Need a little subpanel help...

[KnuckleBuster]

Hey folks. I'd much rather post something like "Hey look at the cool welds I did," but I can't use my new welder until I get my electrical problems sorted out, so here's my predicament:

I just bought a Miller Dynasty 200DX. I also bought a cheap little 120V Craftsman compressor (15 Amp, I think). My detached garage has the worst wiring anyone has ever seen, so I'd like to put in a useable service so I can get welding (I stare at my new welder every night thinking about all the money that sits there unused).

My house has a 100 Amp main panel with a sub panel off either side of it. All of the slots are full. One subpanel is 240 Volt with an empty slot on either side of the 2 double pole breakers that are in it (one 20, the other 30 Amp).

What the heck can I do CHEAPLY to get up and going with this welder. I've dug a trench (about 25 feet) from the house to the garage. I thought I had a 200 Amp panel for some reason, so I was all set to run 2" conduit and put in a 100 Amp subpanel. A trip to the basement after work today killed that dream quick.

I know there are a few guys on here who really know their stuff, so I'm hoping somebody can help me out. I can't really upgrade my house panel (code nightmare). I have a decent enough knowledge of how this works to do the work myself, but I don't want to install an undersized service and waste my money.

Thanks!
Jay

 

[LoneGunman]

You can and should still put a 100 amp subpanel in your garage. The welder is going to draw the same no matter what panel you put out there, I suggest the 100 amp in case in the future you decide to upgrade your main service. All you need is the two spots you say you already have, if not you can always add some tandem breakers to gain some room.

One of the biggest mistakes I see when sub panels are done by homeowners is that they bond the neutral bus when in a sub panel they need to be seperate.

I also suggest running a spare 3/4" conduit out there for low voltage requirements while the trench is already dug.

Upgrading a panel/service is within the ability of most people on this board if they do some research. Before I get all the "No, he should hire a pro", I am an electrician.

 

[KnuckleBuster]

Thanks!

I've been doing my research and I'm pretty confident in my abilities to hook this up. Hell, I figure if I'm going to be welding I ought to be swift enough to figure this stuff out.

I knew about the neutral bus NOT being bonded, but I'm still a litlle foggy on whether or not I can run the panel off that other subpanel. Should I put a 100A breaker in that sub box and just get a lug center (I think it's called) out in the garage or go for a panel with a main breaker? How can I tell if the wire to the sub box will handle the 100A breaker?

I've already got 3/4" coduit going out to the garage, but the wires running through it are junk - 2 black wires and a blue wire - figure that out. I plugged my compressor in right after I bought it and it didn't even complete one full cycle before it flipped the breaker. I figure I'll leave that conduit there for future use.

Thanks for the input!

 

[LoneGunman]

You can feed the garage panel from any of the other panels, you won't find the word "subpanel" in the code book.

I'd prefer a main disconnect in a detached garage over a main lug panel. It's not a bad idea to kill power to a detached garage when you leave the garage.

What size wire is the sub panel you are planning to use fed with and what size breaker is it fed with? Even if it was only fed with number 10's being fed by a 30a breaker a 100 amp breaker would not hurt anything because the panel is still only being fed by the 30a breaker, over 30a and it will trip. I'm by no means suggesting that is the correct way to do things, just making a point.

What I'd be worried about is the panel being fed with number 10's and a 60a breaker ETC.

 

[ovilla]

I know you're looking to set up a subpanel but a cheap alternative could also be just buying a really heavy gauge extension cord so you could build a 50amp 220 line (maybe 50' long). This way you could start using your welder right away. Depending on how much welding you do, this could work out cheaper too, especially considering the rising price of wire. You would just need to add a 220 outlet to any one of your existing panels. Best of luck!

 

[kvom]

I recently built a 25' 50A extension cord for my welder using 6/3 SO cord. Cost me $80 for the cord and another $20 for the plugs on either end. I could have used 8/3 cord for $60, but decided to invest in the extra capacity.

Since OP has a 25' trench, I'd guess he'd need more than that depending on where the house panel is located and where the welder would need to be.

Since he'd still need a 15a 110 circuit for the compressor, I believe the subpanel would make more sense. I have a small 12 gallon compressor that I'ved used with a 15a "freezer outlet" in my garage. It has on occasion tripped the breaker with the startup draw. So if the garage's 110v outlet is 10a his compressor will probably trip the existing circuit.

 

[Flat_Head_Rat_Rod]

I'm not a expert but I recently moved my mobile home to my lot . I have a freind who is a electrican. I told him about the shop i wanted so he suggested a main panel that houses my meter and two main breakers rated at 200 amps from their one breaker runs to 200 amp panel for my house. the other one will be for the panel that will be in my shop. This is probaly a little overkill for what I actually needed but i did not want to ever come close to maxing it out. this is my power set up hope this helps. I understand you want to do it cheap but maxing out your panel will not bve a good thing to do.

