Article 409 and Tap Rules

[rwilsond]

A particular 480V Industrial Control Panel in a "Supervised Industrial Installation" is fed from a large (say 2000 kVA) transformer, without any type of OCPD on the transformer's secondary side, and without a Main CB inside the panel. Instead, the 15-foot long tapped supply conductors terminate onto two separate CB's inside the control panel.

New Article 409 for the 2005 NEC requires that either a single OCPD be located ahead of an Industrial Control Panel, or a Main CB (i.e., ONE CB) be located within the Industrial Control Panel. But 409.21 states that this protection shall be provided in accordance with 240.21 Parts I, II, and IX.

Can the reference above (to 240.21) be interpreted to mean that the Industrial Control Panel is allowed to NOT have a Main CB (Main implies ONE), nor an upstream feeder CB by satisfying one of the tap-rules of 240.21?

 

[EEJaime]

It would seem to me that the reference requiring the feeder to comply with the tap rules of Article 240 would mean that you would still need an OCPD in the tap conductors where they recieve their supply and/or that the feed must comply with the rules regarding termination in a single Main as well as lenght and physical protection limitations.

 

[rwilsond]

What I want to focus in on is the point you made regarding the "single Main" inside the Control Panel. Let's assume that 240.21(C)(3) is satisfied, including the requirement that the OCPD's are "grouped" (i.e., there is no single MCB; but two branch CB's that the supply conductors terminate onto instead). Then it seems that all of 240 is now satisfied. But there is still the nagging 409.21(B) OCPD Location statements that there be a single OCPD ahead of the panel or a MCB (i.e., one) within the panel.

 

[dpc]

I think it's a problem, but in the end, the only opinion that matters is the AHJ.

If you're in NEC-land, you also may need UL labeling of the control panel, and I think that will require a single main device.