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Need to wire in appliance 240 volts, 42 amps

20K views 34 replies 17 participants last post by  ront02769 
#1 ·
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.
 
#2 ·
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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#4 · (Edited)
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.
 
#7 ·
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?

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

Why not a 50a?
See above. What about the rest of the load out there? Lighting? Other receptacles? Heat? A/C?
 
#8 ·
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
 
#9 ·
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?
 
#10 · (Edited)
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.
 
#12 ·
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?
 
#21 ·
Ok. That sounds relatively easy, and cheaper than what I was thinking. Would a branch circuit be up to code and everything, as long as it is done correctly? Do I need to worry about overloading my breaker box, when I have the kiln running?

My mistake...the rectangular prongs on the plug are different sizes, but the ground is circular.
 
#22 ·
Wire Size

Alright, I've got some more questions about this.

I need to know what size/type of wiring I need to run a 60 amp branch circuit to the kiln. The cable on the three prong plug is labeled with "6 AWG 2/C 8 AWG 1/C TYPE ST 105° C."

The kiln is 42 amps, 10.1 kw, and I'll need to run about 85-90' of wire. All the online wire gauge calculators I've found, have said that #8 wire will do. Is this correct?

Also, the main wire to the subpanel breaker box in the garage (40 amp main) is labeled "ESSEX 8-3G NONMETALLIC SHEATHED CABLE TYPE NM-B 600V." Would this wire work for my kiln?
 
#23 ·
No, 8 gauge wire would inadequate for this application. 8 Gauge is only rated for 40 amps (Romex/NM). For your existing sub panel in the garage this is fine, but the kiln requires more power than your sub panel can provide. Your branch circuit is going to be a 60 amp circuit and the breaker must be rated to both protect the wire and support the load. 6 gauge copper wire should be adequate, though considering the load and the distance you may need to bump up one more wire gauge to deal with voltage drop. One of the more experienced electricians on here will chime in and let you know if 4 guage would be required; I don't have a voltage drop calculator handy at the moment.
 
#33 ·
No, 8 gauge wire would inadequate for this application. 8 Gauge is only rated for 40 amps (Romex/NM).

Nope. 8 AWG in raceway or cable with not more than 3 current carrying conductors is rated for 40 amps only for types TW and UF.
THHN, THWN, THHN, etc, which is what 'romex' (non metalic type NM cables) you will get at the big box or electrical counter are rated 50 to 55 amps. See the NFPA "National Electrical Code" article 310-16 in the 1996 code, not sure what section it is in 2022.
 
#25 ·
The branch circuit will run right past the sub panel in the garage. Would it be possible to update the main amperage in the subpanel. It is currently 40 amps. Could I put a 100 amp breaker in the main panel in the house and run that to the subpanel and put a 100 amp main breaker there? And then run a 60 amp circuit from the sub panel? What size wire would I need to support 100 amps?
 
#26 ·
You should condersering the cost of #6-2W/G romex cable .,, Yes some big box store will stock this and make sure you remarked the white wire with red or bleu marker so you know this is a hot conductor.,,

The 6-2W/G is plenty fine and it will only have 1.5% voltage drop on that distance.

The branch circuit will run right past the sub panel in the garage. Would it be possible to update the main amperage in the subpanel. It is currently 40 amps. Could I put a 100 amp breaker in the main panel in the house and run that to the subpanel and put a 100 amp main breaker there? And then run a 60 amp circuit from the sub panel? What size wire would I need to support 100 amps?
No because if you want increase the size of the wire from 40 amp rating to 100 amp and with that kind of distance the cost of wire will add up fast and also I do not know if your subpanel do have 100 amp rating or not.,,

If you go that route.,, with attached garage it will be far much cheaper and easier to string out 6-2W/G Romex than try to pull out new wires for 100 amp capicty which the wire size will be much larger you will need to run #2 copper* or 1/0 AL wires* Just compare the cost per foot and it will add up fast.


* note becarefull depending on which code cycle you are in it will really can change a bit especally true if you are on 2008 NEC code cycle.


Merci,Marc
 
#27 · (Edited)
Is #6-2W/G NM-B Romex rated for 105 degrees C? The cord on the kiln says 105 degrees C, is it important to get a wire rated for that, or will 90 degrees C be adequate?

Also, the kiln draws 10.1 KW. The #6-2W/G NM-B Romex that I am finding is rated for 600 volts??

Somebody please tell me exactly what wire I need to do this.
 
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