Schedule of loads comparison between US and Philippines

[Alaktrical_Gingineer]

Hi! May I ask how you do your Schedule of Loads here? I want to verify if we are doing the same way as you do.

Let us make an example. Suppose I have 230V, Three Phase System. Can you show how much is your 3-phase feeder current (Yellow Highlight) for this specific panel? I've got 50.24 Amperes




For fun and learning only. I am planning to ask a follow-up question after this.
Cheers and keep safe!

 

[tortuga]

Presuming your nominal voltages still are:

2.20.1.5 (a) Voltages. Unless other voltages are specified, for purposes of
calculating branch-circuit and feeder loads, nominal system voltages
of 115, 115/230, 208Y/120, 230, 347, 400Y/230, 460Y/265, 460,
600Y/347, and 600 volts shall be used.

I would sum up all the VA
So 13660 VA
and divide that by the Nominal voltage 230V X SQRT 3 = 398.37
13660 VA / 398.37V = 34.29 Amps

 

[topgone]

Hi! May I ask how you do your Schedule of Loads here? I want to verify if we are doing the same way as you do.

Let us make an example. Suppose I have 230V, Three Phase System. Can you show how much is your 3-phase feeder current (Yellow Highlight) for this specific panel? I've got 50.24 Amperes

View attachment 2561073


For fun and learning only. I am planning to ask a follow-up question after this.
Cheers and keep safe!

My take on your "learning" load schedule:

• The heading "Demand Volt-Ampere" is not correct as you placed the respective currents of the loads under it.
• Your 3-phase motor amperes are not correct as you have to divide the VA by 230V and 1.732. The correct figure should be 3.77A, not 6.52A.
• AT (breaker selection) for Motor 1 and Motor 2 could be too small, use the max. factor of 250% per 430.52. You will see that Motor 1 & 2 should be protected by 20AT breakers while the rest will be 15AT.
• If your purpose here is to compute for the demand amps (sizing conductors and breakers), keep in mind that the receptacle demand will be computed as the sum of the first 3,000 VA plus 35% of the load above 3,000 VA (dwelling units install) or sum of the first 10,000 VA plus 50% of the remaining load above 10,000VA (non-dwelling).
• The demand load for motors, if continuous will have to be multiplied by 125% of the rated loads. Non-continuous loads will be taken at 100%.
• For your example, My calcs for the computed panel demand is 35.9A or a breaker of 40A. Compare that with the computed total load current of 42.8 (max. phase amps sum of single-phase loads X 1.732 + sum of the 3-phase motor loads)

 

[Alaktrical_Gingineer]

My take on your "learning" load schedule:

• The heading "Demand Volt-Ampere" is not correct as you placed the respective currents of the loads under it.
• Your 3-phase motor amperes are not correct as you have to divide the VA by 230V and 1.732. The correct figure should be 3.77A, not 6.52A.
• AT (breaker selection) for Motor 1 and Motor 2 could be too small, use the max. factor of 250% per 430.52. You will see that Motor 1 & 2 should be protected by 20AT breakers while the rest will be 15AT.
• If your purpose here is to compute for the demand amps (sizing conductors and breakers), keep in mind that the receptacle demand will be computed as the sum of the first 3,000 VA plus 35% of the load above 3,000 VA (dwelling units install) or sum of the first 10,000 VA plus 50% of the remaining load above 10,000VA (non-dwelling).
• The demand load for motors, if continuous will have to be multiplied by 125% of the rated loads. Non-continuous loads will be taken at 100%.
• For your example, My calcs for the computed panel demand is 35.9A or a breaker of 40A. Compare that with the computed total load current of 42.8 (max. phase amps sum of single-phase loads X 1.732 + sum of the 3-phase motor loads)

Hi Sir @topgone, thank you for making some time to share your valuable inputs. I recalculated based on what you taught but I can't get your 35.9A answer. Instead, I keep getting 33.3A

May I ask where did I made a difference? Attached is my recalculation.

Follow up question:
For a 33.3A load, one may recommend 40A Circuit Breaker because it is the next higher size. But the code says that a Circuit Breaker should not carry more than 80% of it's capacity. My question is, do we need to multiply the 33.3A by 1.25 and recommend 50A Circuit Breaker instead?

Thank you

 

[petersonra]

What is it you are trying to calculate here? Are you trying to do a load calculation?

Or are you trying to calculate the max ocpd rating for the minimum required feeder conductors?

Those numbers will come out differently.

 

[Alaktrical_Gingineer]

What is it you are trying to calculate here? Are you trying to do a load calculation?

Or are you trying to calculate the max ocpd rating for the minimum required feeder conductors?

Those numbers will come out differently.

Hi Sir @petersonra , I am doing load calculation to be the basis of calculating the OCPD rating of this panel.

 

[petersonra]

Hi Sir @petersonra , I am doing load calculation to be the basis of calculating the OCPD rating of this panel.

The numbers may not be the same. In any case why do you care about the overcurrent protection device rating of the panel? Just get a main circuit breaker type panel with the same rating as the panel. That's the cheapest way usually, in fact usually it's cheaper than getting a main lug only panel. And perfectly legal.

 

[electrofelon]

Just get a main circuit breaker type panel with the same rating as the panel. That's the cheapest way usually, in fact usually it's cheaper than getting a main lug only panel. And perfectly legal.

I have to disagree. The "MB panel is the same cost or cheaper than a main lug panel" rule is typically only true for some single phase load centers. For three phase load centers there's a significant increase in cost for main breaker, and also true for factory order panel boards.

I would typically avoid a main breaker unless I needed it for a series rating, a tap rule, or 408.36 compliance.

 

[petersonra]

I have to disagree. The "MB panel is the same cost or cheaper than a main lug panel" rule is typically only true for some single phase load centers. For three phase load centers there's a significant increase in cost for main breaker, and also true for factory order panel boards.

I would typically avoid a main breaker unless I needed it for a series rating, a tap rule, or 408.36 compliance.

IME. If you want a special size that is certainly true. But, I have found that unless you only have a small number of breakers, getting a PB with a standard sized main breaker is almost always more cost effective than getting a non-standard sized breaker. It is also usually (but not always) cost effective to get a main breaker panel over a MLO panel, even in 240 V 3 phase panels (but not 480 V 3 phase panels). As you mentioned, it is almost always cost effective to buy MCB panels over MLO panels for single phase panels.

This is of course a YMMV kind of thing, and is highly dependant on the discount class you get put in by your supplier, and the exact situation you have. I tend to think of what I get myself into as typical, when it probably is not.

 

[electrofelon]

. It is also usually (but not always) cost effective to get a main breaker panel over a MLO panel, even in 240 V 3 phase panels

.

I just find that hard to believe, I'd be curious if anybody else has had that experience. I buy three phase Siemens load centers frequently and a 200A MLO was always like 210 bucks (pre covid price), and nearly double that for a 200 A main breaker.

 

[electrofelon]

IME. If you want a special size that is certainly true. But, I have found that unless you only have a small number of breakers, getting a PB with a standard sized main breaker is almost always more cost effective than getting a non-standard sized breaker.

I am not really following the scenario you are talking about. I could see in the case of say, having an existing 250 amp feeder that is being repurposed into a 200 amp panel. In that case yes it is probably cheaper and easier to get a 200 amp main breaker panel instead of changing the feeder breaker to 200. I don't run into situations like that often.