Means of Disconnect Location & Type

[short circuit faulted]

Problem. Existing Building with 600A 3P4W 480V Main Service with 600/3 MCB - Client wants to add 332A 480/3 Conditioning equipment - Obviously cannot add this load to existing Main Panel or transformer. - My thoughts are to set exterior pad mount for addtional load, mount OCPD on exterior of building - (Enclosed Circuit Breaker with under voltage shunt in Nema 3R Enclosure) Use a 277V 20/1 out of the Existing Main Panel for under voltage sensing, and route a pushbutton to mount next to existing Main Panel with amply signage to note purpose. This as there is no room within the existing electrical room to mount a OCPD. Undervoltage shunt, shunts breaker open and breaker cannot be operated until power is restored. Thereby when the existing MCB is opened the new OCPD opens and the shunt button can be used to indepentently open OCPD for equipment. Any major holes in this approach from NFPA 70/NEC?

Thanks & Stay Aware out there otherwise you may not be here tomorrow!

Steve

 

[raider1]

This sounds like you are going to supply the building with a second service. Take a look at 230.2 (A) through (D) for where a second service would be allowed to be run to the building.

I don't see any allowance in 230.2 that would permit what you are proposing.

Chris

 

[augie47]

I agree with Chris, from what I see that would not be acceptable here.
One possibility..and I emphasis possibility (depending on your AHJ).. would be if your proposed AirCond service was a different characteristic such as 480 Delta.