How can I wire 7 outdoor posts correctly?

Question

I've seen a few posts on how to wire a single post/column for lighting outdoor but I can't find anything that relates to multiple posts/columns.

I have 7 posts/columns outdoor and I'd like to add lighting at the top of each post. These posts/columns will be used with a fence (in case you are trying to visualize this).

So far this is what I understand I need to do in a nutshell:

• Dig a trench of 18" and bury wiring with PVC piping
• Use existing outdoor GFCI and extend your wiring from that outlet as long as you are not overloading the circuit
• Use a wiring hub that runs power from the outlet being used to the main hub input and then have separate outs from the same hub running to each lamp that will go to each post/column

Here is where I need some guidance:

• What is a good hub to use outdoor? When searching online, I only find extension cords hubs. This isn't what I need. Does it have a different/formal name?
• My run from the outlet at the house to the hub by the posts/columns would be about 60 feet. If I position the hub midpoint of all posts/columns, I have about 40 feet each way (left or right) to the furthest point to supply cable to each lamp on each post/column. Do I need some sort of amplifier so that I don't experience voltage drop? If so, which one and how do I introduce this?
• I've read that looping or daisy chaining just makes it more complex trying to maintain adequate voltage (evenly) on all post so a hub is recommended. Is this correct?

I have a basic understanding of electrical and wiring. I've done some smaller projects at home so tackling this isn't a concern. I'd just like to know what are the right components I need to ensure this is done correctly

Answer 1

A few specific points:

• Use existing outdoor GFCI

Because this is outdoors, it needs to be GFCI protected if there are any receptacles in the circuit outdoors. As noted by Harper, a circuit used only for lighting does not necessarily need GFCI protection. But the original question mentions a receptacle, so we'll consider GFCI to be a requirement. If you can actually put the GFCI protection inside the building (e.g., either at an upstream receptacle or using a GFCI breaker instead of a plain breaker), that will eliminate exposure of the relatively sensitive GFCI electronics to wind/rain/etc. and generally make it last longer.

• Use a wiring hub

That sounds to me like computer networking lingo. In the case of simple lighting, all you are connecting is power (hot/neutral/ground). A "hub" is simply a junction box that has all the wires connected to it - in this case "all in one" would be 1 in, 7 out = 8 x 2 = 16 wires (plus grounds) which is not a big deal. If your "hub" is simply a box at one post then it is 1 in, 3 out (1 to left, 1 to right, 1 to light in the same post) and the other posts just have 3 sets of wires - 1 in, 1 out, 1 to light in the same post (except for the post on each end). Nothing "special" - just ordinary wiring.

• Do I need some sort of amplifier so that I don't experience voltage drop?

Voltage drop depends on both distance and current. Using an online calculator I get 0.42% drop (== "nothing") on 100 ft. of 14 AWG with 1 Amp load. With a 10 Amp load, it is a more significant 4.21%, and switching to 12 AWG with 10 Amp load gives 2.65% (which is not "nothing" but still quite low).

FYI, while 14 AWG is plenty for this type of circuit, if the breaker is a 20 Amp breaker then you must stick with 12 AWG (or larger) wire or replace the breaker with 15 Amp. If this circuit is shared with receptacles as described then if it is 20 Amp go with 12 AWG and keep the breaker 20 Amp so that you don't limit your receptacle loads as much with the extra load of the lighting.

Bottom line: with the distances you are talking about and modern LED lighting, this is just not much of an issue. If each of the 7 posts has a 60 W LED fixture (that is a LOT of light), that is 1/2 Amp per fixture = 3.5 Amps total. So unless you are going to waste energy on halogen floodlights, voltage drop is really not a problem.

Answer 2

Since you are planning on using PVC conduit (this is different than PVC pipe) I would use thwn wire, (most thhn wire is dual rated as thwn or for use in a damp wet location). You would run your conduit to each fixture and daisy chain all the fixtures. I have seen folks run 1 pipe up and 1 back down to make the wire pull easier but I just use a T and 1 pipe to each fixture both methods are legal I think a single pipe looks cleaner.

Answer 3

Hubs are not a thing in mains electrical wiring. All your splices need to be inside junction boxes, and those junction box covers need to be accessible without tools. You can't bury them, for instance.

Realistically you will probably need to bring conduit up to each pole base, going from pole to pole, and make the splices inside the pole base. Most poles provide an access point for this.

As far as voltage drop, your fears are unfounded.

Let's presume absolute worst case of the following: 120V lighting (use 240V)... 60 watt lights (which is an insane amount of light in LED) ... 300 foot string ... and we carry all the power all 300' (which doesn't actually happen)... our voltage drop works out to 4.55%. That is perfectly fine. In practice it will be half that.

If you bumped to 240V lighting it would be 1/8 that. (lighting doesn't need GFCI unless it's near a water feature like a pond, hot tub or pool).

Voltage drop is really not a problem unless you're burning six 400-watt sodium lights or something, but even that would be 6.31% at 240V, actually half that: very acceptable.

But even then. Let's say you want twelve. Okay. You're in conduit. Just run 2 more wires so now you have 2 circuits. Every other light goes on a different circuit. Done. STILL not enough? Run 3 circuits. Run 4. You hit a hard limit at 4 circuits.

Wait. You need more still? Okay. Dump the sodium lights and go with LED lights which cover the same space at 1/3 the power because they are much better-aimed. You can support about 70 of those.

More STILL? Okay, bump the conduit to 3/4" and the wire to #10. Now you can push the wires to 16A breaker limits instead of the 10A we were holding back at, and still have sane voltage drop. So 15,360 watts of lighting.