More than 200ft of Romex in a branch circuit...

[Cow]

Wow - Just when I thought I understood 3 ways.

Do they make a wall switch relay, or does it go in a J-box above the ceiling?

I usually tuck the relay, contactor, etc in a j-box that's readily accessible somewhere close by and obvious. Using relays, contactors, for switching in residential isn't very common compared to commercial but I'd think if you put it nearby someone would be able to find it if they ever had to troubleshoot the circuit.

 

[Ingenieur]

If your High-Bay lighting is selected for line voltage @ 3% VD, Pf=0.85 per NEC Tbl-9,
10A on 12-3 Romex is good for
237ft @ 208vac,
274ft @ 240vac,
547ft @ 277vac.

Even at continuous use, cable termination temperature is below 40°C.
You could bundle four 12-3 cables, with 12ccc's and still keep termination temp below 60°C.

v drop = 2 x D/1000 x 1.7 x 10 = 0.034 x D
237' = 8.06/208 or 3.9%
274' = 9.3/240 or 3.9%
547' = 16.3/480 or 3.4%
???

D = (15 x v)/(z x i) = (15 x v)/(1.7 x 10) = 0.8824 x v
183'
212'
424'

check : 2 x 183/1000 x 1.7 x 10 = 6.22/208 or 3%
or 0.034 x 183 = 6.22/208 or 3%

where am I messing up?

 

[ggunn]

I know that the rule of thumb is to upsize your wire gauge for every 200ft in length. I have a situation where I am wiring a space that is approximately 120 ft by 50 ft. If I run a feeder from the panel to a switch (approx 120 - 150 ft) and branch out to 12 lights, I will be using well over 200ft "worth" of wire. I've never had to take this into account before. Does the rule apply in this situation? And if so, can I run a 10-2 to the switch and then run 12-2 to each light?

Thanks in advance.

One thing you need to at least think about is the resistance of the wire and the OCPD. It is possible to run enough wire that a fault won't draw enough current to trip the breaker.

 

[kwired]

One thing you need to at least think about is the resistance of the wire and the OCPD. It is possible to run enough wire that a fault won't draw enough current to trip the breaker.

If it doesn't draw enough to trip breaker then conductor isn't overloaded, but you also probably have some pretty severe voltage drop.

 

[ramsy]

v drop = 2 x D/1000 x 1.7 x 10 = 0.034 x D
where am I messing up?

I mess with (R), to adjust for termination temperature.
Trying to adjust Temp @ LOAD + # of CCC's (when bundling exceeds 3 wires)

Z = R2*PF+XL*SIN(ACOSIN(PF))/1000*L Can show R2 if desired.

0.35975603 = 1.75237 * 0.85 + 0.054 * .05267827 / 1000 * 237

Also selected 3Ø 120/208Y Transformer = Z*LOAD*1.732

Also selected PVC conduit to approximate NM Cable XR = 0.054

 

[Ingenieur]

I mess with (R), to adjust for termination temperature.
Trying to adjust Temp @ LOAD + # of CCC's (when bundling exceeds 3 wires)

Z = R2*PF+XL*SIN(ACOSIN(PF))/1000*L Can show R2 if desired.

0.35975603 = 1.75237 * 0.85 + 0.054 * .05267827 / 1000 * 237

Also selected 3Ø 120/208Y Transformer = Z*LOAD*1.732

Also selected PVC conduit to approximate NM Cable XR = 0.054

got ya
thnx

 

[Ingenieur]

basic eq for Isc / I for a cable sc at end of run, ie, min sc i
I = sc current
I ~ cable ampacity
D one way dist
Z = nec table

1 ph : (500 x v)/(D x Z x I)
3 ph l-l : (577 x v)/(D x Z x I)
3 ph l-n : (333 x v)/(D x Z xI)

rearranged 1 ph (similar for others)
v/(2 x D x Z/1000 x I) = v / v drop = Isc / I

assume
480/3 v and 10% v drop, 80 fl/100 Ampacity/200 cb
Isc / I = 480/48 = 10 or 1000 A or 1000/200 = 500% x cb rating

takes alot of vdrop to < cb rating

 

[EEEC]

There is a lot of useful information here. Thanks everyone!

 

[Klockopotomis]

I tested this math once at custom home where i put all 110 LED can lights on the same circuit. The house was 5200 sq. ft. The last switch was 15' away from the first switch, so i ran a jumper over, just in case there was noticeable voltage drop i could tie it in and have an equalizing. after it was trimmed I turned it on and to my surprise there was only 1 volt difference from panel to last box! Hundreds of feet of wire. But the comment earlier is the key-what is the load? The load has a large effect on the size of wire and determining VD. IN my case the load was 3 amps.

 

[Ingenieur]

v drop = 2 x D x 0.17/1000 x 3 = 1
D = 1/(2 x 0.17/1000 x 3) = 980' one-way
basically 2000' complete ckt to drop 1 volt

 

[ActionDave]

Am I the only electrician on this forum that thinks this is not something to worry about?

 

[LarryFine]

No, I'm pretty sure there are two or three others.

 

[Cow]

Am I the only electrician on this forum that thinks this is not something to worry about?

I don't think it's the electricians on here that are worried, only the engineers.

 

[Ingenieur]

I don't think it's the electricians on here that are worried, only the engineers.

I don't think anyone is 'worried' lol
but due diligence requires it be checked, and very simple to do

in this case # 12, 200', 10 A you may have an issue
6% drop on this branch alone
if the xfmr, service, feeder were 3%, total is ~10%

 

[kwired]

I don't think anyone is 'worried' lol
but due diligence requires it be checked, and very simple to do

in this case # 12, 200', 10 A you may have an issue
6% drop on this branch alone
if the xfmr, service, feeder were 3%, total is ~10%

And if the load can tolerate it - still might not be a problem. Line losses - still need more information before one can say that is a problem. If load runs 24/7 those losses add up. If it is a very seldom used load maybe not worth any concern at all.

 

[peter d]

Am I the only electrician on this forum that thinks this is not something to worry about?

No, you're not alone. :thumbsup:

 

[ramsy]

I don't think anyone is 'worried' lol
but due diligence requires it be checked..

The electricians that care, are wanabe engineers, or wanabe their own design build shop.