I'm in the process of running a circuit from the panel in my garage to an equipment area for a koi pond I built. Because of some rock at about 16 inches depth in part of the run, I'm taking advantage of the code allowance for 12" depth for the circuit which will be 20A and GFCI protected. In addition, I'm running it in nonmetallic conduit. There will be a receptacle at the equipment location but I'll also use this opportunity to add one at a nearby patio.

I've dug the trench and installed the conduit, no wires pulled yet. Currently I have an outdoor extension cord providing service to the pond and patio. While traveling, a contractor came by to do some work and plugged in on the patio. They ended up tripping the breaker and couldn't reset it (locked garage) so they left. One of my neighbors later noticed that the pond equipment (life support for the koi, really) was off. He called and we got it started. But this got me thinking that it would be pretty easy to have something in the other outlet trip my pond off.

So, I've decided I probably need to forego the patio receptacle. But I was curious. The way 300.5 is written is says max 20A overcurrent protection and GFCI. I've interpreted this as the total of all wires in the trench/conduit. But, is it possible to run 2 circuits in that conduit if each is less than 20A? I'm guessing not, but I don't really understand the full interpretation of that.



3 Answers 3


I am not a code expert, but my understanding of reading 300.5 is that multiple circuits would be permitted, provided:

  • Each circuit <= 20A and GFCI protected
  • Conduit fill requirements are met (not a big deal for small circuits)
  • Conduit multiple circuit derate requirements are met

The last can be an issue. As I understand it from many previous posts on DIY SE, generally speaking 2 circuits are not a problem due to the way wire current ratings are defined but once you have 3 there can be problems and 4 or more is pretty much guaranteed to require large wires than usual.

Assuming all that to be the case, you should be able to run 2 15A and/or 20A circuits in one conduit. Based on this fill table even 1/2" PVC 80 can handle 5 wires = 2 x hot/neutral + 1 x ground.

You may want to consider metal conduit. With the right type of metal conduit, you can go to 6" depth instead of 12".

As far as GFCI, install it inside the building. That can be a GFCI/receptacle or GFCI only or GFCI/breaker. The GFCI electronics will last far longer (and likely fewer nuisance trips) if installed inside (temperature controlled, no rain) than outside. Every receptacle outside must be GFCI protected, no ifs, ands or buts. Another answer noted the issue of exceptions. Those exceptions are for things like fire alarms and, in some jurisdictions, refrigerators. You don't want to risk a ground-fault problem in an outside water feature - the risk to a human (instant injury or death) is far greater than the risk to your koi, as much as you may love them, if their equipment is temporarily off.

If you do get frequent nuisance trips, try to figure out where/how to better protect the equipment. But at least putting the convenience receptacles on a separate circuit will avoid a nuisance trip on that circuit from affecting the koi pond equipment.

  • 1
    As long as the circuits are <=20A, four is not a problem. With 4 circuits in a pipe, #14 wire derates to 17.5A and #12 wire derates to 21A. Assuming it is not UF cable, but UF cable has no business in sanely sized conduit. Nov 1, 2022 at 21:56
  • 2
    "Every circuit outside must be GFCI protected, no ifs, ands or buts" That's not quite right. Outdoor receptacles must be GFCI protected. There is not a general requirement to protect the wiring with an upstream GFCI - GFCI at the receptacle is valid (if arguably a bad idea due to putting electronics outdoors). However, the OP must implement upstream GFCI coverage in order to be allowed to cover their buried conduit with only 12" of cover instead of the usual 24".
    – nobody
    Nov 2, 2022 at 1:55
  • @nobody You are correct. For example, hardwired lighting fixtures do not require GFCI. Nov 2, 2022 at 2:23
  • That's really interesting. My reading of 300.5 was that the circuit itself required GFCI protection, but then I missed all the rest of this too. I have 1" conduit in the trench now so I should be fine on the fill factor. I just ran this size conduit because my experience was it was easier to pull through and not really harder to run.
    – Chris
    Nov 3, 2022 at 14:59
  • Actually you are probably correct with 300.5 for a shallower trench. I'm referring to general outside gfci Nov 3, 2022 at 15:26

Since this is a life safety device for the koi, it should not be on a shared circuit and should not be on GFCI. How the heck do you do that to a water feature?

Low voltage. You knock it down to 24 volts for transmission to the koi pond. 24 volts is not dangerous and can be around water installations.

