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Question about installing a sub panel off another sub panel

Question about installing a sub panel off another sub panel

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  #1  
Old 01-17-14, 09:40 AM
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Question about installing a sub panel off another sub panel

Hi, I just first off want to say I'm definitely not a pro electrician but have some knowledge and have done some wiring, etc.

I am renting a warehouse space that does not have it's own electric. The neighboring unit used to use the space as an office, so they wired it up with lights and outlets but the line feeding it runs back to their breaker. I don't want to use their name but they are an electrical contractor. I don't know the right term but they do "outside" work, nothing inside.

I talked with them and they agreed to flip the breaker back on so I could use it. Very nice people. The problem is I need more juice. The line they have me on is a 20amp breaker, which can probably run my 110v 20amp MIG welder. But I also want to run a 220v single phase 50amp TIG welder. There's another line running off their breaker to my unit which is a 30amp breaker, and it ran a wall mounted heater. The heater didn't work when I tried it, I'm not sure if the breaker/circuit is bad somewhere or if the heater is broken(will figure that out later).

Another problem is if I happen to trip the breaker, I have no access on the weekend to turn it back on.

So what we have in their panel is a 20amp breaker(for my unit), a 30 amp breaker(for my unit), and I noticed there was at least one other 20amp breaker not in use, not even wired up. Could I install a say 70amp(or whatever may be necessary) breaker taking 4 slots, and run a heavy line(whatever gauge required) about 20ft to my unit, and install another panel with a 50amp(for the TIG), 20amp(for the MIG), and another 20amp(for lights, outlets, etc) in my unit?

So basically have a large breaker in their panel always on, and have my own panel with individual breakers for my use. They would let me do it, if I pay for all the materials and do the work. So the question is, is this acceptable or will it not work?

I know I may need to provide further info, like what size panel it is, what the main breaker is, etc. and I can find that out. Please let me know what info I need to provide for you to help me out. Thanks!
 
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Old 01-17-14, 09:56 AM
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This is commercial work and would require permits and inspections. Also since the building is not your you would also have liability issues. Talk to your landlord.
 
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Old 01-17-14, 10:37 AM
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The landlord is fine with it.

I understand, but I guess my question is is this an acceptable way of wiring this unit?
 
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Old 01-18-14, 03:57 PM
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Yes, a subpanel may be run off of another subpanel.

That would actually be the "cleanest" way of doing this project since there could then be just one feed from the next rented space to your rented space.

You would sever the 20 amp circuit going back to the next space and wire that into your new subpanel.

In a typical residence with attached garage, it is not unusual to have both individual 15 and 20 amp branch circuits and a later-installed heavier feed going to that garage, the latter going to a subpanel.

But with separately rentable spaces, it is better to have just one feed. Less confusion later if/when your unit gets a separately metered service.

For separate buildings, for example including a detached garage, you are permitted to have only one feed of any given kind between any two buildings. A 120 volt feed and a 120/240 volt feed are the same kind. A 120 volt feed and a 480 volt feed are different kinds.
 
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Old 01-19-14, 08:35 PM
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Could I install a say 70amp(or whatever may be necessary) breaker taking 4 slots,
Sounds like a solution. You'll only need two vertically adjacent slots though, not four.

One question for you to research: Is the service to the building single phase 120/240V, 3-phase 120/208V or 3-phase 277/480V?
 
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Old 01-20-14, 08:33 AM
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Thanks for the feedback. I'll get in touch with the owner and the other tenant again in the upcoming weeks and find out what the service to the building/his panel is. I'm assuming single phase 120v/240v because I told him I needed 220v and he said I'd have to get that run from the street (he was assuming I needed 3 phase I believe). I then told him I only needed single phase 220v and he said I could get that run from the pole that is about 75ft from the building. I assume that's what he has run to his panel. Will find out and post back. May be a few weeks or so.

Assuming this all works out, and I install a 70amp or so breaker to run from his panel to another subpanel in my unit, what gauge wire would be required for that ~20ft run? I'm thinking 70amp should be plenty for my unit because the TIG (50amp) will never be running in conjunction with anything else other than a radio, lights, etc that I can run off another 15 or 20 amp breaker. Then I'd have one more 20 or 30 amp breaker to run my MIG which again would never run in conjunction with anything other than lights, radio, etc.
 
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Old 01-20-14, 09:33 AM
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Without knowing the existing loads on the panel you are getting power form there is no way to know if your planned load will overload the original panel. A load calculation is needed. If the voltage is different than what is already in the building you will need to add a service grouped with all the other services.
 
