Sub panel to subpanel

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Radecki
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Sub panel to subpanel

Post by Radecki » Sun Jul 16, 2017 3:44 pm

There is a small gazebo near a wide open pond which is 600 feet roughly from our house where the main breaker is but only 450 feet from my workshop where a 100 amp subpanel is installed. I would like to run a few lights and maybe an outlet in the gazebo. Can I wire a sub panel to a sub panel? And if so how many amps should I make the new sub panel and how big of a wire should I have to reach that far without to many voltage drops?

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Aaron
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Re: Sub panel to subpanel

Post by Aaron » Sun Jul 16, 2017 11:44 pm

You shouldn't need a subpanel at all in the gazebo if all you need are just lights and a receptacle or two. Just run some 14/2 cable rated for burial (Type UF in the USA, and Type NMWU-90 in Canada), and bury it 24 inches deep. You need only a dedicated 15A GFCI breaker in the panel feeding the gazebo (either the house panel or the workshop subpanel), and the cable on the gazebo side should just terminate to a regular toggle switch labeled "disconnect" to cut power to the whole gazebo. From that disconnect switch, there you can branch off to receptacles, switches, and lights.

This is the minimum outbuilding code here in my city, but you will want to check with your local authority to make sure this is okay for you.

As for voltage drop, as long as you don't actually draw a sustained 15A, it shouldnt be much issue (say, lights and a stereo or something). If you are concerned about having the power for larger loads, run heavier gauge cable--say 12 or even 10 gauge.

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emtnut
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Re: Sub panel to subpanel

Post by emtnut » Mon Jul 17, 2017 7:28 am

Radecki wrote:There is a small gazebo near a wide open pond which is 600 feet roughly from our house where the main breaker is but only 450 feet from my workshop where a 100 amp subpanel is installed. I would like to run a few lights and maybe an outlet in the gazebo. Can I wire a sub panel to a sub panel? And if so how many amps should I make the new sub panel and how big of a wire should I have to reach that far without to many voltage drops?
You can run as many sub panels as you need, providing you have the capacity.
As mentioned, you really don't need a panel. You could provide a single circuit from the garage.

450' is quite a run ... for a single 15A circuit (assuming non-continuous load) you'd be looking at #6 copper, or #4 aluminum. For that length of cable, the Al is probably your best choice.
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Shannon
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Re: Sub panel to subpanel

Post by Shannon » Mon Jul 17, 2017 7:44 am

Ya I agree with Aaron and Wayne, a sub is not needed for what you are wanting. As Wayne says the aluminum #4 is likely your best bet, this will give you no voltage drop so even in future if you wanna run a few more things you should be fine and should be cheaper then the #6 copper. You could likely get away with a #10 copper but it may be pushing it at that length if you ever have a few things added??
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Aaron
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Re: Sub panel to subpanel

Post by Aaron » Mon Jul 17, 2017 11:41 am

If you do run the heavy #4 aluminum conductors, you're going to need to terminate it at a true disconnect switch or subpanel (as you initially planned) on the gazebo side. You're also going to need to drive down two 8-foot length 1/2" diameter ground rods at least 6' apart on the gazebo side to establish a building ground-bonding system. Between the disconnect switch and the two ground rods, you run #6 copper.

The trenching is the biggest part of the job. Be sure to contact your local utility location service. They will come out and mark where buried utilities (gas, water, sewer, power, communications) are to ensure you have a clear path for your trench.

You need at least a 24" deep trench. After laying the cable and refilling halfway (12") with earth, run some red plastic warning tape with the words "buried electric line" the length of the trench. Then finish filling.

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Re: Sub panel to subpanel

Post by Shannon » Mon Jul 17, 2017 2:43 pm

No matter what you do use a permit
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emtnut
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Re: Sub panel to subpanel

Post by emtnut » Mon Jul 17, 2017 5:53 pm

Aaron wrote:If you do run the heavy #4 aluminum conductors, you're going to need to terminate it at a true disconnect switch or subpanel (as you initially planned) on the gazebo side. You're also going to need to drive down two 8-foot length 1/2" diameter ground rods at least 6' apart on the gazebo side to establish a building ground-bonding system. Between the disconnect switch and the two ground rods, you run #6 copper.


You need at least a 24" deep trench. After laying the cable and refilling halfway (12") with earth, run some red plastic warning tape with the words "buried electric line" the length of the trench. Then finish filling.
There's another difference in our codes !
We don't have to do the ground rods up here, even for a separate building.

In the OPs case, up here he could just mount a junction box and put an al/cu connector, and run the lights and receptacles.

I did hear that in the US, for a 120V feed you only have to go trench down 12". I'm not sure on that, as we don't have that provision up here :?
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Aaron
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Re: Sub panel to subpanel

Post by Aaron » Mon Jul 17, 2017 10:51 pm

emtnut wrote:There's another difference in our codes ! We don't have to do the ground rods up here, even for a separate building.
You don't need ground rods at all?!?

What is your ground source? Because you really can't rely on incoming water lines anymore. In new developments here I've seen them run 1" diameter PEX from the street (no joke!).

Now, unless your plumbing is all nonmetallic, plumbing is something to get grounded, not *be* the ground.

As for outbuilding grounds, reestabling a ground remotely is for different ground potentials to equalize out across the whole system.

