Should We Figure Lighting As A Continuous Load In Commercial Load Calcs?

[wwhitney]

If I have a 100A continuous load and a 100A non-continuous load, then the service OCPD needs to be 225A.

That, by the way, is a consequence of 215.3 as I indicated earlier. But if you don't buy that, it's also a consequence of UL 489. Per the "Molded Case Circuit Breaker – Marking and Application Guide" available here: https://code-authorities.ul.com/molded-case-circuit-breaker-marking-and-application-guide/

"38. 100 Percent Continuous Rated – Unless otherwise marked for continuous use at 100 percent of its current rating, a circuit breaker is intended for use at no more than 80 percent of its rated current where in normal operation the load will continue for three hours or more. . . ."

Cheers, Wayne

 

[tortuga]

If I have a 100A continuous load and a 100A non-continuous load, then the service OCPD needs to be 225A. That has the side effect that the busbars must be rated 225A.

I'll agree for commercial if there are service entrance conductors, there can be situations where you can have no service entrance conductors such as a meter pack.
As we have discussed before if the requirements of 310.12 can be met the service entrance conductors can be sized per 310.12.

 

[wwhitney]

I'll agree for commercial if there are service entrance conductors

Even if there are no service entrance conductors, if there is a singular service OCPD, that service OCPD must at least 100% of the non-continuous load plus 125% of the continuous load, unless it is 100% rated. As per my earlier posts.

Cheers, Wayne

 

[wwhitney]

BTW I do think that the 125% continuous use factor for service entrance conductors in 230.42 could be deleted. As if there is a singular OCPD being supplied, the combination of 215.3 and 230.90(A) has the same effect (other than 240.4(B), but the current partial circumvention of 240.4(B) seems like a bug). And if there isn't a singular OCPD being supplied, as 230.90(A) Exception 3 covers the service conductors, and I see no reason to treat the service entrance conductors any differently.

Cheers, Wayne

 

[tortuga]

Even if there are no service entrance conductors, if there is a singular service OCPD, that service OCPD must at least 100% of the non-continuous load plus 125% of the continuous load

Sorry man not seeing it, I am reading 2023 NEC section 230.79 rating of disconnecting means and 230.90.

 

[wwhitney]

Sorry man not seeing it, I am reading 2023 NEC section 230.79 rating of disconnecting means and 230.90.

See post #21.

Cheers, Wayne

 

[tortuga]

See post #21.

Cheers, Wayne

I don't buy the argument that the busbars in a service panelboard are subject to article 215, due to code arrangement 90.3 408.30 takes over and says just the calculated load.
If I am sizing a underground service lateral to land on the lugs of a meter pack, I am not landing on a OCPD or even a meter lug, and I am not required by the NEC to upsize those conductors for a continuous factor.

 

[wwhitney]

I don't buy the argument that the busbars in a service panelboard are subject to article 215, due to code arrangement 90.3 408.30 takes over and says just the calculated load.

Disagree. 90.3 does not permit Chapter 4 to modify the requirements of Chapter 2.

But even if you were correct, UL 489 certainly says that for a 200A continuous load and a single non-100% rated OCPD, you can't use a 200A service OCPD. You'd need a 250A OCPD. That forces the busbars to be 250A rated.

If I am sizing a underground service lateral to land on the lugs of a meter pack, I am not landing on a OCPD or even a meter lug, and I am not required by the NEC to upsize those conductors for a continuous factor.

If you're sizing any underground service lateral, you don't need a continuous use factor. The continuous use factor applies to the service entrance conductors, and the load through any single non-100% rated OCPD.

Cheers Wayne

 

[tortuga]

I see no reason to treat the service entrance conductors any differently.

Its an interesting subject, it could even be a EE masters thesis. If anyone has info on the studies they did in the 80's it would be interesting to read, they clearly omitted service entrance conductors in 1971, then added them in 1987 then removed them in 1990 then added them again 1999 (I think). that did not happen with branch circuits or feeders, just service conductors here is the removal in 1990:


Also of note is until 1984 the definition of ampacity was kinda vague "the current-carrying capacity of electric conductors expressed in amperes" until they changed it to say "the maximum current, in amperes,that a conductor can carry continuously under the conditions of use without exceeding its temperature rating"
Right then you see the manufacturers make some slight changes like NM cable became NM-B.

When busbars are tested in a panelboard to UL 67 31.1 they (ETL) run the rated current continuously (8hrs or something like that) and none of the supports / bracing etc can exceeding its temperature rating or it fails the test.
I agree on the UL 489 rating of the breakers.

 

[wwhitney]

When busbars are tested in a panelboard to UL 67 31.1 they (ETL) run the rated current continuously (8hrs or something like that) and none of the supports / bracing etc can exceeding its temperature rating or it fails the test.

Except when the panelboard has a main breaker, then per UL67 section 21.3 the test only needs to be run at 80% of rated busbar current. Only MLO panels are required to be tested at 100% of rated busbar current per 21.2.

I agree on the UL 489 rating of the breakers.

Oh good.

Cheers, Wayne

 

[don_resqcapt19]

...
"38. 100 Percent Continuous Rated – Unless otherwise marked for continuous use at 100 percent of its current rating, a circuit breaker is intended for use at no more than 80 percent of its rated current where in normal operation the load will continue for three hours or more. . . ."

