Service Conductor Ampacity 230.42

[Dennis Alwon]

I am having a discussion via email with Mike and I don't want to bother him with this too far so I thought maybe I can get my confusion straightened out here. Btw, this discussion got started over some other issue on one of his images.

230.42(A)(1) & (A)(2) is the issue not the exceptions. A1 seems pretty clear and imo, we would also have to take into consideration de-rating and correction when sizing the conductors.

A2 doesn't mention continuous vs non continuous- it just mentions the load to be served. My thinking is that the load to be served would be continuous at 125% + non continuous load anyway and since correction factor and de- rating must be used anyway what is the difference here

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.

 

[david luchini]

My thinking is that the load to be served would be continuous at 125% + non continuous load anyway and since correction factor and de- rating must be used anyway what is the difference here

The "load to be served" is continuous at 100% + non-continuous at 100%. It's no different than with feeders.

 

[augie47]

My thinking would be A1 tells you to calculate the load based on the 100% + 125% and select the conductor accordingly.
A2 tells you to apply any dereating factors to the load calculated in A1 if necessary .

 

[kwired]

Most if not all loads that you can apply any demand factor to are not continuous type loads. So those don't get a 125% factor either way.

 

[wwhitney]

Here's the way I look at it:

The 125% factor for continuous loads is all about limitations of circuit breakers. They are the weakest link. If circuit breakers were all 100% rated, you'd never have to use the 125% factor. So the 125% continuous load factor only applies at the circuit breaker.

On the other hand, the adjustment and correction factors don't apply at terminations, just the termination temperature limitation applies. So they don't apply at the circuit breaker.

The upshot is that first you check the ampacity at the circuit breaker using the 125% continuous factor and the ampacity based on termination temperature, but no adjustment or correction factors. Then you check the ampacity at the rest of the circuit, using the adjustment and correction factors applied to ampacity based on the insulation temperature, but no 125% continuous factor.

Cheers, Wayne

 

[Dennis Alwon]

My thinking would be A1 tells you to calculate the load based on the 100% + 125% and select the conductor accordingly.
A2 tells you to apply any dereating factors to the load calculated in A1 if necessary .

I am looking for the difference between the 2 sections.

Gus why would they have to say to use de-rating etc if you have to anyway. The sections says to use the larger of the A1 or A2. I don't see them as different. The difference may be that in A2 I don't have to use 125% of the continuous load and in A1 I don't have to apply de-rating. But that can't be correct.

 

[kwired]

I am looking for the difference between the 2 sections.

Gus why would they have to say to use de-rating etc if you have to anyway. The sections says to use the larger of the A1 or A2. I don't see them as different. The difference may be that in A2 I don't have to use 125% of the continuous load and in A1 I don't have to apply de-rating. But that can't be correct.

Kind of have to admit that most if not all of the time A2 should result in lower figure. If there is little or no non continuous load or any loads you can apply demand factors to then A2 sort of doesn't apply anyway.

 

[wwhitney]

The upshot is that first you check the ampacity at the circuit breaker using the 125% continuous factor and the ampacity based on termination temperature, but no adjustment or correction factors.

To clarify, this is what 230.42(A)(1) is asking for.

Then you check the ampacity at the rest of the circuit, using the adjustment and correction factors applied to ampacity based on the insulation temperature, but no 125% continuous factor.

And this is what 230.42(A)(2) is asking for.

Cheers, Wayne

 

[david luchini]

I am looking for the difference between the 2 sections.

If your load was 700A;. 500A noncontinuous and 200A continuous...

A1 would require a minimum conductor size with an allowable ampacity of 750A ( before adjustment/correction)

A2 would require a conductor with an ampacity of at least 700A (after adjustment/correction)

 

[david luchini]

The difference may be that in A2 I don't have to use 125% of the continuous load and in A1 I don't have to apply de-rating. But that can't be correct.

That is exactly correct ?

 

[Dennis Alwon]

That is exactly correct ������

Ok then when would A1 be less than A2

In the end on A1 wouldn't you still have to consider the adjustment factors anyway to size the conductor?

 

[david luchini]

Ok then when would A1 be less than A2

In the end on A1 wouldn't you still have to consider the adjustment factors anyway to size the conductor?

With a 500A+200A service, A1 would require min two sets of 500mcm. If the two sets are in the same conduit, A2 would require two sets of 600mcm.

 

[augie47]

FWIW, This is the ROC from the panel when the Section was changes in 2014:


Substantiation: A similar proposal was submitted to reword the text in
210.19(A)(1) and 215.2(A)(1). The proposals were accepted in principal. The
current text is not clear. Section 230.42(A) is specifying to multiply continuous
loads by 125 percent and then apply the correction and/or adjustment factors.
This is not how it is taught at NFPA seminars. It is also not the way example
D(3)(a) is calculated in Informative Annex D. These are two different and
separate calculations. One calculation considers continuous loads without
considering the correction and/or adjustment factors. The other calculation
considers correction and/or adjustment factors with all loads (continuous and
noncontinuous) calculated at 100 percent.


The Technical Committee added more input at the corresponding 210.19

Panel Statement: The panel continues to accept the text as revised in the
Report on Proposals. The text accepted by CMP-2 at the ROP stage is accurate.
By splitting the requirement a condition is created where the conductor must be
the larger of (a) or (b). Condition (a) requires that the conductor have an
allowable ampacity of 125% of the continuous load plus the non continuous
load. Condition (b) requires that the conductor have an allowable ampacity to
carry the maximum load served after the conductor ampacity has had any
correction or adjustment factors applied. Once the two calculations are
completed, the larger of the two must be used

One of you guys may have to "dumb it down" for me to understand way ....

