panel 93% fill

[Toros]

Hi, the existing 3-phase, M.L.O sub panel board in an commercial space in a high rise bldg is 93% full or (93A) per panel schedule (all load consided, LCL, LML...) and the main cir. brkr in swbd is 100A-3p. My question; what is the capacity of this panel, how much load does it take, where is the limit, is 95% fill is the stop point ????? in sence of code???? Thank you

 

[iwire]

You do a load calculation per Article 220 and if the result is under 100 amps the 100 amp breaker is fine.

 

[GoldDigger]

Are you adding up the breaker sizes or the actual connected loads?
If the latter, especially if some of the loads are continuous, you may already be overloading the panel feeder.
Or if the panel feeder or main is not a 100% breaker you may already be against Code. (80% limit)
But if all of that works out OK, then you could go all the way to 100% of what the Code allows. Just not a fraction of an amp beyond that.

Tapatalk!

 

[ron]

You do a load calculation per Article 220 and if the result is under 100 amps the 100 amp breaker is fine.

Bob,

Would the load calculation per 220 be considered continuous load or non-continuous? If continuous, they should limit to 80% of 100A since the breaker is likely a molded case breaker and not rated for 100% continuous operation.

 

[mwm1752]

Bob,

Would the load calculation per 220 be considered continuous load or non-continuous? If continuous, they should limit to 80% of 100A since the breaker is likely a molded case breaker and not rated for 100% continuous operation.

220.40 the min OCPD for feeders is the result of 125% of continuous load + non continuous load. The demand factors IMO have already been factored with 125% of continuous load + non continuous load therefore a 99 amp feeder/service calculation can be done with a 100 Amp service -- personally not recommended & usually brought up at remodels which add loads. Most compentent contractors oversize the service for future expansion. There are some though who will press the limits legally. Handbook example is very useful

 

[kwired]

Continuous/noncontinuous and demand factors are all taken into account for art 220 calculations. If your calculation is 99.99 amps then a 100 amp overcurrent device and 100 amp conductor is fine, but do not apply same breaker and conductor to a 100.1 amp load.:happyno:

Most of the time if you use 220 to design it and then come back and check actual readings you generally are less current then what 220 came up with.

Also remember just because you have a load calculation of 95 amps now you can get by with a 100 amp supply, but that means if you want to add something in the future you may be upgrading the supply.

 

[david luchini]

Continuous/noncontinuous and demand factors are all taken into account for art 220 calculations.

Where do you find Continuous vs Noncontinous in Art. 220?

 

[kwired]

Where do you find Continuous vs Noncontinous in Art. 220?

I said they are taken into account, if they were in there you would have to factor them in where applicable.

That is just my opinion though.

 

[Toros]

Hi, the existing 3-phase, M.L.O sub panel board in an commercial space in a high rise bldg is 93% full or (93A) per panel schedule (all load consided, LCL, LML...) and the main cir. brkr in swbd is 100A-3p. My question; what is the capacity of this panel, how much load does it take, where is the limit, is 95% fill is the stop point ????? in sence of code???? Thank you

note to everybody that; LCL, continues load already counted in the load calc and finalized to 93-95A. Do I still need to consider 80% of NEC. What articl is that in NEC anyway. I forgot where

 

[Smart $]

note to everybody that; LCL, continues load already counted in the load calc and finalized to 93-95A. Do I still need to consider 80% of NEC. What articl is that in NEC anyway. I forgot where

What does LCL and LML stand for?

Actually need to know feeder ampacity (conductors between swbd and mlo subpanel). It could be as low as 91A and be compliant... and that will limit your loading to whatever it is or the 100A cb rating, whichever is the lesser of the two.

You have to calculate with consideration for continuous and non-continuous loads. Minimum feeder ampacity and ocpd rating is determined by non-continuous plus 125% continuous loads [215.2(A)(1), 215.3].

 

[Toros]

Hi, the existing 3-phase, M.L.O sub panel board in an commercial space in a high rise bldg is 93% full or (93A) per panel schedule (all load consided, LCL, LML...) and the main cir. brkr in swbd is 100A-3p. My question; what is the capacity of this panel, how much load does it take, where is the limit, is 95% fill is the stop point ????? in sence of code???? Thank you

Revising, re-stating my question / statment: the exist M.L.O sub panel in a store according to the panel schedule which is done through load calc of NEC:220; continious load plus LCL (contimous load) and LML (largest motor load) totals off to 93A @ 120/208V, 3-phase, 4w. My question/comment is, #3 thhn, cu is good size feeder from distribution board to M.L.O and 100A main tenant brkr is also good enough Do I still have to increase the feeder size for cont. load @ 125% as 215-2A1 says????? Thank you

 

[Smart $]

Revising, re-stating my question / statment: the exist M.L.O sub panel in a store according to the panel schedule which is done through load calc of NEC:220; continious load plus LCL (contimous load) and LML (largest motor load) totals off to 93A @ 120/208V, 3-phase, 4w. My question/comment is, #3 thhn, cu is good size feeder from distribution board to M.L.O and 100A main tenant brkr is also good enough Do I still have to increase the feeder size for cont. load @ 125% as 215-2A1 says????? Thank you

.. 125% continuous load demand
+ noncontinuous load demand
+ sum of motor loads
+ 25% largest motor load
.. Total <= feeder ampacity, OCPD, panel rating

#3 THHN Cu = 100A (provided no adjustment, correction req'd).
OCPD = 100A
Panel >= 100A?

