Minimum service conductor size Section 230.42(A) & 240.4(B)

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tortuga

tortuga

Code Historian
Location
Oregon
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Electrical Design
I have a calculated load of 187A for a tenant infill in a space with a 4/0 SER cable as the service entrance conductors.
I have done a few back flips to keep the load under 200A so we dont have to upgrade the service.
Now however the rating of the 4/0 SER cable 75C we all know is 180A
From the way I read this I am not allowed to use 240.4(B) "next size up" rule to calculate the ampacity of the minimum size service entrance conductor.

National Electrical Code (C)NFPA said:
230.42 Minimum Size and Rating
(A) General. The ampacity of the service-entrance con-
ductors before the application of any adjustment or correc-
tion factors shall not be less than either 230.42(A)(1) or (A)
(2). Loads shall be determined in accordance with Part III,
IV, or V of Article 220, as applicable. Ampacity shall be de-
termined from 310.15. The maximum allowable current of
busways shall be that value for which the busway has been
listed or labeled.
(1)The sum of the noncontinuous loads plus 125 percent of
continuous loads
Exception: Grounded conductors that are not connected to
an overcurrent device shall be permitted to be sized at 100
percent of the continuous and noncontinuous load.
Click to expand...

It appears to state that the wire at minimum shall have an ampacity of the calculated load.
Hopefully I am wrong
Or do I need another cup of coffee.
Thanks In advance
 
tortuga said:
I have a calculated load of 187A for a tenant infill in a space with a 4/0 SER cable as the service entrance conductors.
I have done a few back flips to keep the load under 200A so we dont have to upgrade the service.
Now however the rating of the 4/0 SER cable 75C we all know is 180A
From the way I read this I am not allowed to use 240.4(B) "next size up" rule to calculate the ampacity of the minimum size service entrance conductor.



It appears to state that the wire at minimum shall have an ampacity of the calculated load.
Hopefully I am wrong
Or do I need another cup of coffee.
Thanks In advance
Click to expand...
As you have indicated, 187A (assuming noncontinuous plus 125% continuous) exceeds the 180A ampacity rating of the conductors.

240.4(B) applies to OCPD's... not the ampacity of the connected conductors.

Another coffee will not help :)

Can you post your load cal'? Perhaps we can find a demand factor you missed or otherwise make a recommendation.
 
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Its a existing probably late 80's heat pump with auxillary heat setup in a small pizza shop.
The one thing I can think of is add a 24vac ice cube relay to shut the heat pumps off if the auxiliary heat is called. Going to find out from hvac people.
Thanks for looking.
 

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Thanks for looking that goes above and beyond anything I would expect on the forums.
I just got off the phone with the inspector / plan reviewer and he approved me on the condition I replace the service conductors with 250kcmil and pointed out that the make up air and the exhaust hood in a commercial kitchen are usually continuous loads (increasing the calc more).

I did have the water heater up in the kitchen demand in an early revision but he thought that since it could serve the bathrooms it had to be moved down.
The HVAC guys did not offer anything to uncouple the auxiliary heat strip from the heat pump.
So redoing the service it is since 240.4 does not apply to sizing minimum size service conductors.
 
tortuga said:
....
I just got off the phone with the inspector / plan reviewer and he ... pointed out that the make up air and the exhaust hood in a commercial kitchen are usually continuous loads (increasing the calc more).

....
Click to expand...
Motor loads are neither continuous nor non-continuous.

For calculating service and feeders, you add up motor loads at 100% each as determined under Article 430, add 25% of the largest connected motor, and that's the total contribution... period.

See 430.24 and Example D3(A) to verify.
 
Smart $ said:
Motor loads are neither continuous nor non-continuous.

For calculating service and feeders, you add up motor loads at 100% each as determined under Article 430, add 25% of the largest connected motor, and that's the total contribution... period.

See 430.24 and Example D3(A) to verify.
Click to expand...


Even if a motor runs 3hr or more it is not a continuous load?

Interesting ... checking out the example.
 
