portable sub panel


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Old 09-15-19, 05:03 PM
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portable sub panel

I am looking to build a subpanel with 6, 15 amp 120 volt circuits. Each circuit in the box would have a breaker and a pair of outlets. My main panel, in the garage, is 200 amps. The difference here is I want the subpanel to be movable around my garage. I would also prefer to have it connect to the main panel via a receptacle of some sort, so I can disconnect it when not in use. Is this possible? What sort of connection and cable would I need to use? I am hoping for a 20 foot cable, to be able to set the box in various spots in the garage.
Thanks for any thoughts on this.
Steve
 
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Old 09-15-19, 05:17 PM
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Welcome to the forums.

I have a sound rental company and have many boxes/panels like that for power distribution.

You could build your box on wheels with a wire rack right on it to roll the wire up. The wire you use to connect it depends on the anticipated connected load. Obviously the higher the load..... the bigger the cable, the connectors and the cost. That panel will be considered a sub panel. I would recommend 6-4 SOOW or SJO rubber cable. The link illustrates that cable. Shop around..... you could find bargains on a bulk piece.
6-4 rubber cable

The plug would be something like...... 120/240v 60A plug
A matching receptacle would be used at the panel on a 2P60A breaker.

This may be a little large for your application. You could look into 8-4 rubber cable with a 50A plug and receptacle. The cable will deliver 120/240v to your subpanel so that three circuits will be on each leg of power.
 
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Old 09-15-19, 07:02 PM
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My only change to Pete's plan would be to use a 50A twist-lock plug and receptacle so you don't have to worry about accidentally pulling out the cord.

But that said, while the concept is fine, I wonder if you really need a moveable subpanel? I'd definitely consider some 15/20A receptacles around your shop with extension cords readily available either from the walls or retractable ceiling mounted ones. That's probably the way I would do it... (though not really knowing your requirements).

Good luck!
 
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Old 09-16-19, 07:27 AM
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Pete and Zorfdt,
Thanks for all that! This gives me a start. Last question: Is there readily-available breaker box that will accommodate both breakers and outlets? Here is my idea of what it may look like. Pete, if you're in the audio business long enough you may recognize these, for which I need the power. One breaker for each stacker.

If the custom breaker box doesn't exist then I can just use a pair of 3-gang boxes for the receptacles, and frame the whole thing together and mount on a small furniture dolly, with space for the cable, as suggested.
 

Last edited by Steve_in_DE; 09-16-19 at 08:25 AM.
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Old 09-16-19, 11:43 AM
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Circuit breaker panels are not "listed" for having additional holes cut into them for receptacles so that idea is out. You could use a general-purpose pull and splice box of sufficient size along with pushbutton auxiliary circuit breakers and single receptacles.
 
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Old 09-17-19, 09:40 AM
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There are prebuilt power distribution boxes that do what you want. For example:
https://www.globalindustrial.com/p/e...i-power-center
But you can get them in almost any size and configuration.

For the home-built route, I usually see a piece of 3/4" plywood used as a backing, where the breaker panel is bolted to, then a collection of 4" square boxes with GFI (or regular) receptacles, with nipples (conduit) connecting them to the panel and screwed to the plywood. (I can't find a picture, but I can sketch it if my description isn't clear enough)
 
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Old 09-17-19, 11:13 AM
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Zorfdt,
So then something (very) roughly, like this?
 
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Old 09-18-19, 09:57 AM
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Very close. 4x4 boxes on short nipples (but giving enough space for the panel cover to not interfere.
 
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Old 09-26-19, 10:45 AM
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Thanks for that. I will get on it and report back when it's built.
I will take a trip to home depot and get:
- a 60 amp 220v breaker,
- a few feet of 6 gauge wire to run from the breaker,
- a 60amp 220v outlet and connector to be mounted nearby the main box,
- 20 feet or so of SOOW cable,
- and everything it takes to build the box you've drawn, including (6) 15 amp 120v breakers for the receptacles.
 
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Old 06-07-20, 09:06 AM
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I am revisiting this project. I finally have actual use for the portable box I am looking to build, so it's time to get going on it.

At this point I am looking to use an existing NEMA 14-50 outlet, which lives a couple of feet from the main breaker panel, on a 50A 240V breaker, as the power source for my panel. Is it still correct to build a six 15amp breaker subpanel (3 per side) using this as it's source?

I am looking at a 20 foot length of 6/4 SOOW between the outlet and the box, as before.
 
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Old 06-07-20, 10:11 AM
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If you are going to have a portable subpanel then by definition you will need several 60 amp or whatever receptacles spaced out around the room for that subpanel to move to.

An alternative would be circuits in the wall with daisy chained 240 volt or whatever receptacles (one size/amperage per branch circuit) going all around the room and no portable subpanel. Some of these branch circuits would be the usual 20 amp 120 volt variey.t
 
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Old 06-07-20, 12:20 PM
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Still sounds like a good plan! Your NEMA 14-50 receptacle provides 240/120, so you're good!
 
