3 wire 2 circuit LV track

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e57

Senior Member
So I have an install coming up with 2-circuit Monorail track - it's 3-wire...
And I roughed in the transformers - and think to myself - 'This could go horribly wrong' - better call the manufacturer..... As the way I think it should be connected might not be right in the end - and too expensive to experiment.

When faced with two LV lighting transformers how would you approach it? Two switch legs from the same 120v branch CB to 2 transformers for 24/12v ungrounded/floating neutral.... I thought about it and came up with one way.
  1. Reverse one of the primaries (Code violation as the conductor is white...)
  2. Connect common taps on secondary of both
  3. Move OCP to non-common taps
Got the wiring diagrams from the manufacturers.... Thought some more - the common taps have the OCP on them....

Since I am using third party transformers I checked the lightnings originally spec'ed transformer instructions - they reversed the secondary, and made no mention about phasing and polarity of the primaries - you could easily have fed this from a 3-wire circuit.... Wow - that could be bad.... Then I checked the manufacturer for the transformers I am using - See attatched - simular. Anyway for both diagrams, the OCP would be on the hot side of one leg, and the neutral side of the other - I thought this odd - what say you???
 
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jrannis

Senior Member
e57 said:
So I have an install coming up with 2-circuit Monorail track - it's 3-wire...
And I roughed in the transformers - and think to myself - 'This could go horribly wrong' - better call the manufacturer..... As the way I think it should be connected might not be right in the end - and too expensive to experiment.

When faced with two LV lighting transformers how would you approach it? Two switch legs from the same 120v branch CB to 2 transformers for 24/12v ungrounded/floating neutral.... I thought about it and came up with one way.
  1. Reverse one of the primaries (Code violation as the conductor is white...)
  2. Connect common taps on secondary of both
  3. Move OCP to non-common taps
Got the wiring diagrams from the manufacturers.... Thought some more - the common taps have the OCP on them....

Since I am using third party transformers I checked the lightnings originally spec'ed transformer instructions - they reversed the secondary, and made no mention about phasing and polarity of the primaries - you could easily have fed this from a 3-wire circuit.... Wow - that could be bad.... Then I checked the manufacturer for the transformers I am using - See attatched - simular. Anyway for both diagrams, the OCP would be on the hot side of one leg, and the neutral side of the other - I thought this odd - what say you???

It seems like they really should not be using the word "neutral" to describe the secondary conductors. That looks to me what is causing the heartburn.
 

Dennis Alwon

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Retired Electrical Contractor
You may have to find a transformer that is designed for this. If there was one switch for both circuits it is a no brainer but if you have 2 switches to control circuits independently you may need a special transformer that will accept 2 feeds and 2 outputs. I am not sure if you can put 2 different tranys together and share one side.
 
jrannis said:
It seems like they really should not be using the word "neutral" to describe the secondary conductors. That looks to me what is causing the heartburn.

Agreed. Tech Lighting's wiring documents label it as COM. I would suspect the primary reason for this wiring method is to avoid overloading on the shared neutral wiring.
For the OP, you might also want to notice in the tech lighting transformer documentation "The system is "ETL" listed for USA and Canada only when all the products used are supplied by Tech Lighting". I don't remember seeing this in the past, so not sure how it might impact your installation.

We have installed this with both circuits on the same phase and on different phases with no noticeable problems.

Speaking of problems...I love to spec this stuff, and it looks GREAT.... I might suggest offering a service contract though... on second thought, having worked with the stuff, maybe not, all those little pieces get really annoying when doing repairs.
 
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I wonder, do you already have the transformers? (third party transformers)
If so, do you see any classification on the transformer such as "Class 2"?


I see in the instructions "25 Amps" as the supply. That would not be Class 2.

I am wondering how you are wiring and protecting the transformers...is this a dwelling?
 

e57

Senior Member
Pierre C Belarge said:
I wonder, do you already have the transformers? (third party transformers)
If so, do you see any classification on the transformer such as "Class 2"?


I see in the instructions "25 Amps" as the supply. That would not be Class 2.

I am wondering how you are wiring and protecting the transformers...is this a dwelling?