Cheers, Wayne

But, that, in my opinion, is just CYA in the product standard to avoid potential nuisance trips. That same standard requires the breaker to hold at 100% forever in a 40°C ambient. That test is done at 40°C, but with only a single breaker in the enclosure. The 80% accounts for heat from the other breakers in an enclosure.
I have seen many breakers in enclosures that carried 110 to 115% of the rating for well over 3 hours. I would expect that two things account for that. One the actual temperature of the breaker may have been below 40°C. The second is that the standard requires a breaker to trip at 135% of rating within one hour, suggesting that a breaker carrying less than 135% is never required to trip.

 

[tortuga]

How about this in your example load (100A + 100A continuous) [might be more real world for the OP]. For a meter pack with say a service lateral landing on lugs then its all internal UL listed busbar up to the 200A continuous rated meter socket then 225A bus to tenant main breaker, 225A breaker is installed for the feeder per article 215, but the service lateral is only allocated to 200A of that tenant load would that fly with you?

 

[wwhitney]

But, that, in my opinion, is just CYA in the product standard to avoid potential nuisance trips. That same standard requires the breaker to hold at 100% forever in a 40°C ambient. That test is done at 40°C, but with only a single breaker in the enclosure. The 80% accounts for heat from the other breakers in an enclosure.

Agreed, but aren't all of the NEC requirements for a 125% factor for continuous loads just to avoid nuisance trips?

Cheers, Wayne

 

[wwhitney]

How about this in your example load (100A + 100A continuous) [might be more real world for the OP]. For a meter pack with say a service lateral landing on lugs then its all internal UL listed busbar up to the 200A continuous rated meter socket then 225A bus to tenant main breaker, 225A breaker is installed for the feeder per article 215, but the service lateral is only allocated to 200A of that tenant load would that fly with you?

I'm a bit unclear on your example--are you saying that there is only one tenant, only one position used, and the only breaker is a 225A tenant breaker? Then 230.90(A) would require that the service lateral and service entrance conductors (if any) be rated at least 225A.

Or are you saying there are two tenants, both positions in use, and each tenant has a load of 100A non-continuous plus 100A continuous? Then the service lateral is only required to be 400A, and if there are no service entrance conductors, 230.42 is moot. The 400A service bus can supply the (2) 225A service disconnects.

Cheers, Wayne

 

[tortuga]

Or are you saying there are two tenants, both positions in use, and each tenant has a load of 100A non-continuous plus 100A continuous? Then the service lateral is only required to be 400A, and if there are no service entrance conductors, 230.42 is moot. The 400A service bus can supply the (2) 225A service disconnects.

Cheers, Wayne

Yeah that one then we agree.
Then now back to the OP.
When calculating the minimum lighting load (T220.42) for that service lateral why have the added 25% factor from the table?
Its not necessary.
I suspect one could remove all the continuous load factor from T220.42.
If you have a condition that requires sizing a continuous load then there should be a part of 220 that guides you on that now second calculation that is required.

 

[wwhitney]

Yeah that one then we agree.

OK, so the only way to "evade" the 125% continuous use factor when sizing service equipment (other than using 100% rated OCPD) is to (a) avoid service entrance conductors and (b) avoid having all the load go through a single OCPD. Then each individual OCPD gets a continuous use factor in its sizing, but the equipment common to all the OCPD typically will have a continuous rating and not require any continuous use factor in its sizing.

Cheers, Wayne

 

[Psychlo]

If you have a condition that requires sizing a continuous load then there should be a part of 220 that guides you on that now second calculation that is required.

Bingo.

Also, guidance is needed on how to treat Show Windows, Track Lighting, and Outside Sign Lighting in regard to their continuous nature. As it sits, it seems to be wholly based on presumed implications derived from the Note to T220.12. [T220.42(A) of 2023 shown below]

 

[tortuga]

Bingo.

Also, guidance is needed on how to treat Show Windows, Track Lighting, and Outside Sign Lighting in regard to their continuous nature. As it sits, it seems to be wholly based on presumed implications derived from the Note to T220.12. [T220.42(A) of 2023 shown below]

View attachment 2572423

Not just that but take a look at the optional calcs for a school 220.86, I have a school with 480V service that has

• 24 EVSE parking spaces that each are a 7kva continuous load branch circuit,
• 35kva of continuous lighting & computer equipment load.
• 100kva of non continuous load.

Largest load is 12kva,
2nd largest is 7.5kva
3rd largest is 7kva.
How do you apply 230.42(A) and size the service entrance conductors for this school?

 

[wwhitney]

How do you apply 230.42(A) and size the service entrance conductors for this school?

What's the uncertainty? [Edit: if your lighting load includes a contribution from Table 220.42(A), you need to break that out separately or downgrade it by a factor of 80% before adding it to the other continuous loads. I'll assume latter has been done if necessary.]

If there's no load management on the EVSEs, then the continuous load is 24 * 7.2 kVA (2023 NEC 220.57) + 35 kVA = 207.8 kVA. The non-continuous load is 100 kVA. So for service entrance conductor sizing, the required ampacity is (1.25 * 207.8 + 100)/0.48/sqrt(3) = 432A if you use non-100% rated OCPD.

Or if you have a single 100% rated service disconnect, it only has to be (207.8+100)/0.48/sqrt(3) = 370A. Maybe be a good application for a 100% rated 400A service disconnect.

Cheers, Wayne

 

[tortuga]

Nevermind that example I got the school demand table mixed up with the farm one, its no longer a school
So now its a large farm with electric grain dryer LOL. But regardless would you not apply any demand factors from a 220.103 optional calc to a 230.42(A) one?