Well, I hope no one minds the occasional homeowner question. For what it's worth, I think I know the basics of residential and I have local help, but I wouldn't mind a few extra opinions on these questions.
I'm adding a detached garage/shop to our house and upgrading the service to 200A. The garage gets a 125A subpanel. I could fit the garage breaker in the panel for the house (the panel is outside and convenient), but the discussion of Welder Woes has made me nervous that this setup might load down or spike the house circuits when I'm welding and the air compressor cycles on. Would separating the house and shop at a main disconnect help anything? The contacts between breakers and a panel bus have always looked small to me, like they might limit current during a high load. If they are, then separating the shop before the house panel might be a way to avoid this problem. Of course, I may be trying too hard to second guess the engineers who designed the panels.
Also, I plan to use GE panels, mainly because GE costs less and you can get parts anywhere on a Sunday. Before I buy though, is there anything to be gained by paying more for Square-D (or Cutler-Hammer or Siemens)? Just looking at them (bus size, breaker to bus connections, etc.), it doesn't look like Sq-D is worth the 50% more that their stuff costs, but a lot of people use it. Does it last that much longer?
I'll call the utility and specifically ask about the welder. They're know about the upgrade (which shouldn't have to be mentioned, but probably does), but we haven't mentioned specific loads.
I was planning on using a GE TM4020RCU (PowerMark Gold load center.) The breaker is a GE TQDL21125. The only limitation I could find is a note in the GE literature that its use requires four one-inch spaces (the breaker itself fills two spaces.)
Incoming power is a standard single family residential setup, all secondary service. The utility supplies a 225A socket. Except for the shop loads, it's a pretty straightforward setup; I'm not sure what else to mention about it.
#956 - 04/10/0109:04 PMRe: Uh Oh, here come the homeowners!
John; I think the gist of the thread you've dug up has to do with ground loops created in certain situations, although i'm somewhat at a loss to exactly explain. for your purposes as pertains to the welder(s) i would not split hairs in art 630 with the duty cycle deal, give it a good solid circuit !
#957 - 04/10/0111:45 PMRe: Uh Oh, here come the homeowners!
John TX, If you can install a 125 amp breaker in the main service panel, and it will fit correctly, then you can do it. That's what Steve [Sparky] was referring to about the breaker. Normally, the largest frame size that can be installed into a panel of 200 amps and less - used in Residential - would be 100 amp. The next frame size is 225 amp - which would be for breakers rated from 125 amp to 225 amp. Make completely sure the breaker will fit the panel before buying it!
If you are able to install the 125 amp breaker, that's fine - just make sure to use wire that is no less than 125 amp.
If you cannot use the 125 amp breaker, just use a 100 amp breaker. Once again, use wire that is no less than 100 amp for the 100 amp breaker [this is the wire feeding the new panel - AKA Subfeed].
It's highly unlikely that you will ever load that subpanel to 100 amps @ 240 Volts [or 100 amps per Line], unless you are running a lot of real heavy loads from it. This would be equal to maybe 2 heat pumps, plus a few 5 horse motors, and the welder - all on the same panel and running at maximum draw at the same time. Then you would run the risk of tripping the 100 amp subfeed breaker.
The better way would be running the subfeed from the main service - that will keep the surges and voltage drop from effecting other stuff too much.
The Welder Woes thread kind of covers this more, plus the possible Harmonic Distortion that could be reflected back into the power system.
I, and most likely others, would like to have you post a follow-up message that explains the way you are going to hookup the new subpanel, such as ampacities of all the conductors, conduit - or cable, plus most importantly the way to ground everything.
Feel free to ask anyone here if you are unsure of ANYTHING that concerns the new panel's installation.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#959 - 04/11/0103:41 AMRe: Uh Oh, here come the homeowners!
I probably am worrying too much about this. A "buzz box" welder is rated at 50A on the label and most home Migs use less power (Sparky, I didn't even consider duty cycle; it's on or it's off.) Hopefully, I'll end up with a 7-1/2hp compressor, which I'm reading as 40A FLA from Table 430-148. Even sizing for worst case, I've got surplus capacity here.
Scott, I understand your concern. I hope I didn't give the impression that I was doing this job without local input. I haven't completed a schematic but will post a link once I have. Thanks again to all.
#960 - 04/11/0106:17 AMRe: Uh Oh, here come the homeowners!