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don_resqcapt19

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By far the most common SDS is a transformer. Unless the transformer is an autotransformer, it is SDS.
 

charlie b

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I would call this one of those times in which language gets in the way of communication.

To my way of thinking, taking the three words at face value, I would say that the "separately derived system" is the set of feeders, panelboards, and branch circuits downstream of the transformer. They collectively form the "system." The transformer is the thing that derives an electrical distribution system that is separate from the system on its primary side.
 

don_resqcapt19

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I would call this one of those times in which language gets in the way of communication.

To my way of thinking, taking the three words at face value, I would say that the "separately derived system" is the set of feeders, panelboards, and branch circuits downstream of the transformer. They collectively form the "system." The transformer is the thing that derives an electrical distribution system that is separate from the system on its primary side.
It is a term that is defined in Article 100 and it is defined as an "electrical source" and does not included anything else.
Separately Derived System. An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.
 

Smart $

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I would call this one of those times in which language gets in the way of communication.

To my way of thinking, taking the three words at face value, I would say that the "separately derived system" is the set of feeders, panelboards, and branch circuits downstream of the transformer. They collectively form the "system." The transformer is the thing that derives an electrical distribution system that is separate from the system on its primary side.
I agree with your assessment of "system" with the exception that the transformer, at least its secondary, is a part of said system. And for the record, there is little if any difference in requirements once you get past the disconnecting means of separately-derived and service-supplied systems.
 

don_resqcapt19

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Why do they set up transformers and generators? Why don't they just use the electricity from the main electrical panel?
Generators are typically for back-up power when you lose the utility supply and transformers are typically for where you need a voltage that is different from the utility supply.
 

Johnnybob

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Colville, WA
Many reasons, with isolation being one. Also, with my plant as an example, our service is 3.2kv, which we transform to 480v which is what all of our 3 phase loads require, so since we already have it, why pay for another 240/120 service? Cheaper to buy and install our own little transformers, feed 'em from an MCC bucket put 'em wherever we need a 240/120 panel:) As my first example states, it is then pretty much isolated from any spikes,(of which we get more than a few in the spring) and all the reactance of our motor circuits! I'd direct you to another post about that that is cleverly disguised as a story about water in a barrel, but methinks that doggy has been on a long enough walk already;)
 

Smart $

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Many reasons, with isolation being one. Also, with my plant as an example, our service is 3.2kv, which we transform to 480v which is what all of our 3 phase loads require, so since we already have it, why pay for another 240/120 service? Cheaper to buy and install our own little transformers, feed 'em from an MCC bucket put 'em wherever we need a 240/120 panel:) As my first example states, it is then pretty much isolated from any spikes,(of which we get more than a few in the spring) and all the reactance of our motor circuits! I'd direct you to another post about that that is cleverly disguised as a story about water in a barrel, but methinks that doggy has been on a long enough walk already;)
That's pretty much how most facilities do it though many go with 208Y/120 3Ø rather than 240/120 1Ø.

Also, these SDS' do not isolate their load equipment from spikes or up-the-line reactance though it can act as a buffer in some cases.
 

don_resqcapt19

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So 300.3(C) Conductors of Different Systems only refers to the "source" conductors???
I don't think the term "different systems" is a code defined term. The definition of SDS has nothing to say about the definition of a "different system".
 

Johnnybob

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Location
Colville, WA
That's pretty much how most facilities do it though many go with 208Y/120 3Ø rather than 240/120 1Ø.

Also, these SDS' do not isolate their load equipment from spikes or up-the-line reactance though it can act as a buffer in some cases.
Not sure what the difference would be between a 50kva tranny and a 1kva "clean power" Sola would be then? As long as it's not an auto-transformer, the secondary is isolated from the primary winding's, with only magnetic connection, right?
 

Smart $

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Location
Ohio
Not sure what the difference would be between a 50kva tranny and a 1kva "clean power" Sola would be then? As long as it's not an auto-transformer, the secondary is isolated from the primary winding's, with only magnetic connection, right?
Yes, but magnetic coupling transforms whatever voltage it is supplied with, and that includes voltage spikes too. A 1kVA Sola "clean power" has "filtering" just for that purpose... suppress transients. Find a high-kVA rated Sola clean power and compare the cost to a same-kVA basic isolation transformer... or simply open one up (de-energized) and you'll see it is more than just a transformer.
 
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Smart $

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Location
Ohio
I don't think the term "different systems" is a code defined term. The definition of SDS has nothing to say about the definition of a "different system".
But if you have an SDS that transforms to another voltage, there has to be some statement which says the SDS output and associated wiring beyond the disconnecting means is a different system for the purposes of 300.3(C).

I realize we are not going to get anywhere in this debate because of said definition(s) or lack thereof. I just believe it's a noteworthy issue.
 

Johnnybob

Senior Member
Location
Colville, WA
Yes, but magnetic coupling transforms whatever voltage it is supplied with, and that includes voltage spikes too. A 1kVA Sola "clean power" has "filtering" just for that purpose... suppress transients. Find a high-kVA rated Sola clean power and compare the cost to a same-kVA basic isolation transformer... or simply open one up (de-energized) and you'll see it is more than just a transformer.
So I just happened to have a 750va Sola on the shelf in my shop, so I did an autopsy. The name is certainly a little miss-leading, it is called a Sola Mini/Micro-Computer Regulator! Sometimes the difference between expensive and inexpensive is the ability to turn a phrase, or dream up a name lol.
Anyway, you are correct in the filtering, in that it has 72 uF worth of capacitors on the secondary winding's, that I assume are to correct for the inductance of the secondary winding's. Also has a very fancy Bakelite finger-safe terminal covers:)
All in all, I don't see anything other than the name to justify any cost difference. I can buy a 24 and a 48uF capacitors for a couple bucks, though Bakelite is rather hard to come by.
Still not sure how you'd pass upstream reactance through a magnetic field?
 
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