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Old 01-20-14, 05:18 PM
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Ok so maybe when I talk to them again I can figure out what they are using and do a load calculation.

A load calculation is simply the total watts to be fed off the panel, correct?

So for my unit I'd have:

TIG 50amp x 240v = 12000
MIG 20amp x 120v = 2400
Lights, etc 20amp x 120v = 2400

Total = 16800

Safety factor 1.2 x 16800 = 20160 watts

Is this correct? This would mean I'd need a 90amp breaker at their panel with two 120v lines(or one 240v line?) feeding my unit's sub panel, right?

Then I assume I compare my units loads(plus their loads) to the service feeding the panel. How do I figure that out? Do I tell that by the main breaker? So if it's say a 100amp breaker and there's two 120v lines feeding it(which I believe for example is how my house is fed) it'd be 100 x 240 = 24000 watts?

Why do some people say 110v and 220v vs 220v and 240v? Sorry I know for you guys that know what you're doing that's probably a very dumb question.
 
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Old 01-21-14, 09:12 AM
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I'll get in touch with the owner and the other tenant again in the upcoming weeks and find out what the service to the building/his panel is. I'm assuming single phase 120v/240v because I told him I needed 220v and he said I'd have to get that run from the street (he was assuming I needed 3 phase I believe). I then told him I only needed single phase 220v and he said I could get that run from the pole that is about 75ft from the building.
So, the other tenant really doesn't know what he has either.

Assuming this all works out, and I install a 70amp or so breaker to run from his panel to another subpanel in my unit, what gauge wire would be required for that
Why do some people say 110v and 220v vs 220v and 240v? Sorry I know for you guys that know what you're doing that's probably a very dumb question.
And you are really not sure what the other tenant has or what you are doing.

Is this correct? This would mean I'd need a 90amp breaker at their panel with two 120v lines(or one 240v line?) feeding my unit's sub panel, right?

Then I assume I compare my units loads(plus their loads) to the service feeding the panel. How do I figure that out? Do I tell that by the main breaker? So if it's say a 100amp breaker and there's two 120v lines feeding it(which I believe for example is how my house is fed) it'd be 100 x 240 = 24000 watts?
This is all why you shouldn't be trying to do any of this. You've already been told that this is commercial work and will require permits and inspections and you really have no clue what you are doing. You should find a licensed contractor who can figure this out and install it all for you. Most likely a contractor can look at this little project and figure out how to do what you want within 20 to 30 minutes and it will be right.
 
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Old 01-21-14, 09:16 AM
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You just cannot make assumptions about the voltage or number of phases available. Many commercial building have different systems some include 277/480 3 phase.

This is not as simple as you are trying to make it.
 
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Old 01-21-14, 11:07 AM
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Wow. I completely understand that I am not currently knowledgeable enough on the subject to do this myself. I've been on many many forums and often get responses like this about how I need a professional to do it. Nothing against professionals and contractors, but there are so many of them out there(in all trades) that do horrible work. Not saying all are that way, but when you don't know what you are looking at it's hard to tell who is good and who is bad.

I've done previous work after much research and posted pictures and have had contractors on forums tell me how good my work was. I'm not the idiot who is going to just start swapping out breakers and running wire without a clue. I am trying to research and see if I can learn the information needed for the job, and do it correctly. If I can't, I'll hire someone else.

Regardless of who performs the work(another contractor) or me(the owner, who is willing to do this), permit will be pulled and inspection done. I assume the owner can act as the contractor even without being licensed. I might be wrong about that.

I'm just mostly surprised that on a DIY forum I'm getting told not to do it myself lol. I understand a lot of DIY work is crap and unsafe, but I'm trying to do it the correct way.

I've fixed a lot of DIY work that was done incorrectly at my house from the PO, it is very frustrating. Some of it electrical, which is where I began to learn some of this. The more I learn about it the simpler and easier it is. Just like anything else. I'd rather learn how to do it than pay someone else. Give a man a fish he eats for a day, teach him to fish he eats for the rest of his life.

If it's really out of reach for me then I'll hire someone else but it really doesn't seem that difficult. Seems like I just need to figure out what the service is coming in to the unit, and what the loads are being fed off his panel.

When people ask me "stupid" questions on other forums like "what oil should I use in my truck" or "where's the drain plug on my motorcycle", I don't tell them they are incapable and should go to jiffy lube or the dealer. I educate them on what they need to know, and the things to watch out for and how they could cause damage, warranty issues, etc. And tell them if they are not comfortable with it then maybe paying someone else is best for them.