So going back to where I started 230.42 gives me 2 options. What your saying is that motors are a 3rd line item that falls under noncontinuous loads.
I would feed better about the example if it mentioned continuous duty motors:
[QUOTE="National electrical Code (C) NFPA
]An industrial multi-building facility has its service at the rear of its main
building, and then provides 480Y/277-volt feeders to additional buildings
behind the main building in order to segregate certain processes. The facil-
ity supplies its remote buildings through a partially enclosed access corridor
that extends from the main switchboard rearward along a path that provides
convenient access to services within 15 m (50 ft) of each additional building
supplied. Two building feeders share a common raceway for approximately
45 m (150 ft) and run in the access corridor along with process steam and
control and communications cabling. The steam raises the ambient tem-
perature around the power raceway to as much as 35?C. At a tee fitting, the
individual building feeders then run to each of the two buildings involved.
The feeder neutrals are not connected to the equipment grounding conduc-
tors in the remote buildings. All distribution equipment terminations are
listed as being suitable for 75?C connections.
[/QUOTE]

So art 220 fails to divide up motor loads into continuous. Thus the by definition continuous motor load is classified as a non for the purpose of 230.42.
I learn something every day.
 
tortuga said:
So going back to where I started 230.42 gives me 2 options. What your saying is that motors are a 3rd line item that falls under noncontinuous loads.
I would feed better about the example if it mentioned continuous duty motors:

So art 220 fails to divide up motor loads into continuous. Thus the by definition continuous motor load is classified as a non for the purpose of 230.42.
I learn something every day.
Click to expand...
Not a third line item. It's covered in the general statement, "Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable." ...and 220.50 is in Part III, which sends us to 430.24, -.25, -.26 and 440.6 to determine motor load contribution. Note in 430.24, noncontinuous and continuous non-motor loads are separated from motor loads while motor loads are not distinguished as either.

Also, Article 220 doesn't divide up loads into continuous and noncontinuous [one small insignificant exception is 230.82(C)(6)]. The dividing of continuous and noncontinuous results for the most part from 210.19(A)(1), 215.2(A)(1), and 230.42(A)(1).

Believe me... if I am wrong, other members will be stepping all over this thread :happyyes:
 
tortuga said:
...
So redoing the service it is since 240.4 does not apply to sizing minimum size service conductors.
Click to expand...
240.4 never lets you change the size of a conductor...it only lets you protect it with an OCPD that has a rating higher than the ampacity of the conductor. The conductor must be sized with an ampacity that is equal to or greater than the calculated load. If the conductor has an ampacity that is equal to or greater than the calculated load and if the ampacity of the conductor is between standard sizes of OCPDs, then 240.4 permits you to use the next larger standard size OCPD.
 
Smart $ said:
... while motor loads are not distinguished as either....
Click to expand...
Thats what I mean by a third line item. If motors are neither continuous or non continuous then its inaccurate to put them under non continuous.
Like in the example you pointed me to D3(a) they sub total the 3 categories continuous, non continuous and motors.
That must be why it never came up for me before.
I looked through some past stuff and I guess I never even thought about it just put them in noncontinuous.

Having them under non continuous may have confused the inspector / plan reviewer. If I made a box like in the example D3(a) and made motor loads there own subtotal with the 220.50 and 430.24 code references it would be crystal clear.
 
tortuga said:
Thats what I mean by a third line item. If motors are neither continuous or non continuous then its inaccurate to put them under non continuous.
Like in the example you pointed me to D3(a) they sub total the 3 categories continuous, non continuous and motors.
That must be why it never came up for me before.
I looked through some past stuff and I guess I never even thought about it just put them in noncontinuous.

Having them under non continuous may have confused the inspector / plan reviewer. If I made a box like in the example D3(a) and made motor loads there own subtotal with the 220.50 and 430.24 code references it would be crystal clear.
Click to expand...
Sounds good.

Just be aware there are some caveats dealing with motor loads and calculated loads. One that I can think of is motor loads determination of the larger of heating and cooling. You wouldn't include unshared motor loads of the lesser and include shared (such as a blower motor) in both for the determination... and definitely make sure you don't double up a motor load in both HVAC and as a motor load. Another caveat is if the lesser of heating and cooling actually has the largest motor. You'd include the extra 25% but not the 100% of motor itself.
 
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