250.21(B), Ground detectors

[jim dungar]

The HO and XO are grounded, would you consider that a SDS?.

Separately derived systems are allowed, actually they are required, to have common grounding connections.

Most utilities 480Y/277V and 208Y/120V services are fed from Yg-Yg transformers.

 

[Deltaforce]

The HO and XO are grounded, would you consider that a SDS?.
They are all 70's era, I know the definition has changed slightly I am genuinely curious what your take is?

The code still consider to be sds as no direct connection between two neutrals
However the issue, code intent of sds to mitigate objectionable current in premise star-star connected transformer no met this way:
As both primary and secondary neutrals connect to building GES, any MV ground fault may cause part ground fault current flow through EGC to LV neutral, LV netral to GES. GES to primary neutral, primary neutral to MV utility source
As egc, lv neutral connections may not rated such mv fault current. they may damage

 

[jim dungar]

As both primary and secondary neutrals connect to building GES, any MV ground fault may cause part ground fault current flow through EGC to LV neutral, LV netral to GES. GES to primary neutral, primary neutral to MV utility source
As egc, lv neutral connections may not rated such mv fault current. they may damage

In the US, all neutrals, across the entire country are electrically bonded together. For utilities this may occur every couple of kilometers as part of their multi-grounded neutral MV distribution. For LV systems this occurs at each service or each transformer secondary. About 30 years ago, the NEC effectively discontinued the use of isolated systems, except in hospital ORs.