it’s connected for a 240, or a 120 as in the top and bottom of the secondary volts, no protection on secondary.
if it’s the middle connection for 120/240 then my vote is secondary protection.
JMO...

 

[curt swartz]

I know you have a number of threads going on this transformer. One thing you need to remember is even if you are permitted to omit secondary protection of the transformer you are still required to protect the secondary conductors and equipment they supply.

 

[texie]

I know you have a number of threads going on this transformer. One thing you need to remember is even if you are permitted to omit secondary protection of the transformer you are still required to protect the secondary conductors and equipment they supply.

If you meet the requirements of 240.21(C)(1) the secondary conductors are considered protected.

 

[texie]

Stuck in a semantic argument w/ myself and require a little bit of clarification...
I'm trying to discern whether or not the following transformer would qualify as a "single voltage, two wire secondary" (see diagram below).

Clearly there are four wires coming off the secondary and the option to wire the secondary for multiple voltages (120V and/or 240V).

I should probably just stop here and acknowledge that this is NOT a "single voltage, two wire secondary," but in an attempt to justify possibly avoiding secondary overcurrent protection and save on cost, my brain does the following...

Per the wiring diagram below, I will be wiring X1 to X3 and X2 to X4 to produce the single voltage of 120V. Leaving the transformer enclosure will be only two wires and a single voltage, which makes me think I could make the argument that these conductors ARE a "single voltage, two wire secondary."

Then I loop back around mentally and remind myself to be honest about the fact that there are actually four wires coming off the secondary and multiple voltages available, even if I am ultimately creating a "single voltage, two wire secondary."

Which is it? Is my initial notion correct about this not being a "single voltage, two wire secondary" or do my semantic games fly? haha.

View attachment 2553356

Yes, you could omit the secondary OCPD on the secondary if it is wired a 2 wire only. However, as a practical matter, depending on the sizes of all the components the math may not work out so that your load is properly protected. For example with a small transformer you may end up with a 15 amp OCPD on the primary and then have the equivalent of a 30 amp secondary which may be a problem for many devices and equipment.

 

[Jerramundi]

I would say if it’s connected for a 240, or a 120 as in the top and bottom of the secondary volts, no protection on secondary.
if it’s the middle connection for 120/240 then my vote is secondary protection.
JMO...

So you would argue that if the four wire leads coming off the transformer secondary are connected to produce a single voltage output, and there are only two wires leaving the enclosure, that these conductors would qualify as a "single voltage, two wire secondary?"

 

[Jerramundi]

One thing you need to remember is even if you are permitted to omit secondary protection of the transformer you are still required to protect the secondary conductors and equipment they supply.

I'm aware, but one thing at a time. First I have to discern if this qualifies as "single voltage, two wire." That is the purpose of this thread.
In response to your comment, I agree with the texie that...

If you meet the requirements of 240.21(C)(1) the secondary conductors are considered protected.

However, you bring up a valid point that equipment on the secondary side may also require overcurrent protection... and it seems open to debate about whether or not transformer primary protection would qualify as protection for the equipment on the secondary side. The conductors are clearly protected per 240.21(C)(1), but the equipment may be another story.

I was musing about this in another thread... about whether a controller/timer on the primary side would be considered (1) a controller/timer for the transformer... or (2) a controller/timer for the secondary load... or (3) both. If you can find my other thread, feel free to comment and I'd be happy to carry out that discussion there... but let's stay on topic for this particular thread so it doesn't get closed for being redundant.

 

[Jerramundi]

Yes, you could omit the secondary OCPD on the secondary if it is wired a 2 wire only....

That's all I'm concerned about with this particular thread. If this particular transformer is wired according to the above wiring diagram to produce only a single voltage... and only two wires leave the enclosure... would the secondary conductors be considered "single voltage, two wire?"

The stipulation being that the transformer secondary itself actually has four wires coming off the secondary and the capacity for more than one voltage output.

 

[Jerramundi]

I've found a few transformers that literally have only two wires coming off the secondary and the capacity for only one voltage output, which makes me think maybe I'm pushing it by trying to make this argument...

They just seem to be rare. It seems most transformers are set up for at least two outputs. Economically speaking, it makes sense. Only one voltage output would result in a product for a more limited type of application and thus more limited sales.

