Breaker size?

[spills]

ok ok, let me give a little more detail:

This is going in a shop behind my friends house where we do all the powdercoating and wrenching and such. I originally had a small 30" home oven for curing. For one reason or another, the circuit panel fried on it and rendered it useless. But when I had first gotten that oven, there was an unused 50a breaker in the breaker box, along with an open wall box where I could mount the receptacle (i.e. no wiring, just the box and breaker were present from the start). The shop was already built when my friend bought the house so we don't know what size wires were run, or what the 50a breaker was even there for if it wasn't being used. A guy I knew at work used to be an electrician and he gave me a couple of feet of wire, I cant remember off the top of my head what gauge it was but I know it was 4 wire) and he said that will be fine, my dumbazz didn't even think about the breaker.

As far as wiring, again I cant remember off the top of my head what gauge it is. But if its the same "gauge" scale as auto wiring, I would assume it's like 8 or 10 (maybe 6), 3 + ground

scottrods: I can see your point about wasting my time switching out the breakers, and after reading that last post I have a better idea of where you're coming from. I was actually thinking the other day that, like your light bulb analogy, if my oven is "rated" at 30a with both top and bottom ovens on full steam, but I only use one element that pulls appx. 15a, then it seems that there would have to be a major malfunction before it would trip even a 30a breaker. On the flipside, if you put in a 15a breaker and use both top and bottom oven circuits, it would trip the breaker everytime. So I can definitely see your point, but for now since I still have space left in the breaker box Im going to re-install the 50a, but also install a 30a 2x throw right next to it and wire the oven to it for the time being. Im going to the shop after awhile, and Ill see if I can get the wire size and all that, I just picked up the plug and receptacle which are both rated at 50a.

SOOOOO, what would the correct wire size be for a 50a circuit? I was at HD today looking at the romex, and I didn't see any amp ratings on the packaging, maybe I wasn't looking hard enough. If nothing else, even if I use the 30a breaker, Id like to have wires that could handle 50a just incase I ever switch to the other 50a breaker.

[ed_denu]

ScottRods, Your analogy and reference to home circuits is misleading and imo invalid. The typical house circuit is designed with the understanding that more than one device would utilize it. The NEC recognizes that every light and small home appliance cannot reasonably be on a circuit of it's own. So as a practical compromise the 15 and now 20 amp standard circuit size was adapted. So comparing this to a dedicated higher aperage circuit isn't a valid comparison.

Also most motor and high load devices such as dishwashers, disposals, refrigerators and stove/ovens require dedicated circuits. Most all, if not all circuits over 20 amps are typically not shared which is why devices such as welders, air compressors, etc. have specific circuit requirements listed in their respective installation requirements. But,since we disagree on this issue I posted a question on an electrical forums BB. Here is the response I received from the moderator who is an Electrical Engineer. I think the last paragraph sums it up.

The breaker is sized to protect the premises wiring which is essentially the wiring installed in the walls up to and including the receptacle. Therefore, if this circuit is wired with #6 (or in some cases #8) copper the 50A breaker is correct for the circuit.

That does not mean that this circuit is appropriate for the appliance in question.

An appliance that draws 13A would not normally be designed for use on a 50A circuit, therefore the designer would put a 20A cord and plug on the unit and use wiring appropriate for 20A. With a 20A plug, you couldn't connect it to a 50A circuit.

If you want to use a 13A appliance on a 50A circuit, you need to use #6 copper cord and plug up to a fuse holder in the appliance where you would install a 20A fuse. After the 20A fuse, it would be okay to use 20A wiring method #12 copper.

Given that this is a homemade appliance, I would probably reduce the breaker to 20A (or install a new 240V 20A circuit), change the receptacle to a 20A receptacle, and put a fuse in the appliance. It's expensive, but you may even want to consider a double-pole GFCI breaker. Appliance manufacturers pay a lot of money for UL safety testing; homemade equipment doesn't have that luxury so any additional protection is warranted in my opinion.
__________________
Good luck with your project!
-Ben

Spills, With all the unanswered questions about the the service panel, wiring size and appropriate breaker sizing you might want to get a qualified electrician to look it all over.

[PhredAre]

Right on Ed, change the Bkr to match the weakest link in the load. Then we can ponder the instanteous trip current of the bkr verus the load current. Fred

[ed_denu]

Originally Posted by spills

SOOOOO, what would the correct wire size be for a 50a circuit? I was at HD today looking at the romex, and I didn't see any amp ratings on the packaging, maybe I wasn't looking hard enough. If nothing else, even if I use the 30a breaker, Id like to have wires that could handle 50a just incase I ever switch to the other 50a breaker.

Spills, If you need to move the oven around then you have a certain dilemma regardless of which way you go. You cannot by code install a 50 amp receptacle on a circuit that has anything less than a 50 amp breaker. And as quoted by Ben in my previous post this will require a #6 (or in some cases # copper wire. That will make using a 30 amp receptacle difficult in they are not designed to easily accept the #6 wire.

If your oven were going to be stationary then I would hard wire it directly to a double gang wall box. That way you could go with a 30 amp breaker today with #6 wire for future use and not worry about plugs and receptacles. The service cord should match the breaker size and you should be ok

[FigureLLC]

before installing our 10hp compressor, i took my time and did a lot of research on breaker sizes. when it came down to it, the electrician at the electrical supply place told me to choose the smallest breaker i could reasonably expect to work, and if i experienced problems with tripping, go a size up. (this was for a 3-phase motor, which pulls a huge current spike at start-up and will trip a breaker rated only for nominal steady-state current.)

[ed_denu]

Originally Posted by PhredAre

Right on Ed, change the Bkr to match the weakest link in the load. Then we can ponder the instanteous trip current of the bkr verus the load current. Fred

Hey Fred, I'm always up for a good discussion and I'm willing to argue instantaneous trip versus time delay or whatever else. I seem to have lost old Scotty boy in this debate. I hope he didn't hurt his neck shaking his head!

Boards been kind of quiet the last couple of days, I hope everyone hasn't jumped off the highest building after watching the market the last couple weeks.

[baz]

Originally Posted by ed_denu

Hey Fred, I'm always up for a good discussion and I'm willing to argue instantaneous trip versus time delay or whatever else. I seem to have lost old Scotty boy in this debate. I hope he didn't hurt his neck shaking his head!

Boards been kind of quiet the last couple of days, I hope everyone hasn't jumped off the highest building after watching the market the last couple weeks.

too busy checking my canadian $ go down
thanks Ed for clearing this breaker size question , i don t have a very big knowledge in electricity but i do have some equipment running on 600 v (2 compressors and 3 large buffers plus 2 ovens running on 240 all of these are running through their own fused main cutoff switches
and to me it did not make sense to tell someone to use the largest possible breaker for an appliance that pulls about 13 amps and also without knowing the wire size