I understand that 24 volt aerators are readily available; some are even designed to be fed off solar. (an interesting option coupled with battery; after all what do the poor dears do during a power outage?)

If you can only get a 120V aerator, then you bump it back up from 24V to 120V as close as possible to the pump, and locally derive that 120V, meaning you need a ground spike right there. But make a real effort for everything out at the pond to be 24V.

Note that low voltage is MUCH more sensitive to voltage drop, so be careful about wire sizing. If cost becomes prohibitive, bump up to #6 or even #2 aluminum. The cheapest way to splice aluminum to copper (in a low-voltage regime) is with bare lug-style terminals (look at a service panel accessory ground bar for an example of those, in fact you can get one and cut it up!) You can get them with plastic molded cases around them (Polaris, ILSCO Mac Block, Alumiconn) but that considerably more than doubles the price, and you can just wrap them a whole bunch of layers of electrical tape.

  • 120V is pretty common with ponds. I have another in a different location that's been fed from a GFCI for about 10 years and never had a nuisance trip happen. It feed three devices at a pond (in my filter builds), a pump an air pump and a UV light. None of these is in the pond (like a submersible pump), they are all about 10-20 feet from the pond, depending on the install.
    – Chris
    Nov 3, 2022 at 14:54

There is nothing wrong with running multiple line voltage circuits in the same conduit. You can't run low voltage in the same conduit. You didn't mention the size of the conduit, so you'll have to learn about fill capacities. Having 2 circuits individually protected by GFCIs would minimize the chances of the "life support" for your pond failing. But being realistic, outdoor circuits often have nuisance trips on GFCIs. I'm not sure, but believe it's code legal on critical circuits to swap out a GFCI breaker with a normal breaker if you are getting nuisance trips. I'm not sure if a Koi pond would count as a critical circuit.

  • 5
    I don't think any GFCI event in a pond should be regarded as a nuisance one. If there ARE nuisance trips, (and there aren't .. but if there are) you should eliminate the source of them so that you can provide and have confidence in GF protection in a situation that badly requires it. In other words ... if water is getting where it shouldn't ... that's not a nuisance trip! If there is some pump motor functioning normally but somehow triggering the GFCI ... throw it out, and get one that doesn't.
    – jay613
    Nov 1, 2022 at 16:23
  • I agree that I wouldn't regard it as nuisance. In fact, when people tell me they are getting a nuisance trip on ANY GFCI my first response is "I know it's a nuisance to you but are you sure there's not a problem?" Many years ago I had trips on a hearing device used to keep a hole in ice in the winter. Electrician said "I see nuisance trips like this all the time." I put it on the bench and, yup, there was a current leak. Thanks.
    – Chris
    Nov 3, 2022 at 14:56
  • Nuisance trips are real, folks. I had a Treager smoker and it would frequently nuisance trip the GFCI outlet. I plugged it into another GFCI outlet and it still tripped it. So I ran an extension cord to a non-GFCI outlet and it worked fine. To test, I used one of those old 2 prong to 3 prong adapters (not a good product BTW!) and tested using a digital multi meter between the smoker and a good known ground. Got nothing, zero zip nada. Tried several times and nothing. Of course I removed the adapter so at least the smoker would be properly grounded. ....Just saying....don't dis on me. Nov 3, 2022 at 15:04
  • 1
    ...continuing nuisance trips are a problem because they can result in food spoilage: If a GFCI trips on a freezer or fridge and there's nobody around (think vacation) you could end up with a ruined freezer full of food. I KNOW I KNOW what you're going to say: "It's better than getting electrocuted and dead". If the fridge, freezer were properly grounded, there would be virtually no chance of injury. Let's be a bit more realistic about this subject. I'll get snipped on this for sure, but come on, let's not let the perfect become the enemy of the good. Nov 3, 2022 at 15:18
  • I'm not dogmatic about it, though I try to keep with the code. In my case the receptacles are outdoors so they really should be GFCI and I really should figure out what's tripping them if they trip. As I see it, GFCI is monitoring the difference in current on the hot and neutral and within a time/magnitude it will trip. If you have a device with a large LC circuit that might distort this, it's probably not good for GFCI. None of the devices I have should have an issue. The rare case where I had a trip it was a heater and it was a real fault.
    – Chris
    Nov 3, 2022 at 15:42

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