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Old 08-31-2008, 07:25 PM   #1
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Need to wire in appliance 240 volts, 42 amps


Hello new here.
I need to wire in a ceramic kiln in my garage. It is 240 volts, 42 amps, 10.1 kw, phase 1. I have a breaker box in my garage that runs through the main box in the house. The main breaker on the one in the garage is only 40 amps, the main in the house is 150 amps. How do I go about wiring this in? What size wiring will I need? Please help me out.

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Old 08-31-2008, 07:42 PM   #2
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Need to wire in appliance 240 volts, 42 amps


You need to run a whole new feeder out to the garage. How big depends on what other loads are out there.
Then from there you run to the kiln.

I will assume a 100A feeder will be required. The kiln drawing 42A alone requires a 60A circuit.

You cannot have more than one line run out there.

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Old 08-31-2008, 07:49 PM   #3
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Need to wire in appliance 240 volts, 42 amps


You never say if the garage is attached or not. If it is, you can have as many circuits as you want going out there. I would keep everything as is and just run a new circuit to the kiln. If it is a detached garage, well, then a new feeder needs to get pulled.
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Old 08-31-2008, 08:11 PM   #4
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Need to wire in appliance 240 volts, 42 amps


Quote:
Originally Posted by Speedy Petey View Post
You need to run a whole new feeder out to the garage. How big depends on what other loads are out there.
Then from there you run to the kiln.

I will assume a 100A feeder will be required. The kiln drawing 42A alone requires a 60A circuit.

You cannot have more than one line run out there.
Hey Speedy, can you elaborate? Why not a 50A?, for the kiln.

Last edited by Steven Jackson; 08-31-2008 at 08:19 PM.
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Old 08-31-2008, 08:18 PM   #5
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Need to wire in appliance 240 volts, 42 amps


The breaker box in the garage runs off a 40 amp circuit breaker from the main breaker box in the house. Can I replace that 40a with a 60a, and then put a 60a for the main in the breaker box in the garage? Why not a 50a?
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Old 08-31-2008, 08:50 PM   #6
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Need to wire in appliance 240 volts, 42 amps


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Hey Speedy, can you elaborate? Why not a 50A?, for the kiln.
Because of the 42A load of the kiln.
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Old 08-31-2008, 08:52 PM   #7
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Need to wire in appliance 240 volts, 42 amps


Quote:
Originally Posted by ekulrenlig View Post
The breaker box in the garage runs off a 40 amp circuit breaker from the main breaker box in the house.
Again, Junk brings up a good point. Is the garage attached or detached?

Quote:
Originally Posted by ekulrenlig View Post
Can I replace that 40a with a 60a, and then put a 60a for the main in the breaker box in the garage?
NO!!! Not unless the wire is rated for 60A. We can only assume if the wire were good for 60 they would have used that from the start

Quote:
Originally Posted by ekulrenlig View Post
Why not a 50a?
See above. What about the rest of the load out there? Lighting? Other receptacles? Heat? A/C?
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Old 08-31-2008, 09:35 PM   #8
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Need to wire in appliance 240 volts, 42 amps


According to code, a breaker can be loaded to 80% of its rating. There are exceptions, very few would apply to anything in a house or garage. A 50 amp breaker can be loaded to only 40 amps, thus a 60 would be needed. If a breaker is loaded over 80%, there's a fair chance it'll trip unnecessarily.

If you can give us the wire size (#6, #4, etc.) and what type of wire it is (THHN in conduit, NM, SE, etc.), and whether it's copper or aluminum, we can tell you how many amps it's good for.

If you just increase the breaker size, there's a pretty good chance of the existing wire overheating, and the oversize breaker will indeed trip, but usually after the fire has started.

Rob
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Old 08-31-2008, 11:32 PM   #9
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Need to wire in appliance 240 volts, 42 amps


The garage is attached.
The main on the breaker box in the house is 150a, but all the other breakers add up to well over that. How high can I exceed the 150a, or how do you know when you need to get a bigger main? Do you have to just make sure that the appliances, lights, ect. are not exceeding the 150a? I have very little knowledge of electrical systems if you can't tell already.

So is it best to replace the 40a breaker in the main breaker box with a 60a or even 100a and then replace that wiring from the house breaker box to the breaker box in the garage, so that it can handle that amperage. And then put a 60a breaker for the main breaker in the garage and another 60a for the breaker for the kiln? Does that make sense?
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Old 09-01-2008, 12:31 AM   #10
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Need to wire in appliance 240 volts, 42 amps


Quote:
According to code, a breaker can be loaded to 80% of its rating.
In most cases breakers can be loaded to 100% of their rating. In this case since the branch circuit is for a kiln and kilns are continuous loads the breaker can only be loaded to 80% unless rated to carry 100%. A 42 amp 240 volt kiln requires 53 amp rated conductors. Therefore a 60 amp branch circuit as Speedy has mentioned. 80% of 60 is 48 amps so a 60 amp breaker will be required to carry the continuous load. 80% of a 50 amp breaker is 40 amps and therefore is not enough breaker to carry the kilns continuous load.

You will also find that kilns will not be allowed to be connected to aluminum wire and copper will almost always be mandated by the manufacturer. They will also require copper wire rated 90C such as nm-b cable or thhn in conduit.
As a rule of thumb in my experience (which isn't too great as far as kilns are concerned) if the kiln is rated 240 volts single phase and 48 amps or under they can be cord and plug connected. Over 48 they are generally hard wired to to disconnect then conduit with thhn wires to the kiln.

If this kiln is to be connected to the sub-panel in the garage then a 100 amp feeder and 100 amp sub panel as Speedy mentioned would be appropriate. Or you could run a 60 amp branch circuit from the house main panel using #6 awg copper nm-b or #6 thhn in conduit. 60 amp double pole circuit breaker would be the selected choice for the branch circuit to the kiln.

Last edited by Stubbie; 09-01-2008 at 12:34 AM.
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Old 09-01-2008, 07:56 AM   #11
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Need to wire in appliance 240 volts, 42 amps


Yeah, now that we know the garage is attached, a new 60A circuit would be the easiest thing.
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Old 09-03-2008, 04:57 AM   #12
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Need to wire in appliance 240 volts, 42 amps


So let me get this straight. I can either...

I can install a 60a breaker in the breaker box in the house. Run the correct wiring to the breaker box in the garage, and connect it seperately to a 60a breaker. And then run to the kiln from there?

Or I can remove the 40a feeder in the house breaker box for the garage, and replace it with a 100a. Run the correct wire to the breaker box in the garage. Then in the garage box, I would replace the 40a main breaker, with a 100a main breaker. And then install a 60a breaker and wire it to the kiln?
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Old 09-03-2008, 02:17 PM   #13
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Need to wire in appliance 240 volts, 42 amps


Or you can leave the panel alone and run a 60A branch circuit to the kiln.
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Old 09-03-2008, 02:18 PM   #14
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Need to wire in appliance 240 volts, 42 amps


Does the kiln have a cord and plug?
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Old 09-04-2008, 05:09 AM   #15
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Need to wire in appliance 240 volts, 42 amps


Yes it has a big 3 prong plug, similar to a dryer plug.

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