Separately Derived Systems
Separately Derived Systems
(OP)
Can anyone here explain the concept/theory of separately derived systems and how it would affect system installations?
Thanks.
Thanks.
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Separately Derived Systems
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RE: Separately Derived Systems
You could also have a generator that once a transfer switch operates, cuts the utility and leaves you with a separately derived source. This source needs to still have proper grounding.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Separately Derived Systems
Generators switched through 4 pole transfer switches (or 3 pole and no neutral brought out of the generator) are separately derived while generators that are paralleled to the utility or switched with transfer switches that do not switch the neutral are not separately derived.
RE: Separately Derived Systems
I may be mistaken and I am away from my books and can't research this just now.
Bill
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"Why not the best?"
Jimmy Carter
RE: Separately Derived Systems
RE: Separately Derived Systems
Now my next question is, what does the NEC or other international Codes say about SDSs? Are there some rules?
Thanks.
RE: Separately Derived Systems
Generation will count as a separately derived system, certainly when it is operating in isolation, and the neutral and earthing arrangements need careful design especially if the set is also capable of parallel operation.
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If we learn from our mistakes I'm getting a great education!
RE: Separately Derived Systems
RE: Separately Derived Systems
Short of that, see this http://www.iaei.org/magazine/?p=4590
Rafiq Bulsara
http://www.srengineersct.com
RE: Separately Derived Systems
check outthe attachment...
RE: Separately Derived Systems
You're almost right -- except when you put the solid bond in there, you no longer have two separately derived systems.
For example, you could use a 3-pole transfer switch with solid neutral to switch between a 4-wire utility and 4-wire generator *so long* as the only N-G bond is at the utility. The utility is then the only separately derived system. The generator is *not* separately derived in this case, it shares a neutral with the utility.
RE: Separately Derived Systems
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Separately derived systems are covered in Article 250, Grounding and Bonding, especially paragraphs 250.20 through 250.35.
If you can get your hands on a copy of the NEC Handbook rather than the plain-Jane NEC, it does a bit better job of describing separately derived systems.
The IEEE Green Book also does a nice job of covering separately derived systems.
Oops, just realized how old this thread is....