Adding 25% of Largest Motor to Grounded Conductor for Dwelling Service Calculation

TomTom24

Member
Location
Baltimore
Occupation
JW Electrician
Trying to buckle down on these service calculations to try and take my Master's. My question is when calculating the the grounded conductor for the service do I add 25% of the largest motor load? And did this change between 08 and now?
I was using a 2008 version of satllcup's masters study guide it says "the largest motor shall be calculated for ungrounded (phase) conductors", and does not account for it in their dwelling calculations.

My instructor said not to use the 25% when calculating the neutral

But recently I got Stallcup's 2017 journeyman study guide (I accidently ordered the wrong one but has calculation problems all the same) and it say "the largest motor motor load shall be calculated for both the ungrounded (phase) conductors and the grounded (neutral) conductors when the motor is connected to a grounded conductor", and accounts for this in the dwelling calculations.

All examples on the internet I saw also account for 25% largest motor on the neutral.
Codes cited were 210.19(A)(1) ex 2 from nec 08
changed to
230.42(A) ex 1 17 nec (also have a hard to understanding how this relates to 25% of the largest motor being applied to the neutral)
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Firstly welcome to the forum

Secondly usually the largest motor is 240v so no neutral is involved however if the motor is 120V and the largest one then IMO the neutral load should be calculated at 125%, I am sure other will disagree,,, LOL
 

TomTom24

Member
Location
Baltimore
Occupation
JW Electrician
Thanks Dennis,
Its weird that these study guides would change their calculation procedures without their being any real change to the code.
 
Top