What's bad about them is that they (at least the non-industrial sized ones ) 
are based on mechanical relays. After some number of switches under load, the 
relay contacts will eventually weld themselves shut. Unfortunately, there is no 
way to detect this condition until the next power fail wherein the relay 
doesn't switch to the alternate power and your critical device goes down.

Raritan makes an interesting unit that is a hybrid. It uses SCRs (like the big 
industrial units) but only to do the initial load transfer. It then closes the 
relays for the long term current carrying. This way there is no arcing of the 
relay contacts. It's a bit more expensive than the other brands, but not 
onerously so.

From: listsad...@lists.myitforum.com [mailto:listsad...@lists.myitforum.com] On 
Behalf Of Joseph L. Casale
Sent: Friday, September 16, 2016 1:09 PM
To: 'ntsysadm@lists.myitforum.com' <ntsysadm@lists.myitforum.com>
Subject: [NTSysADM] RE: Transfer switches

APC sells them, not sure what is bad about them? Pretty common device in all 
but the simplest setups I would think?

jlc

From: listsad...@lists.myitforum.com<mailto:listsad...@lists.myitforum.com> 
[mailto:listsad...@lists.myitforum.com] On Behalf Of Ken Cornetet
Sent: Friday, September 16, 2016 10:48 AM
To: ntsysadm@lists.myitforum.com<mailto:ntsysadm@lists.myitforum.com>
Subject: [NTSysADM] Transfer switches

Does anyone here have experience with AC transfer switches? I find myself in 
the unenviable position of needing some, and pretty much all I hear about them 
is bad. I have some equipment that only has one power supply (no option to add 
a redundant supply) that will be powered by two different mains. Each main will 
go down periodically, but never both at once.

Suggestions?


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