AC and DC wiring in same conduit?

miket · August 2009

Can this be done?

Specifically, two 6 gauge 90c wire for 120vac for my 4kw inverter, and AWG 8 gauge, 48 volt dc PV input wiring, (2 pos. and 2 neg plus ground).

Signal wires for trimetric will go in the same consuit. I'm using schedule 40 1 1/2" inch grey PVC.

Conduit is buried for about 8 feet between house and garage.

PV arrays are on top of house.

Inverter and batteries are in garage and Main AC distribution is to the house.

thanks

Mike

niel · August 2009

Re: AC and DC wiring in same conduit?

2 things i see here are 1> keep the dc and ac circuits separate as meaning in their own conduits and 2> doubling of the dc component wires is not to the nec's liking either unless you have 2 separate strings being fed back to the inverter.
you may want to check the voltage drop calculator sticky in general solar topics
http://forum.solar-electric.com/showthread.php?t=29
to see what gauge would be better for whatever wire run length you'll have for you may not need the higher gauge. i can't say without knowing the total length the + and - wires will be when added together and at what current.

tallgirl · August 2009

Re: AC and DC wiring in same conduit?

niel wrote: »

2 things i see here are 1> keep the dc and ac circuits separate as meaning in their own conduits and 2> doubling of the dc component wires is not to the nec's liking either unless you have 2 separate strings being fed back to the inverter.

I went through this discussion once with the Master Electrician I sometimes work under, and my recollection of Code is that so long as the insulation is rated for greater than the highest voltage in the pipe, there is no reason not to put them all in the same piece of pipe, provided the proper derating is done.

That said, often by the time the conductors are derated it makes sense to get them OUT of the same piece of pipe.

In other words, save the time running numbers and get a shovel and start digging. Unless it's impossible.

Cariboocoot · August 2009

Re: AC and DC wiring in same conduit?

tallgirl wrote: »

I went through this discussion once with the Master Electrician I sometimes work under, and my recollection of Code is that so long as the insulation is rated for greater than the highest voltage in the pipe, there is no reason not to put them all in the same piece of pipe, provided the proper derating is done.

That said, often by the time the conductors are derated it makes sense to get them OUT of the same piece of pipe.

In other words, save the time running numbers and get a shovel and start digging. Unless it's impossible.

Of course you can always get a "gung-ho" inspector who comes along and tells you to take it all out and do it the other way (this applies to whichever way one does whatever).

Check with the local authority and try to get approval before you do all that work.

BB. · August 2009

Re: AC and DC wiring in same conduit?

I am not sure I am understanding your wiring... Is this a Grid Tied, Hybrid or off-grid system?

If you are trenching anyway--I would put them through two different conduits--and I would add a big old piece of ABS (4" or larger) to allow you to pull alarm wires, Trimetric, networking, etc.) wires later. use large right angles, or two 45 degree angles to make the 90 turn (and make it easier to pull).

-Bill

halfcrazy · August 2009

Re: AC and DC wiring in same conduit?

You can mix ac and dc as long as the wire is all rated for the highest voltage in the pipe. The only thing i would be worried about is the trimetric cable picking up noise i like to have my data cables in a separate conduit if possible

tallgirl · September 2009

Re: AC and DC wiring in same conduit?

Cariboocoot wrote: »

Of course you can always get a "gung-ho" inspector who comes along and tells you to take it all out and do it the other way (this applies to whichever way one does whatever).

Check with the local authority and try to get approval before you do all that work.

Never heard of an AHJ insisting more wires had to go into fewer pipes. But definitely seen them insist my otherwise properly rated wires in an otherwise Code compliant install had to be redone.

The inspectors in Austin are a pain. Thank G-d I don't live in Austin.

BB. · September 2009

Re: AC and DC wiring in same conduit?

That is why I was asking what kind of system it is...

Generally, it is a good idea to keep physical isolation (and many be a code requirement--I don't recall for sure) to keep separate power systems separate in the wiring path too...

If, for example, this is a Grid Tied (or Hybrid) System with solar panels and grid connected AC power--the GT inverter has a barrier between the DC and AC sections of the inverter, and that isolation should be maintained in the wiring path too. Can help reduce the risk of surges from one side (like lightning) from coupling into the other side.

Also--this would apply to isolating signal wires (alarm, computer communications, etc.) from AC Line side (you cannot run both sets in one conduit) from a safety/isolation view point.

If this is an off-grid system, and especially if this is a MSW inverter (Modified Sine Wave), there is usually no isolation between the AC and DC side--so it does not really matter.

If this system is not inpected or subject to NEC--of course, you can do anything you like. It is still a good idea not to bundle parallel lines of vastly different types of cables next to each other... Picking up surges and RF noise are two of the issues that can easily be avoided by separating runs.

-Bill

tallgirl · September 2009

Re: AC and DC wiring in same conduit?

BB. wrote: »

Generally, it is a good idea to keep physical isolation (and many be a code requirement--I don't recall for sure) to keep separate power systems separate in the wiring path too...

We already beat the "different power systems" horse to death. We've moved on to dis'ing inspectors who don't actually inspect to Code.

As for not being inspected, some people may hate the Code, but I try to live by it.

Someone upthread made the comment about using a piece of 4" PVC. Putting control and/or AC cables inside a piece of Smurf (blue flexible non-metalic tubing from Carlon, as I recall) might be one way to do a nice install that would have all the benefits of a single time with the trencher AND keeping inspectors from going crazy. Smurf is its own raceway (FNC), so that might get an inspector to back off. AND I think 1/2" Smurf is rated for 4 conductors that are large enough for a respectable 120/240 split single phase system.

miket · September 2009

Re: AC and DC wiring in same conduit?

What an excellent discussion, thanks!!

I am off the grid, and using a Magnum MS 4024 inverter. As for inspectors, it's not really an issue. I do want to do a proper installation regardless.

I use no 240 power so that is not a player.

I always use only 600 volt, 90c, wire, and Carlon PVC conduit components.

My pv arrays are set up as 2 separate 48 volt strings and connect to a Midnite Solar E Panel. The PV circuit is GFI protected as well.

Everything is properly lightning arrested (FWIW) and my ground connection is less than 2 ohms tested using a hand cranked megger

My conduit (fresh from my surplus pile) is considerably over sized for the purpose. given my very low power loading in the house... lighting and the occasional PC use, even with derating, my AC wiring is very substantially oversized. All my larger loads are in the shop/garage and they have their own distribution panel collocated next to the power center.

Based on the discusssion, I 'll add a second 1" conduit to run the the AC line in and then put the PV DC and ground lines, Trimetric wiring, and the Magnum remote panel cabling in the 1 1/2 inch PVC.

Thanks for the inputs. Inspector or no inspector, a job done right is an an end in itself!

Regards

mike

AC and DC wiring in same conduit?

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