wrote:
On Jun 7, 11:22 am, "Ralph Mowery" wrote:
wrote in message

...

No other opinions on this? I was hoping someone could spell out how
the code allows this?
Look about half way down :http://www.sea.siemens.com/step/pdfs/surge_2.pdf


Thanks for pointing me in the right direction. The Siemens article
talks about NEC 280 that covers this stuff. Some googling on that
produced more good stuff.

The Siemens article also includes TVSSs (transient voltage surge
suppressors) which were covered by NEC article 285. That is what you
have. They must be connected downstream from over current protection
(article 280 "surge arresters" can be connected ahead of the service
disconnect).

NEC articles 280 and 285 were reorganized in 2008. In one of the changes
TVSSs are now called SPDs (surge-protective devices) - still under
article 285.

SPDs are covered by UL1449. Since the "second edition", which was
effective in 1998, SPDs (both plug-in and service panel) have been
required to have protection built in to disconnect failing MOVs. It
commonly responds to overheating MOVs and may also include fuses. The
internal protection will protect the wires.


Minimize the wire length and avoid sharp bends. The clamp voltage is
higher the longer the wires are because of voltage drop through the wire
impedance, which is significant for surges. If wires are fairly long
lightly twisting them is a good idea. The rated clamp voltage is for 6"
lead length for SPDs made now. The IEEE guide at
http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf
talks about lead length starting document page 22.

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bud--