Okay here's the deal. I have come across an unusual problem that I am not quite sure how to deal with. I have a residence that was built in the 70's. The home owner did all the wiring (Yuk!). The new owners have had me out there cleaning up some messy work from the previous owner. One of the things nthe owner did was install 7 three bulb post lights. The total lenght of the wire run is about 590 feet. He put it in in #14!. Well the circuit is way over on voltage drop calculations obviously. So my question is will installing 2 boost transformers, one about 125-150 into the line, and the other about 300 feet down the line do the trick. And save me from having to pull a new circuit or burning up my wiring or is it time to do some serious trenching.
Unusual Problem
- Thread starter brandon
- Start date
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curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Re: Unusual Problem
Buck and boost transformers should not be used for this application. The voltage drop on the circuit increases as the load on the circuit increases but it also decrease as the load decreases. If you were to unscrew all of the lamps from the fixtures you would have the same voltage at the end of the circuit the you have at the beginning. Now if you install a transformer to increase the voltage to make up for the voltage drop based on the load of all of the fixtures what happens when some of the lamps burn out? The voltage on the circuit is going to increase and probably going to quickly damage the remainder of the lamps still operating.
The only way to repair this circuit is to install the correct size conductors.
Buck and boost transformers should not be used for this application. The voltage drop on the circuit increases as the load on the circuit increases but it also decrease as the load decreases. If you were to unscrew all of the lamps from the fixtures you would have the same voltage at the end of the circuit the you have at the beginning. Now if you install a transformer to increase the voltage to make up for the voltage drop based on the load of all of the fixtures what happens when some of the lamps burn out? The voltage on the circuit is going to increase and probably going to quickly damage the remainder of the lamps still operating.
The only way to repair this circuit is to install the correct size conductors.
- Location
- Massachusetts
Re: Unusual Problem
I agree with Curt the Buck Boosts are not the way to go here.
But I hate trenching too, so I did some figuring on your circuit.
590 total feet 130 feet from switch to first fixture leaving 460 feet or about 65 feet between the 7 fixtures.
3- 40 watt 120 volt lamps per fixture or 1 amp per fixture.
So my suggestion would be to replace the 14 AWG with 10 AWG from the switch through the first fixture and onto the second fixture, after that leave the rest of the 14 AWG in place.
Starting with 120 volts this will result in the following
117.8 volts at fixture 1
116.8 volts at fixture 2
114.8 volts at fixture 3
113.2 volts at fixture 4
112.0 volts at fixture 5
111.2 volts at fixture 6
110.8 volts at fixture 7
About 8% voltage drop
The real voltage drop will be a little less as the lamps draw less current as the voltage goes down and I did not figure that in.
If this is still to much drop for you use 8 AWG in place of the 10 AWG, this would result in
118.6 volts at fixture 1
118.0 volts at fixture 2
116.0 volts at fixture 3
114.4 volts at fixture 4
113.2 volts at fixture 5
112.4 volts at fixture 6
112.0 volts at fixture 7
Or about 6.5% voltage drop.
This will save about 395 feet of trenching.
I agree with Curt the Buck Boosts are not the way to go here.
But I hate trenching too, so I did some figuring on your circuit.
590 total feet 130 feet from switch to first fixture leaving 460 feet or about 65 feet between the 7 fixtures.
3- 40 watt 120 volt lamps per fixture or 1 amp per fixture.
So my suggestion would be to replace the 14 AWG with 10 AWG from the switch through the first fixture and onto the second fixture, after that leave the rest of the 14 AWG in place.
Starting with 120 volts this will result in the following
117.8 volts at fixture 1
116.8 volts at fixture 2
114.8 volts at fixture 3
113.2 volts at fixture 4
112.0 volts at fixture 5
111.2 volts at fixture 6
110.8 volts at fixture 7
About 8% voltage drop
The real voltage drop will be a little less as the lamps draw less current as the voltage goes down and I did not figure that in.
If this is still to much drop for you use 8 AWG in place of the 10 AWG, this would result in
118.6 volts at fixture 1
118.0 volts at fixture 2
116.0 volts at fixture 3
114.4 volts at fixture 4
113.2 volts at fixture 5
112.4 volts at fixture 6
112.0 volts at fixture 7
Or about 6.5% voltage drop.
This will save about 395 feet of trenching.
