voltage drop

[JJsparks]

I am working on a project that calls for a number of post lights to be installed. The problem is that the landscape engineer never took into account the problem of voltage drop. The posts require 150 watts each( maximum), some runs according to the blueprint will be in excess of 800 feet from the source. Can I use a buck and boost transformer when necessary? I am going to limit the number of posts on a single circuit to 10 and no more.

Thank you for any information that you may provide

 

[iwire]

Can I use a buck and boost transformer when necessary? I am going to limit the number of posts on a single circuit to 10 and no more.

Not really as as soon as some lamps burned out / stopped working the voltage would go to high and damage the working lamps.

What voltage are the circuits?

 

[brian john]

If you wanted to make a relay power transfer scheme with a buck boost you could, but it would be cheaper to account for the VD in your installation.

 

[Hv&Lv]

The runs are 800' long with 10 lamps scattered throughout? Will it really be a problem to worry about? Have you run the numbers at each light? With 1500 watts at the end of a 800 ft run it shouldn't be a problem with #10.

 

[iceworm]

The runs are 800' long with 10 lamps scattered throughout? Will it really be a problem to worry about? Have you run the numbers at each light? With 1500 watts at the end of a 800 ft run it shouldn't be a problem with #10.

Hv -
I don't have a code book in front of me - however, I recall #10 is about 1.2 ohm/1000. 1500W on 120VAC is 12.5A. For a 1600' roundrip, that's 1.9 ohms --> gives a 24V drop. That seems like a lot for a 120V circuit.

I don't know the layout, so looking at a 1500W load at 800 feed, no more than 5% drop (6V):
That gives .48 ohms for 1600' --> .30 ohms/1000'. That's a #4 CU.

As you noted, with the lamps scattered along the route, one may easily go somewhat smaller

unless I'm missing something (which according to my crew - happens regularly) :blink:

ice

 

[iceworm]

I am working on a project that calls for a number of post lights to be installed. The problem is that the landscape engineer never took into account the problem of voltage drop. The posts require 150 watts each( maximum), some runs according to the blueprint will be in excess of 800 feet from the source. Can I use a buck and boost transformer when necessary? I am going to limit the number of posts on a single circuit to 10 and no more.

Thank you for any information that you may provide

As Iwire noted, BB are not a real good idea.

Something I have done before is to use a 120/480V xfm at the panel, then put a 480/120 xfm at the end of the run. This would let you use 5 ohm/1000' - #14 CU would be plenty fat.

Its an accounting problem. Is the fat wire more expensive than the xfms?

ice

 

[bob]

If you use # 10 240 volt 3 wire ckt you should not have a problem if you split the lites up between the conductors.
With all lites at the end of the run the VD is 5% or 12 volts. With the load spread out the VD will be less.

 

[kwired]

Are you still in planning stage or have you already installed conductors? If still in planning stage I would be planning for larger conductors or maybe multiwire circuits as it likely will be less cost than dealing with any transformers. If luminaires are capable of operating at a higher voltage that is another thing to look into.

 

[Hv&Lv]

Hv -
I don't have a code book in front of me - however, I recall #10 is about 1.2 ohm/1000. 1500W on 120VAC is 12.5A. For a 1600' roundrip, that's 1.9 ohms --> gives a 24V drop. That seems like a lot for a 120V circuit.

I don't know the layout, so looking at a 1500W load at 800 feed, no more than 5% drop (6V):
That gives .48 ohms for 1600' --> .30 ohms/1000'. That's a #4 CU.

As you noted, with the lamps scattered along the route, one may easily go somewhat smaller

unless I'm missing something (which according to my crew - happens regularly) :blink:

ice

Even with 24 volt drop that will still be 220 volts with what most utilities deliver. Lights aren't as voltage sensitive as other appliances, so he could get by with more IMO. He could go with the CFl's and be even less.

 

[iceworm]

Even with 24 volt drop that will still be 220 volts with what most utilities deliver. Lights aren't as voltage sensitive as other appliances, so he could get by with more IMO. He could go with the CFl's and be even less.

HV -
I don't know what the lighting spec is. I don't know if the lights are carbon arc, cfi, LED, arc-powered chemical luminesance, laser excited flux capacitors - heck, they could even be incandescant. I don't know the layout - distance from the panel to first light, distance between posts. Neither do the rest of us.

And that's 24 volts drop on 120V nominal - which would give 94V. If they are incandescents, that's pretty dim - but they would never burn out.

As noted by others, one might wish to check the specs on the fixtures for the voltage - could be lower voltage is okay.

However, you have already given the answer:

... Have you run the numbers at each light? ...

Why guess? Check the fixture voltage spec, pick a wire size, calculate the drop at each fixture. If it is in spec for the fixture, great. If not bump up the wire.

And yes, a 3-wire ckt could easily take less copper. 1500W on 240V is only 6.3A. For #10, 1600', that, only 12V or 6V per side - not bad. Of course if lights on one phase burnout, the voltage will go down on the side with none burned out (minorly trickey, but true)

I think like the "laser excited flux capacitors" the best. :roll:

All I've said is true (As long as I didn't write something different than I'm thinking). And yes, I'm having fun with this one.

ice

 

[iceworm]

... I would be planning for larger conductors or maybe multiwire circuits as it likely will be less cost than dealing with any transformers. ....

Uhhhh k -
I promise, I'm not being mean - but have you ever priced out a couple of small xfms? Its just an economics problem. No reason to guess.

ice

 

[Hv&Lv]

HV -
I don't know what the lighting spec is. I don't know if the lights are carbon arc, cfi, LED, arc-powered chemical luminesance, laser excited flux capacitors - heck, they could even be incandescant. I don't know the layout - distance from the panel to first light, distance between posts. Neither do the rest of us.

And that's 24 volts drop on 120V nominal - which would give 94V. If they are incandescents, that's pretty dim - but they would never burn out.

As noted by others, one might wish to check the specs on the fixtures for the voltage - could be lower voltage is okay.

However, you have already given the answer:


Why guess? Check the fixture voltage spec, pick a wire size, calculate the drop at each fixture. If it is in spec for the fixture, great. If not bump up the wire.

And yes, a 3-wire ckt could easily take less copper. 1500W on 240V is only 6.3A. For #10, 1600', that, only 12V or 6V per side - not bad. Of course if lights on one phase burnout, the voltage will go down on the side with none burned out (minorly trickey, but true)

I think like the "laser excited flux capacitors" the best. :roll:

All I've said is true (As long as I didn't write something different than I'm thinking). And yes, I'm having fun with this one.

ice

Yea, I was thinking 240 volts, not 120. But hey, I got the drop right!:lol:

For some reason I can't get 240 lights out of my head...:blink:

I'm running some lights similar to what is described. They will be 240V 200 Watt HPS, 5-6 in an 8-900 ft run down a driveway. I am installing kits in these. They used to be at a McDonalds and are 1000W Merc. Vapor now. I will end up with 5-6 1000Watt "kits" now...Something else to clutter the shop.