Someone told me I was incapable of running a line to my garage for my welder. After talking to some nice helpful people it turned out to be extremely easy. That person just wanted me to pay them to do it. I'd never recommend them now, but I'd highly recommend the other people that helped me out. They were actually concerned with helping me rather than making a quick buck.
 
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Old 01-21-14, 12:05 PM
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Doing electrical work does not carry the same consequences as screwing up an oil change. Also if this was on a house you owned you would probably be getting much more information. I do not know of anywhere that allows commercial work to be done by a renter or even the landlord without hiring a licensed and insured professional. I understand you want a reputable and knowledgeable contractor. This is where references and referrals come into play.
 
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Old 01-21-14, 04:36 PM
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I'm just mostly surprised that on a DIY forum I'm getting told not to do it myself lol. I understand a lot of DIY work is crap and unsafe, but I'm trying to do it the correct way.
DIY electrical work does not include work on systems installed in a property you do not own or otherwise have a right to do work on. It does not include work that requires a permit and inspections until that permit has been issued to the person doing the work. It almost never includes work on commercial electrical services.

When you have the permit in hand we'll consider answering technical questions about the project. Given that, it will likely save you both time and money to hire a licensed contractor to do this work.

Why do some people say 110v and 220v vs 220v and 240v? Sorry I know for you guys that know what you're doing that's probably a very dumb question.
There aren't any dumb questions.

Once upon a time, I'm told - it was well before WWII - power was supplied at 110V line-to-neutral and 220V line-to-line. Since that time, the standard residential service in the U.S. has been a 120/240V single-phase service. That's 120V line-to-neutral and 240V line-to-line. For some reason you still hear the old references sometimes. Just habit, or not understanding the nature of the beast, usually.

BTW, it's 110v and 220v vs 120v and 240v. See how easy it is to slip up on?
 
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Old 01-21-14, 04:48 PM
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But given your situation the more relevant question may be 220/440 or 240/480 (star) One of the first companies I worked for had only 480 coming in. All 240/120 came from the shops transformers.

When Westinghouse first introduced AC he made it 110 because that is what DC promoted by Edison was not because it was the ideal voltage for AC.
 
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Old 01-21-14, 06:27 PM
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Thanks. All points well noted.

At this point I'm gathering info. We'll see where it leads. If the owner can't pull the permit and do the work then that answers the question and a contractor will be hired. If he can, I'll continue to research and decide if I'm up for the job. I know it sounds very odd but the owner is more than happy to pull a permit and do the work with me. If possible, and done correctly, of course.
 
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Old 01-21-14, 06:43 PM
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Many areas only allow licensed persons to pull a permit.
 
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Old 01-21-14, 06:44 PM
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But given your situation the more relevant question may be 220/440 or 240/480 (star)
Or it could be 120/208 Y, 277/480 Y, 240 Delta or 480 Delta. Being a multi-unit warehouse, it's very possible you could have 277/480 4-wire service and transformers to drop down to 120/208, all 3-phase. Do you have any idea what arc flash is? One little error and you won't just get shocked, you'll wish you were dead....that is, if you aren't.
480 Volt Arc Flash Demonstration for Lineman Training - YouTube

It's all about safety when you get to these voltages and not at all like running romex at your house. No offense intended to you, but for your own safety you should not attempt to do this project with instructions from an online forum. There are well qualified electricians that sometimes get hurt just because they forget to give electricity the respect it deserves and other times just from a small accident or error. I know two commercial/industrial IBEW electricians who got seriously hurt just because they weren't paying attention when they should have. One of them left behind a wife and two kids.
 
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Old 01-21-14, 08:35 PM
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I understand. I appreciate the concern.

I don't know if it's the same for commercial but for example I can pull a permit on my house(acting as the contractor) even though I'm not licensed. Only the owner can do this(act as the contractor without a license). Like I said, not sure about commercial.
 
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Old 01-22-14, 11:51 AM
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Of the 20-odd jurisdictions I've worked in, I don't know of any that will issue a permit to a non-professional, except for the homeowner permit.

BTW, at work we refer to the 120/208V systems as the "low voltage" wiring. You do not want to mess with the stuff on the other side of the transformers from that.

Quick tip: If you see any brown, orange or yellow wiring around the warehouse, back off. In commercial and industrial systems, those colors are reserved for high voltage circuits. That means you're either in a high voltage part of the service or someone did sloppy work and mixed those colors into the low voltage system. Either way, I would take it as a danger sign.
 
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