 

[Dennis Alwon]

With a 500A+200A service, A1 would require min two sets of 500mcm. If the two sets are in the same conduit, A2 would require two sets of 600mcm.

That is what I don't understand. Why do you not have to consider de-rating in A1. If I calculate that the system needs 2 sets of 500 kcm then if I install it in one conduit wouldn't I have to de-rate?

 

[Strathead]

My thinking would be A1 tells you to calculate the load based on the 100% + 125% and select the conductor accordingly.
A2 tells you to apply any dereating factors to the load calculated in A1 if necessary .

I was trying to get where you are, but it say A1 OR A2 not and. So, that seems to be contrary .

 

[Strathead]

My thinking would be A1 tells you to calculate the load based on the 100% + 125% and select the conductor accordingly.
A2 tells you to apply any dereating factors to the load calculated in A1 if necessary .

FWIW, This is the ROC from the panel when the Section was changes in 2014:


Substantiation: A similar proposal was submitted to reword the text in
210.19(A)(1) and 215.2(A)(1). The proposals were accepted in principal. The
current text is not clear. Section 230.42(A) is specifying to multiply continuous
loads by 125 percent and then apply the correction and/or adjustment factors.
This is not how it is taught at NFPA seminars. It is also not the way example
D(3)(a) is calculated in Informative Annex D. These are two different and
separate calculations. One calculation considers continuous loads without
considering the correction and/or adjustment factors. The other calculation
considers correction and/or adjustment factors with all loads (continuous and
noncontinuous) calculated at 100 percent.


The Technical Committee added more input at the corresponding 210.19

Panel Statement: The panel continues to accept the text as revised in the
Report on Proposals. The text accepted by CMP-2 at the ROP stage is accurate.
By splitting the requirement a condition is created where the conductor must be
the larger of (a) or (b). Condition (a) requires that the conductor have an
allowable ampacity of 125% of the continuous load plus the non continuous
load. Condition (b) requires that the conductor have an allowable ampacity to
carry the maximum load served after the conductor ampacity has had any
correction or adjustment factors applied. Once the two calculations are
completed, the larger of the two must be used

One of you guys may have to "dumb it down" for me to understand way ....

Yes, now it makes sense. Your first post wasn't either incorrect or worded incorrectly. A2 doesn't tell you to apply the calculation to A1. It tells you to calculate both and use the larger of the two.

 

[david luchini]

That is what I don't understand. Why do you not have to consider de-rating in A1. If I calculate that the system needs 2 sets of 500 kcm then if I install it in one conduit wouldn't I have to de-rate?

I think Wayne explained it well. The derating (adjustment/correction factors) apply to conductor ampacity.

A1 doesn't have anything to do with the conductor ampacity and the load, it has to do with the OCPD and the terminations

The upshot is that first you check the ampacity at the circuit breaker using the 125% continuous factor and the ampacity based on termination temperature, but no adjustment or correction factors.

A2 applies to the conductor ampacity and the load, so you have to apply the derating to find the actual ampacity of the conductor to see if it can support the load.

Then you check the ampacity at the rest of the circuit, using the adjustment and correction factors applied to ampacity based on the insulation temperature, but no 125% continuous factor.

 

[wwhitney]

That is what I don't understand. Why do you not have to consider de-rating in A1. If I calculate that the system needs 2 sets of 500 kcm then if I install it in one conduit wouldn't I have to de-rate?

A1 is the ampacity check at the breaker itself. In a breaker enclosure, there's no need to apply the correction and adjustment factors. But you need the 125% continuous load factor to accommodate the limitations of a breaker's trip curve.

A2 is the ampacity check elsewhere in the circuit, e.g. in a raceway. There the correction and adjustment factors apply, but there's no need to use the 125% factor for continuous loads. The wire's ampacity is already a continuous rating.

Cheers, Wayne

 

[charlie b]

Ok then when would A1 be less than A2?

I will step outside of reality, and pose a purely hypothetical situation. Consider a three phase service, with 400 amps of continuous load and 500 amps of non-continuous load. All loads will be 3-phase, and some will require a neutral, but there will be no non-linear loads. I will only have one conduit to handle all service conductors. The local ambient is 30C.

• (A)(1) calculation:
• 125% of 400 + 500 = 1000 amps.
• I can select four sets of 250 MCM conductors using this article. I will bring four neutral wires in the conduit, but I won’t have to pay attention to whether they are current-carrying.
  

• (A)(2) calculation:
• With no non-linear loads, the neutrals will not count as current-carrying.
• Four sets of three phase conductors would total 12 current-carrying conductors.
• That requires a 50% adjustment factor.
• There is no correction factor for ambient temperature in this example.
• The total load is 900 amps (disregarding the distinction between continuous and non-continuous). I need conductors with a total ampacity of 1800 amps.
• That means each must have an ampacity of 450 amps.
• I would need to select four sets of 700 MCM conductors using this article.

In this example, the conductors for (A)(1) are smaller than the conductors for (A)(2). So I must use the 700 MCM conductors.

Same setup, but this time use 4 separate conduits.

• (A)(1) gives the same result: 4 sets of 250 MCM.
  

• (A)(2) no longer requires an adjustment factor.
• To serve a total load of 900 amps, each set needs an ampacity of 900/4, or 225 amps.
• I can serve this load with four sets of 4/0.

In this example, the conductors for (A)(1) are larger than the conductors for (A)(2). So I must use the 250 MCM conductors.

 

[Dennis Alwon]

Okay I get it. It just seems strange to give an either - or when comparing different things. I see it is done that way for feeders as well.

Thanks all and I am sorry Wayne that I didn't get it on your first post. It actual makes some sense now.