 

[Charles (in GA)]

The panel in the house you wish to come off of, you simply need to move breakers up or down until you have two adjoining openings that you can snap a duplex breaker into. I sounds like you really need to upgrade the house to a 200 amp or larger system, before it gets so hodge-podge that it becomes a hazard.

Charles

 

[KnuckleBuster]

Charles - what do you mean "before" ?

 

[Aceman]

The panel in the house you wish to come off of, you simply need to move breakers up or down until you have two adjoining openings that you can snap a duplex breaker into.

Not a good idea until he verifies the breakers aren't part of a multi-wire branch circuit. Typically the breakers are right next to each, but if his wiring is as screwed up as he says it is, the wires could be landed anywhere.

Lonegunman has you on the right track.

Since it's a detached garage, you need a disconnect. Simplest way is to purchase a main breaker panel.

 

[isaac338]

Since it's a detached garage, you need a disconnect. Simplest way is to purchase a main breaker panel.

Do you need a disconnect other than the breaker in the house? I just wired a pony panel sold to me by the electrician and it's got no main breaker - the only way to shut power to that panel off is by heading into the house and down to the basement.

And of course, adding that switch short of just swapping the panel would probably be pretty aggravating..

 

[LoneGunman]

Do you need a disconnect other than the breaker in the house? I just wired a pony panel sold to me by the electrician and it's got no main breaker - the only way to shut power to that panel off is by heading into the house and down to the basement.

And of course, adding that switch short of just swapping the panel would probably be pretty aggravating..

A main breaker is required if you have six or more breakers to throw to shut everything down. A 2 pole breaker supplying a compressor would only be considered one because one throw shuts the whole circuit, providing a proper two pole breaker was used and not two single poles.

 

[isaac338]

A main breaker is required if you have six or more breakers to throw to shut everything down. A 2 pole breaker supplying a compressor would only be considered one because one throw shuts the whole circuit, providing a proper two pole breaker was used and not two single poles.

Good info. I should look into getting a main switch, I guess. The panel only has 6 or 8 slots, but all but two are filled with the half-width 15A breakers.

On that note, is there anything inherently dangerous about using two 15A breakers to supply power to a 240V circuit? It's probably bad form, but will it burn the shop down?

Sorry for the hijack ;D

 

[LoneGunman]

Good info. I should look into getting a main switch, I guess. The panel only has 6 or 8 slots, but all but two are filled with the half-width 15A breakers.

On that note, is there anything inherently dangerous about using two 15A breakers to supply power to a 240V circuit? It's probably bad form, but will it burn the shop down?

Sorry for the hijack ;D

You mean two breakers that don't have a common trip (physically joined together)? If so yes, that it dangerous. If theres a problem with the equipment and it overloads the breaker it could theoretically trip only one leg of the 240v cicuit. Plus if you are using the thinline breakers youll have to make sure they are not sharing the same section of the bus or you will not get 240 volts from them as they would be on the same phase. They make a common trip that will join two thinlines together even if one breaker is between them.

Also if they are not tied together you can mistakenly think the circuit is off by shutting one down and missing the other.

 

[R1chy]

You mean two breakers that don't have a common trip (physically joined together)? If so yes, that it dangerous. If theres a problem with the equipment....

LoneG - While lurking here read your advise and taken note. I'm sure others also appreciate the time you take the explain the "why" behind your answers. That is part of what this site is all about, learning and getting ideas.

R1chy

 

[LoneGunman]

LoneG - While lurking here read your advise and taken note. I'm sure others also appreciate the time you take the explain the "why" behind your answers. That is part of what this site is all about, learning and getting ideas.

R1chy

Thanks R1chy, just trying to give back from all the great information I have gotten here.

 

[isaac338]

You mean two breakers that don't have a common trip (physically joined together)? If so yes, that it dangerous. If theres a problem with the equipment and it overloads the breaker it could theoretically trip only one leg of the 240v cicuit. Plus if you are using the thinline breakers youll have to make sure they are not sharing the same section of the bus or you will not get 240 volts from them as they would be on the same phase. They make a common trip that will join two thinlines together even if one breaker is between them.

Also if they are not tied together you can mistakenly think the circuit is off by shutting one down and missing the other.

I guess that should be obvious - using slimline breakers won't ever give me 240V. Funny how some stuff that's so simple you really only notice when someone points it out to you

Thanks for your help.

 

[LoneGunman]

I guess that should be obvious - using slimline breakers won't ever give me 240V. Funny how some stuff that's so simple you really only notice when someone points it out to you

Thanks for your help.

LOL, try having 15 years or so in the trade and missing a pair of slimline breakers thats suppose to feed an air compressor, spending an hour trying to figure it out.

Everyone misses the obvious at times.