The Semper Fi Power Supply Transformer is roughed in - not yet terminated - but class 1 wiring both sides, and in a dwelling... Where is there a class determination on amperage? 25a is common - sometimes more....

Dennis Alwon said:
You may have to find a transformer that is designed for this. If there was one switch for both circuits it is a no brainer but if you have 2 switches to control circuits independently you may need a special transformer that will accept 2 feeds and 2 outputs. I am not sure if you can put 2 different tranys together and share one side.
Both are made for the purpose after modification - and even if made with a center tapped primary, and secondary - it would still be two transformers essentially...

Anyway both reverse polarity on the seconday side of one - but my question is the placement of the OCP on the secondary side - they change the so-called common/ungrounded neutral (Code does not allow grounding of it) - but neither change location of the OCP, leaving in place on what is now an ungrounded floating neutral connection, and the other on a hot conductor. Since the neutral can float depending on load - is this placement wise?
 

e57

Senior Member
iwire said:
Check out Table 11(A) in Chapter 9 (not code)

Hmmmm... Interesting

But anyway..... I'm not looking to stray too far away from the original question of the placement of the OCP on a floating neutral lighting system - does the class of the system or it's listing have much to do with it? Am I missing something?

The way I see it - depending on load of the transformers on this ungrounded system - which would change voltage both sides - much the way it would in a lost neutral situation - would one side be left unprotected, or less protected? The way I am thinking about this is that one could easily load one side more than the other, and one less (If say the owner changed configuration - or a lamp or two went out) - shifting the balance of load, and voltage applied to the loads. One side could easily get 18v, the other 6v if loaded unequally since it is ungrounded. (At 18v the amperage is different, just as it is when the same lamping has only 6v...) Since both sides will be dimmed often at different levels - how will that react?

This is how it is wired according to both manufacturers:
3wireT.jpg



Should it not be something like this???? (Which would limit current if only one was on to 12.5 - so this is a bad idea on second thought...)
3wireT2.jpg


Or something like this which is what I orginally thought it might be....
3wireT3.jpg
 
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mdshunk

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Right here.
e57 said:
Any other ideas?
Yeah, use monorail transformers. As Don pointed out to me a couple months ago, these low voltage lighting systems are UL listed as a "system". You can't use 3rd party anything with them.
 

mdshunk

Senior Member
Location
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e57 said:
Marc, thats not an option at this point - nor an answer to the question as both are wired the same way....

If you're serving them from one circuit, I fail to see any real problem. You're just paralleling two co-phased transformers. One secondary hot at each of the far ends, and the neutral in the middle, common to both.
 
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e57

Senior Member
mdshunk said:
The system is "ETL" listed for USA and Canada only when all
the products used are supplied by Tech Lighting.

Ya know Marc.... I just looked up Tech's listing and it seems they only have listed transformers - the track and fixtures do not seem to be - Since I am not using their transformer - I fail to see a problem..... Unless I was using their transformer to serve lighting not made by them.... Nor does that language appear on anything for the fixtures or track or feed canopy fittings - only on the instructions for the transformer.

Once again that is not the question at hand... As even if I were using Tech's tranformer the question would be the SAME.
 
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mdshunk

Senior Member
Location
Right here.
e57 said:
Once again that is not the question at hand...
Very sorry, but I don't have an answer. I was only trying to give as much as I could figure out, just in case it brought on a light bulb for someone else. Part of my malfunction. I sorry I could not give you the answer to your question. All I have is my stupid opinions.

Speaking of stupid, here's a picture of a stupid monorail job from just a few months ago:

monorail3.jpg
 
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e57

Senior Member
mdshunk said:
All I have is my stupid opinions.

Lets not bring Glen Willard into it..... :grin:

Anyway I am sure you too will have the same question the next time someone wants another stupid version of the same install with more heads and seperate switching.

Although it makes sooo much more sense for a situation like this to have a grounded transformer for a 3-wire application (Code violation in 411.5A) - or to use a 4-wire 2-circuit.... It does not seem to be the case. The 3-wire application poses a few problems that I do not think the manufacturers have given much thought. (In terms of a floating neutral and OCP placement due to their own modification instructions.) Because I think - that in an unbalanced situation - it may be possible to load one side more than the 25a that the code limits these systems to.
 
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