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Old 06-07-20, 06:04 PM
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"...Your NEMA 14-50 receptacle provides 240/120, so you're good!... "

Ok thanks, Zorfdt. I read at this webpage that a 50 amp, 240 volt box provides 50 amps at 120 volts per side (which seems like common sense but I needed to confirm), so then my box with 3, 15 amp 120 volt breakers on each side ought to hold up to inspection.

 

Last edited by Steve_in_DE; 06-07-20 at 06:05 PM. Reason: added link
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Old 06-08-20, 10:01 AM
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...my box with 3, 15 amp 120 volt breakers on each side ought to hold up to inspection
Yup! The number of breakers or adding up their max capacities doesn't matter in terms of the power available. If you look at your main panel, I bet the breakers add up to more than 200A. What matters is the load. You obviously can't plan on more than a 50A@240v set of loads off your sub panel. But you could easily add two 50A welder circuits, assuming both will not be used at the same time.
 
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Old 06-10-20, 10:22 AM
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If you look at your main panel, I bet the breakers add up to more than 200A.
Taking a look at my 200A main panel, I see that EACH SIDE adds up to a bit more than 200. Then I note what's on each side, and I see that many of those breakers are pretty underutilized. Mercifully, this subpanel project adds nothing to the main panel as I will be sharing the existing NEMA 14-50 outlet with other things - none of which is used 24/7 or even close.

This makes me wonder - is there is a device that can measure the load on one side of a breaker box? I know for a single outlet there's a gadget called a "kill-a-watt" which can tell you the current load in watts and amps. Is there something for bigger jobs? The kill-a-watt neds to be plugged into the outlet and the devices being measured are plugged into it. Not sure how the panel-sized device would work.
 
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Old 06-11-20, 10:17 AM
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is there is a device that can measure the load on one side of a breaker box?
Of course!

A clamp-on ammeter is a good testing tool to measure current through a wire.
Or if you're looking for a snazzier monitoring solution, Sense has a similar clamp-on ammeter, but a whole app, wifi, and all the bells and whistles someone might want.
 
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Old 06-12-20, 07:39 PM
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I have the box just about assembled - I thought I would share a photo of it before I install the outlets. If you see anything glaring please let me know. Thanks to all for your help!



 
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Old 06-13-20, 05:43 AM
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A few things:
* Check to see if the cover plates fit. With close nipples, you might not have enough space for the plates.
* Consider using an extra nipple to connect each box. Obviously it's not required electrically, but the second nipple will help keep the boxes from twisting. I forget if you said you were mounting this to plywood or something, that would resolve the issue too.

Looks good!
 
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Old 06-13-20, 03:18 PM
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Cover plates: Yes, standard-issue metal plates fit. It's close but they work.
Securing the boxes: Yes I am planning on mounting the assembly to plywood, and mounting it all diagonally on a dolly. I will put a screw or two through each outlet box in addition to the breaker box.
 
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Old 06-13-20, 03:25 PM
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I have been debating (with myself) about the topic of getting this box inspected. It's not permanently wired to the house or the main panel, and no additional breakers were added to the main panel. One could look at it as a severely overgrown waber strip! I don't mind, of course, and I will in fact be getting a permit & inspection for other things I need to do with the main panel - adding a breaker and outlet for a heat pump in the garage. Maybe I can include this subpanel on the list.
 
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Old 06-13-20, 05:36 PM
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I don't know that a code inspector would inspect it. Since it's not wired to the house, and therefore not covered by NEC or your local building codes, it's likely they won't want to sign off on it. I would also be concerned that he doesn't understand the need for it - requiring you to simply install 6 new hard-wired circuits.

I'm usually a believer in focus inspectors on the minimum scope possible.
 
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Old 06-09-21, 02:14 PM
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Better late than never, here are pictures of my functioning "portable power drop", and the rig it is running. The plug for the unit shares the big outlet with my car charger. Thanks much for all the input given here; I literally could not have accomplished this project without the nudges in the right direction.






 

Last edited by Steve_in_DE; 06-09-21 at 03:30 PM.
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Old 06-09-21, 04:13 PM
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Ahhhh...yes. The 3x5 projector setup.

Good job.

Good friend of mine was head of the A/V dept at Ciba-Geigy pharmaceuticals. They became Novartis which I'm sure you've heard of. He had done many shows with racks of projectors. Typically 4x4. Also used the GE Talarias. They were the first large venue light valve projectors at $100 grand each. The good old days.
 
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Old 06-09-21, 04:44 PM
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PJmax,
Are you talking about Robbie Z? I worked for him back in the day, and alongside him later, at Novartis for years.
 
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Old 06-09-21, 05:14 PM
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Yup....one in the same. Small world.
 
 

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