Hello Paul, The location is domestic, but the equipment isn't. The UPS is supplying a few items as well as the POE plugpack, and it is of the sine wave no-break variety which does not have any gap in supply when becoming active. Grounding can be quite problematic, but hopefully we can get it right. The trick is to avoid circulating currents in the shield. Its no good when you Faraday cage radiates its own energy. Given the mast and the PSU don't share any meaningful sort of ground reference it should not be too difficult. Steve. -----Original Message----- From: Public [mailto:public-bounces@talk.mikrotik.com.au] On Behalf Of Paul Arch Sent: Wednesday, 30 April 2014 18:02 To: 'MikroTik Australia Public List' Subject: Re: [MT-AU Public] Problems with multiple RBMetal2SHPn devices.failing at one site Hi Steve, Totally outside the square here.. but here goes... You mentioned an UPS inline to the POE injector. Given your mention of a domestic setup let's assume cheap line interactive ( if that matters ) If the UPS detected mains issues ( brown-out, drop etc ) could the switch over from mains to battery/inverter ( 50ms? ) cause issues downstream to the tik ? I am sure you guys are more well-versed in grounding etc than me, but I have seen electronics so some weird and wonderful stuff because of grounding issues. cheers Paul