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#208951 02/23/13 01:48 PM
Joined: Feb 2002
Posts: 2,233
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I have a question. You have an 800 amp 480 volt 3 phase service. The first piece of equipment in the service is a fusible disconnect that feeds a CT cabinet, then goes to a large 2 piece MDP cabinet. Now if someone taps the busbar inside of the MDP and goes to a separate fusible 400 amp disconnect which then feeds a beaker panel which is connected to a large PV system. That feeder is a tap. Right? It is in pipe and troughs and all that is in the service room. However can you run that unfused tap wire inside of the same trough as all the other wires that all have proper OC protection on them? You are trying to run, fused and non fused wires in the same trough.
Now can you cite sec. 230.7 of the 2011 NEC? The 400 amp wire is a feeder, but is it a tap or a service conductor? It feeds a PV system and other than the original 800 amp fuses, there is no other protection on that 400 amp wire. Plus it runs through a trough with all the other conductors. I know it would be safer if it was in a different conduit run away from the other conductors.

What is your thoughts?

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harold endean #208957 02/23/13 07:48 PM
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I think the short answer is you can't run unprotected service conductors in the same raceway as load side conductors.


Greg Fretwell
harold endean #208959 02/23/13 10:57 PM
Joined: Jun 2004
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If the tap is ahead of the service disconnecting means then it is service entrance conductors...right.They do not belong in the same conduit as non service conductors.

But if the feeder is a tap from the existing feeder...I don't know of a restriction of feeder taps with other circuits?

Also if the service has a 800amp main and 400amps of solar on the backfeed the bus in the MDP must be rated for minimum 1000amps.

2011 NEC 705.12(D)(2) 120% rule:

1000amp bus x 120% = 1200amp
800ampmain = 400amp solar = 1200amp

harold endean #208964 02/24/13 12:46 PM
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Greg,

That is one of my main concerns, however I would need a code section to cite. Since the "tap" is after the main fusible disconnect, it is not technically a service conductor. It would be a feeder wire. Yet, there would only be an 800 amp OCP protecting that feeder and it is running through a trough with all the proper OCP wires.

harold endean #208965 02/24/13 12:49 PM
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Short circuit,

I don't believe the 400 amp feeder wires land on a bus bar but are connected on the bottom of the MDP where there are some extra lugs. That is what the EC told me.


harold endean #208966 02/24/13 12:57 PM
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OK I misunderstood the situation. If all of the conductors are on the load side of the first O/C device, I am not sure there is a violation.


Greg Fretwell
harold endean #208967 02/24/13 01:17 PM
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Greg,

Neither is the EC. Yet, is there a danger? Should the job fail? or pass? You have a 400 amp feeder wire with 800 amp OCP running through a trough with regular branch circuit wires.

harold endean #208968 02/24/13 02:28 PM
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Harold:
You have to get into the tap rules (240.21-(B) etc) may help.

As the PV grid tie conductors are protected at 400 amps at the PV AC disconnect, and the conductors are 500Kcmil CU, this sounds like a normal PV grid tie.

Are the conditions in the field the same as the submitted plans?

Also, what are you refering to as 'regular branch circuit wiring'?



John
harold endean #208969 02/24/13 03:35 PM
Joined: Jun 2004
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If I understand how you are explaining the arrangement then....

This arrangement would still need to comply with 705.12(D)(2)

The bus and the tap conductors would need to be rated for minimum of 1000amps.

800amp main + 400amp solar = 1200amp of power feeding the "bus" and "conductor".

If the "bus" and "conductor" was rated for 1000amps you multiply those values by 120% which equals 1200amps...

It sounds like a load side connection to me. Read 705.12(D)(2) 2011 NEC

harold endean #208970 02/24/13 04:03 PM
Joined: Jun 2004
Posts: 613
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You have to have the connection at a dedicated circuit breaker or fusible disconnect as outlined in 705.12(D)(1)

The bus in that MDP must be rated 1000amps minimum.

This is a hazard IMO.

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