Taps

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electricalist

electricalist

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dallas tx
If a 400 amp fused service disconnect needs to feed a 200 amp mdp and the mdp is a mlo. Do the feeders need to be 200 amp ( assuming its under 200 amp load) and the 400 amp fuses are ok or need to be 200?
 
You could use 200 amp feeder taps as long as you met the appropriate tap rule in 240.21(C) (length etc) but you could not terminate in a MLO panel as 480.36 (and possibly the tap rule depending on which rule was used) would require a main (in or ahead of the panel) with a rating no greater than the panel (buss).
If you went to 200 amp fuses and 200 amp wire it would no longer be a tap and the disconnect could serve as the main for the 200 amp panel.
 
Thanks. Im reading up on taps and the 5 rules should be simple enough yet the wording and rereading get me.
Im gonna say the 10' rule for simplicity.
It seems like the obvious is 400 amp fuses arent ok for 200 amp wire, but lets say the serv. Disc goes to a wireway with parallel 400 amp feeders and taped 200 amp wire to 2 - 200 amp distribution panels.
That sounds like basically the same thing.
I think im missing something
 
Sounds like the same thing .... same rules 408.36 says the panel has to have an overcurrent device not greater than the rating of the panel. If you have a 200 amp panel you have to have a 200 amp OCP device protecting it. (there is an exception for service panels using the 6 disconnect rule)
 
I understand and again thanks for your patients.
Often it seems for services on a commercial bldg it would be a tap can at bldg to raceway to seperate meters then disconnects ,probably apts as well.
Would having a service disconnect be more of a preference. I usually dont see many serv disconnects to taps then meters.
 
Keep in mind "tap conductors " are defined in Art 240 (240.2). Read that definition and you see "other than a service conductor".
Connecting (2) 200 amp conductors to a 400 amp SERVICE conductor is not a tap and Art 230 rules apply rather than Art 240.
408.36 still applies to service panels but there is an exception allowing Art 230.71 to apply so a single main might not be needed.

It's not easy :D
 
Ty augie47 i think you have given me enough articles to keep me busy.
Its amazing how electrics such as services are far more than many will ever know. You deserve a raise.
 
ActionDave said:
This gave me a big chuckle. I'm sure it was auto correct taking over, but after reading Augie's posts here for a few years I can't help but think that some of those he inspects are in fact patients and he has the cure.
Click to expand...

It's probably a sign of my age but I fear that most of my patients in this geographical area are terminal as is my patience. It seems the only folks that give a damn anymore are a select few of my inspector friends and the folks who come here. Sometimes this sight is a refuge from the inept bureaucracy and the 'could care less' attitude of some of the electricians. Pride is seemingly a dying virtue.
(the old man takes wobbly steps off of his soapbox)
 
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