Question regarding branch circuits wire sizing

[codequestion]

I have branch circuit with receptacles #1 to #12. From panelboard to receptacle #1 I am providing lets say #10 AWG wire. From receptacle #1 to receptacle #2 I am providing #12. From receptacle #2 to #3 I am providing #12 AWG so on till receptacle #12 I am providing #12 AWG.

From receptacle #1 to #2 and so on till receptacle #12 can I provide #12 AWG wire or do I have to stick with #10 AWG. From panelboard to receptacle #1 is 50 feet. From receptacle #1 to #2 it is 50 feet, from receptacle #3 to #4 50 feet so on... Please also reference where in NEC I can do that or cannot do that.

 

[user 100]

I have branch circuit with receptacles #1 to #12. From panelboard to receptacle #1 I am providing lets say #10 AWG wire. From receptacle #1 to #2 can I provide #12 AWG wire or do I have to stick with #10 AWG. From panelboard to receptacle #1 is 50 feet. From receptacle #1 to #2 it is 50 feet. Please also reference where in NEC I can do that.

There is no such rule that you must use the same gauge throughout the ckt- only that the ocpd rating must correspond to the ampacity of the smallest conductor.

EX: in your case, if you went with no.12 after the first rec, the max allowable ocpd size would be 20a. Stick w/ #10 the whole way, its 30a- browse 240.4.

 

[codequestion]

how would you calculate voltage drop per NEC then? Please show examples.

 

[steve66]

Yes, you can reduce the wire size going to the second or 3rd or any of the other receptacles.

There isn't anything in the NEC that specifically says you can do this, but its not prohibited anywhere.

Generally, the NEC requires you to size the wires for the branch circuit breaker (lets assume its a 20A breaker for this case.) So you have to use a minimum of #12 wire.

If you increase part of the circuit to a larger wire size for voltage drop, that's fine. It doesn't have any effect on the required wire sizes for the rest of the circuit.

Note however that there is a code section that requires the ground wire to be increased in size when the hot wires are increased in size. So in this case, the ground wire would also be a #10 for the portion of the circuit where the wires are #10.

 

[codequestion]

Yes, you can reduce the wire size going to the second or 3rd or any of the other receptacles.

There isn't anything in the NEC that specifically says you can do this, but its not prohibited anywhere.

Generally, the NEC requires you to size the wires for the branch circuit breaker (lets assume its a 20A breaker for this case.) So you have to use a minimum of #12 wire.

If you increase part of the circuit to a larger wire size for voltage drop, that's fine. It doesn't have any effect on the required wire sizes for the rest of the circuit.

Note however that there is a code section that requires the ground wire to be increased in size when the hot wires are increased in size. So in this case, the ground wire would also be a #10 for the portion of the circuit where the wires are #10.

How can I do percent voltage drop going from panelboard to #1 receptacle, panelboard to #2 receptacle, panelboard to #3 receptacle and so on per NEC. Can anyone tell me? 120V single phase duplex receptacles.

 

[augie47]

how would you calculate voltage drop per NEC then? Please show examples.

There are only a few specific where the NEC requires voltage drop to be considered (Art 695 & 647 come to mind). Voltage drop on "standard" light & receptacle circuits is a design issue although an un-enforceable FPN at 210.19 does provide some guidance.

 

[infinity]

For a worst case scenario you could use a VD calculator and put in the total footage and current at the end of the circuit.

http://www.southwire.com/support/voltage-drop-calculator.htm

 

[steve66]

How can I do percent voltage drop going from panelboard to #1 receptacle, panelboard to #2 receptacle, panelboard to #3 receptacle and so on per NEC. Can anyone tell me? 120V single phase duplex receptacles.

No you go from panel to recept #1, recept #1 to recept #2, recept #2 to #3 and so on.

Then you total all the voltage drops to find the % drop at the last receptacle.

I use an excel spreadsheet I have set up for this.

I don't frequently change wire sizes in the middle of a run for receptacles. Unless the receptacle is for a specific appliance, you generally don't know what the load will be.

However, I do this frequently for outdoor lighting where the loads are very know, and the runs can be 100's of feet.

 

[codequestion]

For a worst case scenario you could use a VD calculator and put in the total footage and current at the end of the circuit.

http://www.southwire.com/support/voltage-drop-calculator.htm

I need help in regards to calculation: panelboard to receptacle #1 lets say I get %x voltage drop. What loads do I take into account when performing voltage drop from panelboard to receptacle #2. Do I take receptacle #1 and receptacle #2 into account or just receptacle #2 load? Also what would the % voltage drop be at receptacle#2?

 

[Dennis Alwon]

If you don't know the loads on the receptacles then use 180VA per receptacle.

180 @ 12 = 2160 Watts or 2160/120 = 18 amps

 

[Dennis Alwon]

I got the 180 Va from here

220.14(I) Receptacle Outlets. Except as covered in 220.14(J)
and (K), receptacle outlets shall be calculated at not less
than 180 volt-amperes for each single or for each multiple
receptacle on one yoke. A single piece of equipment consisting
of a multiple receptacle comprised of four or more
receptacles shall be calculated at not less than 90 volt-amperes
per receptacle. This provision shall not be applicable to the
receptacle outlets specified in 210.11(C)(1) and (C)(2).