Re: Unusual Problem
hey if there is no problem and the lights work just fine , well I say if it aint broke dont fix it. I would explain the cost to the owner let him know it should be fixed but leave it up to him . If the lights work and there has never been a problem then tell the owner it should be ok. why do the extra work or charge the owner extra money if there is no problem. In my area the inspector will let existing remain has long as the owner is aware of the problem and does not want to fix it.
hey if there is no problem and the lights work just fine , well I say if it aint broke dont fix it. I would explain the cost to the owner let him know it should be fixed but leave it up to him . If the lights work and there has never been a problem then tell the owner it should be ok. why do the extra work or charge the owner extra money if there is no problem. In my area the inspector will let existing remain has long as the owner is aware of the problem and does not want to fix it.
Re: Unusual Problem
I agree if it ain't broke do not fix it. 8 to 9 percent voltage drop is not bad for a lighting circuit. Another method you might want to consider is making a "ring circuit" out of it. To make the ring install another 14AWG at the last pole and run it back to the panel and connect it to the feeder. This will cut the voltage drop in half.
I agree if it ain't broke do not fix it. 8 to 9 percent voltage drop is not bad for a lighting circuit. Another method you might want to consider is making a "ring circuit" out of it. To make the ring install another 14AWG at the last pole and run it back to the panel and connect it to the feeder. This will cut the voltage drop in half.
Re: Unusual Problem
If the 40W fixtures are incandescant, you might consider suggesting replacing them with fluorescent fixtures. They would use less current and power (thus less voltage drop) and still put out as much light. Would the screw in type bulbs with their own built in ballast fit in the fixtures and look OK?
Another option might be Metal Halide fixtures.
If you had a fixure that could run at 208Volts, that would solve the voltage drop problem also.
If the 40W fixtures are incandescant, you might consider suggesting replacing them with fluorescent fixtures. They would use less current and power (thus less voltage drop) and still put out as much light. Would the screw in type bulbs with their own built in ballast fit in the fixtures and look OK?
Another option might be Metal Halide fixtures.
If you had a fixure that could run at 208Volts, that would solve the voltage drop problem also.
Re: Unusual Problem
I agree with "if it ain't broke don't fix it."
Voltage drop with regard to incandescent lighting just affects light output. The farther away the dimmer the lights will be IF all are the same watts.
Have you thought about starting out with 40a bulbs at the closest fixtures, 60w bulbs in the fixtures that are farther out and maybe 75w bulbs on the fixtures that are farthest? I would think that the higher wattage would compensate for voltage drop with regard to light output.
I agree with "if it ain't broke don't fix it."
Voltage drop with regard to incandescent lighting just affects light output. The farther away the dimmer the lights will be IF all are the same watts.
Have you thought about starting out with 40a bulbs at the closest fixtures, 60w bulbs in the fixtures that are farther out and maybe 75w bulbs on the fixtures that are farthest? I would think that the higher wattage would compensate for voltage drop with regard to light output.
- Location
- Massachusetts
Re: Unusual Problem
As this circuit is now 590' on 14 AWG the last fixture will have about 95 volts, the deference in light output will be quite noticeable.
I like templdl's suggestion,larger lamps as you move towards the end of the circuit.
A little experimenting and you should get even light output without any digging.
Well something brought this to Brandon's attention, it does not sound like he is trying to make work.
As this circuit is now 590' on 14 AWG the last fixture will have about 95 volts, the deference in light output will be quite noticeable.
I like templdl's suggestion,larger lamps as you move towards the end of the circuit.
A little experimenting and you should get even light output without any digging.
Re: Unusual Problem
How about setting up a low voltage transformer at each pole and installing 12 volt lamps? I know the MR16 75 watt lamps are quite bright. Would require a socket with trhe lamp but I think it can be done very easily. May be an expense but could be the way to go. That should be near zero amps per lamp on the primary side therefore dropping your voltage drop considerably. Just a thought.
How about setting up a low voltage transformer at each pole and installing 12 volt lamps? I know the MR16 75 watt lamps are quite bright. Would require a socket with trhe lamp but I think it can be done very easily. May be an expense but could be the way to go. That should be near zero amps per lamp on the primary side therefore dropping your voltage drop considerably. Just a thought.
