Low voltage transformer

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hhsting

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I have 120V to 12V transformer to feed low voltage light on a structure outside.

Would the transformer be considered separately derived or non separately derived?
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winnie

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Springfield, MA, USA
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Electric motor research
The diagram you posted does not provide the necessary information with absolute certainty.

The key question: is the transformer primary electrically isolated from the secondary. Transformers can he built isolated or not isolated, and if not isolated then the secondary is not considered 'separately derived'.

The diagram doesn't specify isolated or not.

It is very likely that this transformer has an isolated secondary and creates a separately derived system. But if you need to know with certainty then you need more data.

Jon
 
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hhsting

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Glen bunie, md, us
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winnie said:
The diagram you posted does not provide the necessary information with absolute certainty.

The key question: is the transformer primary electrically isolated from the secondary. Transformers can he built isolated or not isolated, and if not isolated then the secondary is not considered 'separately derived'.

The diagram doesn't specify isolated or not.

It is very likely that this transformer has an isolated secondary and creates a separately derived system. But if you need to know with certainty then you need more data.

Jon
Click to expand...

Would this be considered isolating type transformer or not NEC 2017 Article 411.6(B)??
 
don_resqcapt19

don_resqcapt19

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hhsting said:
Would this be considered isolating type transformer or not NEC 2017 Article 411.6(B)??
Click to expand...
In general, all transformers, other than an auto-transformer, are isolating. There are special isolating transformers that have a grounded shield between the primary and the secondary, but the rule does not require that for this application. This is a listed product intended for this use...nothing more to look at.
 
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hhsting

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don_resqcapt19 said:
In general, all transformers, other than an auto-transformer, are isolating. There are special isolating transformers that have a grounded shield between the primary and the secondary, but the rule does not require that for this application. This is a listed product intended for this use...nothing more to look at.
Click to expand...

The transformer is used for outside art structure low voltage 13V light purpose. Its primary 120V to 13V secondary.

I dont see how NEC 2017 Article 411 doesn’t apply?
 
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augie47

augie47

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Art 411 requires a listed power supply. Supposedly you have that so you are set to go,.
Most of the systems I see are "listed assemblies".. power supply, cord & lumaires...just hook it up & drive off.
 
don_resqcapt19

don_resqcapt19

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hhsting said:
The transformer is used for outside art structure low voltage 13V light purpose. Its primary 120V to 13V secondary.

I dont see how NEC 2017 Article 411 doesn’t apply?
Click to expand...
I didn't say the rule does not apply, I said the power supply is listed for the purpose and there is no need to even think about it, let alone look a it.
 
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hhsting

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Location
Glen bunie, md, us
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Junior plan reviewer
augie47 said:
Art 411 requires a listed power supply. Supposedly you have that so you are set to go,.
Most of the systems I see are "listed assemblies".. power supply, cord & lumaires...just hook it up & drive off.
Click to expand...

I dont see in 411 requiring listed supply?

Also data-sheet in OP where it says listed for low voltage?
 
tortuga

tortuga

Code Historian
Location
Oregon
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Electrical Design
Yes its fine, UL 1838 = complies with article 411.
Article 411 was added to the 1999 NEC and the whole listing requirement just adds confusion to a simple install IMO they should allow class1 or class2 to cover it.
Here are the key things to know about landscape lighting xfromers:

* Isolating power supply required 750 VA or less;
* Not over 30V (or not over the peak voltage equivalent of 30V RMS ac, 42.4V);
* 25A maximum size for all circuits on the secondary side;
* The secondary circuits must be ungrounded and insulated from the primary supply by an isolating transformer. Exposed bare conductors are permitted under certain conditions. Bare conductors are permitted at least 7 ft above the finished floor unless specifically listed for a lower height.
* The systems must be supplied from a 20A (max.) branch circuit (any voltage).
 
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