Duplex apartments new service

[Charlie Bob]

I've a lot of these services around here in the past, i've always used 350kcmil for the ungrounded service conductors nd 4/0 for the grounded one. The double meter base that the POCO give us here comes with lugs where the specified torque is shown as size wire is 350 kcmil nd less. It's been a while before my last one so i went nd discuss with inspector what size of wire he wanted nd where in the code book he looks it up ( just to make sure we are on the same page!). He thinks we oughtta use 400 kcmil for ungrounded conductor based on the table for residential services. And 350 kcmil for grounded conductor. I agree with all that as well.

But... in this particular residential set up, having two separated 200 amp disconnects being fed from this double meter base, would you still consider this a 400 amp service?

knowing that not both houses will be using everything at all times, don't you think 400 kcmil is kinda overkill? ( i had to change the lugs in it so i could fit the 400 kcmil wire.)

What size of wire you all use in your neck of the woods?


Thank you all.

 

[kwired]

What is the results of your art 220 load calculations?

 

[Charlie Bob]

less than a hundred, i realy don't recall. I've done several and all of them are the same, so i did my calculations years ago and then do them all the same.I know, shame on me i should konw my calculations The engeneers want me to put 200 amp tho. Ranges, water heaters nd heat are gas. I do provide a range plug for future use. These are standard housing project appartments. 2 and three bedrooms each. where i konw the actual load with everything on is low.

 

[kwired]

less than a hundred, i realy don't recall. I've done several and all of them are the same, so i did my calculations years ago and then do them all the same.I know, shame on me i should konw my calculations The engeneers want me to put 200 amp tho. Ranges, water heaters nd heat are gas. I do provide a range plug for future use. These are standard housing project appartments. 2 and three bedrooms each. where i konw the actual load with everything on is low.

230.90 Where Required.

Each ungrounded service conductor shall have overload protection.

(A) Ungrounded Conductor. Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. A set of fuses shall be considered all the fuses required to protect all the ungrounded conductors of a circuit. Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.

Exception No. 1: For motor-starting currents, ratings that comply with 430.52, 430.62, and 430.63 shall be permitted.

Exception No. 2: Fuses and circuit breakers with a rating or setting that complies with 240.4(B) or (C) and 240.6 shall be permitted.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

Exception No. 4: Overload protection for fire pump supply conductors shall comply with 695.4(B)(1).

Exception No. 5: Overload protection for 120/240-volt, 3-wire, single-phase dwelling services shall be permitted in accordance with the requirements of 310.15(B)(6).

If load calcs are 100 amps then service conductors only need have a 100 amp ampacity even if they supply 2 - 200 amp main breakers. Most people will install a larger conductor but 100 amp would be all that is required.