400 amp service, 2-200 amp mlo panels?

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A

aksparky

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I came across a 400 amp service today, it was installed in 1998 and passed inspection.
The service entrance conductors were parallel 250 kcmil alum and landed in a fused disco with 400 amp fuses.
There is 2- 200 amp, mlo panels fed from the load side of the disco, each panel is fed with 250 kcmil alum.
My first thought was why dont these panels have a main breaker in them.
Looking in the code book I see 240.21.B(1) "tap conductors 10 ft long" which seems to say it is ok to protect the conductors this way as long as the oc doesnt exceed 10X ampacity of the tap conductor and meets some other requirements of the same article.
Then I looked at 408.36 which basically says we need oc protection not greater than that of the panel and on the supply side of the panel but there is a few exceptions, of which I dont think any of them apply to this install.
Is this a legal install and if so where might I find the article that tells me it is legal.
Sorry for the long post but wanted to provide enough info for responses.
Thanks
 
Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
aksparky said:
I came across a 400 amp service today, it was installed in 1998 and passed inspection.
The service entrance conductors were parallel 250 kcmil alum and landed in a fused disco with 400 amp fuses.
There is 2- 200 amp, mlo panels fed from the load side of the disco, each panel is fed with 250 kcmil alum.
My first thought was why dont these panels have a main breaker in them.
Looking in the code book I see 240.21.B(1) "tap conductors 10 ft long" which seems to say it is ok to protect the conductors this way as long as the oc doesnt exceed 10X ampacity of the tap conductor and meets some other requirements of the same article.
Then I looked at 408.36 which basically says we need oc protection not greater than that of the panel and on the supply side of the panel but there is a few exceptions, of which I dont think any of them apply to this install.
Is this a legal install and if so where might I find the article that tells me it is legal.
Sorry for the long post but wanted to provide enough info for responses.
Thanks
Click to expand...

I agree that it does violate 408.36 but what we really need to know is what code was used there in 1998 and if it makes any difference...because I don't know...
 
Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Hey I feel like it's something fundamental....but where is it that allows you to have an install like this? I mean assuming the panels had OCPDs why can you install 250kcmil feeders on a 400a Fuse?
 
A

aksparky

Member
Thanks for the replys,
I figured they got away with the 250 kcmil feeders to the panels using the 10 ft tap rule, 240.21.B(1), but couldnt really see how they passed inspection with mlo panels because of 408.36.
Thanks again for the replys.
 
A

aksparky

Member
I just looked in my 1996 handbook, the tap rules seem to pretty much be the same back then, Panelboards were in article 384 but still had the requirement in 384.16 for oc protection.
Thanks again for the replys, just wanted to make sure I wasnt missing something here.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
What am I missing here? If the service entrance conductor land in a 400 amp fused disco why would you need a main breaker in the load center?
 
infinity

infinity

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Staff member
Location
New Jersey
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Journeyman Electrician
M. D. said:
408.36 ,.a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panel board.....
Click to expand...


And not only that you have one set of 250 kcmil Al (205 amps) to each panel protected by a 400 amp OCPD.
 
R

ronmath

Senior Member
Location
Burnsville, MN
I only have the 2008 NEC with me now, but read 240.21(B)(1)(1)(b). These are taps and do not comply with the tap rule of "The ampacity of the tap conductors is not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
 
acrwc10

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
Do the 200 amp MLO panels have more then 6 handles in each ?
 
A

aksparky

Member
1 of the panels has 10 breakers, the other has closer to 20.
Would the 6 handle rule come into play even when the main 400 amp fused disco is the main disconnect for all power?
Thanks again for the replys
 
Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
ronmath said:
I only have the 2008 NEC with me now, but read 240.21(B)(1)(1)(b). These are taps and do not comply with the tap rule of "The ampacity of the tap conductors is not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
Click to expand...

These taps are code compliant.

You posted it yourself "The ampacity of the tap conductors is not less than the rating of the device supplied by the tap conductors "

Ampacity of tap is 205a. The rating of device supplied by the tap 200a....
 
Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
aksparky said:
1 of the panels has 10 breakers, the other has closer to 20.
Would the 6 handle rule come into play even when the main 400 amp fused disco is the main disconnect for all power?
Thanks again for the replys
Click to expand...

IMO the six handle rule does not apply to this tap if the tap is ten ft or less.

Also I'm assuming all the other requirements of 240.21(B)(1)
 
480sparky

480sparky

Senior Member
Location
Iowegia
The discussion about how many breakers are in the panels and whether or not the six-throw rules applies is moot. From the OP:

aksparky said:
..........The service entrance conductors were parallel 250 kcmil alum and landed in a fused disco with 400 amp fuses...........
Click to expand...

The fused disco is the main service disconnect.

The question is whether the panels can be fed with 250 al off the 400a fuses.

aksparky said:
.............There is 2- 200 amp, mlo panels fed from the load side of the disco, each panel is fed with 250 kcmil alum............
Click to expand...
 
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M. D.

M. D.

Senior Member
The tap rule does not nullify the requirement found in 408.36 ,.. in fact I think that is why they inserted the FPN pointing you there ,.. so IMO the panelboard still rewquires an OCPD
 
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