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- Thread starter Rivers
- Start date

210.20(A) for example:

210.20 Overcurrent Protection (A)Continuous and Noncontinuous Loads. Where a branch

circuit supplies continuous loads or any combination of continuous

and noncontinuous loads, the rating of the overcurrent

device shall not be less than the noncontinuous load plus

125 percent of the continuous load.

The breaker being sized by 125% over the continuous load is the same as not loading the circuit with continuous loads beyond 80% of the breaker rating. 5/4 (125%) is inverse of 4/5 (80%).

A 100A CB loaded at 80% capacity means 80A of continuous loads. Similarly, if you take a 80A continuous load, and then multiply by 1.25 (125%) you get 100A for a CB size.

- Location
- Chapel Hill, NC

- Occupation
- Retired Electrical Contractor

230.42 Minimum Size and Rating.

(A) General. Service-entrance conductors shall have an

ampacity of not less than the maximum load to be served.

Conductors shall be sized to carry not less than the largest of

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 determined from 310.15. The maximum allowable

current of busways shall be that value for which the busway has

been listed or labeled.

(1) Where the service-entrance conductors supply continuous

loads or any combination of noncontinuous and

continuous loads, the minimum service-entrance conductor

size shall have an allowable ampacity not less than the

sum of the noncontinuous loads plus 125 percent of

continuous loads.

Exception No. 1: Grounded conductors that are not connected to an

overcurrent device shall be permitted to be sized at 100 percent of the

sum of the continuous and noncontinuous load.

Exception No. 2: The sum of the noncontinuous load and the continuous

load if the service-entrance conductors terminate in an overcurrent

device where both the overcurrent device and its assembly are listed for

operation at 100 percent of their rating shall be permitted.

(2) The minimum service-entrance conductor size shall have

an ampacity not less than the maximum load to be served

after the application of any adjustment or correction

factors.

- Location
- New Jersey

- Occupation
- Journeyman Electrician

Anyway I am trying to reinforce my work ethics of not loading more then 80% or sizing up 125% of the calculated load. These are individual dwelling units, one, two and four bedroom units with full appliances, HVAC, water heaters etc...

- Location
- NE Nebraska

That calculated load likely has demand factors included in calculations. Actual connected load may very well be over your 1200 amp service, but is likely you seldom or never see 1130 either, presuming those calculations were done correctly.

Anyway I am trying to reinforce my work ethics of not loading more then 80% or sizing up 125% of the calculated load. These are individual dwelling units, one, two and four bedroom units with full appliances, HVAC, water heaters etc...

There is no continuous/non continuous load to deal with when you start getting into using demand factors in the calculations, the total calculation is minimum conductor ampacity and minimum overcurrent protection needed in the application.

1200 amp can still be supplied via panelboards, if you need more than that you need multiple mains (six disconnect rule comes into play) or possibly switchboard if you want a single self contained service gear setup.

Not really unless you need to address continuous loads as mentioned above.I have always followed the rule of not loading a circuit or main breaker more then 80%.

Is there a code article to back this up?

Thank you

Your concern is understandable but you have to remember the NEC is MINIMUM. A calculated load of 1130 amps on a 1200 amp service meets NEC requirements. Taking future loads account your 80% "rule" is likely wise but not required.

- Location
- Illinois

- Occupation
- retired electrician

- Location
- NE Nebraska

Thanks, short version of what I was trying to say.

Read the thread!

- Location
- New Jersey

- Occupation
- Journeyman Electrician

I actually did read the thread and I would ask you to read it again because you've missed the point. The point being that the NEC load calculations are very generous with the actual load at any given point in time being nowhere near the calculated load. If your 1200 amp service has a calculated load of 1130 amps there is nothing to discuss unless you are planning for future expansion.Read the thread!

I actually did read the thread and I would ask you to read it again because you've missed the point. The point being that the NEC load calculations are very generous with the actual load at any given point in time being nowhere near the calculated load. If your 1200 amp service has a calculated load of 1130 amps there is nothing to discuss unless you are planning for future expansion.

Thank you, the damage on the lug is most likely a loose connection. When I submitted this to the electrical contractor that did the job, he asked if there were any unintended loads on this service. I have always worked a 80% rule or sized 125% of the calculated load. This would have meant a 1600 amp service. This is why I questioned if there were concrete articles in NEC. Thank you again.

- Location
- New Jersey

- Occupation
- Journeyman Electrician

You're welcome. Just realize that your 80/125% factors may be good design parameters they are not the required code minimum. It's hard to argue with the contractor who installed a code compliant 1200 amp service that he did something wrong.Thank you, the damage on the lug is most likely a loose connection. When I submitted this to the electrical contractor that did the job, he asked if there were any unintended loads on this service.I have always worked a 80% rule or sized 125% of the calculated load. This would have meant a 1600 amp service. This is why I questioned if there were concrete articles in NEC. Thank you again.

- Location
- Northern illinois

- Occupation
- engineer