 

[kwired]

Revising, re-stating my question / statment: the exist M.L.O sub panel in a store according to the panel schedule which is done through load calc of NEC:220; continious load plus LCL (contimous load) and LML (largest motor load) totals off to 93A @ 120/208V, 3-phase, 4w. My question/comment is, #3 thhn, cu is good size feeder from distribution board to M.L.O and 100A main tenant brkr is also good enough Do I still have to increase the feeder size for cont. load @ 125% as 215-2A1 says????? Thank you

Did you use 125% of continuous loads when doing the calculations that resulted in the 93A? Also any demand factors allowed from art 220 should not need additional adjustments, just use the values the demand factors come up with at 100%.

 

[Smart $]

... Also any demand factors allowed from art 220 should not need additional adjustments, just use the values the demand factors come up with at 100%.

I disagree. Demand factors do not preclude 125% factoring for continuous loads. The requirement to factor continuous loads at 125% is not even in Article 220.

 

[kwired]

I disagree. Demand factors do not preclude 125% factoring for continuous loads. The requirement to factor continuous loads at 125% is not even in Article 220.

You may be right. You never see anyone teaching feeder or service load calculations go through everything that applies to their example from 220 and then come back and add an extra 25% to whatever continuous load they have.

Most items that art 220 has demand factors for are not generally considered continuous loads as well.

The results of art 220 calculations generally gives you a larger feeder or service conductor then you need if you base that need on actual current measurement after it is installed.

 

[mwm1752]

Demand Factor. The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.

Total connected load IMO is non continuous + 125% of continuous = demand factor = service/feeder calcs per Art 220

 

[kwired]

Demand Factor. The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.

Total connected load IMO is non continuous + 125% of continuous = demand factor = service/feeder calcs per Art 220

Well put, that was kind of what my thoughts were before people tried to shoot it down, but I just didn't really know how to express it.

I never hear of anyone going through art 220 and coming up with a load figure then going back and trying to add to it for continuous loading of certain components. So that continuous load is either already factored in or is for some reason disregarded in 220. When it comes to demand factors, the loads that we are able to apply them to are almost never continuous loads. If the loads were continuous what is the point of applying a demand factor in the first place? Something that may be on continuously at a fixed rate is not suddenly going to draw less to allow you to apply a demand factor.

 

[Smart $]

Well put, that was kind of what my thoughts were before people tried to shoot it down, but I just didn't really know how to express it.

I never hear of anyone going through art 220 and coming up with a load figure then going back and trying to add to it for continuous loading of certain components. So that continuous load is either already factored in or is for some reason disregarded in 220. When it comes to demand factors, the loads that we are able to apply them to are almost never continuous loads. If the loads were continuous what is the point of applying a demand factor in the first place? Something that may be on continuously at a fixed rate is not suddenly going to draw less to allow you to apply a demand factor.

The application of demand factors actually put the result closer to the need for factoring continuous loads at 125%.

Say your total load on a feeder is four appliances operated as continuous loads which qualify for demand factoring (e.g. dwelling @75%, non-dwelling kitchen @80%). The application of both factors essentially offset each other. This exemplifies why you should do both. Factoring for continuous is required. Applying demand is an elective.

125% factoring for continuous loads provides padding for the conductor termination temperature limit. You don't want conductors handling current levels for extended periods which cause the conductor temperature to reach its termination temperature limit.

 

[kwired]

The application of demand factors actually put the result closer to the need for factoring continuous loads at 125%.

Say your total load on a feeder is four appliances operated as continuous loads which qualify for demand factoring (e.g. dwelling @75%, non-dwelling kitchen @80%). The application of both factors essentially offset each other. This exemplifies why you should do both. Factoring for continuous is required. Applying demand is an elective.

125% factoring for continuous loads provides padding for the conductor termination temperature limit. You don't want conductors handling current levels for extended periods which cause the conductor temperature to reach its termination temperature limit.

As I said, most items that art 220 allows using a demand factor on are not continuous loads, so you wouldn't add 25% to them anyway, but nothing says you can't if you want to.

 

[david luchini]

Demand Factor. The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.

Total connected load IMO is non continuous + 125% of continuous = demand factor = service/feeder calcs per Art 220

The total connected load is the sum of the branch circuit loads on a feeder/service. The demand load on a feeder/service is the sum of the branch circuit loads after any demand factors in Art 200 Part III, IV or V have been applied. 125% has nothing to do with "demand factor," it is only used in determining minimum conductor and OCPD SIZE.

For example, if you had a feeder with 100A non-continuous load and 55A continuous load, then the load on the feeder is 155A (not 168.75A.)

Per the first sentence in 215.2(A)(1), you would need a feeder conductor with an Ampacity that is not less than 155A.

Per the second sentence in 215.2(A)(1), the minimum feeder conductor SIZE would have to have an ampacity, before adjustment or correction, that is not less than 168.75A. This would be 2/0 AWG.

But consider if the feeder was run in a common raceway with another feeder such that there are 6 ccc's. A #2/0 THHN would have an adjusted ampacity of 195*0.8=156A. A 2/0 THHN with an ampacity of 156A would be large enough for the 155A load.

I never hear of anyone going through art 220 and coming up with a load figure then going back and trying to add to it for continuous loading of certain components.

The Annex Examples D3 and D3a do just that. They calculate the "load" first, then they calculate the minimum feeder and OCPD size by adding 25% to the continuous portion of the load.

There's no harm in calling the load 100% of noncontinuous plus 125% of continuous, it just may force you into a larger conductor size than needed. As in the example above, if you called the load 168.75A instead of 155A, then you cannot use the 2/0 with an adjusted ampacity of 156.