400 amp service
- Thread starter Jasonappignani
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
In theory, but in reality, nothing is going to restrict the amp load on the service other than the size of the overcurrent device ahead of the conductors.
JAP>
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
A 400 amp breaker ahead of 360 amp rated conductor is an NEC Compliant install even though that same 400 amp breaker is not going to limit the amperage of those conductors to 360 amps.
That example in itself would make others question why the NEC would find that to be compliant.
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Jasonappignani
Member
- Location
- Aiken, South Carolina
Yes I am using copper for the feeders.
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kwired
Electron manager
- Location
- NE Nebraska
It is compliant as long as the (NEC) calculated load is under 360 amps. Also true that it potentially can allow 400 amps of current without tripping anything.
Now go to the allowances for multiple service disconnecting means and we can have an even more eye catching situation. Lets say we have two - 200 amp breakers as the service disconnecting means. Lets say we only have 90 amps of calculated load on each disconnect yet choose to use 200 amp disconnecting means. Common service conductor to those two -200 amp disconnecting means only needs to have an ampacity of 180 amps though 400 can flow without interrupting any overcurrent devices.
newservice
Senior Member
To that end, isn't there a table in article 230 or 240 that specifically allows 4/0Al or 3/0 copper cable to be used as service entrance cable for a 200A service? I can only lay my hands on the 96 code book at the moment and cant seem to find it but I know it's there somewhere. Might only apply to SE cable idk.
Last edited:
- Location
- Massachusetts
It's in 310.15 but it only applies to dwelling units.
newservice
Senior Member
Ah. And is there a table for subpanel feeds too, or do you just go by the different general wire ampacity tables. Thanks
- Location
- Massachusetts
That dwelling unit table applies only to services or feeders that supply the entire dwelling unit load.
Subpanels feeders that do not supply the entire home have to use the full size conductors per 310.16 or 310.17 depending on code cycle
newservice
Senior Member
Right. So 310.16 and .17 are what the OP uses to size his feeders.
I'm not arguing the fact of what it allows just saying I know not every good electrician is good at math or all the variables envolved in calculating the load so i would bet there's more non compliant service installs simply because of electricians adding circuits after the service is built since they probably don't even consider upgrading a service until the main starts tripping and the conductors that are already overprotected start causing trouble.
<JAP>
Jasonappignani
Member
- Location
- Aiken, South Carolina
That's what tables I use. 310.16 &. 17 other than dwelling units.
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- Location
- Massachusetts
To me an important consideration is are you giving the customer what they are paying for.
Yes the NEC allows a 400 amp breaker to protect 360 amps of wire but understand that when you do this it is not a 400 amp service, it is a 360 amp service. That may be fine or the customer could feel ripped off paying for a 400 amp service but only getting a 360 amp service
Yes the NEC allows a 400 amp breaker to protect 360 amps of wire but understand that when you do this it is not a 400 amp service, it is a 360 amp service. That may be fine or the customer could feel ripped off paying for a 400 amp service but only getting a 360 amp service
For what its worth, I generally use parallel 3/0 copper for 400 amp services unless the run is long enough and economics play enough of a factor to need to consider using aluminum.
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kwired
Electron manager
- Location
- NE Nebraska
It is all in the details in most instances. If you have continuous load of over 320 amps, you likely are considering more then 400 amp overcurrent device, and should be to comply with NEC, If you calculate your load using art 220 and come up with 360 amps, there is a good chance you never see 360 or at least not for very long.
Most owners will not understand the technicalities, though someone may convince them you ripped them off. But outside of that if the 400 amp main never trips causing outages they will never know anything might be questionable. You could just as easily convince them someone that ran 500 copper ripped them off when parallel 4/0 would have been sufficient.
Doesn't take a very long run at all to make a significant difference.
- Location
- Massachusetts
Do you even read the posts you quote?
I said it may be fine
The problem to me is one of ethics, if the contract or verbal agreement says 400 amps a 360 amp service does not reach that. Think about it, if the butcher shorted your order but it still filled your belly would you be fine with the shortage?
On the other hand I would have no problem at all saying to a customer that we could reduce the price of a 400 service if they were fine with 360.
All I am saying is I feel the customer should be made aware of what they are getting, that does not require teaching them the NEC it just means asking if they want to pay for 360 amps of wire or 400 amps of wire.
Do you even read the posts you quote?
I said it may be fine
The problem to me is one of ethics, if the contract or verbal agreement says 400 amps a 360 amp service does not reach that. Think about it, if the butcher shorted your order but it still filled your belly would you be fine with the shortage?
On the other hand I would have no problem at all saying to a customer that we could reduce the price of a 400 service if they were fine with 360.
All I am saying is I feel the customer should be made aware of what they are getting, that does not require teaching them the NEC it just means asking if they want to pay for 360 amps of wire or 400 amps of wire.
Iagree,and let them sit and stare at you like this.... :huh:
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