But if it's not your code then it's not necessary... You'll still have the ground back at it's source, whatever that is.
emtnut wrote:In the OPs case, up here he could just mount a junction box and put an al/cu connector, and run the lights and receptacles.
Seriously you guys don't require any disconnect whatsoever? Wow.

The least you can get away with here in St. Paul is a light switch as a disconnect on an outbuilding. That is, if you run 14/2 or 12/2.
emtnut wrote:I did hear that in the US, for a 120V feed you only have to go trench down 12". I'm not sure on that, as we don't have that provision up here :?
For UF cable (NMWU-90 in Canada) alone you need to be at least 24", and I would surmise that'd be for any non-conduit cable run. Type THHW in Schedule 80 conduit at least 18". I think low voltage need only be 12".

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emtnut
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Re: Sub panel to subpanel

Post by emtnut » Tue Jul 18, 2017 7:21 am

Aaron wrote:
emtnut wrote:There's another difference in our codes ! We don't have to do the ground rods up here, even for a separate building.
You don't need ground rods at all?!?

What is your ground source? Because you really can't rely on incoming water lines anymore. In new developments here I've seen them run 1" diameter PEX from the street (no joke!).

Now, unless your plumbing is all nonmetallic, plumbing is something to get grounded, not *be* the ground.

As for outbuilding grounds, reestabling a ground remotely is for different ground potentials to equalize out across the whole system.

But if it's not your code then it's not necessary... You'll still have the ground back at it's source, whatever that is.
emtnut wrote:In the OPs case, up here he could just mount a junction box and put an al/cu connector, and run the lights and receptacles.
Seriously you guys don't require any disconnect whatsoever? Wow.

The least you can get away with here in St. Paul is a light switch as a disconnect on an outbuilding. That is, if you run 14/2 or 12/2.
emtnut wrote:I did hear that in the US, for a 120V feed you only have to go trench down 12". I'm not sure on that, as we don't have that provision up here :?
For UF cable (NMWU-90 in Canada) alone you need to be at least 24", and I would surmise that'd be for any non-conduit cable run. Type THHW in Schedule 80 conduit at least 18". I think low voltage need only be 12".
I guess that wasn't too clear :roll:

Obviously the main is grounded ... but for a shed, garage, gazebo etc ... we bond back at the panel ;) (Actually we have the choice... ie, if there was no bond wire, we would pound in a rod)

We can run up to 2 15A circuits without a junction box, or disconnect.
For larger, a panel is required, but it doesn't require a main breaker, since it is fed by a breaker used solely to feed that panel.


And I found the NEC ref for the burial depth for 120V ...
"Table 300.5, Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes, you are permitted 12 inches"

EDIT** looks like that code was a reference in 2003 !!
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Aaron
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Re: Sub panel to subpanel

Post by Aaron » Tue Jul 18, 2017 9:19 am

emtnut wrote:I guess that wasn't too clear :roll:

Obviously the main is grounded ... but for a shed, garage, gazebo etc ... we bond back at the panel ;) (Actually we have the choice... ie, if there was no bond wire, we would pound in a rod)
Yeah down here we've gotta have the rods at outbuildings regardless whether there's a bond wire or not. And the main has to be grounded with rods now. No water pipe dependence for ground source.
emtnut wrote:We can run up to 2 15A circuits without a junction box, or disconnect.
For larger, a panel is required, but it doesn't require a main breaker, since it is fed by a breaker used solely to feed that panel.

And I found the NEC ref for the burial depth for 120V ...
"Table 300.5, Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes, you are permitted 12 inches"
Yeah sure enough. That's weird and counterintuitive. I guess the GFCI provision makes the allowance for that shallow depth. Because if you encase conductors in Sch 80, then it's gotta be 18", so you'd think non-conduit cable should be at least that deep, if not deeper.

I think my city still requires the 24 inches for non-conduit buried cable. That was what my inspector expected when I electrified by garage.

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Re: Sub panel to subpanel

Post by emtnut » Tue Jul 18, 2017 7:09 pm

Aaron wrote: I think my city still requires the 24 inches for non-conduit buried cable. That was what my inspector expected when I electrified by garage.
For your garage, it was probably 240V, and more than 20A ;)

I think the reasoning is that a single 15 or 20A circuit that is GFCI'd, isn't really a safety issue.


As we've said before ... The code is a minimum. If I were to wire a single circuit to my garage, I'd probably go deeper as well :mrgreen:
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Aaron
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Re: Sub panel to subpanel

Post by Aaron » Tue Jul 18, 2017 8:38 pm

emtnut wrote:For your garage, it was probably 240V, and more than 20A ;)


Dammit Wayne, youre absolutely right. 240V/50A with 6/3 run.

I am just not thinking at all. Thanks for looking up Table 300.5, by the way.
emtnut wrote:I think the reasoning is that a single 15 or 20A circuit that is GFCI'd, isn't really a safety issue.
Yeah at 12" it really shouldn't be. I'm still a conduit person though for burial. At least between buildings. I'm good abour heavy multiconductor Aluminum getting buried.
emtnut wrote:As we've said before ... The code is a minimum. If I were to wire a single circuit to my garage, I'd probably go deeper as well :mrgreen:
Right, exactly. Although the code in some cases is just right. Like the number of recepts for the kitchen. Not sure I'd do more than required.

I wish the CEC and NEC would get harmonized, honestly. They're already like 95% the same.

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