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
Re: Unusual Problem
Irollo ; that is nice idea but i don't really recomonded for very long run with low voltages system because the low voltages bulb are more senstive than standard line voltage bulbs are and by the way 75 watts at 12 volts are 6.45 amps each and try to multiply the numbers of 3 per post is 19.35 amps and multiply by 7 post will come out grand total of 135.45 amps :ekk: and wire size will be something like 4/0 or 250 copper so you can understand why low voltage lights are fine for short distance and 75 watts low voltage is super bright normally can use like 50 or 35 watts but the distance that where the curpit will be and low voltage drop are more tighter than standard lights are more like 3 percent drop the most so i rather use one of the sparky ideas to use lower wattage bulbs at first 2 or 3 post then increse wattage due the voltage drop that make sense
just my thought
merci marc
Irollo ; that is nice idea but i don't really recomonded for very long run with low voltages system because the low voltages bulb are more senstive than standard line voltage bulbs are and by the way 75 watts at 12 volts are 6.45 amps each and try to multiply the numbers of 3 per post is 19.35 amps and multiply by 7 post will come out grand total of 135.45 amps :ekk: and wire size will be something like 4/0 or 250 copper so you can understand why low voltage lights are fine for short distance and 75 watts low voltage is super bright normally can use like 50 or 35 watts but the distance that where the curpit will be and low voltage drop are more tighter than standard lights are more like 3 percent drop the most so i rather use one of the sparky ideas to use lower wattage bulbs at first 2 or 3 post then increse wattage due the voltage drop that make sense
just my thought
merci marc
dan55
Member
- Location
- South Dakota
Re: Unusual Problem
If you put the low voltage transformer at each post like Irollo was saying the total load on each transformer will be about 19 amps.It would be 135 amps if he put in one transformer at the beginning. I think you could get by with quite a bit smaller conductors than 4/0.
If you put the low voltage transformer at each post like Irollo was saying the total load on each transformer will be about 19 amps.It would be 135 amps if he put in one transformer at the beginning. I think you could get by with quite a bit smaller conductors than 4/0.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Unusual Problem
Hello Dereck. As always i appreciate your post, your knowledge of electrical far exceeds my own. This "ring" circuit" you speak of... I've never seen it done before, but it sounds to me like a parrellel circuit (smaller than 1/0). Is this code compliant? I apologize if this sounds like a dumb question, but once again, I've never heard of it. Thanks in advance.
Ed MacLaren
Senior Member
Re: Unusual Problem
Ring branch circuits have been used in Europe, and, I believe ring feeders are sometimes used for redundancy.
Ed
Ring branch circuits have been used in Europe, and, I believe ring feeders are sometimes used for redundancy.
Ed
Re: Unusual Problem
Ryan, I do not believe it is a parallel circuit. Take a look at Ed's drawing. Like Ed stated it is used in UK to supply long lightning circuits.
It is a gray area, and some may see it as a parallel conductors. But I like the circuit.
Ryan, I do not believe it is a parallel circuit. Take a look at Ed's drawing. Like Ed stated it is used in UK to supply long lightning circuits.
It is a gray area, and some may see it as a parallel conductors. But I like the circuit.
Re: Unusual Problem
Wow!!!!! I never expected to get so many responses from one single question!!! I decided to post some more info that i found out. A switch was found inside the house that was supposed to control the outside post lights. it was in an obscure spot so it was easy to miss. So we turned it. Yep sure enough they worked, but they tripped the breaker as I suspected they would and you could see the noticeable voltage drop from one post to the next. After staying on for a minute or two the breaker poped. I am pretty sure that it is on a dedicated circuit. And the switch leg began to get really warm and smoke the insulation. Sounds like my best option so far is to run a new cicuit to the first 2 post in #8 wire. The tie the rest in from there. A 15amp breaker should still be fine right? Since this a voltage drop situation and not a overcurent situation. And yes the homeowner would like the problem fixed. Wow once again thank you all for yoour responses I have really enjoyed reading them. The idea of the loop is a great one but would require a huge amout of work and time to get from the end of the run back to the panel.
Wow!!!!! I never expected to get so many responses from one single question!!! I decided to post some more info that i found out. A switch was found inside the house that was supposed to control the outside post lights. it was in an obscure spot so it was easy to miss. So we turned it. Yep sure enough they worked, but they tripped the breaker as I suspected they would and you could see the noticeable voltage drop from one post to the next. After staying on for a minute or two the breaker poped. I am pretty sure that it is on a dedicated circuit. And the switch leg began to get really warm and smoke the insulation. Sounds like my best option so far is to run a new cicuit to the first 2 post in #8 wire. The tie the rest in from there. A 15amp breaker should still be fine right? Since this a voltage drop situation and not a overcurent situation. And yes the homeowner would like the problem fixed. Wow once again thank you all for yoour responses I have really enjoyed reading them. The idea of the loop is a great one but would require a huge amout of work and time to get from the end of the run back to the panel.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Unusual Problem
If the 15A breaker trips and this is a dedicated circuit with nothing else on it there is something else going on here. The voltage drop to those fixtures shouldn't cause an over current problem.
If the 15A breaker trips and this is a dedicated circuit with nothing else on it there is something else going on here. The voltage drop to those fixtures shouldn't cause an over current problem.
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