all transformers are sds?

[mborino]

Are all transformers in an electrical system considered separately derived systems? Even the downstream transformers?

 

[templdl]

Re: all transformers are sds?

When they provide isolation. Auto transformers, i.e. buck-boost, do not.

 

[charlie b]

Re: all transformers are sds?

I agree.

But I will add that, in my view, to say a "transformer" is an "SDS" is inaccurate. The "system" in the phrase "separately derived system" includes the transformer, all the loads that receive power from that transformer, and all the wiring and devices between the transformer and the loads.

 

[jes25]

Re: all transformers are sds?

So all you typical 480/208 transformers qualify for SDS?

 

[charlie b]

Re: all transformers are sds?

I have yet to design a system for which a 480 to 120/208 transformer was not part of an SDS. I won't say that it can't happen, but I have not done it myself.

 

[kiloamp7]

Re: all transformers are sds?

Same for me, charlie b.

 

[roger]

Re: all transformers are sds?

Okay, in the memory of Bennie, any grounded system that is bonded from Primary to Secondary, even if only through the enclosure, is not an SDS.

An ungrounded Delta to an ungrounded Delta, or a truly ungrounded secondary as used in 517.160 would be a couple of examples that would qualify as a true SDS's, otherwise, the term is not correct.

Roger

[ December 14, 2005, 10:20 PM: Message edited by: roger ]

 

[jes25]

Re: all transformers are sds?

Aren't we using the NEC defintion?

 

[charlie b]

Re: all transformers are sds?

Whatever would we do that for?

 

[roger]

Re: all transformers are sds?

Roger