 

[Jerramundi]

...and then have the equivalent of a 30 amp secondary which may be a problem for many devices and equipment.

I actually found a 10A 2-Pole Breaker, which I didn't even know existed. Not sure if I can use it as it would be considered a "nonstandard ampere rating," but again... I digress.

 

[winnie]

There is the legalistic code and there is the physics of the situation. They should align but sometimes this doesn't work out. IMHO if there are two plausible interpretations of the legalistic code, then the one that matches the physics should prevail.

As long as only 2 wires go in for the primary and come out for the secondary, the current on the secondary conductors should be proportional to the current on the primary (disregarding magnetizing current) and primary OCPD can plausibly protect the secondary, presuming correct sizing per the turns ratio of the transformer and conductor sizes.

I can see the legalistic argument that what matters is the number of conductors coming off the secondary _as connected_ and the legalistic argument that what matters is the number of conductors that could possibly come off the secondary. I believe that the _as connected_ conductor count makes more sense.

-Jon

 

[Jerramundi]

I believe that the _as connected_ conductor count makes more sense.

So you are in agreement with Hv&Lv that if this particular transformer's secondary 4 wire leads w/ multiple potential voltage outputs... are connected in such a way that they produce only one voltage and only two wires leave the transformer enclosure, that this would qualify as a "single voltage, two wire" secondary?

 

[winnie]

So you are in agreement with Hv&Lv that if this particular transformer's secondary 4 wire leads w/ multiple potential voltage outputs... are connected in such a way that they produce only one voltage and only two wires leave the transformer enclosure, that this would qualify as a "single voltage, two wire" secondary?

Yes.

 

[LarryFine]

I must dissent. How you wire the transformer does not alter the characteristics of the transformer itself.

If "single voltage, two wire secondary" does not address this situation, what else could it be referring to?

 

[ptonsparky]

Two wire means two at the xfmr.

You could take/tap eight conductors out of the transformer. Does that mean it is no longer a two wire?

 

[Jerramundi]

If "single voltage, two wire secondary" does not address this situation, what else could it be referring to?

Dissent is welcome

Well, 99.9% of the secondary conductors will be two wire and only carrying a single voltage. It's just those four small wire leads coming off the secondary coil that brings the popular opinion, shared between Hv&Lv, Winnie, and (in-part) myself, into question.

The only other thing I can think of that means 100% "single voltage, two wire secondary," with ZERO room for semantic arguments, is a transformer with quite literally only two wire leads coming off the secondary coil and quite literally the capacity for only a single voltage output.

I've seen these in the form of autotransformers, so they are a real product... which makes me think that perhaps I'm pushing this semantic argument too far...

 

[texie]

Dissent is welcome

Well, 99.9% of the secondary conductors will be two wire and only carrying a single voltage. It's just those four small wire leads coming off the secondary coil that brings the popular opinion, shared between Hv&Lv, Winnie, and (in-part) myself, into question.

The only other thing I can think of that means 100% "single voltage, two wire secondary," with ZERO room for semantic arguments, is a transformer with quite literally only two wire leads coming off the secondary coil and quite literally the capacity for only a single voltage output.

I've seen these in the form of autotransformers, so they are a real product... which makes me think that perhaps I'm pushing this semantic argument too far...
[/QUOTE

If it wired and installed as a 2 wire secondary you can take advantage of the code allowance in my view. The purpose of the rule is to prevent the conductors from being overloaded. If there is nothing connected and no provision made in the installation to connect load it is a 2 wire secondary.

 

[LarryFine]

If it wired and installed as a 2 wire secondary you can take advantage of the code allowance in my view. The purpose of the rule is to prevent the conductors from being overloaded. If there is nothing connected and no provision made in the installation to connect load it is a 2 wire secondary.

Then what does "single voltage, two wire secondary" mean, and why bother mentioning it?

If the code meant "when connected as . . . " it certainly could and would have stated it that way.

A dual-winding/dual-voltage secondary transformer obviously does not meet the definition.

 

[electrofelon]

I recall this topic coming up in the past. I am in the camp of the "what is used" people. I certainly see how the wording says/could be interpreted as "what the transformer has" but Im going to let the laws of physics tip the scales. Perhaps a code change/clarification is in order.

 

[LarryFine]

The description of "single voltage, two wire secondary" refers to how the unit is manufactured, not how it's wired or used.