Should I use a GFCI breaker or receptacles for my shed run?

Question

In my question about running a circuit to my backyard shed, a discussion arose in the comments about whether I should use a GFCI breaker or have the convenience outlet be a GFCI. Instead of debating it in comments, I thought I'd ask a new question where the answer will be more obvious and findable for future generations.

To recap the situation: I'm running a single circuit out of my sub-panel to my backyard shed for lighting and 1 convenience outlet. This is a storage shed, not a workshop, so there will be only the 1 outlet and loads will be minimal.

My plan was to use a GFCI breaker which will allow me to run conduit with only 12" of cover according to Row 1, Column 4 of table 300.5.

However, it was suggested that I not use the GFCI breaker since that would put all the lighting under GFCI protection. Instead, as I understand it, the recommendation is to use a standard breaker and use a GFCI outlet for the convenience outlet. As I understand it that would put me in Row 1, Column 3 of table 300.5 and require 18" of cover over my conduit. I'm not certain that this suggestion was made with the full recognition that the lights are plug-in, not hard-wired or if that would make a difference.

Obviously, less digging is better than more digging, so I'm all about needing only 12" of cover over my conduit. I'm pretty sure a GFCI receptacle is cheaper than a GFCI breaker and saving cash isn't a bad thing either. However, if there are repercussions of running the lights with GFCI protection that I'm not aware of, the extra work and money saved is worth it.

Bearing in mind that the lights I'm planning on using are plug-in and are not hard-wired, the question is:

What is the reason for not running the lighting in the shed off of a GFCI breaker?

If the reason is simply "that's what code states" then I'll meet code. If there are preferences, concerns, and considerations but lighting on GFCI protection is allowed, I'd like to know what things I need to consider before I determine which route to take.

Note, I'm looking for reasons for/against, code implications, general concerns, etc. i.e., it appears that I can spend a few extra bucks to do less digging and that would be my preference, but if there are significant concerns, I'll dig a deeper trench and throw the few bucks at the kid to have him put his back into it.

Answer 1

Because if an appliance trips the GFCI breaker, there go the lights

The issue with having your whole shed on a GFCI consists of two parts:

1. some things (power tools, hot things) can pose a stored-energy hazard after shutdown for a little while
2. tripping the GFCI breaker will plunge you into the dark as the lights will have to be on it as well

Being in the dark around a stored energy hazard, such as a spinning saw blade, is bad, so we don't want the lights to go out if that device malfunctions and trips the GFCI. Furthermore, with the GFCI tucked inside the shed, that keeps it reasonably protected from the weather; this isn't an issue for most folks, but can be if your breaker panel is outside (say, on a meter-pole).

Besides, the difference between 12" and 18" burial depth isn't significant in terms of trenching costs as far as I know; if you really care that much about trench depth, you're better off using RMC and matching non-threaded fittings, as that gets you down to 6" of cover anyway.

Answer 2

In my area, a few years ago, I ran a conduit in a trench to an outbuilding and didn't get the trench quite deep enough for the inspector, so he wanted GFCI protection in the panel supplying the run. I think it was about 14" deep.

Your situation sounds pretty simple. Will this be inspected? But if not, you sound as if you want to do this according to code anyway. So I'd run a conduit in a little over 12" deep trench and protect it with a dual function (GFCI and AFCI) breaker in the sub-panel.

Without running 2 circuits separating lighting from outlets, if you tripped the breaker, the light would obviously go out. I doubt that would be the end of the world, but up to you. If you ran single wire such as THHN or THWN it would be easy to make it into a MWBC with just one more wire. You would have two outlets in the shed, one for the lighting and the other for the convenience outlet, 2 hots, a shared neutral and of course a ground. You don't need separate grounding electrodes (rods) in this case at the shed. The hot legs would need to be on opposite poles in the sub-panel with handle ties on the breakers. hmmmm....does that work with dufi breakers? Harp? you know?

Answer 3

In my opinion, the GFCI Breaker offers the highest degree of safety. The point of GFCI is to protect any user in areas that can become wet. In the event you decide the lighting is not adequate and decide to replace the light with a droplight, anything plugged into the droplight would not be protected if the convenience outlet is the only protected supply. Protecting at the source not only protects you in the shed itself, but offers protection all the way across the yard. If someone in the future decides to dig a trench, put in a fence pole or drive in a Horseshoe stake for that matter without knowing there is a service below the only result would be a dead toolshed, not a resident.