 

[codequestion]

Let me repharse the question:

I need help in regards to calculation: panelboard to receptacle #1 lets say I get %x voltage drop assuming 180VA on load on receptacle. What loads do I take into account when performing voltage drop from panelboard to receptacle #2. Do I take receptacle #1 and receptacle #2 (360 VA) into account or just receptacle #2 load (180VA)? Also what would the % voltage drop be at receptacle#2?

 

[MAC702]

How was that not answered by this:

220.14(I) Receptacle Outlets. Except as covered in 220.14(J)
and (K), receptacle outlets shall be calculated at not less
than 180 volt-amperes for each single or for each multiple
receptacle on one yoke.

 

[Dennis Alwon]

I would calculate the vd from the panel to the 1st receptacle at 20 amps (18 if you want). I would then measure the length from receptacle 1 to 12 and calculate the load based on 2160 va - 180va since the first receptacle is not on the load of the rest of the circuit

 

[augie47]

If you select to use the 180va number and assume 5 outlets, the VD on the first would be figured at 900 va (5 x 180). Take the new voltage after applying the drop and the next section would be that number using and 720va for the remaining 4 outlets, etc.

Somewhat a useless exercise unless you know the actual loads

 

[codequestion]

seems like I may have to start a new poster. There are two questions original one which I got the answer. I am not looking for code help. I am looking for actual calculation help...how to calculate %voltage drop with multiple loads not just single load.

 

[infinity]

seems like I may have to start a new poster. There are two questions original one which I got the answer. I am not looking for code help. I am looking for actual calculation help...how to calculate %voltage drop with multiple loads not just single load.

Tell us the load at each receptacle and all of the distances between them.

 

[drktmplr12]

seems like I may have to start a new poster. There are two questions original one which I got the answer. I am not looking for code help. I am looking for actual calculation help...how to calculate %voltage drop with multiple loads not just single load.

You would need to have a different amperage for each segment of the receptacle circuit. It is necessary to calculate the voltage drop on each segment of wire between the receptacles based on the amperage and distance. If you have a drop of 2 volts from panelboard to receptacle 1, the voltage at receptacle 1 is 118. If the drop from 1 to 2 is 1.9 voltage, the voltage at receptacle 2 is 118-1.9=116.1 Volts.

This is really a theoretical exercise and no permitting department that I am aware of will enforce voltage drop requirements for general purpose receptacles. Dedicated purpose receptacles with high amperage loads and long distances are a different animal. You can see there is a large amount of effort required considering we have no way to know what anyone is going to plug into any give receptacle.

1. Calculate the voltage drop of each segment based on the following, fill in the table:

For single phase loads:

VD= 2 * Ze * d/1000 * I / Runs, Vd%=VD / V
Ze =R * pf + XL sin ( cos-1 (pf))

R = AC resistance of wire, depending on conduit type. (NEC Table 9) (Ohms)
XL = Reactance of wire, depending on conduit type. (NEC Table 9) (Ohms)
Ze = Effective Impedance
pf = power factor
I = current (Amps)
Runs = # of parallel runs
V = Voltage (Volts)
VD = Voltage Drop (Volts)
Vd% = Voltage Drop %

2. Fill in your actual distances and calculate the voltage drop and the remaining volts at each receptacle.

Receptacle	Distance (ft)	Load (VA)	Voltage Drop (Volts)	Remaining Volts
1		2160	2.0	118.0
2		1980	1.9	116.1
3		1800	1.8	114.3
4		1620	1.3	113.0
5		1440	1.0	112.0
6		1260	0.7	111.3
7		1080	0.5	110.8
8		900	0.4	110.4
9		720	0.3	110.1
10		540	0.2	109.9
11		360	0.1	109.8
12		180	0.1	109.7

The voltage drop and remaining volts provided are hypothetical and for illustration purposes.

 

[codequestion]

Tell us the load at each receptacle and all of the distances between them.

Well here is where i am trying to get at i have engineering drawing that states following:

120V circuit, 20 amps overcurrent protection device, single phase use the following

65 to 120 feet: for homerun use #10, for circuit run use #12.

Homerun is defined as panelboard to closest outlet and circuit run is defined as closest to the farthest outlet or device.

How can i verify homerun size and circuit run size would give me 3 percent voltage drop?

Sent from my SM-G935U using Tapatalk

 

[infinity]

Well here is where i am trying to get at i have engineering drawing that states following:

120V circuit, 20 amps overcurrent protection device, single phase use the following

65 to 120 feet: for homerun use #10, for circuit run use #12.

Homerun is defined as panelboard to closest outlet and circuit run is defined as closest to the farthest outlet or device.

How can i verify homerun size and circuit run size would give me 3 percent voltage drop?

With the information provided you cannot determine what you're asking. The engineering note is quite clear, is there a specific reason why you need to know this?