200A Panels on 400A Disconnect

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krista

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I am doing design work on a building that has a 400A service. There is a 400A, 3-phase disconnect at the service entrance. This 400A disconnect serves two 200A MLO panels in parallel. My Electrical Contractor tells me that the "Rule of Six" allows up to six MLO panels run from one service. But I fail to see how these panels are protected.

Can anyone explain this to me?

Thanks!
~KMT
 
Re: 200A Panels on 400A Disconnect

Your saying you have a disconnect with 400 amp fuses/breaker feeding two main lug panels.
The 200amp wire going to the individual panels has to have 200amp overcurrent protection either at the start of the feeder or at the back end of the tap (article 240.20)

Plus the 400amp panel would have to have the proper lugs for the two sets of wire.

You have one main for the service equipment. The four hundred amp switch satifies the article 230.71 requirement of "not more than six switches or sets of circuit breakers"
 
Re: 200A Panels on 400A Disconnect

Krista,
The installation may be code compliant. If the 200 amp panels are "power panels" and do not have more than 10% of the breakers rated at 30 amps or less, they do not require line side protection. All that is required is that the panel have a rating of not less than the computed load. 240.21(B)(1) would permit the feed to the panel to be protected by the 400 amp main if all of the conditions are met. Remember that the panel itself is a device when applying this section. I would prefer that the panels have a 200 amp OCPD in or on the line side, but under some conditions the code does not require this protection.
Don

[ January 22, 2004, 12:11 PM: Message edited by: don_resqcapt19 ]
 
Re: 200A Panels on 400A Disconnect

Hey Don I just ran across this explanation of this on the UL web site.

Section 408.14 of the
NEC 2002 defines a
lighting and appliance
panelboard as a panelboard having
more than 10 percent of its
overcurrent devices rated 30A or
less, for which neutral connections are provided.
Click to expand...
Does this mean that the 10% circuits are only the the ones that use a neutral?
 
Re: 200A Panels on 400A Disconnect

Wayne,
In my opinion, if the "neutral" is in the panel and more than 10% of the OCPDs are 30 amps or less then it is a lighting and appliance branch circuit panel. I don't think that the section requires that the circuits being protected by the 30 amp or less OCPDs have a neutral as part of the circuit. It just requires that a neutral is available in the panel.

Note that I did not comment on the neutral in my other post in this thread. If less than 10% of the OCPDs are 30 amps or less the neutral does not enter in to the issue.

Don

[ January 23, 2004, 08:33 AM: Message edited by: don_resqcapt19 ]
 
Re: 200A Panels on 400A Disconnect

A lighting and appliance branch circuit must have a connection to neutral and be 30A or less. 408.14

If there are more than 10% of these, then it's a lighting and appliance branch circuit panel.

Once you determine what type of panel it is, then, if a power panel, you worry about whether it needs a main. 408.16B
 
Re: 200A Panels on 400A Disconnect

The 2002 handbook describes a lighting and appliance branch-circuit panelboard in the commentary to 408.14(A). It seems to imply that only circuits with a neutral count toward the 10% limit.

The commentary for 408.14(B) describes a power panelboard. It states "any panelboard that is not classified as a lighting and appliance branch circuit panelboard is a power panelboard." It also defines a power panelboard as having less than 10% of the installed overcurrent devices supplying lighting and appliance branch circuits. It doesn't say anything about the presence or absence of a neutral.

That gives us another way to see if a panelboard is power or appliance. If it doesn't meet the definition of power, it is an appliance panelboard.

Steve
 
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