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Subject - Combination continuous & noncontinuous loads
David Hyatt We have 4 circuits in a conduit. Single phase system. 4 phase wires 2 neutrals and a ground. Total 7 #12THHN wires in 1/2 inch conduit. Commercial building with known number of general purpose receptacles.

On one circuit: how many lights and receptacles can be installed on that particular circuit?

10 receptacles and 3 (4 lamp troffer) ( 32watt bulbs T-8)
More than 3 CCC = 80% of 30 amps which is 24amps, so no problem yet.
Conduit fill: still no problem.
Ambient temperature still no problem.
10 receptacle= 180va X 10 = 1800w/120volts= 15amps
3 troffers= 32w x 4 = 128w x 125% = 160/120= 1.3333amps x3= 3.99
total amperage 19 amps on 20 amp CB. Am I calculating this right?
justinelect You have to use ballast amperage on flourescent fixtures. 220.4 (B) I think you may still be under 20 amps, but it will depend on the draw of the ballasts.
David Hyatt Yes Justin, I agree. Thats my next question in my post named (unit amperage) But Assuming the 128w is correct in this formula, have I calculated this correctly? Continuous and noncontinuous combination loads is not a calculation I have done before. It has been either or.
I posted the specs of the troffer but can't tell the unit amperage so I used the lamps just as a calculation figure.
David Hyatt How about it folks, is this the proper way of calculating? Not counting the extra for the ballast, once I get an exact answer on the ballast issue I can change the numbers in the formula.
justinelect 210.19(A)(1) Branch circuit conductors = non-continuous load + 125% continuous load. 210.20(A) OCPD = non-continuous load + 125% continuous load. David you are correct.


Justin
KSsparky It has always been my position that the code does not specify the number of outlets on a circuit. The 180 va figure is for calculating the load on the service. The number of outlets on a circuit does not limit the load. A 20 amp circuit will only supply 20 amps, whether it is through 1 outlet or 20. To specify the number of outlets would be a design issue, and therefore not a code matter. Anyone agree, or am I out here on my own on this one ?
Ryan_J
quote:
Originally posted by KSsparky

It has always been my position that the code does not specify the number of outlets on a circuit. The 180 va figure is for calculating the load on the service. The number of outlets on a circuit does not limit the load. A 20 amp circuit will only supply 20 amps, whether it is through 1 outlet or 20. To specify the number of outlets would be a design issue, and therefore not a code matter. Anyone agree, or am I out here on my own on this one ?


Your on your own onthis one, sorry. I agree with you for dwellings, because it specifcially exempts the 180 requirement, but the 180 requirement for commercial applies to branch circuits as well.
KSsparky That's O.K. Ryan, I have no problem with different points of view. Just curious, do you count the number of outlets on a circuit during an inspection, or leave it to the EE to draw it up that way ? I've never had an inspector count them for me. Any idea who came up with the 1.5 amps per receptacle in the first place ?
Ryan_J I look at it on the plan review and hope the electrician does it that way, to tell you the truth. I'm not sure where the 180VA came from, but it would be interesting to know.
iwire
quote:
Originally posted by KSsparky

It has always been my position that the code does not specify the number of outlets on a circuit. The 180 va figure is for calculating the load on the service.


That is what I believed for the first, oh, 20 years I was in the trade.

It was not till very recently I was convinced that I was mistaken.

However I agree with you, the number of outlets has little to do with the load applied. In a commercial space they may plug in one laser printer that draws 15 amps, or they may not plug anything into dozens of corridor receptacles.
KSsparky I'm not saying that I'm convinced just yet. But I'm always open to an education.
justinelect 220.3 Computation of Branch Circuit Loads
220.3(B)(9) Receptacle Outlets. Except as covered in 220.3(B)(10), which covers dwelling occupancies, receptacle outlets shall be computed at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke...

Just to add to the mess, lol, here they have limited us to the number of outlets on a 20 amp circuit to ten--residential or commercial. Naturally this is a local code, and I have heard of some inspectors counting the outlets on one circuit. Like Bob said this doesn't help if large loads like copiers or printers end up located on the same circuit. Where I work lately they have been moving everybody around and we have run into this problem several times. Dedicated circuits had already been installed to supply the big copiers and such, but the people who move in have to change location on everything and it ends up being a lot of work for us.

Justin