Tiny kiln with huge cord

[lewp]

I have a very small -- interior about 13" x 17" -- kiln that I got with a larger one from a woman who made porcelain dolls. This says 120 volts and 19 amps on it and yet has a cord that seems suited to 220. Does this mean that the cord could have been swapped out at some point, and if so could I switch it back? What cone could it comfortably go to? Not sure what I need to consider here. I doubt that the kiln was rewired as well but I suppose  it is possible. Thank you

[Bill Kielb]

Good picture. You will need to open it up and see how they wired it. Likely not, but could be, so for instance if the control that operates it requires 120v control voltage and this was rewired to use 240 v then a neutral would have been included along with a ground so that would be a four wire plug. That is assuming a bunch though. My guess is they put that plug on as a dedicated circuit plug for 120v. Only one way to be sure though, open the machine and see how it is connected. Take pictures when you do if uncertain what you are looking at.

[neilestrick]

Code says that the kiln must be on a circuit breaker that is 25% greater than the draw of the kiln, but no more than 50% greater. So 19 x 1.25 = 23.75, which means it should be on a 25 amp breaker. It could also be on a 30 amp breaker and still be within code. That looks to be a NEMA 5-30 plug, which is rated for 30 amps. It should say somewhere on it what the amperage rating is. The cord itself is slightly oversized with 8 gauge wiring, but too big is not a problem. You could go smaller with 10 gauge wire if you wanted to, but if it's in good condition and the connections in the kiln box all look good, I'd leave it. No need to change anything, just make sure the electrician wires up the circuit for the kiln with the correct breaker.

[liambesaw]

Looks appropriate to me as well.  120v doesn't mean a normal plug.  You plug that kiln into a normal outlet and brrrrzt.

[lewp]

Ah thanks that is so helpful. I will look inside to see how it is wired.

To clarify:  this kiln should be plugged into a 220 outlet, not 120? Is that what you mean by brrrzt? I will need to change the plug since that's not the shape outlet I have, but I have the designated 220 line with the breaker already set up for two larger kilns. I did not understand why it said 120V on the label if it needed a 220.

Thanks.

[neilestrick]

The kiln says 120, so that's what you need. The size of the plug does not determine if it's 220 (240 actually) or 120. The size of the plug depends on amperage. Do not plug it into a 240 volt outlet or you'll have double the voltage it needs, which would be bad. You need a 120 volt, 25 amp circuit for that kiln. It's an odd size circuit, but can easily be done.

[liambesaw]

Exactly, just because the plug looks like a 240v plug, doesn't mean it is.  You can look at this chart and see all the possible plug choices based on voltage and amperage.  

 

The kiln has that plug to prevent someone from plugging it into a normal household 120v outlet.  Normal outlets can handle a maximum of either 15 (standard) or 20 amps.  This is due to the wire size used in a typical household circuit.  

If you plug a 19 amp kiln into a 15 amp receptacle, brrzt is the sound of your circuit breaker flipping instantly.  

This kiln requires a circuit with 12 gauge wire and a 25 or 30 amp breaker.  You'll need to consult an electrician to install a suitable breaker and make sure the wiring is up to par before adding the appropriate receptacle.

Since the kiln will be using up the entire amperage of the circuit, it's best to have a dedicated circuit.  Meaning the kiln is the only thing on that circuit breaker.

[neilestrick]

7 minutes ago, liambesaw said:

This kiln requires a circuit with 12 gauge wire and a 25 or 30 amp breaker

10 gauge wire would be best.

[Mark_H]

depends how long the cord is also.  If it's a 100' cord, then it needs to be oversized to account for voltage drop.  If it's an 'average' length cord, I'd leave it like Neil said.

 

Edit: another reason to oversize wires is if ambient temp is higher (example would be a sweatshop factory on a mezzanine) then you have to de-rate the wire's amperage and oversize it.  I doubt this applies to your case, but wanted to throw it out there that the amp/wire chart in the NEC doesn't always apply.

[neilestrick]

4 hours ago, Mark_H said:

If it's a 100' cord, then it needs to be oversized to account for voltage drop.

'Cord' means power cord. I assume you're referring to the length of the run from the circuit breaker to the outlet, not the power cord? Power cords on kilns are generally 6' long. The electrician will be able to calculate for voltage drop.

[Bill Kielb]

23 hours ago, neilestrick said:

Power cords on kilns are generally 6' long.

Neil’s all over it, power cords or flexible connections (Flexible conduit) including lighting in a ceiling are generally  limited to 6’ actually by code for loading and acceptable disconnect reasons. A good reason that you will rarely see a manufactured  product power cord. exceed six feet.

Pendant power and extension cord use as well as temporary power are defined differently under most codes to address the special circumstances they present.  Most codes address those situations very specifically  and require derating, suspension, protection, gfi,  etc.....

[lewp]

Now I see! You guys are the best, as ever. Thanks.

[Mark_H]

On 3/2/2021 at 2:41 PM, neilestrick said:

'Cord' means power cord. I assume you're referring to the length of the run from the circuit breaker to the outlet, not the power cord? Power cords on kilns are generally 6' long. The electrician will be able to calculate for voltage drop.

Yep, thanks Neil.  Not cord I meant line.  Cords are limited in length and/or can be "temporary."  I shouldn't post prior to my full coffee dose.  And my ambient temp comment would effect ampacity derating of the wire.  Yes, sparky can calc voltage drop, typically works out about one wire size per 100'.