450.3(B)

[hyattjay]

OK, so I am trying to make sense of the 125% rule for primary OCPD and if secondary OCPD is actually required. Application is 50kVA 480v 1P primary, 120/240v 1P secondary, only load is a UPS. UPS is listed at 80A, 240v in, 240v out (nameplate listing) and feeds a single pnl brd, that feeds 6 120vac, 1P, 6A loads (FLA) (all control panels) and LED lighting that is ~240vac at ~7kVA, the lighting has a load shed relay after 1hr all lights connected turn off. Transformer is outside, NEMA 4X, dry type, area is onshore and withing 60 of 70ft of the water and sits on the eastern side of small electrical enclosure where the UPS is installed, moderate rainfall during the year, highs will reach 100 to 105F, never drops below 50F.

The AHJ wants a 100A fused disconnect on the secondary - 125% of the 80A nameplate rating. The design that was permitted was for 100A NF disconnect, to only isolate the UPS when maintenance is needed and of course the client will LOTO the primary CB at the distribution panel as well, the site is only accessible to authorized personnel and is under security monitoring (physical) and operations staff 24/7-365. When operations are tending a vessel, the access is even more closely limited.
So what exactly is the rule for secondary protection? I read 450.3 (B) and it appears that only primary protection is required for I>9A and if secondary I>9A. Am I wrong to pushback on the secondary OCPD (fused disconnect)?

 

[CoolWill]

It's late so I'm in no position to look up exactly what the code says, but you still need to protect the secondary conductors in accordance with article 240.

 

[hyattjay]

The UPS has a 60A CB on the Bypass and a 175A main CB.

 

[don_resqcapt19]

You have to remember that the rules in Article 450 only apply to the protection of the transformer itself. The rules for the protection of the secondary conductors are found in 240.21(C). Since you have a 120/240 volt secondary, the transformer primary protection is not permitted to protect the secondary conductors.
How long are the conductors from the transformer to the UPS? Are they inside or outside?

 

[hyattjay]

Conductors transition from outside where the xfrmr is located (see above) to the input side (direct connection) at the UPS which inside. All conductors are in conduit and transition to OH cable tray inside to get to the UPS. Secondary cable is 3/C triplex or multi-conductor w/integral gnd wire. Distance is less than the 25ft rule. Also as noted, the UPS has a main CB - accessible from the front panel and the Bypass has two 60A CB (input side and outlet side) accessible from the front panel - see above. Since there two CBs that the secondary of the xfmr connects to, can these count as secondary protection. In my mind, seems no different if the transformer connects to a pnl brd with a main CB - there are several dozen on site now and have been for the past 25-30yrs; xfrmer of 100kva and less installed in the same way, outdoors, conduit to pnl brd inside that has a main CB. There is nothing else connected to the xfmr, no pnl brd in between and it is a fully supervised site, accessible to authorized personnel only and the non-fused disconnect is locked and is only to isolate the UPS if it needs to serviced.

 

[don_resqcapt19]

Can you post a one line showing this installation?

 

[tortuga]

Distance is less than the 25ft rule.

If its not nearest the point of entrance look at 225.31(B) "disconnect nearest the point of entrance", but you could look at Exception 1 seems like it would qualify, I'd ask for a code reference from AHJ.

 

[hyattjay]

I appreciate all of the comments. In discussing with the EOR, we jointly determined to nix the disconnect on the secondary feeders before entering the electrical room where the UPS is installed and it was determined that the UPS main breaker and that of the bypass provide the required OCP for the secondary. If the inverter is bypassed the the OCPD is that of the bypass and if the inverter is not bypassed the OCPD is that of the inverter.
The UPS output is through the Bypass either way and it has an OCPD there as well, the Bypass connects to the pnl brd which has a main CB, which we could possibly mix as well.